气候变化领域集成服务门户

Holocene paleotemperature reconstructions across the western Arctic suggest strong spatial variations in air temperature despite zonally uniform Northern Hemisphere insolation forcing. Although most paleotemperature reconstructions across the Eastern Canadian Arctic place the Holocene thermal maximum >3 kyr after peak summer insolation, other records indicate maximum summer warmth was coincident with peak summer insolation. To address this discrepancy, we use radiocarbon inventories in plants and rocks recently exposed by receding ice caps to reconstruct early Holocene changes in glacier dimensions, a reliable proxy for summer air temperature. Fourteen radiocarbon ages from newly exposed plants in growth position collected at the margins of eight retreating ice caps on Baffin Island indicate ice caps expanded 9.3 +/- 0.3 ka, and remained over these sites until recent summer warming, indicating peak early Holocene summer warmth occurred prior to similar to 9.3 ka. We test this conclusion using in situ cosmogenic C-14 (in situ C-14) inventories in rocks at four sites with dated plants. In situ C-14 production simulations using realistic Holocene ice-cover histories constrained by plant C-14 ages show that measured in situ C-14 concentrations are consistent with centuries to millennia of pre-93 ka exposure, followed by continuous ice burial. The combination of plant and in situ C-14 data provide firm evidence that the Eastern Canadian Arctic experienced peak Holocene summer warmth prior to similar to 9.3 ka, consistent with peak summer insolation, followed by continuously colder summers until modern warming. (C) 2019 Elsevier Ltd. All rights reserved.