12.06.2017: The Ocean works as a gigantic heat sink and thereby is an important factor in mitigating global warming. Since warming water expands, warming oceans cause a rise in sea-level. This poses a significant risk to coastal areas. Existing methods of global temperature monitoring only detected changes in surface temperatures. Changes in the Ocean’s interior remain widely hidden. GFZ scientists from section Earth System Modelling now developed a method that allows for monitoring temperature changes in the Ocean’s interior. Their study, published in the journal Geophysical Research Letters, was nowdistinguished as a “research spotlight” by the news platform EOS of the American Geophysical Union AGU. Like this, EOS honors “the best accepted articles” that were published in an AGU journal.

Due to its high salinity sea water serves as a good electric conductor. This is why ocean currents emit electromagnetic signals: an “ocean current magnetic field” referred to as electromagnetic ocean tide signatures (EMOTS). These characteristic signals can be detected from outside the water body. Changes in temperature and salinity of the water are reflected in changing EMOTS. Sensor systems of satellite missions like the Swarm mission of the European Space Agency ESA, where the GFZ is a partner in, can be used to measure changes in these signals and thereby hopefully in the future allow for monitoring changes in temperature and salinity.

In numerical experiments with state of the art climate models that are also used in the latest Global Climate Report the GFZ scientists demonstrated that EMOTS changes are dependent on climate change. Therewith, EMOTS can be used to monitor future climate change. Simulations of this century showed that the expected climate change has a large impact on the EMOTS. Most extreme impacts are predicted for the Northern Hemisphere, where ocean warming causes a strengthening of the ocean current magnetic field of 30 percent.

Knowledge on the effect of global warming on the oceans and the effects on sea surface rise can help support future adaption measures like the enhancement of dike systems in coastal areas. (ak)

Original study: Saynisch, J., Petereit, J., Irrgang, C., Thomas, M., 2017. Impact of oceanic warming on electromagnetic oceanic tidal signals: A CIMP5 climate model-based sensitivity study. Geophysical Research Letters DOI: 10.1002/2017GL073683

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