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Popular Science: Subglacial silicon as another player in global nutrient cycling

As recently published in Nature, methane released from subglacial meltwater is a significant source of greenhouse gas emissions to the atmosphere. However, it is not only subglacial methane which is responsible for changes in greenhouse gas concentrations. The international team of scientists, in collaboration with three polar ecologists from the Department of Ecology, found that there is another important nutrient influencing atmospheric greenhouse gas concentrations, fortunately by the utilization of carbon dioxide. The name of this player is Silicon.

Maybe you are now asking yourselves, why silicon? Well, the increasing melt rates of glaciers results in a higher discharge of glacier rivers and consequently in a higher level of erosion within glacier bedrock. Eroding bedrock influences the silicon concentration within meltwaters, its input into coastal marine ecosystems, and thus biochemical nutrient pathways within polar habitats. The dominant compound of polar marine phytoplankton are diatoms which are well-known for their siliceous cell walls. If the input of silicon and other essential nutrients such as carbon, nitrogen, and phosphorus (e.g. available from melting sea ice during the beginning of the season) is sufficient, diatoms can grow, reproduce, and also bind carbon dioxide.

Source: www.cryoeco.eu

Apart from focusing on the release of silicon from the subglacial environment, this study also investigated the silicon isotopic signatures of subglacial meltwaters. The isotopic signatures showed differences between rivers of glacial and non-glacial origin, which is reflected in the composition of marine primary producers. The authors used a considerable number of published data together with the data from their own sampling. Surprisingly, they found that water from subglacial rivers have a larger amount of lighter silicon isotopes than water from non-glacial rivers. Moreover, they found that the isotopic composition of subglacial water is influenced by the duration of water flow through the bedrock. The isotopic ratios are not constant during the season and they can change with sudden subglacial drainage events as well. In any case, the major finding of this study was the confirmation that high erosion rates within subglacial areas result in a greater release of the lighter silicon isotope into the environment.

It is highly probable that isotopic ratios within marine waters will change with the increasing input of glacial meltwaters from the glacier’s retreat. It will potentially result in coastal community structure changes with diatoms having the advantage in case they are Si limited or it will shape their Si isotopic ratios. Diatoms preferably use lighter silicon isotopes; thus, marine waters tend to be enriched by heavier forms which are not efficiently utilized. Therefore, it is necessary to focus on biochemical processes influencing the isotopic ratios within subglacial meltwaters to understand the cycling of essential nutrients within polar coastal and open-ocean waters.

Hatton J. E., Hendry K. R., Hawkings J. R., Wadham J. L., Opfergelt S., Kohler T. J., Yde J. C., Stibal M. and Žárský J. D. (2019). Silicon isotopes in Arctic and sub-Arctic glacial meltwaters: the role of subglacial weathering in the silicon cycle. Proceedings of the Royal Society A475(2228), 20190098.

Tereza Jaroměřská

Published: Dec 09, 2019 06:55 AM

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