UC Irvine

Coastal waters connect the terrestrial and marine carbon cycles and are the location of a large portion of the organic carbon (OC) burial in the ocean. Anthropogenic activity has affected the carbon (C) cycling in these waters. However, the heterogeneity of these systems makes generating global estimates challenging. Thus, detailed information about the mechanisms and long-term trends of C fluxes and storage are needed to assess past and future changes to the coastal C cycle.

This dissertation examines the mixing of multiple pools of C in coastal waters using C isotopes (13C and 14C). First, we performed a series of laboratory experiments that examined whether sorption of riverine dissolved OC to sediments could be isotopically selective. We found that compounds with higher ∆14C values and lower ?13C values were selectively sorbed by the sediments. Lignin phenols and black C were suspected as possible sorbed compounds. Second, we report a timeseries of ∆14C and ?13C values from dissolved inorganic C at the Newport Beach Pier, CA. This record showed a steady decrease in the ∆14C and ?13C values over the study period that indicates an increasing quantity of fossil fuel derived CO2 dissolved in the surface waters. Third, we compare the magnitude and composition of particulate OC and sedimentary OC from the Santa Clara River Estuary during periods of extreme precipitation and extreme drought. The results mirror the change in the C isotope values of atmospheric CO2 and show that even in low precipitation years, significant quantities of eroded petrogenic OC are exported by this watershed. The amount of recently produced plant- and algae-derived OC is highly variable in the estuary while the amount petrogenic OC is relatively stable over the study period. Together, these studies enhance our understanding of the processes that control C cycling within coastal waters.