Neoglacial Ice Cap Expansion in Northeast Greenland: Insights from Subfossil Tundra Vegetation

Abstract

Glaciers have an intricate relationship with Earth’s climate system. They both respond to and fuel climate change through a suite of feedback loops. Researching glacier history, or the past fluctuations of glaciers, reveals trends in climate variability, painting a picture of Earth’s historical conditions. In situ subfossil tundra vegetation and lake sediments are paleoclimate proxies applied to constrain glacial expansion associated with late- Holocene, or Neoglacial, cooling.

The pilot study (Chapter 1) employs tundra plants to investigate Neoglacial responses of ice caps in Kangertittivaq (Scoresby Sund), East Greenland, including Istorvet. Two radiocarbon dates produced from the pilot study (~2720, ~520 cal yr BP) align with Neoglacial cooling pulses interpreted from results of paleoclimate proxy data in previously published research. This suggests that small ice caps around Kangertittivaq may respond to climate change similarly to glaciers elsewhere in the Arctic.

Chapter 2, a standalone study, uses subfossil moss in conjunction with proglacial threshold lake sediments to build a Neoglacial chronology of Østtungerne, a ~120 km² ice cap in Germania Land, Northeast Greenland. Ice-marginal subfossil moss-kill dates illustrate that the glacier advanced episodically at ~1700 (n=2), ~1000 (n=3), and ~670 (n=2) cal yr BP (~250, ~950, and ~1280 CE). Individual dates ~2200, ~1200, and ~500 cal yr BP (250 BCE, 750 and 1450 CE) may also indicate Neoglacial advances at these times due to agreement with previously published dates from other studies. Radiocarbon dates of plant macrofossils from below the age of contact in the proglacial lake sediments suggest that the onset of Neoglacial advance for Østtungerne was underway by sometime after ~3 ka. The chronology agrees with other published accounts of glacier responses to Neoglacial cooling in the Arctic.

Overall, this thesis contributes new ice-killed moss data to the field of paleoclimate reconstructions, revisiting a previously studied location (Kangertittivaq) and shedding light on a previously unstudied location (Germania Land). We find that glaciers in Northeast Greenland are smaller than any other time in the last 2000 years, because of anthropogenic climate forcings.