Ocean temperature

[1] In polar regions, the upper layers of ocean water are cold and fresh.

[3] The ocean temperature also depends on the amount of solar radiation falling on its surface.

It is driven by global density gradients created by surface heat and freshwater fluxes.

Changes in temperature and density move the cold water back towards the equator as a deep sea current.

These include mixing versus stratification, ocean currents and the thermohaline circulation.

[15][16] The main driver of this increase was caused by humans via their rising greenhouse gas emissions.

At this time low wind speed and a lot of sunshine may lead to the formation of a warm layer at the ocean surface and big changes in temperature as you get deeper.

Experts call these strong daytime vertical temperature gradients a diurnal thermocline.

[24] The basic technique involves lowering a device to measure temperature and other parameters electronically.

Scientists can deploy CTD systems from research ships on moorings gliders and even on seals.

[28] The Advanced Very High Resolution Radiometer (AVHRR) is widely used to measure sea surface temperature from space.

These include the Nansen bottle, bathythermograph, CTD, or ocean acoustic tomography.

Examples are those deployed by the Global Drifter Program and the National Data Buoy Center.

[29] A small test fleet of deep Argo floats aims to extend the measurement capability down to about 6000 meters.

[40] The cause of recent observed changes is the warming of the Earth due to human-caused emissions of greenhouse gases such as carbon dioxide and methane.

[42] Growing concentrations of greenhouse gases increases Earth's energy imbalance, further warming surface temperatures.

Reduced mixing of the ocean layers stabilises warm water near the surface.

Prevailing winds and the different densities of saline and fresh water are another cause of currents.

Near the poles, cool air sinks, but is warmed and rises as it then travels along the surface equatorward.

Global warming on top of these processes causes changes to currents, especially in the regions where deep water is formed.

Reconstructed proteins from Precambrian organisms also provide evidence that the ancient world was much warmer than today.

[48][49] The Cambrian Explosion approximately 538.8 million years ago was a key event in the evolution of life on Earth.

[50] Such high temperatures are above the upper thermal limit of 38 °C for modern marine invertebrates.

[53] Data from an oxygen isotope database indicate that there have been seven global warming events during the geologic past.

Graph showing ocean temperature versus depth on the vertical axis. The graph shows several thermoclines (or thermal layers) based on seasons and latitude. The temperature at zero depth is the sea surface temperature .
Sea surface temperature since 1979 in the extrapolar region (between 60 degrees south and 60 degrees north latitude). [ 9 ]
The ocean heat content (OHC) has been increasing for decades as the ocean has been absorbing most of the excess heat resulting from greenhouse gas emissions from human activities. [ 13 ] The graph shows OHC calculated to a water depth of 700 and to 2000 meters.
The illustration of temperature changes from 1960 to 2019 across each ocean starting at the Southern Ocean around Antarctica. [ 34 ]