Cold halocline, increased nutrients and higher chlorophyll off Oregon in 2002

Observed changes in the nutrient levels in the halocline of the California Current during 2002 indicated a natural eutrophication that was accompanied by increased chlorophyll and oxygen in surface water. Decreased oxygen in the lower water column over the shelf indicated that much of the phytoplankton production was respired rather than passed on to higher trophic levels. In 2002 the halocline water was >1degreesC colder than usual and 0.5degreesC colder than any previous observation. Four transect lines off the coast of Oregon show a 50% increase in nitrate, phosphate and silicate at 33 psu in 2002 compared to 1998-2001. The increase in nutrients resulted in a 2-fold increase in chlorophyll standing stocks during the summer of 2002 compared with the preceding four years. A significant portion of the increased production was subsequently respired resulting in low oxygen water over the shelf.