The Holocene recent issues

Radiocarbon chronology of Holocene colluvial (debris-flow) events at Sletthamn, Jotunheimen, southern Norway: a window on the changing frequency of extreme climatic events and their landscape impact

Wed, 18 Nov 2009 06:05:46 PST

The history of colluvial events over the last 8500 years is reconstructed in three Norwegian alpine slope-foot mires fed by three independent debris-flow systems. Chronologies for each site are constructed based on 155 radiocarbon-dated peat samples. At the multimillennial scale, debris-flow activity was greatest during the transition from the Holocene Thermal Maximum to the late Holocene (c. 4300—2800 cal. BP) when debris-flow events occurred with a frequency of 1 in 33 years: two peaks in activity, characterized by 1 event in 14 years and 1 event in 25 years, were reached at the beginning and end of this interval, respectively. Least activity occurred during the Holocene Thermal Maximum from c. 8000 to 7100 cal. BP, with one event in 900 years. Eight distinct century- to millennial-scale phases of high debris-flow frequency (>3 events per 100 years) are identified at c. 8300—8000, 7100—7000, 4300—3700, 3200—2800, 2200—1900, 1500—1200, 800—700 and 300—0 cal. BP. Similarities in the records from the three sites suggest underlying climatic variations linked to the frequency of intense summer and autumn rainfall events (the primary meteorological trigger of slope failure in the source areas). Differences between the records reflect local site sensitivity to the initiation of debris-flow activity and the triggering of each subsequent debris-flow event. It is also inferred that each debris-flow system passes through multimillennial stages of at first increasing and later decreasing sensitivity as its source area expands. The climatic signals in the debris-flow record appear to differ in various respects from those derived from other precipitation-sensitive proxies from southern Norway (river floods, snow avalanches and glacier variations). Debris-flow records provide, therefore, complementary information relating to extreme climatic events and demonstrate instabilities in the Holocene landscape but provide little or no support for the concept of an increasing landscape impact of debris flows in response to global warming.

A summer temperature proxy from height increment of Scots pine since 1561 at the northern timberline in Fennoscandia

Lindholm, M., Ogurtsov, M., Aalto, T., Jalkanen, R., Salminen, H. — Wed, 18 Nov 2009 06:05:46 PST

Height increments of 60 Scots pine trees were used to reconstruct mean June—August temperature variability at interannual to decadal scales from 1561 to 2004. Three standardization methods (67%, 33% flexible splines, and a fixed 22 years spline) were compared in building chronologies in order to optimize the frequency response in relation to major climatic forcing factors. The height-growth chronology built using the 33% spline standardization proved to have the most consistent and time-stable relationship with the summer temperatures. Among the monthly precipitation and temperature variables from previous June to current August, previous July shows the highest correlation with height growth. In addition, both previous June and previous August have significant positive correlations. Our final transfer model accounts for 32.5% of the dependent instrumental temperature variance between 1909 and 2004. The Fourier spectra of the height-growth chronology and mean summer temperature are very similar in appearance, both series having peaks at 2.7—3.2 years, 6.7 years and 15.7 years. Thus, the 444 years long summer temperature reconstruction is limited to high and medium frequencies. The coldest three summers in this record were experienced in years 1601, 1790 and 1903. Correspondingly, the summers of 1626, 1689 and 1598 were the warmest. The 1820s experienced the warmest 10-year mean, while the first decade of the twentieth century was the coldest. Among the 14 non-overlapping 30-year periods between 1561 and 1980, the period 1621—1650 was the warmest and the period 1591—1620 the coldest.

Changes in northeast Pacific marine ecosystems over the last 4500 years: evidence from stable isotope analysis of bone collagen from archeological middens

Misarti, N., Finney, B., Maschner, H., Wooller, M. J. — Wed, 18 Nov 2009 06:05:46 PST

Changes in food web dynamics and ocean productivity over the past 4500 years are investigated using stable isotope analysis of nitrogen and carbon in collagen from animal bones preserved in coastal archeological middens on Sanak Island, along the eastern edge of the Aleutian archipelgo. Samples included Steller sea lions, Harbor seals, Northern fur seals, sea otters, Pacific cod and sockeye salmon. Sea otters had the highest ¹³C (–11.9 ± 0.7) and lowest ¹⁵N values (14.5 ± 1.4), Northern fur seals had the lowest ¹³C values (–13.6 ± 1.4), and Steller sea lions had the highest ¹⁵N values (18.4 ± 1.4) of the marine mammals. Cod isotope values were consistent with those of demersal organisms from near shore habitats (–12.5 ± 0.9 ¹³C, 16.1 ± 1.4 ¹⁵N), while salmon values were consistent with those of organisms existing in an open ocean habitat and at a lower trophic level (–15.2 ± 1.4 ¹³C, 11.5 ± 1.7 ¹⁵N). When comparing six different prehistoric time periods, two time periods had significantly different ¹³C for salmon. Otters had significantly different ¹⁵N values in two out of the six prehistoric time periods but no differences in ¹³C. The mean ¹³C, corrected for the oceanic Suess Effect, of modern specimens of all species (except Northern fur seals) were significantly lower than prehistoric animals. Several hypotheses are explored to explain these differences including a reduction in productivity during the twentieth century in this region of the Gulf of Alaska. If true, this suggests that North Pacific climate regimes experienced during the twentieth century may not be good analogs of North Pacific marine ecosystems during the late Holocene.

Palaeoclimatic indicators in soils buried under archaeological monuments in the Eurasian steppe: a review

Wed, 18 Nov 2009 06:05:47 PST

The Russian experience of the local reconstruction of the Eurasian steppe climate during the last 5000 years based on geoarchaeological approaches is reviewed. Examples of traditional palaeoclimatic reconstructions in Russia based on organic matter, highly soluble salts and gypsum content and location of salts and gypsum horizons in the profile of buried soils are given. Pedogenic carbonate as a palaeoclimatic indicator is considered. The possibilities of the quantitative reconstruction of the palaeoprecipitation based on magnetic properties of buried soils are observed. The innovative approach of palaeoclimatic reconstruction based on soil microbiology methods is reviewed. The problem of temporary transformation of palaeoclimatic indicators in buried soils is shown. A methodology for the interpretation of palaeoclimatic indicators of buried soils for a local palaeoclimatic reconstruction is given.

The Holocene landscape history of the NW Italian coasts

Bellini, C., Mariotti-Lippi, M., Montanari, C. — Wed, 18 Nov 2009 06:05:47 PST

Cores from four coastal plains of the Mar Ligure Sea in N Tuscany and E Liguria (Italy) were investigated by means of pollen analysis to delineate the Holocene landscape history of the NW Italian coasts. In the first half of the Holocene (c. 9800—7000 cal. yr BP) all four sites show elevated percentages of Abies pollen which suggest the local presence of fir woods (with Ulmus, Tilia, etc.). In the second half of the Holocene (from 7000 cal. yr BP), Abies becomes locally extinct along the coasts leaving space for the development of mosaic landscapes formed by open meso-thermophilous woods (with deciduous Quercus, Alnus , Corylus) and Mediterranean maquis (with Erica cf. arborea). The new data represent a significant contribution to the reconstruction of the landscape history of the NW Italian coasts and of the history of fir in Italy. Along all examined cores discontinuous pollen records show that initially the coastal areas were characterized by retrodunal wetlands; after c. 6000 cal. yr BP only the larger plains in N Tuscany remained extensively damp while the smaller plains in E Liguria were buried (and/or drained). Thus, these buried deposits of ‘fossil’ coastal wetlands proved to be only partially useful for high-resolution environmental archaeology and history studies. Nonetheless they are unique traces of ecosystems that provided important local economic resources for millennia and formed elements of the coastal cultural landscapes which have almost totally disappeared today.

Historical records of Cipreses glacier (34{degrees}S): combining documentary-inferred 'Little Ice Age' evidence from Southern and Central Chile

Araneda, A., Torrejon, F., Aguayo, M., Alvial, I., Mendoza, C., Urrutia, R. — Wed, 18 Nov 2009 06:05:47 PST

The historical behaviour of Cipreses glacier from the nineteenth through the early twentieth century is described based on written records, cartography, iconography and photographs. These data allow us to infer that the last maximum advance of Cipreses glacier attributable to the ‘Little Ice Age’ occurred around AD 1842. The first historical retreat was recorded in 1858 and, since then, the glacier has shown a clear retreating trend with no new advances. All this information was compared with the historical data gathered for San Rafael glacier, which shows the occurrence of a cold period contemporary with the European LIA. Whereas Cipreses glacier was retreating by 1858, San Rafael glacier was advancing, reaching its last maximum between 1857 and 1875. The dates for the advances and retreats reveal a time-lag of approximately 30 years in the responses of these glaciers. The comparison of timing in glacier advances suggests that this time-lag is due to changes in precipitation and temperature associated mainly with fluctuations of the Westerlies.

