Ocean Science

Heavyweight Measurements

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Science  21 Sep 2012:
Vol. 337, Issue 6101, pp. 1435
DOI: 10.1126/science.337.6101.1435-b
CREDIT: GEOFF HARGREAVES/NATIONAL OCEANOGRAPHIC CENTRE

One of the potentially most serious consequences of global warming is the rise of sea level that will occur as the polar ice sheets shrink. Part of that sea-level rise will be due to ocean warming, because warmer water occupies a larger volume than an equivalent amount of colder water; the other part will be due to more water in the sea; i.e., to a larger mass of water. Good measurements of ocean temperatures are available, but how does one go about measuring the mass of the ocean? There may be an easy way, according to Hughes and colleagues from the UK National Oceanography Centre and the School of Civil Engineering and Geosciences of Newcastle University.

It turns out that there are places on the ocean floor where the pressure of the overlying water does not change much in response to the wide array of causes (such as ocean dynamics, tidal forcing, and changes in atmospheric pressure, among others) that can make it vary independently of ocean volume changes. In such a spot, one could theoretically install a single ocean-bottom pressure (OBP) sensor and measure how whole-ocean mass was changing. The authors used models to identify a suitable spot and OBP measurements from the Pacific Ocean to illustrate the technique's potential. If their idea is correct, and if OBP sensors with low enough measurement drift can be developed, there may be a sweet spot for monitoring ocean mass changes.

Geophys. Res. Lett. 39, L17602 (2012).

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