Changes in the δ13C of surface water particulate organic matter across the subtropical convergence in the SW Indian Ocean

作者：Roger François, Mark A. Altabet, Ralf Goericke, Daniel C. C McCorkle, C. Brunet, Alain Poisson · 发表于：Global Biogeochemical Cycles · 年份：1993 · DOI：10.1029/93gb01277 · 被引用次数：273 · 研究领域：Isotope Analysis in Ecology、Geology and Paleoclimatology Research、Marine and coastal ecosystems

We have measured the carbon isotopic composition of particulate organic matter suspended in surface waters (POM) between 59°S and 30°S in the SW Indian Ocean during the austral summer. In an attempt to further document the pattern and causes of covariance between POC‐δ13C and [CO2aq], we concurrently measured surface water pCO2, temperature, salinity, nitrate concentration, POM concentration, chlorophyll a and the δ13C of total dissolved inorganic carbon. While we found the previously reported general negative correlation between POC‐δ13C and [CO2aq], we also observed a prominent maximum in POC‐δ13C in the region immediately north of the Subtropical Convergence, coinciding with a maximum in [POM] and chlorophyll a, and with a minimum in pCO2. The increase in POC‐δ13C between 59°S and the Subtropical Convergence is consistent with the trend expected if [CO2aq] were the main factor controlling the isotopic composition of POM. In contrast, data from the region north of the Subtropical Convergence clearly illustrate that POC‐δ13C can also vary independently of [CO2aq] as a 5 per mil decrease in POC‐δ13C was found in a region characterized by nearly constant [CO2aq]. We review several physiological factors which may account for these observations and discuss their implications for paleoceanographic reconstruction of [CO2aq] from the carbon isotopic composition of sedimentary organic matter.