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SUMMARY:The link between the global carbon cycle and the interplay between
  calcium and sulfur in marine pore fluid - Hal Bradbury\, Dept of Earth Sc
 iences\, Uni of Cambridge
DTSTART:20201022T103000Z
DTEND:20201022T113000Z
UID:TALK151798@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:The removal of carbon from the surface of the planet is a crit
 ical component of the long-term carbon cycle\; this removal is through the
  deposition and subsequent burial of carbonate minerals in the ocean. Sedi
 mentary\, post-depositional processes play a key role in the global carbon
  cycle because much of the organic carbon in sediments is microbially oxid
 ized back to dissolved inorganic carbon. The oxidation of organic carbon i
 n anaerobic sediment through the reduction of sulfate can consume protons\
 , raising pH\, and leading to some of the dissolved inorganic carbon preci
 pitating as in situ\, or authigenic carbonate. Because this authigenic car
 bonate has a different carbon isotope composition to marine carbonate\, it
  may influence the overall carbon isotope balance at Earth's surface and c
 ritically\, our interpretation of global shifts in the carbon cycle over g
 eological time. In today's ocean the two main processes that produce alkal
 inity and drive authigenic carbonate formation are the organiclastic reduc
 tion of sulfate and the anaerobic oxidation of methane\, coupled to microb
 ial sulfate reduction. However\, each of these produces authigenic carbona
 te with a different carbon isotope composition\, and it is unclear how imp
 ortant these processes were in past oceans with limited sulfate concentrat
 ions.\nI will discuss how we can identify the processes that are linked to
  the precipitation of authigenic carbonate\, and how we can utilise the gl
 obal ODP/IODP pore fluid database to examine these processes on a global s
 cale. Here we concentrate on the relative change in alkalinity\, methane a
 nd sulfate concentrations to predict regions of anaerobic methane oxidatio
 n versus organiclastic sulfate reduction and the relative decrease in calc
 ium concentration to predict the amount of authigenic carbonate formed. Id
 ealized carbon isotope profiles for dissolved inorganic carbon then allow 
 us to determine the global carbon isotopic composition of the authigenic c
 arbonate sink today. I will present a machine-learning approach to identif
 y the distribution of these processes in the modern ocean tuned with chlor
 ophyll\, temperature\, water depth and distance from the coast to predict 
 the extent of anaerobic methane oxidation versus organiclastic sulfate red
 uction to extend the sites with observations to those areas that have none
 .\n\nThis knowledge is then applied to a simple steady-state model to disc
 uss how the formation of authigenic carbonate would have been impacted by 
 the lower sulfate and higher calcium concentrations found in Cretaceous se
 awater. 
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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