Diving into Ancient Oceans: The Southern Ocean, Climate Change and the Silicon Cycle

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• Dr Katharine Hendry, Cardiff University
• Wednesday 26 September 2012, 11:00-12:00
• British Antarctic Survey, Room 330B.

If you have a question about this talk, please contact Dr Andrew Meijers.

Ice cores and marine sediments record archives of past atmospheric carbon dioxide (pCO2), which show that levels of this important greenhouse gas have fluctuated throughout Earth’s history. The oceans, in particular the Southern Ocean, have been implicated in these changes, in part because of the control they exert on the supply of nutrients that feeds the growth of marine phytoplankton. The marine cycling of the element silicon (Si) plays a crucial role in the regulation of pCO2. Over relatively short timescales – thousands or tens of thousands of years – the growth of photosynthetic algae, diatoms, forms an important sink of carbon in the oceans. Diatoms make their intricate tests from silica and, when the cells die and sink, result in export of nearly half of the organic carbon produced in the sea surface to the seafloor. Understanding changes in the rate and concentration of dissolved silicon (silicic acid) in major water masses and upwelling waters is essential for understanding past climate for two reasons. Firstly, it is essential to be able to reconstruct past changes in the supply of silicon to surface waters to understand past changes in diatom growth and carbon uptake. This is because diatoms take up silicon efficiently from ambient water, and rely on upwelling sources of silicic acid for growth. Secondly, biogeographic variations in algal production and ocean circulation impart distinct silicic acid concentrations in the major water masses in the global oceans, such that dissolved silicon concentrations can be used as a form of water mass “tracer”. Recent developments in the use of geochemical proxies of surface silicon cycling based on biogenic silica from diatoms, as well as archives of deep-water silicic acid concentration from deep-sea sponges, have led to a greater understanding of silicon cycling in marine waters through time. Here, I will present some new records of diatom and sponge silicon isotopes that highlight the important role played by the Southern Ocean in the distribution and cycling of essential nutrients in the global system.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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