An international team of scientists led by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) have managed to open a new window into the climate history of the Arctic Ocean. Using unique sediment samples from the Lomonosov Ridge, the researchers found that six to ten million years ago the central Arctic was completely ice-free during summer and sea-surface temperature reached values of 4 to 9 degrees Celsius. In spring, autumn and winter, however, the ocean was covered by sea ice of variable extent, the scientists explain in the current issue of the journal Nature Communications. These new findings from the Arctic region provide new benchmarks for groundtruthing global climate reconstructions and modelling.
The researchers had recovered these unique sediment samples during an expedition with Germany's research icebreaker RV Polarstern in summer of 2014. "The Arctic sea ice is a very critical and sensitive component in the global climate system. It is therefore important to better understand the processes controlling present and past changes in sea ice. In this context, one of our expedition's aims was to recover long sediment cores from the central Arctic, that can be used to reconstruct the history of the ocean's sea ice cover throughout the past 50 million years. Until recently, only a very few cores representing such old sediments were available, and, thus, our knowledge of the Arctic climate and sea ice cover several millions of year ago is still very limited," Prof. Dr. Ruediger Stein, AWI geologist, expedition leader and lead author of the study, explains.
Ice was in the news quite a lot last week. There was, for example, the news that Antarctica could be gaining, not losing, ice, at least for now.
Lest you were tempted to breathe a sigh of relief, critics pointed to contrary evidence. And there were also these unsettling findings about the gigantic West Antarctic Ice Sheet.
But far to the north, some equally important news unfortunately got less attention. For the long and short of it, see the animation above.
I created it to portray in visual form what a study published last week has revealed: Unless we start reining in greenhouse gas emissions, “our projected impact on the climate system will change the face of Arctic sea ice,” says Katy Barnhart, who led the study while she was at the University of Colorado’s Institute for Arctic and Alpine Research. (Full disclosure: I’m a professor at the University of Colorado.)
The animation shows computer model simulations of how Arctic sea ice is likely to respond to continued human-caused warming. More specifically, it models how the number of days of open water change each year from 1920 to 2100 under a “business-as-usual” scenario. By 2100, according to the study, much of the Arctic has greater than 150 additional days of open water as compared with the pre industrial period prior to 1850.
But we won’t have to wait that long to see significant changes. If greenhouse gas emissions continue to rise, the entire coastline of the Arctic, and most of the Arctic Ocean itself, will see at least 60 additional days a year of open water by mid-century. Some sites will even see 100 additional open water days.
Features, provenance, and tectonic significance of Carboniferous-Permian glacial marine diamictites in the Southern Qiangtang–Baoshan block, Tibetan Plateau
Authors:
Fan et al
Abstract:
In this study, we conducted profile measurements, gravel composition analyses, and U-Pb dating on detrital zircons from a representative glacial marine diamictite in the Gangmaco–Dabure area of the Southern Qiangtang–Baoshan block, Tibetan Plateau. We conclude that the diamictite was formed in a glacial marine environment from the outer edge of the continental shelf to the continental slope and deep sea, in what is now the Southern Qiangtang–Baoshan block. Four distinct glacial-interglacial cycles were identified in the diamictite, which record a minimum of four stages of Gondwana glaciation in the area of the Southern Qiangtang–Baoshan block. Combined with regional geological information, we also conclude that during the Carboniferous-Permian, sediments containing the glacial marine diamictite derived from Gondwana, in the region extending from India to the Tethys Himalaya area, Lhasa and Southern Qiangtang–Baoshan blocks, recorded the transition from continental, neritic to abyssal environments. Gravel assemblages and U-Pb dating of detrital zircons in the glacial marine diamictite indicate that the provenance of the diamictite was Indian Gondwana. We infer that during the Late Paleozoic, the northern margin of the Indian Gondwana continued to be influenced by the Early Palaeozoic tectonic set-up, when Indian Gondwana was under an erosional regime, and the Tethys Himalaya area, Lhasa and Southern Qiangtang–Baoshan blocks were deposited on a passive continental margin.
