Pronounced summer warming in northwest Greenland during the Holocene and Last Interglacial

Abstract

Projections of future rates of mass loss from the Greenland Ice Sheet are highly uncertain because its sensitivity to warming is unclear. Geologic reconstructions of Quaternary interglacials can illustrate how the ice sheet responded during past warm periods, providing insights into ice sheet behavior and important tests for data-model comparisons. However, paleoclimate records from Greenland are limited: Early Holocene peak warmth has been quantified at only a few sites, and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period. Here, we discuss findings from a lacustrine archive that records both the Holocene and the Last Interglacial (LIG) from Greenland, allowing for direct comparison between two interglacials. Sedimentary chironomid assemblages indicate peak July temperatures 4.0 to 7.0 °C warmer than modern during the Early Holocene maximum in summer insolation. and chironomids in LIG sediments indicate July temperatures at least 5.5 to 8.5 °C warmer than modern. These estimates indicate pronounced warming in northwest Greenland during both interglacials. This helps explain dramatic ice sheet thinning at Camp Century in northwest Greenland during the Early Holocene and, for the LIG, aligns with controversial estimates of Eemian warming from ice core data retrieved in northern Greenland. Converging geologic evidence for strong LIG warming is challenging to reconcile with inferred Greenland Ice Sheet extent during the LIG, and the two appear incompatible in many models of ice sheet evolution. An increase in LIG snowfall could help resolve this problem, pointing to the need for hydroclimate reconstructions from the region.

Early Holocene Temperature Oscillations Exceed Amplitude of Observed and Projected Warming in Svalbard Lakes

“…Following from the above, we argue that a combination of radiative forcing, increased ocean heat advection and ice‐free ocean waters resulted in summer temperatures that exceeded modern values on Svalbard ~10 ka BP. Placed in a regional context, our findings support a number of recent studies that suggest an earlier, warmer and more distinct Arctic Holocene optimum (Lecavalier et al, ; McFarlin et al, ). Collectively, this body of work stresses the need for data‐model comparisons as simulations neither reproduce this reconstructed pattern nor its magnitude (Figure c; Zhang et al, ).…”

“…Warmth was greatest around 10 ka BP, when temperatures were up to ~7 °C higher than present in response to high radiative forcing and intensified ocean heat advection. In agreement with a growing body of recent work (e.g., Lecavalier et al, ; McFarlin et al, ), these findings indicate an earlier and warmer Holocene Optimum in the High Arctic then previously suggested. Moreover, comparison with model output shows that the amplitude of warming was on par with 21st century emission scenarios, but that temperatures rose much slower than today.…”

Early to Late Holocene Surface Exposure Ages From Two Marine‐Terminating Outlet Glaciers in Northwest Greenland

“…At that site, exposure ages indicate that the initial retreat of the GIS occurred at 10.8 ± 0.6 ka; surficial mapping and maximum‐limiting radiocarbon ages from shells within moraine sediments indicate that Harald Moltke Bræ advanced after 10.2–9.8 ka. This is further supported by a lacustrine paleotemperature record of chironomid assemblages near Thule that indicates onset of rapid deglaciation of the local GIS margin at ~10 ka (McFarlin et al, ).…”

Local ice caps in Finderup Land, North Greenland, survived the Holocene Thermal Maximum

“…ka BP was ~4 to 7 °C warmer than present (McFarlin et al . ) whereas δ 18 O values of chironomid head capsules have shown that summer temperatures were ~2.4 to 4 °C warmer than present from ~7.7 to 6 cal. ka BP (Lasher et al .…”