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| Titel |
Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes |
| VerfasserIn |
P. J. Bartlein, M. E. Edwards, S. W. Hostetler, S. L. Shafer, P. M. Anderson, L. B. Brubaker, A. V. Lozhkin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 9 ; Nr. 11, no. 9 (2015-09-24), S.1197-1222 |
| Datensatznummer |
250117405
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| Publikation (Nr.) |
 copernicus.org/cp-11-1197-2015.pdf |
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| Zusammenfassung |
| 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 modeling and paleo-observations.
The subcontinental region of Beringia (northeastern 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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