"Highlights
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- We reconstruct Holocene summer temperatures and ice cap fluctuations in NW Greenland.
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- This and other studies suggest >4 °C local temperature decline through the Holocene.
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- Peak warmth in this region occurred in the first few millennia of the Holocene.
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- North Ice Cap grew to present size ∼1850 AD, was smaller through most of Holocene.
Abstract
Arctic
temperature shifts drive changes in carbon cycling, sea ice extent and
Greenland Ice Sheet mass balance, all of which have global
ramifications. Paleoclimate data from past warm periods provide a unique
means for assessing the sensitivity of these systems to warming
climate, but the magnitude and timing of past temperature changes in
many parts of the Arctic are poorly known. Here we assess orbital-scale
Holocene temperature change in northwest Greenland near the margin of
the ice sheet using subfossil insect assemblages from lake Deltasø.
Based upon sedimentation history in this currently proglacial lake, we
also place constraints on Holocene extents of the adjacent North Ice
Cap, a large independent ice cap. Reconstructed summer temperatures were
warmer than present at the onset of lacustrine sedimentation following
regional deglaciation by the Greenland Ice Sheet, sometime between 10.8
and 10.1 ka BP. Deltasø experienced the warmest summer temperatures of
the Holocene between ∼10 and 6.2 ka BP, followed by progressive cooling
that continued through the late Holocene as summer insolation declined,
culminating in the lowest temperatures during the pre-industrial last
millennium. Deltasø chironomids indicate peak early Holocene summer
temperatures at least 2.5–3 °C warmer than modern and at least 3.5–4 °C
warmer than the pre-industrial last millennium. We infer based upon lake
sediment organic and biogenic content that in response to declining
temperatures, North Ice Cap reached its present-day size ∼1850 AD,
having been smaller than present through most of the preceding Holocene.
Our synthesis of paleoclimate evidence from northwest Greenland,
Ellesmere Island and northern Baffin Bay supports the timing of
temperature trends inferred at Deltasø, and suggests that quantitative
temperature reconstructions from Deltasø may represent a minimum bound
on regional early Holocene warming. Collectively, records from the
region indicate >4 °C summer cooling through the Holocene. Intense
early Holocene warmth around northwest Greenland argues against delayed
onset of warmer-than-present conditions due to the influence of the
nearby waning Laurentide Ice Sheet, and has implications for
understanding the Greenland Ice Sheet's sensitivity to climate change."
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