A shoaling hypoxic zone on the Oregon coast: genesis and mechanisms

Oregon State University, Corvallis OR

Investigators

Abstract

In summer 2002, Dr. Bruce Menge and collaborators observed the occurrence of hypoxic conditions in depths as shallow as 8 m, and as close as 100 meters to shore, along the Cape Perpetua region of the Oregon coast. The shallow depth, closeness to shore, and persistence (~ 2 mo) of such a hypoxic zone was unprecedented for the Oregon coast. The novelty of these observations, the high mortality of fishes and invertebrates observed in the 672 km2 area covered by this oxygen?depleted tongue of water, and its link to similar conditions occurring simultaneously further offshore in deeper water, suggest the possibility that they witnessed the early stages of an extensive and important shift in coastal oceanographic conditions, with potentially important consequences for coastal ecosystems. This SGER project will study the physical and biological processes in shallow (5?75 m) depths of the inner shelf region along the central Oregon coast from May through September 2003. The most immediate goal is to characterize the seasonal changes in the dynamics of water column oxygen and associated biogeochemical and physical drivers in the inner shelf should hypoxic conditions observed in 2002 recur in 2003. A second goal is to provide a detailed atlas of the changing oceanic dynamics of this region, and to relate them to responses by phytoplankton, invertebrates and fish. Third, is to couple the dynamics revealed by surveys in the inner shelf region to those revealed by simultaneous, larger scale oceanographic surveys scheduled for summer 2003 off the Oregon coast. A fourth goal is to gather and synthesize evidence in order to infer the genesis of hypoxia, elucidate the mechanisms likely for such changes and assess the potential sensitivity of the inner shelf system to further recurrences of hypoxia. Alternatively, if hypoxia does not recur, data collected during 2003 can provide a direct contrast to data collected by this group and by the LTOP GLOBEC program in 2002 when hypoxic conditions were extensive and persistent. Therefore, regardless of whether the hypoxic event recurs, we expect to obtain insight into factors underlying the genesis of such unusual occurrences.