Modern pollen--vegetation relationships along an altitudinal transect in the central Pyrenees (southwestern Europe)

Canellas-Bolta, N., Rull, V., Vigo, J., Mercade, A. — Wed, 18 Nov 2009 06:05:47 PST

Modern proxy-calibration studies are a powerful tool for paleoecological interpretation. This paper analyzes the relationships among modern pollen rain, vegetation and altitude in the central Pyrenees, where several paleo-palynological studies have been developed, but a modern analog survey is still unavailable. The work analyzes the pollen content of moss polsters from different vegetation communities along an altitudinal transect, as well as the flora and vegetation using the Braun-Blanquet system. DCCA showed that altitude satisfactorily explains both vegetation (r² = 0.988) and pollen (r² = 0.841) gradients. Besides the complexity of pollen—vegetation relationships, some regularities were found to be useful for paleoecological and paleoenvironmental interpretation. In general, altitudinal vegetation and pollen patterns show similarities, but pollen belts and boundaries are less well defined, likely because of the homogenizing effect of upward wind transport. Palynological differentiation of montane from subalpine/alpine belts is straightforward from the trends of the more significant pollen types, mainly the low-altitude deciduous trees and the high-mountain herbs. Palynological differences between subalpine and alpine belts, which boundary coincides with the treeline, are more subtle and need quantitative criteria and complementary proxies. From an individual point of view, four main groups of pollen were distinguished, in relation to their usefulness as vegetation and altitudinal indicators: (1) very good indicators, (2) good indicators, (3) non indicators, and (4) allochthonous pollen types. The first two groups resulted to be useful as indicator taxa for modern analogs for paleovegetational and paleoaltitudinal reconstruction, while the latter two groups should be interpreted with caution in paleoenvironmental studies.

High-resolution chironomid-inferred temperature history since ad 1580 from varved Lake Silvaplana, Switzerland: comparison with local and regional reconstructions

Larocque-Tobler, I., Grosjean, M., Heiri, O., Trachsel, M. — Wed, 18 Nov 2009 06:05:47 PST

Chironomids were used to reconstruct mean July air temperatures between c. AD 1580 and 2001 at Lake Silvaplana, a varved lake located in the Engadine, eastern Swiss Alps. The goal of this study was to reconstruct temperature changes at near-annual resolution, and validate the reconstruction by comparison with records based on early instrumental data, documentary proxy evidence, dendrochronology, geochemical (biogenic silica (BSi)) and mineralogical data (quartz/mica ratios) at local and regional scales. Warmer than-the-climate-normal (AD 1961—1990) mean July air temperatures were inferred between c. AD 1610 and 1662, AD 1710 and 1740, AD 1790 and 1866, AD 1940 and 1960 and AD 1990 and 2001. Colder-than-the-climate-normal July air temperatures were reconstructed between c. AD 1662 and 1710, AD 1740 and 1790, AD 1866 and 1919, and AD 1970 and 1990. The 420-year chironomid-inferred mean July air temperature record was significantly (p < 0.01) related to June—September (JJAS) temperatures reconstructed from early instrumental and documentary data at regional scale, JJA temperature inferred from documentary proxy evidence at local scale and summer temperatures based on early instrumental data in central Europe. When the Z-scores of warm/cold periods were compared between records, only one period (c. AD 1740—1790) did not show significant correlations between the chironomid record and any of the eight other records considered here, probably because of increased precipitation and changes in the sediment composition which influenced the chironomid assemblages. 75% of the periods considered had significant correlations between the chironomid records, and both the reconstruction based on quartz/mica ratios and the inferred JJAS early instrumental and documentary proxy evidence, while 60% of the periods showed significant correlations between the chironomid-based record and the reconstruction based on early instrumental data of Central Europe. These results suggest that chironomids in the sediment of Lake Silvaplana yield valid temperature reconstructions at regional scales for the last 420 years.

Holocene agriculture in the Guanzhong Basin in NW China indicated by pollen and charcoal evidence

Li, X., Shang, X., Dodson, J., Zhou, X. — Wed, 18 Nov 2009 06:05:47 PST

The emergence and rapid spread of agriculture from the early Holocene has made a great impact on the development of human societies and landscape change. Guanzhong Basin in the middle of Yellow River valley has a long continuous history of agriculture since the Neolithic. The pollen and charcoal records from Xindian in western Guanzhong Basin, together with the known distribution of archaeological sites, provide proxies to reconstruct the history of agricultural activity and landscape change. The concentration and percentage of Poaceae pollen increase from about 7700 yr BP ago and the concentration of charcoal shows the same trend. These records indicate that the ‘slash-and-burn’ cultivation for agriculture began around 7700 years ago. Between 7700 and 5500 yr BP, the evidence of cereal crops remained strong and charcoal concentration and archaeological sites increased greatly, which all indicate increased agricultural activity and the expansion of human populations. This was enhanced by the continuous development of new cultivation tools and techniques between 4700 and 3300 yr BP, especially in the Bronze Age of the pre-Zhou Dynasty. The original agricultural landscape had been settled after 3300 yr BP. Buckwheat became an important crop from around 5500 yr BP, perhaps because of increasing aridity. This is the earliest record of cultivated buckwheat in Neolithic China.

Holocene benthic foraminifera from Bahia Blanca estuary: a review and update of systematic and palaeoenvironmental aspects

Cusminsky, G. C., Bernasconi, E., Calvo-Marcilese, L. — Wed, 18 Nov 2009 06:05:47 PST

Assemblages of benthic foraminifera in a Holocene core from the outer area of Bahía Blanca estuary in Argentina were studied. The systematic of the group was updated, and provided 28 genera distributed among 59 species, six species with nomenclature aperta. The main species recorded were Buccella peruviana f. campsi (Boltovskoy), Ammonia beccarii (Linné), Elphidium gunteri Cole, Elphidium galvestonense Kornfeld, Elphidium articulatum d’Orbigny and Elphidium discoidale (d’Orbigny). These species allowed an estuarine environment to be determined. Qualitative and quantitative studies conducted on the faunistic content in the core allowed identification of three subenvironments closely linked to sea-level fluctuations during the mid Holocene: a lower zone (6350 yr BP) corresponding to a high intertidal environment, an intermediate zone (2460 yr BP) representing a low intertidal environment related to a system of channels and variations in environmental energy, and an upper zone characterized by the development of a high-energy littoral environment affected by the action of waves, tides and tidal currents, which underwent progressive change until it attained present-day conditions.

Impact of river capture on hydrography and water resources: case study of Ula and Katra catchments, south Lithuania

Linkeviciene, R. — Wed, 18 Nov 2009 06:05:47 PST

Based on cartographic material from three time periods during the nineteenth and twentieth centuries, the impact of river capture, which started in the middle of the nineteenth century, on transformations of the watershed and hydrographic network of two Lithuanian rivers, Ula and Katra, is analysed. It has been determined that river capture conditioned marked transformations of water supply and distribution. As a result of the capture, the area of Ula catchment has increased by 62% and its mean discharge by 63%, whereas the area of Katra catchment decreased by 23% and its mean discharge by 27%. The total area of the five largest lakes in the recent Ula catchment has been reduced by 95%. The transformations of water resources in the Ula catchment since the first half of the nineteenth century are the following: Ula runoff volume has increased almost by 100 million m³/yr whereas the water volume of lakes has been reduced by almost 30 million m³.

Tracing the history of highland human management in the eastern Pre-Pyrenees: an interdisciplinary palaeoenvironmental study at the Pradell fen, Spain

Wed, 18 Nov 2009 06:05:47 PST

Although high mountain areas have traditionally been viewed as predominantly grazing areas, with low population and a high degree of land-use stasis, recent research suggest that land-use complexity and change over time has been underestimated. This interdisciplinary palaeoenvironmental analysis has been carried out on the Pradell calcareous fen, located in the eastern Pre-Pyrenees (Spain) at 1975 m a.s.l., and it comprises different environmental indicators: pollen, stomata, non-pollen palynomorphs, macrocharcoal particles, lithostratigraphy, sedimentology and geochemistry. The results of this high temporal resolution study are integrated with archaeological data, and together provide strong evidence for the complexity of the high-mountain land-use system over the last 1500 years. Archaeological fieldwork has shown the rise of highland mining activities during the Roman period. Later, frequent fires resulted from the farming and settlement that followed the Christian conquest. Geochemical analysis of sediment cores records late-Mediaeval metal production, while the expansion of feudal cropping and the advent of several Mediaeval crises are clearly recorded in both the pollen and the historical data. Finally, the rise of a mixed economy system based on transhumance, farming, metallurgy and woodland exploitation was established during Modern and Contemporary times. The high correlation between the palaeoenvironmental, archaeological and historical data at the Pradell fen stresses the value of calcareous fens for palaeoenvironmental reconstructions of historical landscapes. Results obtained also depict high mountain landscapes as the result of the long-term interaction of many human practices, including mining and smelting, grazing, cropping and tree exploitation for the production of wood, charcoal and resin.

