The author(s) will give a talk

Late Holocene temperature and hydroclimate reconstruction from southern Greenland: evidence from biomarkers in lake sediments

Zhao, Boyang 1 ; Castañeda, Isla S. 2 ; Bradley, Raymond S. 3 ; Salacup, Jeff M. 4 ; Schneider, Tobias 5

1 University of Massachusetts Amherst
2 University of Massachusetts Amherst
3 University of Massachusetts Amherst
4 University of Massachusetts Amherst
5 University of Massachusetts Amherst

Southern Greenland was colonized by Norse settlers from 985 AD until the early 15th century when they abruptly left (McGovern, 2014). Despite being a topic of many studies, reasons for the abandonment of the Norse Eastern Settlement have been controversial and debated for a long time. As some previous investigations have suggested, the demise of Norse settlement could have resulted from multiple issues, including climate change, management failure, economic collapse, or social stratification (Dugmore et al., 2012; McGovern, 2014). To test whether climate change contributed to settlement abandonment, we collected a short sediment core from Lake 578 (61°5' N, 45°37' W) in southern Greenland, a site that contains Norse ruins within the lake catchment, and constructed an age model based on 210Pb and 137Cs activity (upper sediments) and terrestrial macrofossils 14C dating. Further, we employed branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lake sediments to generate a summer water temperature record, based on a site-specific calibration (Zhao et al., 2021), and measured sedimentary leaf wax hydrogen isotopes to reconstruct relative humidity changes (ΔRH) using a dual-biomarker approach model (Rach et al., 2017). Our temperature reconstruction shows a general agreement with other local records from sites across the Eastern Settlement, indicating an overall prominent cooling trend in the past ~1700 years, which coincides with a decrease in summer insolation at 61°N. Importantly, there is no evidence of an unusually abrupt temperature drop around the time when Norse settlements were abandoned. Our reconstructed ΔRH indicates a persistent wet interval from 580–950 AD, prior to the arrival of the Norse. After ~950 AD, reconstructed ΔRH depicts a long-term drying trend until the 16th century, becoming relatively stable thereafter. This drying trend is concurrent with a change in the Norse diet from one based on terrestrial animals to one that relied on sea mammals (Arneborg et al., 1999; McGovern and Palsdóttir, 2006). A drier environment would have significantly reduced grass production, which was the critical food source for their livestock and essential for over-wintering. Collectively, we conclude that increasingly dry conditions likely played a more important role in driving the demise of the Eastern Settlement rather than minor changes in temperature. Overall, our organic biomarker investigation of Lake 578 demonstrates the potential of using brGDGTs to generate high-resolution temperature records from Arctic lakes and leaf wax hydrogen isotopes to reconstruct local hydrological conditions.

Arneborg, J., Heinemeier, J., Lynnerup, N., Nielsen, H.L., Rud, N., 1999. Change of diet of the greenland vikings determined from stable carbon isotope analysis and "c dating of their bones. Radiocarbon 41, 157–168.

Dugmore, A.J., McGovern, T.H., Vésteinsson, O., Arneborg, J., Streeter, R., Keller, C., 2012. Cultural adaptation, compounding vulnerabilities and conjunctures in Norse Greenland. Proceedings of the National Academy of Sciences of the United States of America 109, 3658–3663.

McGovern, T.H., 2014. Management for extinction in Norse Greenland, in: The Anthropology of Climate Change: An Historical Reader. pp. 131–150.

McGovern, T.H., Palsdóttir, A., 2006. Preliminary Report of a Medieval Norse Archaeofauna from Brattahlið North Farm (KNK 2629), Qassiarsuk, Greenland. National Geographic 1–22.

Rach, O., Kahmen, A., Brauer, A., Sachse, D., 2017. A dual-biomarker approach for quantification of changes in relative humidity from sedimentary lipid D/H ratios. Climate of the Past 13, 741–757.

Zhao, B., Castañeda, I.S., Bradley, R.S., Salacup, J.M., de Wet, G.A., Daniels, W.C., Schneider, T., 2021. Development of an in situ branched GDGT calibration in Lake 578, southern Greenland. Organic Geochemistry 152, 104168.