A High-Resolution Lacustrine Alkenone Record Demonstrates Progressive Cold Season Warming During the Holocene in Arctic Alaska
Abstract
Holocene temperature trends observed in Northern Hemisphere paleoclimate reconstructions generally deviate from those simulated by global climate models (GCM). Most paleoclimate records suggest declining annual temperatures over the Holocene, attributed to declining summer insolation, whereas GCMs simulate increasing annual temperatures due to retreating ice sheets and increasing CO2. The disagreement may originate from a summer bias in annual temperature reconstructions from the northern hemisphere, since the vast majority of proxies reflect summer growth season temperatures. Here we develop and apply a new proxy for spring lake temperature - alkenone unsaturation in freshwater lacustrine haptophytes, - which in-situ observations and forward modeling experiments show to record changes in air temperature and lake ice phenology in the winter and spring. We reconstruct winter-spring temperature changes for the past 16,000 years from Lake E5, Northern Alaska at multi-decadal resolution. We find that winter-spring temperatures warmed abruptly during the deglaciation (at 16 and 14 Ka), similar to summer temperatures. However, in contrast to summer temperature records we observe steady warming during the Holocene (8-1 Ka; 0.3 °C/1,000 years). The timings, trends and seasonality of these changes implicate greenhouse gas and ice sheet forcing as well as sea ice feedbacks as important controls on cold season temperature in Arctic Alaska. An ensemble of global climate models indicates cooler temperatures during winter and spring (JFMAM) at 6 Ka relative to the pre-industrial and present day. Thus, our cold season temperature reconstruction from Arctic Alaska provides support for Holocene warming trends in annual temperature derived from GCM simulations. Together, these data also demonstrate the utility of a novel winter-spring temperature proxy based on freshwater lacustrine alkenone biomarkers and they highlight the importance of constraining seasonality in paleotemperature reconstructions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMPP54B..08L
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1620 Climate dynamics;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 4904 Atmospheric transport and circulation;
- PALEOCEANOGRAPHY