“Sea Deserts” Are Expanding

A significant change in subtropical ocean biology, potentially linked to the warming of surface waters, has been occurring according to a study undertaken by the National Oceanic and Atmospheric Administration (NOAA) and the University of Hawaii. These researchers measured a noticeable recent expansion of underwater barrenness in subtropical parts of the Atlantic and Pacific Oceans called gyres, which are the whirling spans of water on either side of the equator. The desert-like conditions in these expanses are now found in roughly 20% of the world’s oceans—a pattern characterized by relatively plankton free and thus fish sterile stretches of ocean. Plankton are a diverse group of minute animals (zooplankton) and plants (phytoplankton) that freely drift in the water and serve as food for many aquatic species. Plankton are the first link in the marine food chain, so these losses in plankton life could prove devastating to a variety of fish populations.

According to this study, which appears in Geophysical Research Letters, these vast spans of saltwater with low surface plant life grew by 15 percent or 6.6 million square kilometers over a nine year period between the 1998 and 2007. The expansion occurred at the same time that the sea surface temperatures were continuously warming each year, thus preventing deep ocean nutrients from rising to the surface and creating plant life which in turn feeds fish life. The changes were measured by use of the SeaWiFS instrument which assesses the abundance of plankton by mapping color variances in ocean water.

It is not perfectly clear whether the loss of plankton life is related to climate change or simple variation over time, butit is worth exploring further given the profound need to slow this trend for the sake of crucial marine life. “The fact that we are seeing an expansion of the ocean’s least productive areas as the subtropical gyres warm is consistent with our understanding of the impact of global warming. But with a nine-year time series, it is difficult to rule out decadal variation,” noted Jeffrey J. Polovina, an oceanographer with NOAA’s National Marine Fisheries Service in Honolulu, who authored the study along with NOAA’s Evan A. Howell and Melanie Abecassis of the University of Hawaii.

Sources: National Oceanic and Atmospheric Administration (NOAA), University of Hawaii, New York Times