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: These data include highly-branched isoprenoids (IP25, HBI II, HBI III and HBI IV) and isoprenoid GDGTs from marine sediment cores MD99-2269 and JR51-GC35 from the North Iceland Shelf. Total lipids were extracted and purified following standard procedures on an ASE and using silica-gel columns, respectively. HBIs were then analyzed on GC-MS and GDGTs on HPLC-MS. Both records have age models derived from radiocarbon-dated molluscs and foraminifera that are published elsewhere, and the above lipid biomarker records cover the last 8000 years. Temporal resolution varies between multi-centennial to sub-centennial. From MD99-2269, data also include complete planktic and benthic foraminifera assemblages. Foraminifera were wet-picked from sediment subsamples. Using established transfer functions, we also present SST and BWT records derived from the planktic and benthic foraminifera assemblages, respectively. Planktic assemblage data cover the last 10000 years whereas benthic assemblage data only cover the last 8000 years. Temporal resolution varies between multi-centennial to sub-centennial. These data were collected in order to document the Holocene paleoceanography of the North Iceland Shelf. In other words, to study when Arctic/Polar versus Atlantic Waters bathed the region, how the temperatures of these currents changed, when and how sea ice was advected to the region, and how pelagic productivity was impacted by all these oceanographic variables.