Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific

Abstract

Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the world's fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.

Experimental assessment of the effects of shade on an intertidal kelp: Do phytoplankton blooms inhibit growth of open coast macroalgae?

“…However, the Morel equation has been validated only for Chl a concentrations up to 30 mg m 23 ; surf-zone Chl a concentrations along the Oregon coast have reached levels at least five times that (Grantham et al 2004). In this analysis we used a static estimate of k c to represent the relatively shallow and well-mixed surf zone that overlies intertidal habitats, because our empirical estimate of k c was best described as a linear relationship between K dPAR and Chl a concentration (Kirk 1994).…”

Chapter 1 Impacts of the Oceans on Climate Change

“…Climate models suggest that the O 2 levels may Impacts of the Oceans on Climate Change 39 actually increase in some regions despite the decline in the global average due to the complex response of dissolved O 2 to circulation changes (Matear and Hirst, 2003;Schmittner et al, 2008). Changes in climate may also contribute to increasing coastal hypoxia (Grantham et al, 2004).…”

Oceanography: Dead in the water

“…But on his first day out, Chan found that at a depth of 50 metres the inner coastal waters off Oregon were hypoxic -oxygen levels there were lower than 1.43 millilitres per litre, so low that fish can't survive 1 . Many regions of the world have hypoxic coastal waters, usually caused by agricultural fertilizers leaking into the ocean.…”