Capturing dynamics of marine inorganic carbon fluxes from diurnal to decadal timescales
Chu, Sophie N.
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The marine carbon cycle plays an important role in regulating Earth’s climate. The vastness of the open ocean and the large variability in the coastal ocean provide obstacles to accurately quantify storage and transport of inorganic carbon within marine ecosystems and between marine and other earth systems. Thus far, the open ocean has been the only true net sink of anthropogenic carbon dioxide (Canthro) emissions. However, ocean storage of Canthro is not uniformly distributed. Changes in water chemistry in the Northeast Pacific were quantified to estimate the amount of Canthro stored in this region over the last decade. This additional Canthro was found to cause acidification and aragonite saturation horizon shoaling at rates towards the higher end of those found in Pacific and Atlantic Ocean basins, making the Northeast Pacific one of the most sensitive regions to the invasion of anthropogenic carbon dioxide. Due to large variability in biogeochemical signals in coastal oceans, it is challenging to accurately assess carbon fluxes across different boundaries, such as tidal exchange between coastal wetlands and coastal oceans. Coastal salt marshes have been suggested to be a large net CO2 sink, thus designated as a type of “blue carbon.” However, accurate and dynamic estimates of carbon fluxes to and from tidal marshes are still premature, particularly carbon fluxes from marshes to the coastal ocean via tidal exchange, often referred to as marsh lateral fluxes. In this thesis, lateral total alkalinity (TA) and dissolved inorganic carbon (DIC) export fluxes were realistically quantified using high frequency time-series, in situ data. High-resolution fluxes permitted a closer look at how marsh generated TA and DIC are being exported over diurnal, spring-neap, and seasonal scales. I investigated the best way to capture variability of marsh exports via traditional bottle sampling and assessed uncertainties associated with different sampling strategies. Marsh TA and DIC exports significantly modified buffering capacity of coastal waters. This work contains the first realistic estimate of TA exports from a tidal salt marsh. Accurate estimates of DIC and TA fluxes indicate the significance of salt marshes to the coastal carbon and alkalinity budgets.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017
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