Towards Understanding Key Processes Affecting Heat and Salinity Balance in the Global Ocean

Abstract

Ocean heat content is compared among nine analyses of global ocean temperature during 1960-2002. Two are independent of numerical modeling, and the rest rely on data assimilation, which utilizes an ocean general circulation model and observations to create an analysis. Most analyses show gradual warming of the global ocean with an ensemble trend of 0.77 × 10<super>8</super> J m<super>&#8722;2</super> (10 yr)<super>&#8722;1</super> (=0.24 W m<super>2</super>) as the result of rapid warming in the early 1970s and again beginning around 1990. Three explanations for this decadal variability are proposed and tested: the effect of three major volcanic eruptions, the uncorrelated contribution of heat content variations in individual ocean basins, and the effect of time-dependent bias in the set of historical observations. It was found that the second hypothesis contributed significantly to heat content variability.

Uncertainties in latent and sensible heat fluxes are examined through a comparison between two flux estimates that differ in methodology and data used: the French Research Institute for Exploitation of the Sea (IFREMER) and the Woods Hole Oceanographic Institution's Objectively Analyzed air-sea Fluxes (WHOI OAFlux). The focus is on the Atlantic during 1996-2005. The variables that enter the bulk formulae for fluxes (wind speed, sea surface and air temperature, and specific humidity) are also analyzed. The estimates are also compared to three buoy experiments, using the method of Bourras (2006) to determine uncertainty compared to buoy data. Specific air humidity and air temperature contribute the most to biases of IFREMER fluxes. Modified flux estimates with the IFREMER approach using 10 m specific humidity and air temperature from Jackson et al. (2009) show improvement in test cases at PIRATA buoys.

Finally, results from an eddy-resolving numerical simulation are examined to quantify advective and diffusive contributions to the salt balance in the upper 100m of the subtropical oceans. Advection is important, especially horizontal, while time-mean diffusive processes and salt storage are several orders of magnitude less, but could still be important seasonally in areas of maximum surface salinity.