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

Surface ocean water δ 13 C measurements near Bermuda are examined in an attempt to find the annual decrease caused by the addition of anthropogenic CO 2 to the atmosphere. We refer to this trend as the surface ocean 13 C Suess effect. Interannual variability, which may be related to the El Niño ‐ 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 CO 2 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 CO 2 . 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 CO 2 . 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 δ 13 C observations at additional locations, we believe this approach will lead to a useful estimate of oceanic uptake.