The Ocean’s Cobalt Cycle and its Correlations with other Metals

Abstract

The metal cobalt is an essential nutrient for many important marine organisms, but its distribution across the oceans is not well known. When cobalt concentrations correlate with phosphate it is acting as a nutrient to marine organisms, but when it correlates with manganese it is normally an indication that there is a strong geological influence. Other metals such as manganese and phosphate are prominent elements in seawater compared to cobalt which is why they are used as proxies to cobalt (Zeng, 2019). Cobalt concentrations for over 100 samples from the TARA Oceans expedition were measured across the global ocean. The focus is on four regions: the North Pacific, South Pacific, West Pacific and the North Atlantic, which demonstrate how other elements can trace the cobalt cycle in the ocean. Cobalt exhibits similar behavior to phosphate in some regions and manganese in others. In the North-east Pacific region, Mexican and Central American coastal waters had a small correlation with manganese: cobalt concentration is higher when manganese is high. In the Southeast Pacific and South American coast, an increase in cobalt is detected when manganese is elevated. Cobalt concentrations from the Western Pacific region have not been reported previously. We observed increased cobalt concentrations off the coast of Australia, New Caledonia, and the coast of Papua New Guinea due to input from river systems from the land masses, as well as at the equator, to the upwelling of deep nutrient rich waters. Interestingly, Co and phosphate are correlated in the North Atlantic and Caribbean Sea. In this paper cobalt is traced by two metals from different sources that can paint a picture of the metal’s cycle and influence. By correlating cobalt with these two metals that are more easily measured elements, we can broaden our understanding of the cobalt cycle and its sources.