Holocene book review: Shore processes and their palaeoenvironmental applications Edward J. Anthony, Oxford: Elsevier, 2009, 519 pp., {pound}83.00, hardback. ISBN 978 0 444 52733 2

Hansom, J. — Wed, 18 Nov 2009 06:05:47 PST

Holocene book review: Encyclopedia of global warming and climate change Edited by S. George Philander, London: Sage Publications, 2008, 1552 pp. (3 volumes), {pound}205.00, hardback. ISBN 978 1 4129 5878 3

Robertson, I. — Wed, 18 Nov 2009 06:05:47 PST

Holocene book review: A new green history of the world: the environment and the collapse of great civilizations Clive Ponting, New York: Penguin Books, 2007, 452 pp., US$16.00, paperback. ISBN 9780143038986

Vadjunec, J. M. — Wed, 18 Nov 2009 06:05:47 PST

Lago di Bargone, Liguria, N Italy: a reconstruction of Holocene environmental and land-use history

Cruise, G.M., Macphail, R.I., Linderholm, J., Maggi, R., Marshall, P.D. — Fri, 23 Oct 2009 04:07:53 PDT

Sediment micromorphology, chemistry and magnetic susceptibility of basin edge deposits at the small, mid-altitude peat site of Lago di Bargone, eastern Liguria, Italy, is compared with a full Holocene palynological sequence and radiocarbon dates from the central part of the peat bog. Micromorphology and MS550 results show that Neolithic to Copper Age forest disturbances and clearings as inferred from the pollen diagrams, occurred during a period of lower water-tables and intermittent drying out of the basin edge deposits. Extensive deforestation and expansion of heath and grassland during the Iron Age and Roman periods is associated with increases in soil erosion and in micromorphological indications of burning. It is argued that the very fine size range of the charred fragments seen in thin sections and the seeming absence of charcoal of coarser size range suggest a system of light, controlled burning, possibly akin to the local tradition of using fire to control weeds and to encourage new grass and herbaceous growth, and not local forest clearance by fire. Micromorphology of the late-Holocene peat contains herbivore dung possibly indicating the use of the site as a watering hole by domesticated stock. The overlying colluvium displays evidence of deep-seated erosion of the local soils and geology which is most likely to have been associated with local mining activities.

Lateglacial and Holocene paleoenvironmental changes recorded in lake sediments, Brock Plateau (Melville Hills), Northwest Territories, Canada

Fri, 23 Oct 2009 04:07:54 PDT

Sediments from South Lake, Brock Plateau (Melville Hills), Northwest Territories, provide one of the longest postglacial records from the mainland western Canadian Arctic, outside of eastern Beringia. Sedimentation commenced at least 13 900 cal. yr BP, and possibly as early as 16 000 cal. yr BP, in response to early deglaciation of the site. Pollen is present throughout the record, with an initial Artemisia-Salix assemblage indicative of very cold conditions, consistent with a locally severe Younger Dryas Stade or simply continued proximity of the Laurentide Ice Sheet margin (c. 12 700 to 11 500 cal. yr BP). At c. 11 000 cal. yr BP, abiotic proxies signal a transition to warmer conditions, corroborated by a pollen assemblage dominated by Betula and Cyperaceae. Although South Lake was biologically productive during the early Holocene (c. 11 000 to 7000 cal. yr BP), diatoms and other siliceous organisms are notably absent from the record, suggesting severe silica limitation. Rises in Alnus crispa and Picea mariana pollen at c. 7000 cal. yr BP suggest cooling and/or an increase in effective moisture. Wetter conditions and increased hydrological inputs and silica supply likely led to the establishment of a pioneering diatom community at c. 6500 cal. yr BP. Decreased organic sedimentation after c. 2000 cal. yr BP suggests cooler conditions. Additionally, changing niveo-eolian deposition of sand on lake ice varied with a c. 3000-year periodicity through the entire record. The South Lake multiproxy record supports the hypothesis that the Brock Plateau was one of the earliest deglaciated regions during the late Wisconsinan.

Holocene palaeofire records in a high-level, proximal valley-fill (Wilson Bog), Mount Lofty Ranges, South Australia

Fri, 23 Oct 2009 04:07:54 PDT

An elevated valley-fill peat bog (Wilson Bog) near Mount Lofty, South Australia, failed in November 2005 following a flooding event, and exposed representative sections of the sediment infill. Two distinct units were revealed: 2 m of coarse-grained, siliciclastic sand/gravel, overlain by 2 m of peat. A simple charcoal extraction technique based on floatation and skimming was developed to extract coarse charcoal from coarse-grained gravels to determine the palaeofire record at a proximal site of sedimentation. Optically stimulated luminescence (OSL) dating of basal sediments revealed a minimum age of deposition of 7.02 ^+0.50_—0.56 ka, while the oldest charcoal peak yielded a radiocarbon age of 6000—5740 cal. yr BP. The lower half of the siliciclastic unit contains three distinct charcoal peaks suggesting there were infrequent but intense fires associated with wetter conditions during the Holocene climatic optimum 8000—5000 years ago. The period from 4000 to 2000 cal. yr BP is characterised by more frequent charcoal peaks and higher background levels of charcoal, which is consistent with more regular but less intense fires during drier, cooler conditions. The sharp transition from siliciclastic sedimentation to peat formation began ~1200 cal. yr BP, which may relate to a return to wetter conditions. However, fire frequency appears to have increased in this time suggesting augmentation by anthropogenic or ENSO-related factors. Charcoal-rich layers in the siliciclastic unit are associated with poorly sorted, bimodal sediments with high proportions of clay, silt and gravel, which supports the hypothesis that there is an association between past fire events and rapid, coarse-grained, post-fire aggradation. By analogy with active colluvial aggradation following recent fires at nearby Mount Bold, it is evident that fire plays a significant role in hillslope destabilization and subsequent sediment movement, leading to rapid valley-fill aggradation — a chain of events to which we apply the term ‘pyrocolluviation’.

Comparison of radiocarbon dating of buried paleosols using arbuscular mycorrhizae spores and bulk soil samples

Fri, 23 Oct 2009 04:07:54 PDT

Ten paleosols from four separate soil pits located in Kärkevagge, a glaciated trough in Swedish Lapland, were dated using radiocarbon. Each soil was dated using both conventional bulk soil organic material (SOM) and a pure sample of arbuscular mycorrhizae (AM) fungal spores. The latter are produced by ubiquitous mycorrhizal fungi associated with the roots of many plant genera and may be viewed as a fossil material that has not interacted with any soil constituent subsequent to its emplacement in the soil — at a time presumed to mark the cessation of a favorable soil-forming environment. Regional deglaciation is presumed to have been about 10 000 BP, while a cosmogenic exposure date obtained from the valley floor in Kärkevagge dated at 13 100 ± 1638 BP. The youngest paleosol, buried at ~6 cm in soil pit M3, produced a spore date of 0—281 cal. yr BP (1). However, bulk SOM dates of the same paleosol A horizon gave widely divergent dates and varied with the sample pretreatment, ie, the combustion temperature and the acid-base treatment. For example, the bulk SOM dates for that paleosol ranged from a post-bomb date of 0—314 cal. yr BP (1) to 2366—2710 cal. yr BP (1) when subjected to different pretreatments (acid only, acid-base-acid) and ignition temperatures (400, 800, or 900°C). The oldest paleosol in the set, buried at ~61 cm in soil pit M6, dated at 5479—5698 cal. yr BP (1) using spores, but beyond calibration using bulk SOM. The spore dates were all within the range to be expected of postglacial paleosols, but the bulk SOM dates were frequently beyond the generally accepted time of deglaciation. In addition, all of the spore dates followed a conventional age/depth pattern while the bulk SOM dates did not. There are known possible sources of geogenic carbon contamination in Kärkevagge which may well account for the obviously invalid older bulk SOM dates. An additional complication is that the spore dates vary somewhat with their density and diameter. However, where other types of fossil or charcoal are unavailable it appears that the enormously broad distribution of spores and their lack of interaction within the soil and persistence may well offer the prospect of an unusually useful radiocarbon dating medium within paleosols.

Wild or cultivated Olea europaea L. in the eastern Mediterranean during the middle--late Holocene? A pollen-numerical approach

Fri, 23 Oct 2009 04:07:54 PDT

Assessment of the wild or cultivated origin of Olea europaea L. during the middle to late Holocene according to pollen analyses is of palaeoecological and evolutionary interest as olive is thought to be one of the earliest cultivated trees and is still one of the most important fruit trees of the eastern Mediterranean. This paper considers data from the Bronze—Iron Age harbour-town, Tell Tweini, of the Ugarit Kingdom, in the Syrian coastal lowland near Jableh (17 m a.s.l.) and from the Hellenistic—Roman Moatra-Bereket (1410 m a.s.l.), in the territory of Sagalassos, in Turkey’s western Taurus Mountains. Both of these sites have recorded the rise and collapse of early eastern Mediterranean urban systems from 4200 to 1600 cal. yr BP. The Syrian data suggest that the Olea pollen-type originated from wild varieties during the Bronze and Iron Ages despite archaeological evidence for olive cultivation in the northern Levant. For Turkey, the results of the pollen-numerical analyses support the existing archaeological evidence of a wealthy oleoculture in Hellenistic and Roman Anatolia and suggest important anthropogenic pressures on local ecosystems.

