Stoichiometry among bioactive trace metals in the Chukchi and Beaufort Seas

Abstract

he distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater was investigated in the Chukchi and Beaufort Seas of the western Arctic Ocean in September 2000. The unfiltered and filtered seawater samples were used for determination of total dissolvable metal (TDM) and dissolved metal (DM), respectively. The concentration of labile particulate metal (LPM) was estimated with the difference between that of TDM and DM. The concentrations of TDAl, TDMn, TDFe, TDCo and TDPb varied substantially in the study area. The high concentrations occurred at stations near the Bering Strait, in the Mackenzie delta, and above reductive sediments on the shelf and slope. These elements were mostly dominated by labile particulate species, such as Fe–Mn oxides and species adsorbed on terrestrial clay. DCo was correlated with DMn over the study area (r = 0.78, n = 135), and the slope of the regression line was 27 times higher at a pelagic station than at a shelf station. TDNi, TDCu, TDZn and TDCd showed relatively small variations and were generally dominated by dissolved species. There was a moderate correlation between DCd and phosphate for all samples (r = 0.79), whereas there were no significant correlation between the other DMs and nutrients. TDNi and TDCu showed a remarkable linearity for most stations except those near the Bering Strait (R[2] = 0.95, n = 126). These results suggest that biogeochemical cycling including uptake by phytoplankton and remineralization from settling particles has only minor control over the distribution of trace metals in this area. Using the present data, the annual input of bioactive trace metals form the Bering Strait and the Mackenzie River was estimated. Also, the trace metal compositions of major water masses were evaluated. The dissolved elemental ratio was P:Al:Mn:Fe:Co:Ni:Cu:Zn:Cd = 1:1.2 × 10[−2]:4.4 × 10[−4]:1.4 × 10[−3]:3.7 × 10[−5]:3.7 × 10[−3]:1.4 × 10[−3]:4.5 × 10[−3]:2.2 × 10[−4] for Canada Basin deep water (CBDW). This ratio was significantly different from that for Pacific deep water and Bering Sea water, suggesting substantial modification of the trace metal compositions of seawater in the study area.