An Assessment of the XBT Fall-Rate Equation in the Southern Ocean

AbstractIn this study a set of 157 collocated XBT (DB/T7 type) and CTD stations distributed across three different regions of the Southern Ocean is explored using the manufacturer’s fall-rate equation (FRE), which is a classic correction method, and new correction methods to investigate how the regional environment characteristics may impact a probe’s descent and the corresponding depth estimates. Regional coefficients were estimated for all three basins and for the Southern Ocean as a whole. The manufacturer’s FRE proved to perform better in high latitudes than in the rest of the World Ocean, overestimating the true depth by only 2%. The overall depth bias was positive, further supporting the hypothesis of a regional dependence of the XBT fall rate on water temperature, which leads to a general overestimation of ocean heat content in the upper layer (~4.79 × 109 J or ~10%). The pure thermal bias was found to be mostly negative, which is likely to be related to temperature errors. However, the Southern Oc...