The response of a jack pine forest to late-Holocene climate variability in northwestern Wisconsin

Tweiten, M. A., Hotchkiss, S. C., Booth, R. K., Calcote, R. R., Lynch, E. A. — Fri, 23 Oct 2009 04:07:54 PDT

Terrestrial plant communities have the potential to respond to climate change rapidly, if dominant species are killed by a series of extreme events, or slowly, if the cumulative effects of shorter-term climate fluctuations result in long-term compositional change. We used pollen and charcoal records from a lake and a testate amoebae-derived history of water-table depth in a nearby peatland to assess the response of the jack pine-dominated forests of northwestern Wisconsin to the climate variability of the last ~2000 years. The hydrology record and the charcoal record indicate that the climate near Warner Lake over the last ~2000 years was characterized by multidecadal variation in moisture availability with no apparent multicentennial-long trends in moisture balance or fire frequency. However, the pollen record suggests that there were multicentennial-scale changes in the vegetation composition around Warner Lake. Direct comparison of the three proxy records is challenging, because of their differing temporal resolutions and the complexity of potential ecological responses to climate variability. Therefore, we developed an interpretive model to compare multiple simulated proxies under two scenarios of environmental variability in order to determine under what conditions apparently contradictory records are likely to be found. The interpretive model reveals that a record of multicentennial-long change in vegetation is possible if multidecadal climate variability interacts with ecological processes influencing the direction and magnitude of succession. Compositional changes in the Warner Lake pollen record could reflect long-term variation in temperature, seasonality or other climate factors independent of moisture balance; however it is also possible that multidecadal moisture variability interacted with ecological processes affecting recruitment and mortality of species following fires of varying size and severity. Decadal-scale climatic variability can lead to altered successional pathways and to changes in forest composition that last for centuries.

A 700 year record of temperature and nutrient changes in a small eutrophied lake in southern Finland

Luoto, T. P., Sarmaja-Korjonen, K., Nevalainen, L., Kauppila, T. — Fri, 23 Oct 2009 04:07:54 PDT

This study aimed to distinguish natural and anthropogenic environmental changes, mainly in climate and nutrient conditions, during the past c. 700 years in Lake Hampträsk, southern Finland. We used sedimentary assemblages of aquatic organisms and physical properties of the sediment as proxies for the past environmental conditions. The results of diatom-inferred phosphorus reconstruction indicated that the lake was already meso-eutrophic at c. AD 1400, possibly because the preceding cultivation of the area had increased the lake’s nutrient condition. Chironomid-inferred temperatures indicated favourable climatic conditions at the end of the ‘Medieval Warm Period’, but the temperatures steadily decreased until a significant drop in the values occurred at c. AD 1700, representing the coldest period of the ‘Little Ice Age’ (LIA) in southern Finland. This cold period was illustrated by major changes in the lake’s ecosystem and physical environment. After the LIA, the chironomid-inferred temperatures increased, as expected in the light of modern observations. However, the diatom-inferred phosphorus showed a decreasing trend, which is in contrast to the measured phosphorus values that imply a currently eutrophic condition. The reason for the underestimation may be the predominance of periphytic taxa that are assigned low TP optima in the inference model.

The development and local stand-scale dynamics of a Picea abies forest in southeastern Norway

Bjune, A.E., Ohlson, M., Birks, H.J.B., Bradshaw, R.H.W. — Fri, 23 Oct 2009 04:07:54 PDT

The local development and forest history have been studied based on pollen, plant macrofossil, stomata and charcoal analysis from a small forest hollow situated within an old-growth, closed Picea abies forest, rich in epiphytic lichens and wood-decaying fungi in southeastern Norway. The main aims of this study are to identify the natural development, the disturbance history and the role of human impact of this forest stand during the last 9650 years. Forest trees have always been dominant in the landscape around the forest hollow. The forest was first dominated by Betula and Pinus sylvestris, and later these were co-dominant with thermophilous deciduous trees such as Corylus, Fagus, Fraxinus excelsior , Quercus, Tilia cordata and Ulmus. During the last 1000 years, Picea abies (spruce) has become the dominant tree in this area, but its presence can be traced back about 9300 years. The establishment of spruce caused a major shift in the ecosystem. Human impact and fire seem to have been the driving factors to create openings for spruce to establish. Based on estimates of palynological richness, the most diverse pollen assemblages are found in periods with intermediate levels of disturbance.

The timing and causes of the final pre-settlement expansion of Betula pubescens in Iceland

Erlendsson, E., Edwards, K. J. — Fri, 23 Oct 2009 04:07:54 PDT

Palynological data from southern and western Iceland show rising values for the pollen of Betula pubescens for the period AD 600—800. The increased values for B. pubescens probably stem from both improved flowering conditions and increased coverage and density of woodlands associated with short-lived climatic amelioration within a phase of longer-term harsh climate. The swift response to climate change in the palynological record and good correlation with comparative data from other proxies indicates that Icelandic palynology offers an important, yet largely underexploited, tool for the reconstruction of Icelandic Holocene environments.

Holocene comment and reply: The disappearance of S. imbricatum from European raised bogs: a comment on McClymont et al

Robroek, B. J.M., Waucomont, J. G.M., Schouten, M. G.C. — Fri, 23 Oct 2009 04:07:54 PDT

McClymont et al. (The Holocene 18 (2008) 991—1002) present data on several environmental proxies to explore the disappearance of Sphagnum imbricatum from a peat bog in northern England, Wales and Ireland, respectively. McClymont et al. used their results to argue that a combination of rapid water-table rise and increased aeolian nutrient input from surrounding (agricultural) areas may have caused the disappearance of S. imbricatum from European raised bogs. The paper contributes to a growing body of literature focusing on the ‘abrupt’ decline of S. imbricatum (S. austinii) AD 1000—1700. From the literature it becomes apparent that determining the exact mechanism for the decline of S. imbricatum (S. austinii) is difficult. Hence, many potential mechanisms have been suggested, amongst which increased wetness, increased interspecific competition, local burning and increased nutrient input are just a few examples. Although we do not comment on the quality of the science, there are a few things to be considered in order to get a complete picture.

The disappearance of Sphagnum imbricatum from Butterburn Flow, UK: a reply to comments by Bjorn Robroek et al

Fri, 23 Oct 2009 04:07:54 PDT

We welcome the comments by Bjorn Robroek et al. (The Holocene 19 (2009) 1093—1094, this issue) on our paper (McClymont et al., The Holocene 18 (2008) 991-1002) and the opportunity to discuss further the complexities that surround the disappearance of Sphagnum imbricatum from Butterburn Flow (our study), and the implications for understanding the disappearance of this species in northwest Europe. We also wish to clarify our site of study; we presented data only from Butterburn Flow, northern England. Although we note that the disappearance of S. imbricatum here is part of a wider European decline in the late Holocene, we did not present data from Wales or Ireland as suggested in the opening paragraph of Robroek’s comment. We also noted that the replacement of S. imbricatum by S. magellanicum occurred over c. 44 years, but proposed that it may have been longer owing to evidence for reduced peat accumulation across the transition.

Holocene book reviews: Where our food comes from: retracing Nikolay Vavilov's quest to end famine: Gary Paul Nabhan, Washington: Island Press/Shearwater Books, 2008, 266 pp., US$24.95, hardback. ISBN 978-1-59726-399-3

Bost, J. B. — Fri, 23 Oct 2009 04:07:54 PDT

Holocene book review: La Cordillera Oriental Colombiana Transecto Sumapaz: (Studies on tropical Andean ecosystems, volume 7) Edited by Thomas van der Hammen, Stuttgart: Gebruder Borntraeger-Cramer Verlag, 2008, 1009 pp., 169.00, hardback. ISBN 978 3 443 50032 0

Urrego, D. H. — Fri, 23 Oct 2009 04:07:54 PDT

Holocene book review: Quantitative modeling of earth surface processes: Jon D. Pelletier, Cambridge: Cambridge University Press, 2008, 304 pp., {pound}40.00, hardback. ISBN 978-0-521-85597-6

Hindmarsh, R. C.A. — Fri, 23 Oct 2009 04:07:54 PDT

Holocene book review: Grasses and grassland ecology: David J. Gibson, Oxford: Oxford University Press, 2008, 320 pp., {pound}34.95, paperback, {pound}70.00, hardback. ISBN 978-0-19-852919-4 (paperback); ISBN 978-0-19-852918-7 (hardback)

Wragg, P. D. — Fri, 23 Oct 2009 04:07:54 PDT

Paleoprecipitation record from coral Sr/Ca and {delta}18O during the mid Holocene in the northern South China Sea

Deng, W.-f., Wei, G.-j., Li, X.-h., Yu, K.-f., Zhao, J.-x., Sun, W.-d., Liu, Y. — Fri, 14 Aug 2009 07:59:40 PDT

Coupled high-resolution Sr/Ca and ¹⁸O records of a modern and a mid-Holocene coral from Sanya in the southern Hainan Island, northern South China Sea (SCS), were reported and the residual ¹⁸O (¹⁸O) were calculated to indicate precipitation change in this region. Unlike other paleoclimate studies, this study focused on changes of precipitation time rather than precipitation amount. As negative ¹⁸O peaks in coral generally correspond to peak precipitations or rainy seasons in the surrounding region, the time offsets between negative ¹⁸O peaks and other seasonal indicators, such as sea surface temperature (SST), can well indicate the time of rainy seasons, and the precise time offsets can be estimated by the method of cross spectral analysis. The results of the modern coral indicate that the variation of the coral ¹⁸O lags that of the instrumental measured precipitation by about 2 months, and about 3 months to the SST derived from coral Sr/Ca ratios. This agrees well with the modern observation that the salinity change in the southern coastal regions generally lags that of the precipitation in Hianan Island by about 2 months, and the precipitation change lags about 1 month behind the SST in this region. Thus, coral ¹⁸O records can be a reliable proxy for the change of rainy seasons in this region. The results of the mid-Holocene coral show about 2.5 months’ leading of the ¹⁸O variation ahead of the SST. By compensating the approximate 3 months’ lag of the ¹⁸O variation behind the SST in modern time, the occurrence of rainy seasons during the mid Holocene may have advanced about 5—6 months. In detail, it may start around December and end around April to May with maximum occurring around February. Therefore, rainy seasons mainly occur in winter through early spring during the mid Holocene, compared with that from May through October in modern times. Such precipitation patterns appear to agree with the mid-Holocene pollen records in this region. Variations of large-scale circulation may possibly result in such a different precipitation pattern. Further studies, in particular climate model studies collaborated with meteorologists, are required for a better understanding of the mechanism.

