Abstract:
The climatic changes of the Neoproterozoic time, 630-720 million years ago, included episodes of extreme glaciation, during which ice may have covered nearly the entire ocean for several million years. The likely cause of the snowball events was a reduction of the atmospheric greenhouse effect resulting from disturbance to the global carbon cycle that affected levels of both carbon dioxide and methane.
Energy-balance climate modeling of the albedo-temperature feedback indicated that if sea ice advances to about 20°-30° latitude it will proceed catastrophically to the equator. After millions of years the snowball events would have been terminated by the slow buildup of atmospheric CO2 from volcanic emissions, when the atmosphere was too cold for removal of CO2 into rainwater and rock-weathering.
The snowball events were qualitatively different from the Pleistocene ice ages, during which land-based ice sheets advanced and retreated over mid-latitude continents. On the snowball planet, by contrast, much of the action would have been in the ocean. "Sea glaciers" (flowing like modern ice shelves in response to their thickness gradient, but not dependent on continental glaciation) could flow as much as 7-50 m/yr even when they covered the entire ocean.
Despite the name, the Earth would not have been entirely snow-covered. At low latitudes in the regions of net sublimation, the ocean surfaces would at first consist of bare sea ice with salt inclusions, and would then develop a lag-deposit of salt over the ice. After several thousand years the sea ice would be crushed by the inflow of sea-glaciers from higher latitudes, which thereafter would dominate the tropical ocean. As sea-glaciers flowed equatorward into the tropical region of net sublimation, their surface snow and subsurface firn would sublimate away, exposing bare glacier ice to the atmosphere and to solar radiation.
The albedos we measured for sea-glacier surrogates in Antarctica are in the range that favors ice hundreds of meters thick on the tropical ocean, thus severely limiting the possible liquid-water refugia available for photosynthetic surface life. That conclusion is in striking conflict with biological evidence against widespread extinctions, and with evidence for the survival not only of photosynthetic algae but also of primitive animals, all of which argue that the refugia must have been larger in area, and longer lasting, than small pools at geothermal hot-springs near the coasts of volcanic islands. Other possible refugia are at the end of narrow oceanic bays surrounded by desert, and on desert land fed water by occasional snowmelt.
What is the Joint Oslo Seminar (JOS):
- Atmospheric and climate sciences have a stronghold in Oslo among the four institutions University of Oslo, the Meteorological Institute, CICERO and NILU.
- This joint seminar invites renowned international experts to contribute to an informal series of lectures, meant to create interaction with the Oslo atmospheric and climate science community on recent highlights and analysis in the field.
- Normally seminars will be held on Thursdays (12:15 pm -1pm).