EXCESS NITRATE IN THE EAST CHINA SEA

'Excess nitrate' was found in waters with salinities below 30.5 in the top 10-15 m of waters covering one-third to one-half of the East Chin a Sea in the summer of 1992. In these waters, significant concentratio ns of [nitrate + nitrite], up to about 6 mu M, could be found while th e corresponding concentrations of phosphate remained at or below 0.07 mu M. Thus, the ratio of [nitrate+nitrite] to phosphate in these water s was far in excess of that at which these two essential nutrients are utilized by marine phytoplankton. ('Excess nitrate' is the concentrat ion of [nitrate+nitrite] in excess of that which may be utilized by ma rine phytoplankton at the observed concentration of phosphate.) As a r esult, in contrast to the open marine systems in general, primary prod uction in a significant portion of the East China Sea may be phosphate -limiting rather than nitrogen-limiting. The area covered by this laye r of combined nitrogen-rich water could be temporally variable. While no 'excess nitrate' was detected in the south-eastern East China Sea a long the Chinese coasts in the summer of 1992, significant quantities of 'excess nitrate', up to 4 mu M, were found at the same location in the early spring of 1993 in waters with salinities as high as 34.5. (C ) 1998 Academic Press Limited.