Possible complexity of the climatic event around 4300--3800 cal. BP in the central and western Mediterranean

Fri, 14 Aug 2009 07:59:40 PDT

This paper presents an event stratigraphy based on data documenting lake-level changes as well as volcanic eruptions over the period 4500—3500 cal. BP from sediment sequences of Lakes Accesa in Tuscany (north-central Italy) and Maliq (Albania) in the central Mediterranean. The available data make it possible to recognise a tripartite climatic oscillation between c. 4300—3800 cal. BP. A phase characterised by drier conditions at c. 4100—3950 cal. BP appears to have been bracketed by two phases marked by wetter conditions and dated to c. 4300—4100 and 3950—3850 cal. BP, respectively. The deposition of the Avellino tephra occurred during the first humid phase, slightly before 4300 cal. BP, and that of an interplinian tephra AP2-AP4 (or Pr1) around 4050 cal. BP during the dry intermediate phase. This dry median episode may be related to the so-called ‘4.2 ka event’ observed in tropical areas as well as in northwestern Italy. A comparison of the Accesa lake-level record with palaeoclimatic terrestrial and marine records suggests that this complex climatic oscillation around 4300—3800 cal. BP affected the central and western Mediterranean area. The key position of the 4300—3800 cal. BP climatic oscillation at a crucial transition from mid to late Holocene in the Mediterranean and tropical areas, deserves major consideration in further investigations.

Extreme fires under warmer and drier conditions inferred from sedimentary charcoal morphotypes from Opatcho Lake, central British Columbia, Canada

Enache, M. D., Cumming, B. F. — Fri, 14 Aug 2009 07:59:40 PDT

Predictions of the extent of forest fires under warmer and drier conditions in boreal regions require knowledge of long-term relationships between fire and climate. However, many long-term studies that utilize the remains of total charcoal in lacustrine sediments fail to demonstrate a relationship between climate change and fire activity. A new approach to reconstruct the relative-area burned based on specific types of charcoal particles (the charcoal-morphotype (CM) fire index) has shown significant correlations to recorded forest fires. Here we assess the utility of the CM derived from an analysis of charcoal morphotypes in sediment cores from Opatcho Lake (British Columbia, Canada) using two independent paleoclimate proxies over the last 400 years, and since the mid Holocene. Over the past 400 years, significant correlations between the CM fire index and independent climate reconstructions (diatom-inferred salinity, dendroclimatic reconstructions of temperature and precipitation, and reconstructions of the Pacific Decadal Oscillation) range from 0.35 to 0.42. Similarly, since the mid Holocene the correlation between the CM fire index and independent proxies of past climate (diatom-inferred salinity and temperature inferences from chironomids from the southern interior of British Columbia) range from 0.70 to 0.76. These significant correlations strongly contrast with the very low and insignificant correlations between the CM fire index and total charcoal, suggesting that this approach provides paleofire information not available from traditional techniques. The CM fire index suggests that fires were at least two- and five-fold larger than those observed during the instrumental period, over the last 400 and 6000 years, respectively.

Fire frequency and landscape management in the northwestern Pyrenean piedmont, France, since the early Neolithic (8000 cal. BP)

Rius, D., Vanniere, B., Galop, D. — Fri, 14 Aug 2009 07:59:40 PDT

Both quantitative reconstruction of fire frequency from charcoal counts and pollen analysis were undertaken on a 312 cm sediment core from Gabarn peat bog. An 8000 yr cal. BP palaeofire record and vegetation history were established on the basis of nine ¹⁴C (AMS) dates. As anthropogenic Inferred Fire Frequency (IFF) has seldom been studied, we test and discuss two different methods of frequency calculation. Our results shows a clear Holocene bipartition at c. 3500—4000 cal. BP characterized by a three times decrease in Mean Fire Interval (MFI): from 7000 to 4000 cal. BP, MFI = 530 yr; from 4000 to 400 cal. BP, MFI = 160 yr. In an Atlantic vegetation context, we hypothesize this fire regime with such episode frequency to be mainly controlled by human activities. This hypothesis is supported by comparisons with other European quantified palaeofire regimes (Swiss Alps, northern Italy) whether they are controlled by climate, man or both. Taking into account the pollen record, we interpret the Gabarn palaeofire record links with human pressure and land use. Our results suggest that the relationship between fire frequency and human pressure is not always linear. Fire frequency could also reflect land-use shifts and changing use of fire within agro-pastoral activities.

Biodiversity changes in highly anthropogenic environments (cultivated and ruderal) since the Neolithic in eastern France

Brun, C. — Fri, 14 Aug 2009 07:59:40 PDT

In highly anthropogenic plant communities, environmental conditions and human practices play a significant role in the composition, structure and diversity of the flora. This paper presents a study of current and past floras of two anthropogenic habitats (cultivated and ruderal) in eastern France that have been the subject of numerous palaeoenvironmental studies (pollen and seed analysis). To understand the different components that constitute the biodiversity of these floras, it is necessary to develop a transdisciplinary method combining ecology, phytogeography and palaeoenvironmental sciences. As a first step, a distinction has been made between native and alien plants as well as between two categories of the latter: archaeophytes (alien taxa introduced into a study area before AD 1500) and neophytes (alien taxa which became established after AD 1500). Second, the study of ecological characteristics of these species and the knowledge of human and climatic history of the region allow the elaboration of a synthesis of biodiversity evolution in these environments from the Neolithic to the present day. The results of this analysis show that there has been a constant enrichment of the anthropogenic flora by alien species through time. Two main periods can be emphasized: the first began in the late Neolithic and reached a peak in the late Bronze Age, the second began with the advent of Modern times. This kind of study has a double implication: first, by distinguishing between native and alien species (archaeophytes and neophytes) and by refining their ecological characteristics, the method allows a critical evaluation of the modern phytosociological units which are traditionally used to interpret fossil assemblages and to discriminate species that are ‘strong’ indicators of human activities. Second, the recognition of native and alien species also has implications for species invasion studies and for species conservation and vegetation management in anthropogenic habitats.

A quantitative high-resolution summer temperature reconstruction based on sedimentary pigments from Laguna Aculeo, central Chile, back to AD 850

von Gunten, L., Grosjean, M., Rein, B., Urrutia, R., Appleby, P. — Fri, 14 Aug 2009 07:59:40 PDT

We present a pigment-based quantitative high-resolution (five years) austral summer DJF (December to February) temperature reconstruction for Central Chile back to AD 850. We used non-destructive in situ multichannel reflection spectrometry data from a short sediment core of Laguna Aculeo (33°50'S/70°54'W, 355 m a.s.l., central Chile). Calibration-in-time (period AD 1901—2000, cross-validated with split periods) revealed robust correlations between local DJF temperatures and total sedimentary chlorin (relative absorption band depth (RABD) centred in 660—670 nm RABD_660;670: r=0.79, P<0.01; five-years triangular filtered) and the degree of pigment diagenesis (R_{660nm/670 nm}: r=0.82, P<0.01; five-years triangular filter). Root Mean Squared Error values are small (between 0.24 and 0.34°C) suggesting that most of the reconstructed decadal-scale climate variability is significant. Our data provide quantitative evidence for the presence of a Medieval Climate Anomaly (in this case, warm summers between AD 1150 and 1350; T = +0.27 to +0.37°C with respect to (wrt) twentieth century) and a very cool period synchronous to the ‘Little Ice Age’ starting with a sharp drop between AD 1350 and AD 1400 (–0.3°C/10 yr, decadal trend) followed by constantly cool (T = –0.70 to –0.90°C wrt twentieth century) summers until AD 1750. The structure of variability is consistent in great detail with annually resolved tree-ring based warm-season temperature and river discharge reconstructions from northern Patagonia (42°S) for the past 400 years, with qualitative climate reconstructions from Andean glacier fluctuations, and with hydrological changes in Patagonian lake sediment records.

