Reconstructing Marine Nutrients, their Utilization, and Role in Past CO2 Sequestration using Cadmium Isotopes



The marine primary producers that inhabit the sunlit upper part of the ocean consume climatically-significant quantities of carbon from surface seawater and the atmosphere.  On a global scale, phytoplankton ‘pump’ nutrients and carbon into the ocean interior, where some material escapes decomposition and is deposited on the sea floor.  The sum of these processes is known as the biological pump, which serves to modulate atmospheric concentrations of carbon dioxide (pCO2) on a range of timescales.  The efficiency of the pump depends largely on the availability of nutrients; studying how nutrients have interacted with marine biota on centennial to millennial timescales through proxy records is thus a key motivation for paleoceanography.  The distributions and isotopic compositions of key trace metals (Cd, Zn, Fe, etc.) have recently attracted much interest because of their important roles in phytoplankton physiology and because they are often well preserved in marine sediments, allowing for reconstructions of past nutrients.  Cadmium is a particularly promising tracer of marine nutrients as its elemental distribution tracks phosphate concentrations, whilst its stable isotopic composition reflects nutrient utilization.  However, a significant obstacle to interpreting trace metal isotope records is ambiguity in modern Cd cycling.  Here, we seek funds to constrain key aspects of the modern oceanic cycling of Cd by performing Cd isotopic analyses of marine particles collected in situ via large volume seawater filtration.  The funds requested here will elucidate potentially important controls on marine Cd cycling that will form the basis of larger funding solicitations.