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SUMMARY:Diving into Ancient Oceans: The Southern Ocean\, Climate Change an
 d the Silicon Cycle - Dr Katharine Hendry\, Cardiff University
DTSTART:20120926T100000Z
DTEND:20120926T110000Z
UID:TALK39396@talks.cam.ac.uk
CONTACT:Dr Andrew Meijers
DESCRIPTION:Ice cores and marine sediments record archives of past atmosph
 eric carbon dioxide (pCO2)\, which show that levels of this important gree
 nhouse 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 fe
 eds the growth of marine phytoplankton.  The marine cycling of the element
  silicon (Si) plays a crucial role in the regulation of pCO2.  Over relati
 vely short timescales - thousands or tens of thousands of years - the grow
 th of photosynthetic algae\, diatoms\, forms an important sink of carbon i
 n the oceans.  Diatoms make their intricate tests from silica and\, when t
 he cells die and sink\, result in export of nearly half of the organic car
 bon produced in the sea surface to the seafloor.  Understanding changes in
  the rate and concentration of dissolved silicon (silicic acid) in major w
 ater masses and upwelling waters is essential for understanding past clima
 te for two reasons.  Firstly\, it is essential to be able to reconstruct p
 ast 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 concentratio
 ns in the major water masses in the global oceans\, such that dissolved si
 licon concentrations can be used as a form of water mass “tracer”.  \n
 Recent developments in the use of geochemical proxies of surface silicon c
 ycling based on biogenic silica from diatoms\, as well as archives of deep
 -water silicic acid concentration from deep-sea sponges\, have led to a gr
 eater understanding of silicon cycling in marine waters through time.  Her
 e\, I will present some new records of diatom and sponge silicon isotopes 
 that highlight the important role played by the Southern Ocean in the dist
 ribution and cycling of essential nutrients in the global system.
LOCATION:British Antarctic Survey\, Room 330B
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