Ocean Science

Shallow Chills

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Science  06 Oct 2006:
Vol. 314, Issue 5796, pp. 19-21
DOI: 10.1126/science.314.5796.19d

Observations show that the world oceans as a whole have been warming for the past 50 years. This result is an important confirmation of global warming inferences based on surface atmospheric temperature measurements, as the oceans have more than a thousand times the heat capacity of the atmosphere. The rise in ocean heat content has not been spatially or temporally uniform, however, and because most models do not reproduce such unforced variations, their origin remains an open question.

Lyman et al. have taken advantage of the rapidly expanding network of Argo autonomous profiling floats to present a global temperature data set for the upper 750 m of the world oceans. The study reveals a large cooling since 2003. These data also have implications beyond the pattern and extent of cooling. For instance, because it is unlikely that so much heat was transferred so quickly to the deeper ocean, the measurements indicate that a whole-ocean cooling has occurred, a phenomenon expected to induce a decrease in sea level due to thermal contraction of the water. Sea level rise has not slowed during the time period, however, suggesting that other factors such as increased rates of glacial melting are more than adequate to compensate for the thermal effect on volume. — HJS

Geophys. Res. Lett. 33, L18604 (2006).

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