Date of Award
Open Access Thesis
Geothermal convection and sediment compaction drive large-scale flow in continental shelves. We suggest that this flow is an overlooked control on the major ion chemistry of the ocean. Conventional ocean chemical budgets are constructed using river discharge, axial mid-ocean ridge (MOR) convection and CaCO3 production, but these budgets are still poorly quantified. We synthesized data from 17 passive continental margin basins to calculate a range of estimated groundwater and chemical fluxes from continental shelves, considering five major ions (Ca2+, Na+, K+, Mg2+, and Cl-). When extrapolated globally, volumetric groundwater flux estimates were comparable to those for MOR axial circulation, and our maximum volumetric flux estimates exceeded MORs by ~an order of magnitude. Net chemical fluxes were calculated assuming seawater was the starting composition for groundwater discharging from the basins. Chemical compositions of four likely basinal fluid archetypes were synthesized from the literature. We estimated chemical and groundwater fluxes from passive margins required to close chemical budgets using a mass balance model which also included chemical input from rivers, MORs, and CaCO3 production. We found that passive continental margins have the potential to remove Mg2+ from the oceans in a quantity which balances input from the other chemical sources for three out of four considered fluid archetypes. We suggest that passive margins also contribute significant quantities of Ca2+ and K+ to the oceans, though not in a magnitude large enough to balance chemical budgets on their own.
Osborne, A. W.(2021). Groundwater Discharge From Passive Continental Margins: Rethinking Marine Chemical Budgets. (Master's thesis). Retrieved from https://scholarcommons.sc.edu/etd/6531