The Fate of Organic Carbon in the Gulf of California
Carol J. Pride, Robert C. Thunell, and Eric J. Tappa
The Gulf of California is an ideal site to study the controls on sedimentary organic carbon (OC) accumulation and preservation. A 5-year sediment trap record provides an estimate of export production in the Gulf. Low C/N ratios (7.3) and heavy ^dgr13Corg values (-20.5^pmil) of trapped OC show that it is predominantly of marine origin.
Surface productivity is not the only control of OC deposition in the Gulf, This is shown by OC fluxes that can be high even under oligotrophic summer conditions. These high summer fluxes cannot be attributed to input of terrestrial biomass since variability in the C/N ratio is not seasonal.
The efficiency of scavenging and transport mechanisms may play an important role in determining OC export. OC fluxes correlate better with the fluxes of total bulk sediment and of lithogenic sediments than they do with fluxes of opal and of productivity-sensitive foraminiferal species. The efficiency of recycling within the photic zone is also important in controlling OC export. At most, 3% of surface production escapes recycling within the photic zone.
A comparison of sediment trap results with OC accumulation rates in underlying box cores, shows that there is more sedimentary OC than can be accounted for by export production alone. Controls on OC preservation are tested by a comparison of box cores from within and below the oxygen minimum zone. The deeper oxic cores consistently had greater OC A.R. and %OC than did the anoxic cores. Preferential preservation within anoxic sediments is thus not a significant control on OC accumulation in the Gulf and downslope transport must contribute to the organic content of slope sediments.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California