In an effort to find out how ocean mass affects tectonic plates, a team of German scientists has recently taken on one of the most difficult sets of measurements possible in nature, namely to determine how much the sea “weighs.” Unlike calculating variations in sea levels, which is relatively simple, finding out the mass of the water is far more complex, as a large number of factors contribute to changes in this number.

Additionally, the oceans are not static, as in ideal models, so the number varies considerably over short time frames.

Scientists at the Helmholtz Association’s GFZ German Research Centre for Geosciences and the Alfred-Wegener Institute for Polar and Marine Sciences, working together with colleagues from the University of Bonn, say they have solved the riddle by coming up with calculations so precise that they observed even short-term fluctuations in the spatial distribution of water masses inside the body of water.

“For our study we, therefore, combined different procedures so as to be able to judge changes in mass,” Dr Juergen Kusche writes. The scientist is a geodesist at the University of Bonn, and also a coauthor of a new scientific paper detailing the findings which appears in the latest issue of the respected Journal of Geophysical Research.

The two main elements that a scientist needs to know in order to calculate the mass of the ocean are the topography of its bottom and also the height of the sea level. There are, however, other elements at work as well, such as temperature and the salt content. Water expands when heated. Warm water, thus, weighs less than the same quantity of cold water.

Data from the German-American satellite mission GRACE and knowledge of the “bookshelf effect” were used. The ocean floor bends similarly to that of the shelves of an overfilled bookshelf. Thus, stationary GPS-gauging stations on land drop by up to one centimetre and move closer by a few millimetres. The heavier the water, the stronger is this movement.

“We combined these data with numerical models of the ocean. In this way we were able to prove, for the first time, that in particular in the higher latitudes, significant fluctuations of the water mass occur and that this takes place within a time period of only one to two weeks,” Dr. Kusche writes.

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