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Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes

Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes
Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes
Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modelling and paleo-observations. The sub-continental region of Beringia (Northeast Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia’s early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present day simulations of regional climate, one with modern and one with 11 ka geography, plus another simulation for 6 ka. In addition, we performed five ? 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka “Control”, which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal vegetation types distributed as suggested by the paleoecological record, (iv) thaw lakes, which used the present day distribution of lakes and wetlands; and (v) post-11 ka “All”, incorporating all boundary conditions changed in experiments (ii)–(iv). We find that regional-scale controls strongly mediate the climate responses to changes in the large-scale controls, amplifying them in some cases, damping them in others, and, overall, generating considerable spatial heterogeneity in the simulated climate changes. The change from tundra to deciduous woodland produces additional widespread warming in spring and early summer over that induced by the 11 ka insolation regime alone, and lakes and wetlands produce modest and localized cooling in summer and warming in winter. The greatest effect is the flooding of the land bridge and shelves, which produces generally cooler conditions in summer but warmer conditions in winter and is most clearly manifest on the flooded shelves and in eastern Beringia. By 6 ka continued amplification of the seasonal cycle of insolation and loss of the Laurentide ice sheet produce temperatures similar to or higher than those at 11 ka, plus a longer growing season.
1814-9332
1197-1222
Bartlein, P.J.
ea489709-789d-4cd0-bd48-36b4e21194df
Edwards, M.E.
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Hostetler, S.W.
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Shafer, S.L.
75dd6fd6-df09-45a8-9eaf-abf5c87e9ec9
Anderson, P.M.
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Brubaker, L.B.
1db136ea-b200-4834-845c-6d581a53378f
Lozhkin, A.V.
365fdf75-9023-404d-85bd-cbb9a937444e
Bartlein, P.J.
ea489709-789d-4cd0-bd48-36b4e21194df
Edwards, M.E.
4b6a3389-f3a4-4933-b8fd-acdfef72200e
Hostetler, S.W.
bfbf997d-84fa-4263-8e04-48fce80b94ae
Shafer, S.L.
75dd6fd6-df09-45a8-9eaf-abf5c87e9ec9
Anderson, P.M.
604400ce-7c43-41cd-a459-efe34c78a2ef
Brubaker, L.B.
1db136ea-b200-4834-845c-6d581a53378f
Lozhkin, A.V.
365fdf75-9023-404d-85bd-cbb9a937444e

Bartlein, P.J., Edwards, M.E., Hostetler, S.W., Shafer, S.L., Anderson, P.M., Brubaker, L.B. and Lozhkin, A.V. (2015) Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes. Climate of the Past, 11 (9), 1197-1222. (doi:10.5194/cp-11-1197-2015).

Record type: Article

Abstract

Arctic land-cover changes induced by recent global climate change (e.g., expansion of woody vegetation into tundra and effects of permafrost degradation) are expected to generate further feedbacks to the climate system. Past changes can be used to assess our understanding of feedback mechanisms through a combination of process modelling and paleo-observations. The sub-continental region of Beringia (Northeast Siberia, Alaska, and northwestern Canada) was largely ice-free at the peak of deglacial warming and experienced both major vegetation change and loss of permafrost when many arctic regions were still ice covered. The evolution of Beringian climate at this time was largely driven by global features, such as the amplified seasonal cycle of Northern Hemisphere insolation and changes in global ice volume and atmospheric composition, but changes in regional land-surface controls, such as the widespread development of thaw lakes, the replacement of tundra by deciduous forest or woodland, and the flooding of the Bering–Chukchi land bridge, were probably also important. We examined the sensitivity of Beringia’s early Holocene climate to these regional-scale controls using a regional climate model (RegCM). Lateral and oceanic boundary conditions were provided by global climate simulations conducted using the GENESIS V2.01 atmospheric general circulation model (AGCM) with a mixed-layer ocean. We carried out two present day simulations of regional climate, one with modern and one with 11 ka geography, plus another simulation for 6 ka. In addition, we performed five ? 11 ka climate simulations, each driven by the same global AGCM boundary conditions: (i) 11 ka “Control”, which represents conditions just prior to the major transitions (exposed land bridge, no thaw lakes or wetlands, widespread tundra vegetation), (ii) sea-level rise, which employed present day continental outlines, (iii) vegetation change, with deciduous needleleaf and deciduous broadleaf boreal vegetation types distributed as suggested by the paleoecological record, (iv) thaw lakes, which used the present day distribution of lakes and wetlands; and (v) post-11 ka “All”, incorporating all boundary conditions changed in experiments (ii)–(iv). We find that regional-scale controls strongly mediate the climate responses to changes in the large-scale controls, amplifying them in some cases, damping them in others, and, overall, generating considerable spatial heterogeneity in the simulated climate changes. The change from tundra to deciduous woodland produces additional widespread warming in spring and early summer over that induced by the 11 ka insolation regime alone, and lakes and wetlands produce modest and localized cooling in summer and warming in winter. The greatest effect is the flooding of the land bridge and shelves, which produces generally cooler conditions in summer but warmer conditions in winter and is most clearly manifest on the flooded shelves and in eastern Beringia. By 6 ka continued amplification of the seasonal cycle of insolation and loss of the Laurentide ice sheet produce temperatures similar to or higher than those at 11 ka, plus a longer growing season.

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Accepted/In Press date: 18 August 2015
Published date: 24 September 2015
Organisations: Palaeoenvironment Laboratory (PLUS)

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Local EPrints ID: 394423
URI: http://eprints.soton.ac.uk/id/eprint/394423
ISSN: 1814-9332
PURE UUID: c961cb28-a858-4d87-aabf-4c9146c646d3
ORCID for M.E. Edwards: ORCID iD orcid.org/0000-0002-3490-6682

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Date deposited: 18 May 2016 12:55
Last modified: 17 Dec 2019 01:50

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Contributors

Author: P.J. Bartlein
Author: M.E. Edwards ORCID iD
Author: S.W. Hostetler
Author: S.L. Shafer
Author: P.M. Anderson
Author: L.B. Brubaker
Author: A.V. Lozhkin

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