| Domain | Oceanic | Description | Sub-surface temperature is a fundamental variable required to monitor variability and change in the physical environment of the ocean, energy flows, climate patterns and sea level, and is essential to the understanding of changes in many other variables in the realms of marine biogeochemistry and biology. Ocean heat content directly derived from sub-surface temperature is of paramount importance in the monitoring of the Earth’s climate system and marine environment. Many other physical variables are derived from sub-surface temperature along with sub-surface salinity, including sub-surface density, geostrophic circulation, heat transport and steric sea level. These variables are essential to understanding of variability and change in ocean stratification, circulation patterns (uptake and redistribution of heat and freshwater) and sea level. Heat uptake by the global ocean accounts for more than 90% of the excess heat trapped in the Earth system in the past few decades. This ocean heat uptake helps to mitigate surface warming but in turn increases the global ocean volume through thermal expansion, and thus results in global-mean sea level rise, accounting for about one third of the increase observed over the past few decades. Changes in sub-surface temperature induce changes in mixed-layer depth, thermal/density stratification, mixing rates and currents. All of these physical changes can affect marine biology, not only directly but also indirectly through changes in marine biogeochemistry, such as nutrient and oxygen recycling, uptake of carbon emissions, ocean acidification, and so on. [GCOS-195 5.4.1] |