The average sea temperature is an important parameter of the global climate. The oceans are the largest global heat reservoir. The global temperature increases as a result of man-made global warming. Most of the anthropogenic heat added to the climate system has been taken up by the ocean. However, it is difficult to determine an accurate average value across all sea depths and regions of the world. The results heavily depend on location, season, or sea depth. Bernhard Bereiter, Scripps Institution of Oceanography University of California San Diego, La Jolla, USA, and colleagues have developed a method to measure ocean temperatures over the last 24,000 years with high accuracy.
The layers of eternal ice function as an archive of the atmosphere. Dust particles, other solids, air, and other gases are trapped in bubbles. The researchers determined the concentration of noble gases (krypton, argon, xenon) in ice cores from the Antarctic. As cooling water absorbs noble gases from the atmosphere and warming water releases noble gases into the atmosphere, the concentration of noble gases in the atmosphere allows to draw conclusions about the average global temperature of the sea.
The drill cores from the Antarctic ice cover the period of the past 24,000 years. During this time, the transition from the last ice age to the current warm age took place. The researchers found a rise in mean ocean temperatures of 2.57 ± 0.24 °C over this period.
According to the researchers, their study clearly approves the connection between the concentration of noble gases in the atmosphere and the average ocean temperature and shows that their method works. However, this type of temperature measurement can currently only be applied to very large periods of time. Methodes need to become much more precise.
- Mean global ocean temperatures during the last glacial transition,
B Bereiter, S Shackleton, D Baggenstos, K Kawamura, J Severinghaus,
Nature 2018, 553, 39–44.