Posted: 18 Feb 2015 06:30 AM PST
A new report in NATURE suggests that global warming may increase upwelling in several ocean current systems around the world by the end of this century, especially at high latitudes, and will cause major changes in marine biodiversity. Since upwelling of colder, nutrient-rich water is a driving force behind marine productivity, one possibility may be enhancement of some of the world’s most important fisheries. However, solar heating due to greenhouse warming may also increase the persistence of “stratification,” or the horizontal layering of ocean water of different temperatures. The result could be a warm, near-surface layer and a deep, cold layer. If this happens to a significant extent, it could increase global “hypoxic,” or low-oxygen events, decouple upwelling from the supply of nutrient-rich water and pose a significant threat to the global function of fisheries and marine ecosystems. The projected increase in upwelling, in other words, appears clear and definitive. But researchers say its biological impact is far less obvious, which is a significant concern. These upwelling systems cover less than 2 percent of the ocean surface, but contribute 7 percent to global marine primary production, and 20 percent of global fish catches…. Among the findings of the study:
* The change in upwelling may be more pronounced in the Southern Hemisphere, due to the local influences of land masses, coastline, water depth and other issues.
* Major current systems will be affected off the western coasts of North America, South America, Africa and parts of Europe.
* The general increase in upwelling is going to be driven by a strengthening of alongshore winds, due to a differential in land and ocean heating.
* At high, but not low latitudes, the upwelling season will start earlier, last longer and be more intense.
* At tropical and sub-tropical latitudes, upwelling will become almost a year-round phenomenon.
* The findings are consistent with different research which shows that coastal upwelling has intensified over the past 60 years.
* Impacts on the California Current System are expected to be less pronounced because of other climatic forces at work, such as the Pacific Decadal Oscillation, the El Nino-Southern Oscillation, and the North Pacific Gyre Oscillation.
Daiwei Wang, Tarik C. Gouhier, Bruce A. Menge, Auroop R. Ganguly. Intensification and spatial homogenization of coastal upwelling under climate change. Nature, 2015; 518 (7539): 390 DOI: 10.1038/nature14235