Spice and barrier layers: An Arabian Sea case study

Abstract

Barrier layers (BLs) are a frequent occurrence in low-latitude oceans, but variations in identification methods and quantitative descriptors used, as well as analyses of their lifetimes, lead to differing views on their overall impact. Herein a new method is proposed for identifying BLs that relies on the vertical spice profile rather than arbitrary temperature thresholds. Using 13 years of Argo profiling float data from the Arabian Sea, this method is shown to produce reasonable assessments of BL characteristics in the region. Similarly, use of the spice variable to identify formation mechanisms shows promise for using limited observational data and climatology to reproduce mechanisms proposed from modeling studies. Upper-ocean stability calculations combining profiling float and atmospheric forcing data are used to suggest the most likely one-dimensional mechanisms for erosion of BLs and to calculate the expected lifetimes of BLs throughout the year. Consistent with the evidence about the seasonal spatial extent and frequency of BLs, their duration is expected to be 2–3 times longer during the northeast monsoon than the southwest monsoon. However, the most likely erosion mechanisms vary widely throughout the year, as do the associated changes to the upperocean structure and thus likely impacts on SST.