Chapter 5 - Exchanges through the ocean surface

The ocean–atmosphere exchanges of heat, water, and momentum are key elements of the global climate system. The processes controlling these exchanges, methods by which they may be estimated, and their impacts on the ocean are reviewed, with an emphasis on developments in the past decade. The main characteristics of the long-term mean exchange fields are presented with reference to atmospheric reanalysis, remote sensing, and ship observation-based datasets. Flux measurement and evaluation techniques are discussed in the context of the key observational reference datasets, particularly the critically important growing network of surface flux buoys. A short review of the many flux datasets that are now available is presented with a focus on the ocean heat budget closure problem that remains a leading unresolved issue. Variability in the exchanges is also considered with a focus on (a) changes associated with large-scale modes of atmospheric variability, (b) the effects of anthropogenic climate change, and (c) transfers under extreme conditions. The ocean impacts of changes in the surface fluxes are explored with a focus on modification of near-surface properties, water mass transformation, and the ocean’s overturning circulation. Finally, prospects for future improvements to flux datasets through advances in the synthesis of data from different sources and enhanced observational constraints are discussed.