Abstract
Glaciers and ice caps (GICs) respond rapidly to changes in temperature and precipitation. Thus, records of their past fluctuations yield valuable information on past climate. However, relatively little is known about the long-term, Holocene history of Greenland's local GICs, peripheral to the Greenland Ice Sheet. Here we report sediment records of Holocene glacier activity from two distally fed glacial lakes near Buksefjord, southwest Greenland. The two lakes’ watersheds host modern GICs of contrasting size. The Pers Lake (informal name) watershed drains part (3 km2) of a single small ice cap. In contrast, nearby Lake T3's (informal name) watershed drains numerous GICs totaling 100 km2. At the time it emerged from the sea ∼8.6 ka BP, Pers Lake was receiving no glacial meltwater input. Sediment physical and geochemical properties indicate persistent meltwater input and regrowth of the ice cap within the Pers Lake catchment beginning at ∼1.4 ka BP, after almost 3000 years of sporadic meltwater input beginning ∼4.3 ka BP. The ice cap above Pers Lake reached a maximum late Holocene extent during the final phase of the Little Ice Age (LIA), ∼0.1 ka BP. The complementary Lake T3 sediment record suggests continued meltwater input from the larger suite of upstream GICs from the time of the lake's isolation from the sea ∼8.4–7.5 ka BP through to the present. This indicates that some GICs here probably survived the Holocene Thermal Maximum (HTM), although were significantly reduced in size for an extended period (of unknown age and duration). Combined with evidence from Pers Lake and prior studies that show GICs at low and intermediate elevations in this region melted away completely during the HTM, and evidence for GIC presence at Lake T3, we provide lower and upper bounds on regional HTM equilibrium-line altitudes (ELAs). We estimate that regional ELAs were between ∼1370 and 1470 m above sea level in the early-to-middle Holocene. From the middle to late Holocene, our results, along with other regional GIC studies, indicate progressive lowering of regional glacier ELAs in response to Neoglacial summer cooling of ∼2.7 °C, assuming no change in precipitation.
| Original language | English (US) |
|---|---|
| Article number | 106529 |
| Journal | Quaternary Science Reviews |
| Volume | 246 |
| DOIs | |
| State | Published - Oct 15 2020 |
Funding
This research was supported by National Geographic Society grant 9694-15 and U.S. National Science Foundation (NSF) Polar Programs CAREER grant 1454734 awarded to YA, NSF Geography and Spatial Sciences DDRI grant 1812764 awarded to LL and YA, and Northwestern University undergraduate research assistant program (URAP) funds that supported BG. We thank S. Funder for sharing relative sea-level data; A. Masterson, G. Schellinger, K. Berman, and P. Kotecki for lab access and assistance; Woods Hole Oceanographic Institution–National Ocean Sciences Accelerator Mass Spectrometry facility for radiocarbon analysis; the United States Geological Survey (USGS) and the Polar Geospatial Center (PGC) for satellite imagery; S. Ólafsdóttir and B. Gray for field assistance and T. Axford for building field equipment. We thank the people and the Government of Greenland for site access (under scientific survey license VU-00090 and export permit 062/2015) and Pinngortitaleriffik (Greenland Institute of Natural Resources) and M. Rosen for essential field support. Geospatial support for this work provided by PGC under NSF-OPP awards 1043681 and 1559691. We thank Nicolaj Krog Larsen and one anonymous reviewer for improving this manuscript. Cosmogenic 10Be exposure ages along a transect near Buksefjord suggest rapid retreat of the GrIS from the outer coast to the present-day ice margin in the early Holocene (between 10.7 ± 0.6 and 10.1 ± 0.4 ka BP) (Larsen et al., 2014). This suggests that the coastal, low elevation (∼7 m a.s.l.) land from which Lake T3 subsequently formed was ice free by ∼10.7 ka BP. Radiocarbon dates from marine shells in the Lake T3 cores support this result and show marine sedimentation at the site by at least ∼10.6 ka BP. C:N values in the T3 basal units average < 10 and δ13C values range between −17 and −23‰ which is consistent with a predominantly marine organic matter source (Fig. 6) (Leng and Lewis, 2017). In addition, we suggest that the presence of small rocks in Lake T3's basal sediments along with some variability in %C, %N, and their isotope values (especially in the Lake T3 U9 core), may reflect the influence of ice-rafted debris and streamflow from the rapidly retreating GrIS. Although no marine shells were found in the Pers Lake cores, the physical and geochemical properties of the basal sediments (i.e. high S and Ca concentrations) also suggest a glacio-marine depositional environment and a relatively high sedimentation rate as a consequence of meltwater discharge from the rapidly retreating GrIS in the early Holocene.This research was supported by National Geographic Society grant 9694-15 and U.S. National Science Foundation (NSF) Polar Programs CAREER grant 1454734 awarded to YA, NSF Geography and Spatial Sciences DDRI grant 1812764 awarded to LL and YA, and Northwestern University undergraduate research assistant program (URAP) funds that supported BG. We thank S. Funder for sharing relative sea-level data; A. Masterson, G. Schellinger, K. Berman, and P. Kotecki for lab access and assistance; Woods Hole Oceanographic Institution–National Ocean Sciences Accelerator Mass Spectrometry facility for radiocarbon analysis; the United States Geological Survey (USGS) and the Polar Geospatial Center (PGC) for satellite imagery; S. Ólafsdóttir and B. Gray for field assistance and T. Axford for building field equipment. We thank the people and the Government of Greenland for site access (under scientific survey license VU-00090 and export permit 062/2015) and Pinngortitaleriffik (Greenland Institute of Natural Resources) and M. Rosen for essential field support. Geospatial support for this work provided by PGC under NSF-OPP awards 1043681 and 1559691. We thank Nicolaj Krog Larsen and one anonymous reviewer for improving this manuscript.
Keywords
- Equilibrium-line altitudes
- Glaciers and ice caps
- Greenland
- Holocene
- Isolation basins
- Lake sediments
- Paleoclimate
ASJC Scopus subject areas
- Global and Planetary Change
- Ecology, Evolution, Behavior and Systematics
- Archaeology
- Archaeology
- Geology