REGULATION OF COPPER CONCENTRATION IN THE OCEANIC NUTRICLINE BY PHYTOPLANKTON UPTAKE AND REGENERATION CYCLES

Similar sigmoidal relationships were observed between cellular Cu:C ratios and free cupric ion concentration for the neritic alga Thalassiosira pseudonana and two oceanic species (Thalassiosira oceanica and Emiliania huxleyi) grown in trace metal ion buffered media. Only 5-9-fold variations in cell Cu:C were observed for these species over the [Cu2+] range 3 x 10(-15) to 3 x 10(-12) M, with increasing cell copper vs. [CU2+] slopes above and below this range. At the mean [Cu2+] for the euphotic zone of the North Pacific (10(-13.2) M), cell Cu:C ratios for the three species were 4.4, 4.4, and 3.8 mu mol mol(-1), similar to values for plankton taken from North Pacific waters. These values also match the mean Cu:C ratio of 4.1 mu mol mol(-1) determined from slopes of linear relationships between Cu and PO, in the nutricline of the central North Pacific and the ''Redfield'' C:PO4 ratio in plankton of 106:1. This agreement provides strong evidence that copper concentrations in remote oceanic nutriclines are regulated by phytoplankton uptake and regeneration processes.