Rapid deforestation of South Island, New Zealand, by early Polynesian fires

McWethy, D. B., Whitlock, C., Wilmshurst, J. M., McGlone, M. S., Li, X. — Fri, 14 Aug 2009 07:59:40 PDT

In most parts of the world where people have colonized and modified their landscapes for several millennia or more, it is often difficult to discriminate anthropogenic burning from natural fire regimes that are linked to climate regimes. New Zealand provides a unique setting for identifying human influence on fire occurrence because it was settled recently (c. AD 1280) at a time when climates are considered to be similar to today. Late-Holocene pollen and charcoal records from New Zealand provide striking evidence for initial Polynesian (Maori) arrival being strongly associated with widespread burning and loss of native forest. The duration of initial forest clearance and the spatial pattern of burning that led to this transformation are still poorly understood. We present high-resolution charcoal and pollen analyses of sediment cores from five lakes, located on the deforested eastern side of the Southern Alps. These records document the local fire history of the last 1000 years and the response of vegetation and watersheds to burning. Our results suggest that one to several high-severity fires occurred within a few decades of initial Maori arrival, and this ‘Initial Burning Period’ (IBP) resulted in the majority of forest loss and erosion. Changes in sedimentation rates, soil chemistry and magnetic susceptibility occurred simultaneously with the first fires at some sites, and marked the end of the IBP at others, suggesting substantial and rapid alteration of watershed vegetation, soil and biochemistry. Timing of the beginning of the IBP varied across sites but the duration of this period was brief (decades to a century). Our results suggest that Maori burning of native forests was deliberate and systematic. These forests had no previous history of fire and thus showed little resilience to the introduction of a new disturbance.

Holocene weak monsoon intervals indicated by low lake levels at Hulun Lake in the monsoonal margin region of northeastern Inner Mongolia, China

Xiao, J., Chang, Z., Wen, R., Zhai, D., Itoh, S., Lomtatidze, Z. — Fri, 14 Aug 2009 07:59:40 PDT

A 170 cm long sediment core spanning the last 10 000 years was recovered from Hulun Lake in the northeastern margin of the East Asian summer monsoon. The sediment core was analyzed at 1 cm intervals for grain-size distribution and sedimentary component partition. These data provide a proxy record of the monsoon variability on millennial to centennial scales during the Holocene. We used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions. Three coarse components representing nearshore suspension, saltation and traction, together with the sand-fraction percentage and the median grain size of bulk samples, indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation. Higher percentages of the nearshore components accompanied by more sand-fraction proportions and coarser median grain sizes reflect lower lake stands resulting from weaker monsoon circulations. The results show low levels at Hulun Lake c. 8000—7850, 6400—6050, 5150—4900, 4500—3800, 3050—2800, 1650—1400, 1150—900, 700—600, and 400—350 cal. yr BP, indicating the weakened East Asian summer monsoon during these intervals. We suggest that these weak monsoon events would not only result from the reduced ocean—atmosphere interacting processes in the western tropical Pacific, but could also be related to cold climatic conditions in the Northern Hemisphere high latitudes.

A 9111 year long conifer tree-ring chronology for the European Alps: a base for environmental and climatic investigations

Fri, 14 Aug 2009 07:59:40 PDT

An ultra-long tree-ring width chronology (9111 years long, 7109 BC to AD 2002) has been established based on the analysis and dating of 1432 subfossil/dry dead wood samples and cores from 335 living trees. The material was collected from treeline or near-treeline sites (c. 2000 to 2400 m a.s.l.) mainly in the Eastern Alps. The availability of preserved samples through time at high altitudinal sites is influenced by Alpine forest history and is partly climatically controlled, as shown by comparisons of the sample depth record of the Eastern Alpine Conifer Chronology (EACC) with the Holocene glacier record. The similarity of variations over time between the sample depth of the chronology and the mid-Holocene GISP2 ¹⁰Be record suggest a relationship between sample depth and solar activity. The Eastern Alpine Conifer Chronology has already been used as a dating base in environmental studies, eg, on glacier fluctuations, as well as in archaeological studies.

The origin and development of a minerotrophic soak on an Irish raised bog: an interpretation of depth profiles of hydrochemistry and peat chemistry

Fri, 14 Aug 2009 07:59:40 PDT

The peat and pore-water biogeochemistry of an Irish oceanic raised bog are reported with a view to understanding the origin and development of a minerotrophic soak contained within an ombrotrophic bog. Depth profiles of electrical conductivity, pore-water chemistry and peat chemistry were recorded from the mire surface down to a maximum depth of 10 m (approximately 1 m into the underlying mineral soil) from the centre of Lough Roe, a minerotrophic soak on Clara Bog in the Irish midlands, and from a location in the surrounding bog. Distinct differences in the hydrochemistry and peat chemistry between both sites are evident in the upper 5 m of the profile, indicating that conditions differed during the latter development of the mire, despite both sites being located on the apex of the raised bog dome. As expected, the profiles recorded from the ombrotrophic bog are characterised by low ionic concentrations in the upper bog peat with an increase in the concentration of calcium and other ions in the lower fen peat (from 5.5 m depth). At the Lough Roe site, the profile shows relatively high concentrations of calcium and other ions in the upper part of the profile. To our knowledge, this is the first report of such detailed minerotrophic chemical profiles from the central area of a raised bog dome. We hypothesize that the relevant minerals originate from the underlying clay layer and fen peat within the basin of the bog and the minerals prevailed within the soak because of (1) the generation of a flow of water from the developing bog through the minerotrophic fen peat towards the soak during its early development, and (2) increased rates of decomposition within the soak throughout its existence. The implications for the future conservation management of the site are discussed.

Multiproxy lake sediment records at the northern and southern boundaries of the Aspen Parkland region of Manitoba, Canada

Teed, R., Umbanhower, C., Camill, P. — Fri, 14 Aug 2009 07:59:40 PDT

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using ²¹⁰Pb and ¹⁴C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40— 60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie—forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics.

Land subsidence in the Nile Delta: inferences from radar interferometry

Becker, R. H., Sultan, M. — Fri, 14 Aug 2009 07:59:40 PDT

The Nile Delta formed by progression of a complex system of deltaic fans throughout the Pleistocene, with the Modern delta being formed from sediments supplied by at least ten distinct distributaries throughout the Holocene. With an average elevation of approximately 1 m above sea level within 30 km of the coast and a predicted rise in sea level of 1.8—5.9 mm/yr the subsidence of the northern delta has become a topic of major concern to the Egyptian population and government. The Nile Delta is home to more than 50 million people and the major agricultural production area for Egypt. We evaluated the modern rates of subsidence of sections of the northeastern Nile Delta (a total length of 110 km, up to 50 km from the coastline) using persistent scatterer radar interferometry techniques applied to 14 ERS-1 and ERS-2 scenes. The area covered includes the present active depocenter of the Damietta promontory, and the nearby Mendesian depocenter that was active up to recent times (to 2500 years ago). The highest subsidence rates (~8 mm/yr; twice average Holocene rates) do not correlate with the distribution of the thickest Holocene sediments, but rather with the distribution of the youngest depositional centers (major deposition occurred between ~3500 yr BP and present) at the terminus of the Damietta branch. The adjacent, slightly older (8000—2500 yr BP) Mendesian branch depositional center is subsiding at slower rates of 2—6 mm/yr. Results are interpreted to indicate that: (1) modern subsidence in the Delta is heavily influenced by compaction of the most recent sediments, and (2) highly threatened areas are at the terminus of the Damietta and possibly the Rosetta branches, where active deposition is occurring.

A multistory gigantic subaerial debris flow in an active fault scarp in NW Anatolia, Turkey: anatomy, mechanism and timing

Ocakoglu, F., Acikalin, S., Gokceoglu, C., Karabacak, V., Cherkinsky, A. — Fri, 14 Aug 2009 07:59:40 PDT

Mass instability in the uplifting footwall blocks of normal faults involves a range of regional and local factors including, among others, climatic setting, topography, lithology and particularly ground shaking during earthquakes. Morphological and sedimentological investigations backed by ¹⁴C dating on a huge debris flow and its zone of depreciation provided favorable insights for dynamics and causative factors of this mass wasting. Our observations showed that Ismetpasa Debris Flow with a volume of 96 km³ involves three individual flows of decreasing significance in the late Pleistocene—Holocene period. The primary flow occurred in relation to a huge landslide developed on highly fractured and altered basaltic lavas near the crest of fault scarp c. 18.7 ka BP and probably conditioned by high precipitation rates in the early Interglacial. Although, most of the blocky debris flow transferred into the neighboring graben to form a 2 km wide debris fan, some remnant blocks and flow-induced valley-side slickensides can still be observed in the zone of depreciation. One km long secondary flow was sourced from the remnants of primary flow and was realized at 7.9 ka BP in another humid period of the Holocene. The third, though minor (less than 100 m long), mobilization of the flow occurred on one of the steep faces of secondary flow in 1960s when the mean precipitation was higher than that of today. Good coincidence of timing of individual debris flows with the humid phases of the late Pleistocene—Holocene period showed that long-term antecedent precipitation is the dominant causative factor.

