BGC-09 Biogeochemistry in Subtropical Oceans
Sectional Distributions of Ni and Cu in the Subtropical Northwestern Pacific and Their Relationships to Macronutrients
Jinchang Yang* , State Key Laboratory of Marine Environmental Science, Xiamen University
Zhimian Cao, State Key Laboratory of Marine Environmental Science, Xiamen University
Chengwang wang, State Key Laboratory of Marine Environmental Science, Xiamen University
Pingping Zhang, State Key Laboratory of Marine Environmental Science, Xiamen University
Nan Zhang, State Key Laboratory of Marine Environmental Science, Xiamen University
Junbo Yang, State Key Laboratory of Marine Environmental Science, Xiamen University
Yaojin Chen, State Key Laboratory of Marine Environmental Science, Xiamen University
Yihua Cai, State Key Laboratory of Marine Environmental Science, Xiamen University

As bioavailable trace metals, Ni and Cu are of great significance for marine ecosystem and its function. Based on samples and data collected during the GEOTRACES-GPpr15 process study cruise in summer 2020, this work presents the sectional distribution patterns of Ni and Cu in the subtropical Northwestern Pacific. Both elements generally show low concentrations in the surface water and enhanced values at depth. In contrast to Cu nearly completely depleted in the surface water, the surface concentration of Ni maintains around 2 nM. Ni achieves a maximum value of about 9 nM around 1500 m depth, whereas Cu displays a nearly linear increase with increasing water depth. In surface waters (10-15 m) and intermediate waters (300-450 m) near the Philippine Islands, concentrations of both Cu and Ni are markedly higher than that in other offshore areas, suggesting influences from the terrestrial or shelf sediment inputs. The strong linear relationships between Cu and Ni and both phosphate and apparent oxygen utilization (AOU) within 200-1000 m depth indicate that the two metals are mainly controlled by organic matter remineralization in the intermediate water. Below 800 m, an increase in AOU from 160 to 290 umol/kg is concurrent with a decrease in the Ni/PO4 (by ~48%) and Cu/PO4 (by ~75%) ratios. This indicates that particle scavenging is an important sink for dissolved Cu and Ni and exerts more influences on Cu in the deep waters.