The C-13 Suess effect in the world surface oceans and its implications for oceanic uptake of CO2:Analysis of observations at Bermuda

Surface ocean water delta(13)C measurements near Bermuda are examined in an attempt to find the annual decrease caused by the addition of anthropogenic CO2 to the atmosphere. We refer to this trend as the surface ocean C-13 Suess effect. Interannual variability, which may be related to the El Nino - Southern Oscillation in the Atlantic Ocean, is apparent. We try to correct the data for this variability so as to better determine the trend. The trend has implications for the uptake of anthropogenic CO2 by the oceans. We employ a three-dimensional model of ocean chemistry to relate the trend at Bermuda to the average ocean trend, then use the average ocean trend to estimate the vertical diffusivity K in a one-dimensional ocean model, and finally use this model to calculate the oceanic uptake of CO2. Uncertainties associated with the estimation of the Suess effect at Bermuda and in the analysis procedure preclude a firm estimate of the oceanic uptake of CO2. Results are, in general, consistent with the low side of the Intergovernmental Panel on Climate Control estimation of 2.0 +/- 0.8 GtC yr(-1). With a longer record at Bermuda and delta(13)C observations at additional locations, we believe this approach will lead to a useful estimate of oceanic uptake

Exchanges of Atmospheric CO2 and 13CO2 with the Terrestrial Biosphere and Oceans from 1978 to 2000. I. Global Aspects

From 1978 through 1999 the global average concentration of atmospheric carbon dioxide increased from 335 ppm to 368 ppm according to measurements of air samples collected at an array of ten stations extending from the Arctic to the South Pole. The global average rate of increase varied widely, however, with highest rates occurring in 1980, 1983, 1987, 1990, 1994, and 1998, all but the first of these calendar years near times of El Nin˜o events. The 13C/12C isotopic ratio of carbon dioxide, measured on the same air samples, varied in a similarly irregular manner, suggesting that exchange of atmospheric CO2 with terrestrial plants and soil is the dominant cause of both signals. Quantitative analysis of the data by a procedure called a "double deconvolution" supports this hypothesis but also suggests a variable exchange with the oceans, opposite in phase to the terrestrial exchange. This result may be in error, however, because it depends on an assumption that the global average isotopic discrimination of terrestrial plants has been constant. Allowing for a variation in discrimination of only about 1°/°° would eliminate the opposing fluctuations in oceanic flux, if its phasing has been opposite to that of the observed fluctuations in rate of change of CO2 concentration. In three companion articles that follow, we further deduce regional exchanges of CO2, making use of latitudinal gradients computed from the same atmospheric carbon dioxide data used in this global study

Spatiotemporal Patterns of Carbon-13 in The Global Surface Oceans and The Oceanic Suess Effect

A global synthesis of the C-13/C-12 ratio of dissolved inorganic carbon (DIC) in the surface ocean is attempted by summarizing high-precision data obtained from 1978 to 1997 in all major ocean basins. The data, mainly along transects but including three subtropical time series, are accompanied by simultaneous, precise measurements of DIC concentration and titration alkalinity. The reduced isotopic ratio, delta(13)C, in the surface ocean water is governed by a balance between biological and thermodynamic processes. These processes have strongly opposing tendencies, which result in a complex spatial pattern in delta(13)C with relatively little variability. The most distinctive feature in the spatial distribution of delta(13)C seen in our data is a maximum of delta(13)C near the subantarctic front with sharply falling values to the south. We attribute this feature to a combination of biological uptake of CO2 depleted in C-13 (low delta(13)C) and air-sea exchange near the front and upwelling further south of waters with low delta(13)C resulting from the remineralization of organic matter. Additional features are maxima in delta(13)C downstream of upwelling regions, reflecting biological uptake, and minima in the subtropical gyres caused by strongly temperature dependent thermodynamic isotopic fractionation. At the time series stations, two in the North Atlantic Ocean and one in the North Pacific, distinct seasonal cycles in delta(13)C are observed, the Pacific data exhibiting only about half the amplitude of the Atlantic. Secular decreases in delta(13)C caused by the invasion of isotopically light anthropogenic CO2 into the ocean (the C-13 Suess effect) have been identified at these time series stations and also in data from repeated transects in the Indian Ocean and the tropical Pacific. A tentative global extrapolation of these secular decreases yields a surface oceanic C-13 Suess effect of approximately -0.018 parts per thousand yr(-1) from 1980 to 1995. This effect is nearly the same as the C-13 Suess effect observed globally in the atmosphere over the same period. We attribute this response to a deceleration in the growth rate of anthropogenic CO2 emissions after 1979, which subsequently has reduced the atmospheric C-13 Suess effect more than the surface ocean effect