Ocean heat content
Oceanic heat content (OHC) is the heat stored in the ocean. Oceanography and climatology are the science branches which study ocean heat content. The changes in the ocean heat play an important role in sea level rise, because of thermal expansion. It is with high confidence that Ocean warming accounts for 90% of the energy accumulation from global warming between 1971 and 2010.
Definition and measurement
It is defined as:
- water density, - sea water specific heat capacity, h2 - bottom depth, h1 - top depth, - temperature profile.
OHC is computed from temperature measurements, often taken with a Nansen bottle. The ARGO float project deployed 3000 floaters around the worlds Ocean, which periodically dive to take temperature and salinity measurements. The World Ocean Database Project is the largest database for temperature profiles from all of the world’s oceans.
Several studies in recent years, found a multidecadal increase in OHC of the deep and upper ocean regions and attribute the heat uptake to anthropogenic warming. Studies based on ARGO indicate that ocean surface winds change ocean heat vertical distribution. Especially the subtropical trade winds in the Pacific ocean have provided a mechanism for vertical heat distribution. The effect are changes in the ocean currents, increasing the subtropical overturning, which are also related to the El Niño and La Niña phenomenon. Depending on stochastic natural variability fluctuations, during La Niña years around 30% more heat from the upper ocean layer is transported into the deeper ocean. Model studies indicate that ocean currents transport more heat into deeper layers during La Niña years, following changes in wind circulation. Years with increased ocean heat uptake have been associated with negative phases of the interdecadal Pacific oscillation (IPO). This has become of particular interests to climate scientist who use the data to estimate the ocean heat uptake.
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