NOAA/WDS Paleoclimatology - Limnaea So, West Greenland, Alkenones, Isotopes, Carbonate, and Magnetic Susceptibility Data during the past 9,000 years

The transition from the Last Glacial Maximum was punctuated by several abrupt cooling periods, the last of which occurred ~8.2 ka BP. These cooling events are thought to have occurred when collapse of the impounding ice along the Laurentide Ice Sheet margin released massive volumes of freshwater into the Labrador Sea. Ice core records from the Greenland Ice Sheet (GIS) show modest cooling of ~2–4°C over ca. 200 years during the 8.2 ka event. Here we present an alkenone-based temperature reconstruction from Limnaea Sø, a West Greenland lake proximal to the GIS margin that indicates a cooling as much as 8°C, although potential biases in the seasonality of production or non-stationarity in the alkenone-water temperature relationship may account for a significant portion of the signal (~half). Carbonate isotope records indicate concurrent hydroclimate changes, while clumped isotope temperatures provide important insight into seasonal timing of carbonate accumulation. These data indicate that the amount of cooling along the GIS margin may have been 2–3 times larger than the GIS summit, which is likely attributable to sea ice changes in the Labrador Sea, as predicted by climate models. Resumption of the Atlantic Meridional Overturning Circulation following the 8.2 ka slowdown brought abrupt warmth back to Greenland within ~140 years, raising lake temperatures by potentially up to 11°C and resulting in a greater contribution of 18O-depleted meltwater into proximal lakes that produced a marked d18O reduction in Limnaea Sø carbonates. The considerable cooling associated with the 8.2 ka event in this terrestrial environment indicates that relatively small climate forcing can have an outsized impact on high-latitude lake systems due to regional feedbacks related to snow/ice cover, meltwater input, and shifts in climate seasonality.