Magnitude and seasonality of climate change in South Greenland over the past 12,000 years from midge assemblages and oxygen isotopes of chitin

New paleoclimate reconstructions are accumulating from unglaciated terrestrial areas of Greenland. However, archives spanning the entire Holocene remain sparse, and spatial heterogeneity in timing and/or magnitude of key climate features (e.g., Holocene Thermal Maximum, 8.2 ka cooling) are unknown. In addition, disentangling seasonal signals in paleorecords is necessary to resolve broad-scale climate dynamics. In this study, we present a paleoclimate reconstruction from Pincushion Lake (N 60.697°, W 45.410° 480 m asl), a small high-elevation lake in South Greenland. To reconstruct the Holocene climate history, we combine new summer temperature estimates from chironomid assemblages, based on modern training sets from North America, Baffin Island, and Iceland, with seasonally-integrated estimates from oxygen isotopes of chitin.

Chironomid assemblages 11.7-10.9 kcal BP were dominated by cold-indicator Oliveridia/Hydrobaenus, and temperature estimates suggest summers were ~10.5 °C colder than present. These taxa declined after 10.9 kcal BP as regional deglaciation proceeded, replaced by Tanytarsus and Corynocera, followed by a shift ~ 7.5 kcal BP to Micropsectra and warm-dwelling Psectrocladius. Modern training sets differ in temperature estimates, but all suggest low-magnitude changes compared to other Greenland areas. Assemblages indicate a brief 1.3°C summer temperature excursion corresponding to the 8.2 ka cooling observed in North Atlantic records. Chironomid δ¹⁸O values are highest (mean = 10.8‰) from 9-7 kcal BP, suggesting either warmer annual temperatures (ΔT=0.45°C) or precipitation amounts shifted to summer. Isotope values subtly decline thereafter, suggesting cooler winter temperatures or an increase in the proportion of winter relative to summer precipitation. Principal component analysis reveals a distinct assemblage shift 2.5 kcal BP, driven by increased cold-tolerant Heterotrissocladius. However, estimates from transfer functions disagree in this part of the record, highlighting the need for improved taxonomic resolution in regional training-set data. This new dataset provides a more complete picture of the spatial heterogeneity of Holocene climate change in Greenland, and relatively rare information about conditions in the earliest part of the Holocene.