Is there an element of circular reasoning here? Carbon dioxide levels have historically followed temperature changes, bringing any supposed causation into question.
Upside-down “rivers” of warm ocean water may be one of the causes of Antarctica’s ice shelves breaking up, leading to a rise in sea levels.
Using computer simulations, the research suggests that an increase in sea ice could significantly alter the circulation of the ocean, ultimately leading to a reverse greenhouse effect as carbon dioxide levels in the ocean increase and levels in the air decrease.
“One key question in the field is still what caused the Earth to periodically cycle in and out of ice ages,” University of Chicago professor and the study’s co-author, Malte Jansen, said in a statement. “We are pretty confident that the carbon balance between the atmosphere and ocean must have changed, but we don’t quite know how or why.”
The last major ice age ended at the end of the Pleistocene era, about 2.5 million years ago, as glaciers have periodically grown and then gotten smaller.
Researchers believe that changes to the Earth’s orbit may be partly responsible for some of the Earth’s cooling, but additional factors have likely played a part, Jensen added.
“The most plausible explanation is that there was some change in how carbon was divided between the atmosphere and the ocean,” Jansen continued. “There’s no shortage of ideas about how this happens, but it’s not quite clear how they all fit together.”
Researchers also believe a mini-ice age may have occurred roughly 12,800 years ago. It likely stems from an asteroid impact that “rocked the Northern Hemisphere” and led to the Younger Dryas climate event.
Jansen pointed out that the Southern Ocean around Antarctica “plays a key role in ocean circulation” due to the deep waters in the region, leading it to have “outsize[d] consequences.”
“What this suggests is that it’s a feedback loop,” said the study’s lead author, Alice Marzocchi. “As the temperature drops, less carbon is released into the atmosphere, which triggers more cooling.”
Full report here.
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Study: Global cooling linked to increased glacial carbon storage via changes in Antarctic sea ice – Nature Geoscience.
Palaeo-oceanographic reconstructions indicate that the distribution of global ocean water masses has undergone major glacial– interglacial rearrangements over the past ~2.5 million years. Given that the ocean is the largest carbon reservoir, such circulation changes were probably key in driving the variations in atmospheric CO2 concentrations observed in the ice-core record. However, we still lack a mechanistic understanding of the ocean’s role in regulating CO2 on these timescales. Here, we show that glacial ocean–sea ice numerical simulations with a single-basin general circulation model, forced solely by atmospheric cooling, can predict ocean circulation patterns associated with increased atmospheric carbon sequestration in the deep ocean. Under such conditions, Antarctic bottom water becomes more isolated from the sea surface as a result of two connected factors: reduced air–sea gas exchange under sea ice around Antarctica and weaker mixing with North Atlantic Deep Water due to a shallower interface between southern- and northern-sourced water masses. These physical changes alone are sufficient to explain ~40 ppm atmospheric CO2 drawdown—about half of the glacial–interglacial variation. Our results highlight that atmospheric cooling could have directly caused the reorganization of deep ocean water masses and, thus, glacial CO2 drawdown. This provides an important step towards a consistent picture of glacial climates.
via Tallbloke’s Talkshop
October 30, 2019 at 08:30AM