The Holocene current issue

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