ALBERT

Description: Records of Neoglacial glacier activity in the Arctic constructed from moraines are often incomplete due to a preservation bias toward the most extensive advance, usually the Little Ice Age. Recent warming in the Arctic has caused extensive retreat of glaciers over the past several decades, exposing preserved landscapes complete with in situ tundra plants previously entombed by ice. The radiocarbon ages of these plants define the timing of snowline depression and glacier advance across the site, in response to local summer cooling. Although most dead plants recently exposed by ice retreat are rapidly removed from the landscape by erosion, where erosive processes are unusually weak, dead plants may remain preserved on the landscape for decades. In such settings, a transect of plant radiocarbon ages can be used to construct a near-continuous chronology of past ice margin advance. Here we present radiocarbon dates from the first such transect on Baffin Island, which directly dates the advance of a small ice cap over the past two millennia. The nature of ice expansion between 20 BCE and ~1000 CE is still uncertain, but episodic advances at ~1000, ~1200, and ~1500 CE led to the maximum Neoglacial dimensions ~1900 CE. We employ a two-dimensional numerical glacier model to reconstruct the pattern of ice expansion inferred from the radiocarbon ages and to explore the sensitivity of the ice cap to temperature change. Model experiments show that at least ~0.44 °C of cooling over the past 2 ka is required for the ice cap to reach its 1900 margin, and that the period from ~1000 to 1900 CE must have been at least 0.25 °C cooler than the previous millennium; results that agree with regional climate model simulations. However, ~3 °C of warming since 1900 CE is required to explain retreat to its present position, and, at the same rate of warming, the ice cap will disappear before 2100 CE.

Description: Lipid and environmental data were compiled from previously published datasets of modern samples that used the most recent chromatographic methods that separate 5- and 6-methyl isomers. The compiled dataset (n = 3129) consisted of bone (n = 202), groundwater (n = 7), lake water meso/microcosm (n = 36), lake surface sediment (n = 343), lake water SPM (n = 228, including sediment traps (n = 115) and water filtrates (n = 113)), low DO lake water SPM (n = 138, including sediment traps (n = 29) and water filtrates (n = 109)), authigenic carbonates from a marine methane cold seep (n = 13), marine surface sediment (n = 325, including deep ocean trench sediments (n = 31)), marine SPM (water filtrates, n = 25), peat (n = 473), riverine surface sediments (n = 71) and SPM (water filtrates, n = 85), and soil (n = 1183, including permafrost active layer (n = 17)). Data from other sample media, including hot springs, speleothems, and hydrothermal vents, could not be included as these studies did not separate the 5- and 6-methyl isomers. Fractional abundances (FAs) were calculated according to Raberg et al., (2021). We compiled the brGDGT FAs and, to the best of our ability, associated temperature and pH values from previously published datasets. We selected temperature parameters that were widely supported in the literature when possible. Where a consensus had yet to be reached (e.g., marine sediments), we selected standardizable and accessible parameters (e.g., sea surface temperatures). These selections are not intended to opine on these areas of research, only to allow for broad comparison with other sample types in this study.