Australia: The Land Where Time Began

A biography of the Australian continent 

The Cryosphere - Biosphere Interactions

The cryosphere has many influences on the biosphere, including the preference of marine mammals for the edge of the sea ice, the rhythm of the  hibernation of bears, the negative effect of rain and snow events of Peary caribou, and the importance of deep snowpacks to woodland caribou that use the increased elevation provided by the depth of the snowpack to reach higher in spruce, cedar and fir trees to forage in winter. In rivers and lakes at high latitudes there is a close connection between the snow cover and photosynthetic activity and ecological rhythms.

The role of snow, ice and permafrost in the global carbon cycle is poorly understood, according to the author1. It is suspected that open water, as opposed to sea ice cover, would be conducive to the open water in the polar regions functioning as a sink for atmospheric carbon dioxide. This is at least partly based on a tendency for polynya to be enriched in nutrients making them ecological hotspots associated with the drawdown of CO2 into the ocean in polar regions. The author1 suggests that as there are algae that thrive in sea ice so the carbon-ice-ocean exchanges are is not fully predictable.

Carbon stored in the landscape is altered by glacier and permafrost cover. Vegetation and soil is overridden by glaciers which effectively removes this carbon from the system. Subglacial storage can account for some of this organic carbon, as is evidenced by glacier retreat, though most is washed out in subglacial meltwater, once it has been  decomposed, to leave an organic subglacial and periglacial environment that is relatively barren. In the till deposits from most glacier forefields that have been exposed by the retreat of the glaciers after that Little Ice Age in the 19th century, soil is still in the process of becoming established.

Permafrost is present in muskeg and peatlands, that are organically rich and have a high content of soil moisture and carbon, in much of northern Canada, Russia, Alaska and Scandinavia. This carbon is removed from the atmospheric cycle when frozen, remaining locked up in the permafrost until the permafrost melts, which can mean it is out of circulation for long periods, though as the climate warms it is more likely to melt, and the active layer can be deepened, releasing the carbon back into the atmosphere as carbon dioxide (CO2) and methane (CH4). It is has been suggested that as expansion of biomass and vegetation continues at high elevations, and in high northern latitudes, the carbon fluxes from thawing permafrost may be offset by the increased uptake of carbon. It is suggested by the author1 that the biological uptake of carbon may increase in high-latitude oceans, and as the growing season is extended in midlatitudes that become increasingly snow-free. The result is that the impact of cryosphere change on the carbon cycle is unclear.

Understanding of the carbon cycle remains incomplete as problems associated with the variations of CO2 and CH4 during the glacial-interglacial cycles have not been solved. During the glaciations of the Pleistocene the levels of both these gases in the atmosphere declined symmetrically, as is observed in gas bubbles in the ice cores from Antarctica and Greenland. There is a correlation between the concentrations of CO2 and CH4, air temperature and the total volume of ice on the Earth, that the author1 describes as remarkable, which makes it clear that reductions of the atmospheric concentrations of these greenhouse gases acted as an important feedback in the driving of the world into and out of glaciations. The nature of the carbon sink operating in the glacial period remains uncertain. As there are negligible amounts of carbon in ice sheets, they are clearly not that saought for carbon sink.

The author1 suggests that the direct effect of the ice sheets of the Pleistocene should be to release carbon from the vegetation and soil, that had been overrun by the advancing ice sheets, to the atmosphere leading to decreased terrestrial CO2 and increased atmospheric CO2. This should have led to even more CO2 needing to be absorbed by the oceans or tropical vegetation during the glaciations. Carbon sequestration in frozen ground may have been 1 aspect of the cryosphere that was implicated in the carbon sink. During the glaciation permafrost at midlatitudes may have acted as a major carbon sink beneath the ice sheets and in the proglacial regions. If this was the case it would indicate there was an extremely tight coupling between the the advance/retreat of ice sheets and uptake/release of this carbon, which implies a response time on a century scale for carbon storage in permafrost.

Sources & Further reading

  1. Marshall, Shawn J., 2012, The Cryosphere, Princeton University Press. 
Author: M. H. Monroe
Last updated 01/05/2013

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