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Warming-Induced Increases in Ocean Productivity
Volume 10, Number 19: 9 May 2007

In setting the stage for their important new study, McGregor et al. (2007) say "coastal upwelling occurs along the eastern margins of major ocean basins and develops when predominantly along-shore winds force offshore Ekman transport of surface waters, which leads to the ascending (or upwelling) of cooler, nutrient-rich water." In addition, they note that these regions of coastal upwelling account for about 20% of the global fish catch while constituting less than 1% of the area covered by the world's oceans. Thus, in an attempt to better understand the nature of this productivity-enhancing phenomenon of great practical and economic significance, they studied its long-term history along the northwest coast of Africa - in the heart of the Cape Ghir upwelling system off the coast of Morocco - by analyzing two sediment cores having decadal-or-better resolution that extend from the late Holocene to the end of the 20th century, i.e., from 520 BC to AD 1998.

This work revealed an anomalous cooling of sea surface temperatures during the 20th century, which the four researchers say "is consistent with increased upwelling." In addition, they note that the "upwelling-driven sea surface temperatures also vary out of phase [our italics] with millennial-scale changes in Northern Hemisphere temperature anomalies and show relatively warm conditions during the Little Ice Age and relatively cool conditions during the Medieval Warm Period."

How does this happen?

One potential scenario discussed by McGregor et al. starts with an impetus for warming that leads to near-surface air temperatures over land becoming warmer than those over the ocean. The greater warming over the land then "deepens the thermal low-pressure cell over land while a higher-pressure center develops over the slower-warming ocean waters." As this occurs, "winds blow clockwise around the high and anticlockwise around the continental low." With the coast representing the boundary between the two centers, the resulting wind is "oriented alongshore and southward (equator-ward), which thus drives the upwelling and negative sea surface temperature anomalies."

In addition to their observations of this phenomenon, McGregor et al. state that similar anti-phased thermal behavior - i.e., the cooling of coastal waters that leads to enhanced coastal upwelling during periods of hemispheric or global warming - has been observed in the Arabian Sea and along the Iberian margin, as well as in parts of the California Current and the Peru-Chile Current. Consequently, it would appear that by enhancing the upwelling of cooler nutrient-rich waters along the eastern margins of major ocean basins, global warming helps to significantly enhance global-ocean primary productivity, which leads in turn to an increase in global-ocean secondary productivity, as represented by the global fish catch.

Somewhat analogous findings were reported in the same issue of Science by Boyd et al. (2007), in their major review of iron enrichment experiments that were conducted between 1993 and 2005, which experiments have conclusively demonstrated, in their words, that "phytoplankton grow faster in warmer open-ocean waters, as predicted by algal physiological relationships." Hence, it can be appreciated that this conglomerate of results clearly suggests total ocean productivity should have benefited immensely from 20th-century global warming, and that it will likely continue to benefit from continued global warming, just as total terrestrial productivity has likewise benefited from the historical increases in both the atmosphere's temperature and its CO2 concentration (see the many pertinent items we have archived under Greening of the Earth in our Subject Index).

All told, therefore, both on land and in the sea, things appear to be looking ever better for the biosphere in terms of earth's thermal environment and its atmospheric composition, in spite of the unrelenting din of denial of this profusely-documented fact that emanates unceasingly from the world's climate alarmists.

Sherwood, Keith and Craig Idso

References
Boyd, P.W., Jickells, T., Law, C.S., Blain, S., Boyle, E.A., Buesseler, K.O., Coale, K.H., Cullen, J.J., de Baar, H.J.W., Follows, M., Harvey, M., Lancelot, C., Levasseur, M., Owens, N.P.J., Pollard, R., Rivkin, R.B., Sarmiento, J., Schoemann, V., Smetacek, V., Takeda, S., Tsuda, A., Turner, S. and Watson, A.J. 2007. Mesoscale iron enrichment experiments 1993-2005: Synthesis and future directions. Science 315: 612-617.

McGregor, H.V., Dima, M., Fischer, H.W. and Mulitza, S. 2007. Rapid 20th-century increase in coastal upwelling off northwest Africa. Science 315: 637-639.