Bering Sea Ice Extent Is At Most Reduced State In At Least Last 5,500 Yearshttps://phys.org/news/2020-09-bering-sea-ice-extent-state.htmlA newly published paper in the journal
Science Advances describes how a peat core from St. Matthew Island is providing a look back in time. By analyzing the chemical composition of the core, which includes plant remains from 5,500 years ago to the present, scientists can estimate how sea ice in the region has changed during that time period.
"It's a small island in the middle of the Bering Sea, and it's essentially been recording what's happening in the ocean and atmosphere around it," said lead author Miriam Jones, a research geologist with the U.S. Geological Survey. Jones worked as a faculty researcher at the University of Alaska Fairbanks when the project began in 2012.
The ancient sea ice record comes in the form of changes in the relative amounts of two isotopes of the element oxygen— oxygen-16 and oxygen-18. The ratio of those two isotopes changes depending on patterns in the atmosphere and ocean, reflecting the different signatures that precipitation has around the globe. More oxygen-18 makes for an isotopically "heavier" precipitation, more oxygen-16 makes precipitation "lighter."
By analyzing data from a model that tracks atmospheric movement using the isotopic signature of precipitation, the authors found that heavier precipitation originated from the North Pacific, while lighter precipitation originated from the Arctic.
A "heavy" ratio signals a seasonal pattern that causes the amount of sea ice to decrease. A "light" ratio indicates a season with more sea ice. That connection has been confirmed though sea ice satellite data collected since 1979, and to a smaller extent, through the presence of some microorganisms in previous core samples.
"What we've seen most recently is unprecedented in the last 5,500 years," said Matthew Wooller, director of the Alaska Stable Isotope Facility and a contributor to the paper. "We haven't seen anything like this in terms of sea ice in the Bering Sea."Jones said the long-term findings also affirm that reductions in Bering Sea ice are due to more than recent higher temperatures associated with global warming. Atmospheric and ocean currents, which are also affected by climate change, play a larger role in the presence of sea ice.
"There's a lot more going on than simply warming temperatures," Jones said. "We're seeing a shift in circulation patterns both in the ocean and the atmosphere."M.C. Jones el al.,
"High sensitivity of Bering Sea winter sea ice to winter insolation and carbon dioxide over the last 5500 years," Science Advances (2020).
https://advances.sciencemag.org/content/6/36/eaaz9588... The substantial rate of anthropogenic CO2 inputs into the atmosphere over industrialization suggests that a loss in Bering Sea sea ice extent is accelerating or is already committed to complete sea ice loss as a result of delayed response to anthropogenic forcing. Low winter sea ice anomalies in CE 2018 and CE 2019 indicate future conditions that favor an ice-free Bering Sea. Widespread effects of Bering Sea winter sea ice loss are expected to occur. Ecosystem responses to low sea ice in CE 2018 included altered food webs that led to sea bird die-offs and may represent a harbinger of future low sea ice extent.
Further intensification of observed North Pacific influence in the Bering Sea leading to a reduction in sea ice can further affect heat transport to the Arctic Ocean basin. Although the Bering Strait throughflow may be relatively small (<1 Sv; 1 Sv = 106 m3 s−1), it can have a disproportionate influence on heatflux into the Arctic Ocean basin, and recent increases have been linked to weakening northerly winds (32), signifying enhanced winds originating from the North Pacific could amplify Arctic Ocean sea ice decline via increasing winds from the south.
Simultaneously, the increased frequency and duration of winter cyclones in the Arctic have led to the large reductions in freezing degree days in Arctic Ocean winters (33, 34). A loss of sea ice can also increase coastal erosion and increase land temperatures that result in permafrost thaw (35), further amplifying warming (36).