Distribution of alkalinity in the surface waters of the major oceans

Abstract

In recent years the total alkalinity (TA) of seawater has been measured with high precision (∼±2 μmol kg−1) in the Atlantic, Pacific, and Indian oceans. In this paper we have analyzed the surface alkalinity of the major ocean basins using these measurements as well as those obtained during the GEOSECS and TTO studies. The salinity normalized alkalinity (NTA=TA×35/S) in subtropical gyres between 30°S and 30°N is remarkably invariable except in upwelling areas (e.g., the Eastern Equatorial Pacific). The NTA increases toward high latitudes (>30°) and is inversely proportional to sea surface temperature (SST). This increase in NTA with latitude (or decreasing temperature) is attributed to the upward transport of deep waters with higher NTA due to the dissolution of CaCO3(s). The distribution of surface NTA in the major ocean basins shows that the major basins can be divided into regions where different trends of NTA are observed and boundaries between the regions are similar to those of the major ocean currents. The linear behavior of NTA (∼±5 μmol kg−1) with respect to SST makes it possible to provide regional maps of NTA. These maps can be used to estimate TA in surface waters in large areas of the ocean from values of SST and salinity (S). By combining the estimates of TA using SST and S (from the Climatological Atlas of the World Ocean) with underway fCO2 measurements (by ships, moorings, and satellites), it is possible to map the detailed distribution of TCO2 for surface waters over a large area of the ocean. Calculations of TCO2 from measurements of fCO2, SST, and S in the subtropical Pacific Ocean agree with the coulometrically measured values to ±5 μmol kg−1.