Arctic sea ice coverage continued its below-average trend this year as the ice declined to its annual minimum on Sept. 17, according to the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder.
Over the 2014 summer, Arctic sea ice melted back from its maximum extent reached in March to a coverage area of 1.94 million square miles (5.02 million square kilometers), according to analysis from NASA and NSIDC scientists. This year's minimum extent is similar to last year's and below the 1981-2010 average of 2.40 million square miles (6.22 million square km).
"Arctic sea ice coverage in 2014 is the sixth lowest recorded since 1978. The summer started off relatively cool, and lacked the big storms or persistent winds that can break up ice and increase melting," said Walter Meier, a research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
"Even with a relatively cool year, the ice is so much thinner than it used to be," Meier said. "It's more susceptible to melting."
This summer, the Northwest Passage above Canada and Alaska remained ice-bound. A finger of open water stretched north of Siberia in the Laptev Sea, reaching beyond 85 degrees north, which is the farthest north open ocean has reached since the late 1970s, according to Meier.
Due to global warming, larger and larger areas of sea ice melt in the summer and when sea ice freezes over in the winter it is thinner and more reduced. As the Arctic summers are getting warmer we may see an acceleration of global warming, because reduced sea ice in the Arctic will remove less CO2 from the atmosphere, Danish scientists report.
"If our results are representative, then sea ice plays a greater role than expected, and we should take this into account in future global CO2 budgets", says Dorte Haubjerg Søgaard, PhD Fellow, Nordic Center for Earth Evolution, University of Southern Denmark and the Greenland Institute of Natural Resources, Nuuk.
Only recently scientists have realized that sea ice has an impact on the planet's CO2 balance.
"We have long known that the Earth's oceans are able to absorb huge amounts of CO2. But we also thought that this did not apply to ocean areas covered by ice, because the ice was considered impenetrable. However, this is not true: New research shows that sea ice in the Arctic draws large amounts of CO2 from the atmosphere into the ocean", says Dorte Haubjerg Søgaard.
Antarctic sea ice control on ocean circulation in present and glacial climates
Authors:
Ferrari et al
Abstract:
In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur.
The first evidence for massive and abrupt iceberg calving in Antarctica, dating back 19,000 to 9,000 years ago, has now been documented by an international team of geologists and climate scientists. Their findings are based on analysis of new, long deep sea sediment cores extracted from the region between the Falkland Islands and the Antarctic Peninsula. The study in the May 28, 2014 issue of Nature bears witness to an unstable Antarctic ice sheet that can abruptly reorganize Southern Hemisphere climate and cause rapid global sea level rise.
"One of the iceberg events in our data that is of particular interest took place 14,600 years ago and coincided with a huge ice-sheet melt, the famous Meltwater Pulse 1A, which according to previous studies led to a global sea level rise of about 4 meters within 100 years," says lead author of the study, Michael Weber at the University of Cologne in Germany.
"This is the first direct evidence that instabilities of the Antarctic ice sheet caused rapid sea level rise during the last glacial termination," says co-author Peter Clark, professor at Oregon State University.
Late Cretaceous winter sea ice in Antarctica?
Authors:
Bowman et al.
Abstract:
The Late Cretaceous is considered to have been a time of greenhouse climates, although evidence from Maastrichtian sediments for rapid and significant sea-level changes suggests that ice sheets were growing and decaying on Antarctica at that time. There is no direct geological evidence for glaciation, but we present palynomorph records from Seymour Island, Antarctica, that may suggest Maastrichtian sea ice. The dinoflagellate cyst Impletosphaeridium clavus is dominant. We propose that its profusion may signify the accumulation of resting cysts from dinoflagellate blooms related to winter sea ice decay. Prior to the Cretaceous-Paleogene transition, I. clavus decreased dramatically in abundance; we link this with climate warming. Terrestrial conditions inferred from pollen and spore data are consistent with our climate interpretations based on I. clavus together with δ18O values from macrofossils. These data and our interpretation support the presence of ephemeral ice sheets on Antarctica during the latest Cretaceous, highlighting the extreme sensitivity of this region to global climate change.
