Timing of the Holocene Thermal Maximum in South Greenland Inferred from Insect (Diptera: Chironomidae) Assemblages and Oxygen Isotopes
Abstract
Paleoclimate reconstructions from non-glacial areas of Greenland are sparse, representing a key knowledge gap regarding spatial heterogeneity of high-latitude climate change, including the timing and magnitude of the Holocene Thermal Maximum. In this study, we present a Holocene paleoclimate reconstruction from Pincushion Lake (N 60.697°, W 45.410° 480 m asl), a small high-elevation non-glacial lake in South Greenland. We combine oxygen isotope analyses of chironomid headcapsules with reconstructions of chironomid assemblages, and interpret these data in context of sediment geochemistry from scanning X-ray fluorescence. Chironomid assemblages 11.7-10.9 kcal BP were dominated by Oliveridia/Hydrobaenus (up to 95% abundance), which has cold temperature optima in modern North American training sets. These taxa declined after 10.9 kcal BP as regional deglaciation proceeded and were replaced by Tanytarsini (e.g., Tanytarsus, Corynocera), coinciding with high Fe, Rb, and Sr concentrations, Rb:Sr, and magnetic susceptibility, suggesting high mineral inputs to the lake in the early Holocene. By the middle Holocene, assemblages were dominated by Micropsectra, a ubiquitous taxon in many Greenland lakes, and warm-dwelling Psectrocladius. Preliminary chironomid δ18O values are overall high but variable before (mean = 10.4‰) compared to after (mean = 9.7‰) 6.5 kcal BP, possibly related to changing atmospheric circulation. Principal component analysis reveals a distinct assemblage shift 2.5 kcal BP, driven by increased abundances of cold-tolerant Heterotrissocladius and reduced Psectrocladius. This same assemblage shift and timing occurs in a high-resolution mid- to late-Holocene record from nearby Scoop Lake (>0.4 km away). Together, these data suggest that the HTM occurred between 6.5 and 2.5 kcal BP in this region, compared to early Holocene maximum temperatures in other Arctic areas, supporting hypotheses from a recent synthesis of existing paleoclimate records from Greenland and NE Canada. This new, more complete dataset allows us to assess whether HTM warming was indeed delayed in South Greenland relative to other high latitude areas, and we are currently increasing temporal resolution of isotope and assemblage data to examine other periods of interest, including the 8.2 kcal BP cold event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP41B..03C
- Keywords:
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- 9315 Arctic region;
- GEOGRAPHIC LOCATIONDE: 1621 Cryospheric change;
- GLOBAL CHANGEDE: 1630 Impacts of global change;
- GLOBAL CHANGEDE: 1637 Regional climate change;
- GLOBAL CHANGE