Legacy of the past land-use changes and management on the 'natural' upland forest composition in the Apuseni Natural Park, Romania

Feurdean, A. N., Willis, K. J., Astalos, C. — Fri, 14 Aug 2009 07:59:40 PDT

The Apuseni Natural Park (ANP) in northwestern Romania was founded in 1990 to protect the old-growth forests in this region and their high species diversity. We present results from palaeoecological investigation (pollen, micro- and macrocharcoal) of two sedimentary sequences from ANP alongside regional archaeological and historical records to explore (1) the degree to which the present-day vegetation in this part of the reserve is a consequence of past land-use systems and forest management; (2) how this forest differs from what was there prior to human activity; and (3) how the understanding of correlations between historical land-use and vegetation changes is directly relevant for reserve conservation strategies and sustainable management of this reserve. Results indicate that anthropogenic activities had little influence on the forest dynamics prior to 200 BC but became evident thereafter as a consequence of forest burning, seasonal pastoralism and small-scale deforestation. From AD 1550, anthropogenic activities also included wood clearances for smelting, and over the last 150 years it is apparent that these forests have been industrially exploited and managed. Despite this legacy of these past land uses, most of the tree species growing presently in the forests are native. Humans have, however, altered their original relative abundance, leading to a great reduction of Fagus sylvatica and Abies alba, and to less extent of Ulmus, Tilia, Fraxinus excelsior and the enrichment with Picea abies, Betula, Alnus, Pinus and some Quercus, Carpinus betulus, Corlyus avellana .

Holocene book review: Archaeology and landscape in central Italy: papers in memory of John A. Lloyd (Oxford University School of Archaeology: Monograph 69) Edited by G.R. Lock and A. Faustoferri, Oxford: School of Archaeology, 2008, 253 pp., US$76.00, hardback. ISBN 978-1-905905-06-5

Launaro, A. — Fri, 14 Aug 2009 07:59:40 PDT

Holocene book review: Snails: archaeology and landscape change. Paul Davies, Oxford: Oxbow Books, 2008, 208 pp., {pound}40.00, hardback. ISBN 978-1-84217-317-6

Limondin-Lozouet, N. — Fri, 14 Aug 2009 07:59:40 PDT

Abrupt forest ecosystem change in SW Sweden during the late Holocene

Gustavsson, G., Lemdahl, G., Gaillard, M.-J. — Wed, 15 Jul 2009 03:42:44 PDT

A peat profile from a small raised bog, situated in SW Sweden, was studied for insect, pollen and charcoal analyses in order to reconstruct the late-Holocene forest history of the area. The palaeoecological records cover the last 3700 cal. years. The results were compared with archaeological data, historical documents and palaeoclimate reconstructions from the region. From 1650 cal. yr BC to AD 1310 cal. yr, the study area was characterized by deciduous woodland with a diverse invertebrate fauna. The recorded insects indicate a relatively open or mosaic forest environment with abundance of dead wood. This forest environment was probably maintained by disturbances such as cattle grazing, fire, wood coppicing and small-scale cultivation. At around AD 1310, a major and rapid change in the forest ecosystem occurred, ie, species-rich deciduous woodland was replaced by a species-poor beech forest. The data indicate that a change in land use was the likely reason for the shift in forest type. Grazing and fire ceased, while tree cutting increased. The shift in land use correlates well with political—societal changes in the region during Mediaeval time. Climate changes seem to have influenced the wetland environment, but there is no obvious correlation between major or minor shifts in forest ecosystem and reconstructed climate changes. Today, nature conservationists regard the beech forests of Halland as remains of primeval forests hosting a unique flora and fauna. Our results give new insights and challenge that view.

Climate, cod and crops: coastal land use in the SW Barents Sea region during the past 2.5 ka

Sjogren, P. — Wed, 15 Jul 2009 03:42:44 PDT

The SW coast of the Barents Sea is a historical transition zone between the traditional agrarian cultures of western Europe and Sami hunter-gatherers of northern Fennoscandia. It is today north of the climatic limit of cereal cultivation and the economy is primarily based on fisheries. The pollen content of two peat profiles from the outer coastal island Sørøya (c. 70.5°N) were examined. Increased anthropogenic influence was seen in the pollen assemblages at 600—100 BC, AD 150—550, AD 1300—1550 and AD 1700—2000, as well as a general environmental shift around AD 950, probably towards a wetter climate and more open vegetation. The results largely confirm the general held view on agrarian expansion phases in North Norway. These different phases are discussed from a regional, historical, economic and environmental perspective. During the early Iron Age the arctic limit for agriculture is extended northward along the coast into the Barents Sea area, probably during periods of more favourable climate. From the late Middle Ages onwards the development towards an efficient market economy allowed better exploitation of the marine recourses, which reduced the dependence on climatically sensitive agrarian activities.

Holocene evolution of a wetland in the Lower Seine Valley, Marais Vernier, France

Wed, 15 Jul 2009 03:42:44 PDT

Estuaries like that of the Seine River in NW Europe developed in incised fluvial valleys after the last glacial maximum. Since the 1940s, several authors have studied the largest wetland of the Seine estuary, the Marais Vernier, to understand depositional environments during Holocene infilling. We reinterpret previous research based on new and published data (for example fill thickness and material source) to (1) describe facies and depositional environments; (2) reconstruct palaeoenvironmental evolution; (3) show the influence of local and global forcing on depositional environments. Before 7000—6000 cal. BC, terrestrial material was deposited because of catchment erosion related to changes in climate. Just before 7000—6000 cal. BC, estuarine material began to be deposited in low-lying areas in response to sea-level rise, while terrestrial material still settled at higher elevations. After this, but before 5850—5710 cal. BC, estuarine material areas began to accumulate at both high and low elevations. This marked a general flooding of the Marais Vernier, synchronous with that at the Seine estuary mouth. Soon after, peat accumulated over a wide area as a response to a local change in accommodation and a worldwide drop in sea level. A tidal channel developed to the west of the Marais Vernier, providing minerogenic material. After 1130—900 cal. BC, human influence becomes increasingly clear in the record. This record of regional change during the Holocene can serve as a reference for further studies in the area.

High-resolution, well-preserved tritium record in the ice of Bortig Ice Cave, Bihor Mountains, Romania

Kern, Z., Molnar, M., Svingor, E., Persoiu, A., Nagy, B. — Wed, 15 Jul 2009 03:42:44 PDT

Two 2 m long ice cores (BA and BB) were extracted from the floor ice of Borstig Ice Cave in December 2005. Below a co-existing dust horizon (~13 cm underneath the 10 December 2005 ice surface) neither core presented any sign of hiatus, so the ice deposition is considered to be continuous. Tritium concentration of 94 samples from a 1.85 m long ice section were analysed by liquid scintillation counting technique. Samples from the lower 0.33 m of the sequence did not contain tritium above the critical level (7.2 TU). The highest value of tritium content (166.4±4.0 TU) was found at ~96 cm below the surface. This salient value is considered to be synchronous with the climax of tritium concentration in the Northern Hemisphere's atmospheric precipitation (1963). Beside this characteristic global radiochemical marker event, minor events were also detected, and dated (ie, 1954, 1958 and 1975) by corresponding peaks in the tritium concentration record of BB ice core to peaks of an estimation of tritium activity of past precipitation at Borstig Ice Cave location. The estimation was based on a data set from four nearby stations of the Global Network of Isotopes in Precipitation. The highest annual accumulation rate (6.74 cm/yr) was between 1958 and 1963 and gradually decreased to 0.54 cm/yr for the recent decades. The mean ice accumulation rate was 4.34 cm/yr over the 1954—1986 period. The estimated age at the bottom of the 21 m thick ice block assuming constant accumulation is roughly 500 years.

Isotopic analysis of wetland development in the American Southwest

Minckley, T. A., Clementz, M. T., Brunelle, A., Klopfenstein, G. A. — Wed, 15 Jul 2009 03:42:44 PDT

The analysis of stable isotope and elemental fractions of organic material collected from San Bernardino Ciénega was used to understand the history of vegetation composition and climate change within this desert wetland. A 4000-yr record of sediment buildup, based on four ¹⁴C measurements, provides unique opportunities for the study of environmental conditions within an arid landscape and documents climate shifts from drier to wetter conditions in the late Holocene. ¹³C, ¹⁵N, and C:N values were measured from a 3.8 m deep sedimentary section to understand the dynamics of vegetation and hydrology in desert wetlands. Through this section we observe ¹³C and C:N values indicating a shift in the dominant source of organic matter within the section: prior to 850 cal. yr BP (below 60 cm), aquatic vascular plants and occasionally terrestrial vegetation were the primary organic sources, whereas freshwater algae were the dominant organic matter source above this level. These values indicate that while conditions remained arid at this locality, the amount of standing water on the ciénega has increased over time. These results document both climate change and vegetation evolution on the ecotone of the Sonoran and Chihuahuan deserts and demonstrate how the study of local sediment accumulation in ciénegas can provide critical information on changing conditions within arid environments.

