Stunning spikes of Arctic heat in interglacial periods, far warmer than predicted by existing climate models, may be caused by rapid melting of Antarctic ice. The ocean overturning circulation around Antarctica may have suddenly shut down, triggering rapid warming of the north Pacific and north Atlantic oceans and the northern hemisphere. A continuous record Arctic climate of the past 2.8 million years is preserved in sediments of a deep lake formed by impact of a massive meteorite 3.6 million years ago in north east Siberia. Climate scientists studying the sediment cores were shocked to find multiple episodes of temperatures 4C to 5C (7 to 9 degrees Fahrenheit) greater than normal interglacial periods. Standard climate models could not predict these super warm periods. However, the researchers found that shutting down the Antarctic overturning circulation, the opposite of popularized episodes of "shutting down the Gulf Stream", could cause the sudden onset of extreme Arctic heating.
Fresh water released by the rapid melting of Antarctic ice could cause this rapid shift in ocean circulation patterns. This shut down of the southern hemisphere's equivalent of the north Atlantic overturning circulation could happen again if global warming rapidly destabilizes Antarctic ice sheets. The research was published ahead of print in highly-respected Science Magazine.
Linkages between extraordinary warmth at Lake El’gygytgyn and Antarctic ice volume imply strong intra-hemispheric climate coupling that could be related to reductions in Antarctic Bottom Water (AABW) formation (47) during times of ice sheet/shelf retreat and elevated fresh water input into the Southern Ocean. This is supported by distinct minima in AABW inflows into the southwest Pacific during MIS 11 and MIS 31 (48). As a consequence, changes in thermohaline circulation (THC) during MIS 11 and MIS 31 might have reduced upwelling in the northern North Pacific (49), as indicated by distinctly lower BSi concentrations compared to interglacials at ODP Site 882 (50, 51). A stratified water column during the super interglacials would have resulted in higher sea surface temperatures in the northern North Pacific, with the potential to raise air temperatures and precipitation rates over adjacent land masses via effects on the dominant pressure patterns (Siberian High and Aleutian Low) that dominate the modern climatology at thelake (52).In summary, the scientists found when cold water stopped sinking around Antarctica, it stopped welling up in the north Pacific, triggering rapid warming of surface waters in the north Pacific ocean. The warm north Pacific caused warming of the Arctic and the northern hemisphere.
NSF press release about article in Science magazine.
To quantify the climate differences, the scientists studied four warm phases in detail: the two youngest, called "normal" interglacials, from 12,000 years and 125,000 years ago; and two older phases, called "super" interglacials, from 400,000 and 1.1 million years ago.Modeling and paleoclimate records have shown when the ice cap in Greenland melts rapidly, it may cause sudden onset of cold episodes in North America and Europe (and rapid warming in Antarctica. Thus if warming rates caused by increasing GHG levels are rapid, wild oscillations of hot and cold might be triggered in Europe and north America by the oscillations in the overturning circulations in the southern ocean and the north Atlantic.According to climate reconstructions based on pollen found in sediment cores, summer temperatures and annual precipitation during the super interglacials were about 4 to 5 degrees C warmer, and about 12 inches wetter, than during normal interglacials.
The super interglacial climates suggest that it's nearly impossible for Greenland's ice sheet to have existed in its present form at those times.
Simulations using a state-of-the-art climate model show that the high temperature and precipitation during the super interglacials can't be explained by Earth's orbital parameters or variations in atmospheric greenhouse gases alone, which geologists usually see as driving the glacial/interglacial pattern during ice ages.