Biogeochemical evidence for hydrologic changes during the Holocene in southeast Greenland
Abstract
Here we present evidence for hydrologic changes during the Holocene using a lake sediment record from southeast Greenland. Flower Valley Lake is located near the village of Tasiilaq on Ammassalik Island. A 1.6-m core was recovered that spans the last 8.9 cal ka BP. Bulk biogeochemical properties (TOC, C/N, δ13Corg) and molecular biomarkers (n-alkanes; C16 - C31) show changes in the relative input of terrestrial- and aquatic-derived organic matter. Hydrogen isotope analysis was also performed on mid-chain (C25, C27) and long-chain (C29, C31) length n-alkanes, which we interpret as being produced by aquatic and terrestrial plants, respectively. From 8.9-4.1 cal ka BP, δD values of n-alkanes derived from aquatic plants are more positive relative to the δD of terrestrial plant n-alkanes, which likely shows evaporative enrichment of the lake water relative to precipitation during the early to mid-Holocene. After 4.1 cal ka BP, δD values of aquatic and terrestrial plant n-alkanes indicate a significant decrease in evaporative enrichment of the lake water. There is also an abrupt transition to more unstable lake conditions marked by sharp increases in magnetic susceptibility, C/N, δ13Corg, and the concentration of long-chain n-alkanes, which we interpret as an increase in the delivery of terrestrial organic matter and clastic sediment to the lake. Holocene climate in the Arctic is strongly controlled by trends in summer insolation, which decreased from mid- to late Holocene. At Flower Valley Lake, higher insolation during the mid-Holocene likely resulted in a warmer and drier climate with longer ice-free conditions in the summer and greater evaporation. Decreasing insolation during the late Holocene and colder temperatures caused a reduction in evaporation of lake water and was also accompanied by wetter conditions either during the summer as rainfall or from greater winter snowfall and more intense spring melting that was able to carry terrestrial sediment into the lake after 4.1 cal ka BP. The timing of this change corresponds with the advance of local glacial activity interpreted from the sediment record of a nearby proglacial lake that we have analyzed. The late Holocene Neoglacial period is characterized by the expansion of glaciers and our data show that a distinct hydrologic change also defines this transition in southeast Greenland.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP23B2047B
- Keywords:
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- 0458 BIOGEOSCIENCES / Limnology;
- 1616 GLOBAL CHANGE / Climate variability;
- 9315 GEOGRAPHIC LOCATION / Arctic region