Land--sea linkage of Holocene paleoclimate on the Southern Bering Continental Shelf

Wed, 15 Jul 2009 03:42:44 PDT

Detailed diatom records within surface and core sediments from the Southern Bering Continental Shelf (SBCS) reveal that the Holocene evolution of sea-ice distribution is associated with low pressure patterns. Holocene sea-ice distribution over the SBCS was mainly controlled by the location of the Aleutian Low. The corresponding paleoceanographic and paleoclimate conditions can be divided into three stages: (1) the early Holocene (before 7000 cal. yr BP) was characterized by extensive sea-ice distribution under two low-pressure cells, which covered the western Bering Sea and the Gulf of Alaska, respectively. (2) Between 3000 and 7000 cal. yr BP, the low-pressure system over the Gulf of Alaska became weak, causing total sea-ice mass over the SBCS to retreat. (3) In the past 3000 years, prevailing southwesterly winds over the SBCS due to the developing Aleutian Low have reduced further sea-ice cover on the SBCS. These paleoclimatic changes were probably a response to ENSO variation. The timings of water mass exchanges on the SBCS coincided with sea-level change along the Alaskan Peninsula. As a result, subsequent morphologic alterations have also influenced the paleoceanographic condition of the SBCS. The effect of the surface coastal water and bottom marine water on the SBCS intensified about 6000 cal. yr BP when sea level increased.

Stomatal-based inference models for reconstruction of atmospheric CO2 concentration: a method assessment using a calibration and validation approach

Finsinger, W., Wagner-Cremer, F. — Wed, 15 Jul 2009 03:42:44 PDT

We investigated changes in atmospheric CO₂ concentration (hereafter [CO₂]) over the period AD 1700—2002 as reconstructed using the inverse relationship between stomatal frequencies (SF) of Betula nana leaves from northern Europe and [CO₂]. The predictive ability of SF-inference models was assessed using a method of independent validation that involves two steps: (1) a training set of leaves grown between AD 1843 and 2002 was used to generate inference models; (2) the models were then applied to a fossil SF record of leaves grown between AD 1700 and 2002 that was split into two parts, a validation period (after AD 1850) and a reconstruction period (AD 1700—1850). Although our inference models had uncertainties comparable with other SF-inference models (root mean square error (RMSE) = c. 18—19 ppmv), uncertainties arising from the independent validation were larger (RMSE = c. 31—34 ppmv). Smoothed SF-inferred [CO₂] values after AD 1850 corresponded better to the industrial [CO₂] increase observed from instrumental records and from high-resolution ice cores, corroborating the accuracy of the reconstruction method in capturing a long-term (decadal- to centennial-scale) signal. This also indicates that in our record higher-frequency signals (eg, [CO₂] maxima around AD 1750) are potentially less reliable. In an attempt to estimate the maximum reconstruction uncertainty (± 67 ppmv), we considered (i) the RMSE of the validation (validation error) and (ii) the maximum difference between reconstructions obtained with different inference models during the validation period (method error). We suggest that reconstruction uncertainties may be reduced by reducing the uncertainty of our inference models, with a subfossil record characterized by lower variability in the SF time series over the validation period, and by smoothing the reconstruction. This study shows that independent validation is an important step to assess the precision and accuracy of quantitative proxy-based reconstructions.

Holocene vegetational landscapes of NE Iberia: charcoal analysis from Cova de la Guineu, Barcelona, Spain

Allue, E., Vernet, J.-L., Cebria, A. — Wed, 15 Jul 2009 03:42:44 PDT

This paper presents the anthracological results of Cova de la Guineu. This cave, which is located at the NE of the Iberian Peninsula, has provided charcoal samples from the early Neolithic to the Iberian period enabling the identification of different phases on the basis of flora assemblage interpretation. The results show how Mediterranean forests have been present since the early Holocene stages. At the early phases of the sequence the assemblage records dominant meso-screrophyllous taxa (deciduous Quercus, Taxus baccata), then thermophilous taxa (evergreen Quercus) spread, and finally a late phase of transformation dominated by thermophilous and heliophilous taxa (Mediterranean Pinus). The interpretation and discussion deals with the development and transformation of primary and secondary forests due to human disturbances and climatic variations. The anthracological record from Cova de la Guineu suggests that both elements were important and define the evolution of vegetation during the Holocene in the region.

Sea ice and marine climate variability for NW Iceland/Denmark Strait over the last 2000 cal. yr BP

Andrews, J.T., Belt, S.T., Olafsdottir, S., Masse, G., Vare, L.L. — Wed, 15 Jul 2009 03:42:44 PDT

MD99-2263 is a 46 cm box core collected from Djupall, a trough that cuts across the NW Iceland Shelf and ends above Denmark Strait. We provide a multiproxy record that documents changes in the regional marine climate over the last ~1700 yr. The depth/age model is based on seven calibrated radiocarbon dates on mollusk shells and on ²¹⁰Pb and ¹³⁷Cs. Sediment accumulation rates were variable (0.2—0.8 mm/yr) but increased dramatically ~AD 1500. Grain-size, magnetic properties, quantitative mineral composition of the <2 mm sediment fraction, benthic foraminiferal composition, benthic and planktic ¹⁸O ratios, and abundances/fluxes of the sea ice biomarker IP₂₅ were determined. To better compare the various proxies, 12 of the critical climate proxies were co-ordinated into 100-yr/sample time series, which were examined by Principal Component Analysis. The 1st axis explained 49% of the variance and the 2nd axis explained an additional 17%. The variables most strongly associated with the 1st axis were sediment properties (phi mean, clay%) and the sea ice biomarker. Mineralogical indicators of drift ice rafting, such as the presence of quartz and potassium- and sodium-feldspars, coincide with the IP₂₅ biomarker data and show an increase after AD 1200, but high values of quartz and some feldspars also occurred between c. AD 300 and 900 with pronounced minima between AD 900 and 1100. Overall, our data suggest a simple two-fold division in climate conditions over the last 1700 yr, with the major change occurring c. AD 1200. In the last few decades, conditions have reverted towards those experienced prior to AD 1200.

Testing a cellular modelling approach to simulating late-Holocene sediment and water transfer from catchment to lake in the French Alps since 1826

Welsh, K.E., Dearing, J.A., Chiverrell, R.C., Coulthard, T.J. — Wed, 15 Jul 2009 03:42:44 PDT

This paper describes the application of a hydrogeomorphological numerical model (CAESAR) to simulate, at hourly time steps, changes in the hydrological and sediment regime of the Petit lac d'Annecy catchment. The outputs of the model were validated in three ways. In the short term (~5 years), water discharge outputs were compared against observed instrumental data. Over the longer term, modelled sediment discharge (AD 1825—2005) was compared with proxies for detrital sediment influx (environmental magnetism) and accumulation rates discerned from a ²¹⁰Pb chronology for the lake sediments. Finally, spatial validation of the modelled erosion and deposition of sediment was undertaken by comparison with a field and remotely sensed survey of catchment geomorphology. The results suggest that while minor perturbations in forest cover during the last 180 years have partially conditioned the response of the sediment system, the bulk of modelled sediment discharge and particularly the peaks in sediment discharge were controlled by flood duration and magnitude, which in turn is driven by precipitation (storms/floods) and snowmelt. Basin geometry and geomorphology of each sub-catchment (Ire and Tamie) were also important in producing differences in the modelled sediment discharge. In essence, these differences were a function of sediment accommodation space and the ability of each system to store and release sediments. Modelled sediment discharge and _para (lake sediments) display similar histories, and thus are both interpreted as reflecting variations in detrital sediment supply. Intriguingly the style of modelled sediment discharge from the Ire, a confined mountain torrent, displays a greater similarity to and perhaps dominates the lake sediment record. These results provide partial validation of the CAESAR model and indicate that perhaps in the future it may be used as an exploratory and predictive tool in determining the impact of changes in climate, meteorology and land use on lake-catchment systems.

Equifinality and uncertainty in the interpretation of pollen data: the Multiple Scenario Approach to reconstruction of past vegetation mosaics

Bunting, M.J., Middleton, R. — Wed, 15 Jul 2009 03:42:44 PDT

The long-term goal of pollen analysis has always been the reconstruction of past vegetation mosaics. However, the pollen signal is spatially integrated, and ecologically distinct vegetation structures can produce identical pollen signals. This paper proposes an iterative approach to reconstruction, the Multiple Scenario Approach, which involves creating a large number of hypothetical landscapes using a combination of deterministic and probabilistic `rules' for plant placement coupled with environmental parameters such as topography, simulating the pollen assemblage produced by each, and comparing them statistically with a sedimentary pollen signal to identify possible reconstructions. The method expressly aims to find multiple possible reconstructions, and also gives some insight into the spatial aspects of the vegetation being reconstructed in addition to its composition.

Holocene book review: Climate and society in colonial Mexico: a study in vulnerability: Georgina H. Endfield, Oxford: Wiley-Blackwell Publishing, 2008, 235 pp., {pound}24.99/US$39.95, paperback. ISBN 978-1-4051-4582-4

Doolittle, W. E. — Wed, 15 Jul 2009 03:42:44 PDT

Holocene book review: The great warming: climate change and the rise and fall of civilizations: Brian M. Fagan, New York: Bloomsbury Press, 2008, 282 pp., US$26.95, hardback. ISBN 978-1-59691-392-9

Porter, J. C. — Wed, 15 Jul 2009 03:42:44 PDT

Holocene book review: Natural climate variability and global warming: a Holocene perspective: Edited by Richard W. Battarbee and Heather A. Binney, Oxford: Wiley-Blackwell, 2008, 276 pp., {pound}55.00, hardback. ISBN 978-1-4051-5905-0

Matthews, J. A. — Wed, 15 Jul 2009 03:42:44 PDT