CLIMATOLOGY

No Deepwater Slowdown?

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Science  27 Jul 2001:
Vol. 293, Issue 5530, pp. 575
DOI: 10.1126/science.293.5530.575b

The deepest waters of the ocean—North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW)—originate from polar surface waters that sink and then spread over the ocean bottom toward the opposite poles, redistributing heat, salinity, and nutrients. Formation rates of NADW and AABW have varied considerably over glacial-interglacial cycles, and it has been proposed that during the 20th century the production of AABW may have slowed as part of a 1500 year-long cycle of iceberg rafting.

Orsi et al. compare measurements of CFCs and radiocarbon, and observations from current meters, in AABW and NADW to show that ventilation rates from the poles are comparable and that they provide no evidence of a recent reduction in AABW formation. Their analysis does not rule out the possibility that significant variability in formation rates has occurred since the Little Ice Age 500 years ago or that global warming will affect the rates in the future. — HJS

Geophys. Res. Lett. 28, 2923 (2001).

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