Posted onNovember 14, 2023|Comments Off on Walrus and polar bear population size changes in the N. Atlantic over the last 20k years
This is a lesson in how to assess the potential worth of scientific papers. One of two similar Arctic evolution studies got media attention, at least in Canada — about the polar bears, of course — but in my opinion the walrus research conclusions are much better supported, less biased by climate change rhetoric, and lack the hubris present in the polar bear paper.
Both studies use similar sample sizes for the regions they had in common (North Atlantic) and used computer models to determine genetic diversity and population size changes since the LGM. However, the tone of the walrus paper was less emotionally-charged and the caveats of the work were appropriately stated. In my opinion, papers like the polar bear example contribute to eroding the public’s trust in science.
The last Ice Age peaked between about 27,000 and 19,000 years ago. At this time the Arctic was buried under kilometers of glacial ice sheets, and so marine mammals were pushed southwards to areas of ice floes and more open water. Walrus survived in some areas of the Atlantic located further to the south, and as soon as climates warmed again, the ice edge retreated and walrus populations pushed quickly northwards again. This combination of warming and climate-driven dispersal led to local walrus populations becoming more genetically differentiated. Walrus study, Lund University press release 27 September 2023
Posted onJanuary 9, 2016|Comments Off on Paleoclimate + genetic study confirms: Arctic species adapted to sea ice changes
A new paper that combines paleoclimatology data for the last 56 million years with molecular genetic evidence concludes there wereno biological extinctions [of Arctic marine animals] over the last 1.5M years despite profound Arctic sea ice changes that included ice-free summers: polar bears, seals, walrus and other species successfully adapted to habitat changes that exceeded those predicted by USGS and US Fish and Wildlife polar bear biologistsover the next 100 years.
Thomas Cronin is a USGS paleoclimatologist at the Eastern Geology and Paleoclimate Science Center, and Matthew Cronin is a molecular geneticist at the University of Alaska Fairbanks (see previous posts here and here about Matt’s work on the genetics of polar bear evolution).
From the Abstract:
Arctic climatic extremes include 25°C hyperthermal periods during the Paleocene-Eocene (56–46 million years ago, Ma), Quaternary glacial periods when thick ice shelves and sea ice cover rendered the Arctic Ocean nearly uninhabitable, seasonally sea-ice-free interglacials and abrupt climate reversals.
The final discussion and two summary graphics from this paper (copied below) are especially useful:
Posted onApril 21, 2015|Comments Off on Polar bears barely survived the sea ice habitat changes of the last Ice Age, evidence suggests
While the polar bear is an Ice Age species, genetic and fossil evidence suggests it barely survived the profound sea ice changes associated with the Last Glacial Maximum, one of the most severe glacial periods of the Pleistocene.
A map of sea ice extent at the climax of the Last Glacial Maximum (both perennial and seasonal ice), prepared with the help of a colleague, makes it possible to discuss what genetic and fossil evidence can tell us about the probable effects of glacial conditions on polar bears and ringed seals.
Posted onNovember 13, 2012|Comments Off on How long have polar bears lived in Hudson Bay?
The unique geographical position and oceanographic properties of Hudson Bay make it very different from other Arctic regions that polar bears inhabit.
Hudson Bay is a large shallow basin that freezes over every winter – somewhat like an enormous salt-water lake. This ice cover melts completely every summer, in part because it is well south of other truly “arctic” regions. As a consequence, while Hudson Bay offers excellent seal-hunting conditions for polar bears from winter through early summer, the long ice-free period with no or few feeding opportunities presents a unique challenge that polar bears elsewhere do not routinely encounter (see previous posts here, here and here).
Modern polar bears on the sea ice of Hudson Bay (Wikipedia photo and map).
But Hudson Bay also has a unique geological history. Since the end of the last ice age Hudson Bay has been available as polar bear habitat about half as long as other Arctic regions. This phenomenon is rarely discussed in the polar bear literature (although Andrew Derocher, in his new book [reviewed here] does mention it). In this post, I’ll summarize the geological history of Hudson Bay over the last 30 thousand years, as it pertains to polar bear habitat.