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Note: The abstract that appears below has been modified from the original text. The Greek letters "delta" (as in delta13C) and "Sigma" (as in SigmaCO2) are spelled out in English in this version because the characters cannot be displayed on this web page in their native format.
ABSTRACT: Observed distributions of alkalinity, pCO2 and delta13C(SigmaCO2) indicate that dissolved inorganic carbon (DIC) was primarily supplied to San Francisco Bay by ocean, Delta, and municipal waste waters during the low Delta-outflow period from March 1976 to March 1977. Delta-derived alkalinity was typically about half that of ocean water and increased slightly with time. The pCO2 values were highest (2 to 3 times the atmospheric value of approximately 325 ppm) in the Sacramento River and southern boundary of South Bay and decreased to near atmospheric values seaward of the Golden Gate. The delta13C(SigmaCO2) was lowest in the Sacramento River (approx. -10‰), increasing to marine values in the Gulf of the Farallones (approx. +2‰). Golden Gate values were approximately 2‰ less than those seaward, indicating that at least 10% of the Sigma CO2 was biogenic and is apparently the product of respiration and the mineralization of organic matter in the Bay. South Bay alkalinity and pCO2 levels increased southward, whereas delta13C(SigmaCO2) and salinity decreased. Municipal waste discharged into South Bay is the most probable source of the excess biogenic CO2. Distributions of particulate organic carbon (POC) in North Bay were influenced by in situ phytoplankton production and seaward dilution of riverine and estuarine POC. Apparent depletions of pCO2 in North Bay coincide with chlorophyll a, POC, and delta13C(SigmaCO2) increases. The delta13C(POC) values during March 1977 approached those predicted for in situ algal production, suggesting that about 80 to 90% of the POC was produced in the seaward part of the estuary. In situ algal production was an important source of POC in the river. However, in the null-zone associated turbidity maximum, less than two-thirds of the POC appears to be riverborne, the remaining one-third being produced in the estuary or associated with resuspended bottom sediment. South Bay suspended POC appears to be a mixture of resuspended bottom sediments, in situ produced POC and land-derived organic carbon. Based on delta13C data, Spartina salt-marsh grass does not appear to be a significant source of detritus in the Bay. The delta13C of sediment total organic carbon (TOC) indicates that riverine carbon from the Delta is diluted in the Bay by estuarine and marine carbon. The suspended POC and sediment TOC delta13C-measurements approached marine values seaward of the Golden Gate.
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