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Isotopic variation in modern lake waters from western Greenland

NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

N. John Anderson

Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark

The stable-isotope composition of lake waters along Sïndre Strïmfjord in western Greenland have been measured both spatially (coast to ice sheet) and temporally (up to five times between 1998–2000) and the data compared to local climatic information. There is a climatic gradient along Sïndre Strïmfjord, with the head of the fjord characterised by a low Arctic continental climate, while the coast has a more maritime climate (increased precipitation and reduced annual temperature range). The change in climate from continental to maritime is reflected in the isotopic composition of the lakes. The inland lakes have ¹⁸O and dD values which lie on evaporation trends away from meteoric water composition. The coastal lakes have ¹⁸O and dD compositions close to meteoric water. Short-term seasonal trends are superimposed on longer term variation. For example, the relatively dry years (precipitation lower than the long-term annual mean) of 1998 and 1999 are seen in the smaller lakes as isotopic enrichment, but the larger lakes are buffered in their response to short-term changes. The small coastal lakes tend to have depleted ¹³C derived predominantly from organic material, while the inland lakes have contributions from both organic carbon and from exchange with isotopically heavier atmospheric CO₂. This study demonstrates the importance of characterizing local hydrological settings in the interpretation of lacustrine isotope records. In the Arctic, this type of information is especially useful for identifying lakes that have the potential to record arid intervals since precipitation/evaporation adjustments, especially toward greater aridity, may not be recorded in the Greenland ice-core records.

Key Words: Stable isotopes • 18O • dD • 13C • lakes • climate • modern analogues • Greenland

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