Emodnet-Arctic

Internal energy (time-series)

Sub-challenge: time-series of average annual internal energy of sea
The internal energy of the sea can mean many things; mechanical motions like waves and currents contain energy (BOEM (Bureau of ocean energy management)); energy created by external forces like wind, tides, freshwater input and atmospheric pressure also add energy to, or deplete the ocean of energy; or thermal energy like geothermal heat or air-sea latent heat (Ferrari, R.; Wunsch, 2008). In physics chemical bonds and potential energy within an object would also be considered part of the internal energy as it is all the energy contained in a system (HyperPhysics). The ocean also has a heat content which tracks warm water flows and is used in the prediction of El Niño and La Niña events (National Oceanic and Atmospheric Administratio). If we consider the internal energy of the Arctic sea, the majority of internet search results involve energy derived from mixing and internal waves. However, if we consider the internal energy of sea ice the majority of internet searches result in data on thermal energy.

Even if we consider either wave energy or thermal energy in sea as internal energy, it is still a complex challenge. Thermal dynamics of sea in the arctic area also involve the complex thermal dynamics of sea ice. Thermal energy in sea ice can be caused by shortwave radiating heat, within the sea ice. As this energy warms the ice from the inside, brine pockets can develop. These pockets store latent heat, melting the ice from the inside out. The amount of heat capacity and thermal conductivity following this is dependent on the temperature and salinity of the sea ice (McCaa, 2004). Furthermore, data (GIS) can also be found on wave energy (National Snow and Ice Data Center) but is generally focussed on wave energy at coastlines rather than in the open ocean.


Results:

Data on heat content of the entire ocean is available and is used in the prediction of El Niño and la Niña events (Ocean Climate Laboratory (OCL) of National Oceanographic Data Center (NODC)). Data is however limited to the resolution of the entire ocean or Northern or Southern hemisphere, and lacks the detail of smaller scale, specific areas. It does however have a temporal range from 1955 until 2017.

World ocean heat content
Figure 1 Source: https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/basin_data.html

Data use, availability and gaps
For this challenge there is no definite conclusion on the availability of data. There is no data found when search key words like ‘internal energy’ are used. However Internal energy contains all of the energy in a system. Quite often parts of the internal energy like thermal energy or wave energy are documented. Actual data on the entire internal energy means combining all separate elements of internal energy. A huge task given datasets are on different temporal and spatial scales.

Conclusion and lessons learned
The question asked in this challenge needs to be reviewed and made explicit. Is it necessary to have specific information on the internal energy of the sea, including mechanical energy, external energy and thermal energy and potential energy? Or is there a need for data on subsets of internal energy like thermal energy or wave energy?

Recommendations
The internal energy of the sea is not a very well-known parameter, even though it has a direct relationship with climate change. Monitoring for Internal energy means monitoring for all the component parts of internal energy and is quite time and cost intensive. For this reason, we do not recommend an extension of the current challenge. Further extension of specific research should always be promoted, especially considering climate change. However, we recommend research on more obvious parameters, like thermal or wave energy.


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