Abstract
Nickel stable isotopes (δ60Ni) provide insight to Ni biogeochemistry in
the modern and past oceans. Here, we present the first Pacific Ocean
high-resolution dissolved Ni concentration and δ60Ni data, from the US
GEOTRACES GP15 cruise. As in other ocean basins, increases in δ60Ni
towards the surface ocean are observed across the entire transect,
reflecting preferential biological uptake of light Ni isotopes, however
the observed magnitude of fractionation is larger in the tropical
Pacific than the North Pacific Subtropical Gyre. Such surface ocean
fractionation by phytoplankton should accumulate isotopically lighter Ni
in the deep Pacific, yet we find that North Pacific deep ocean δ60Ni is
similar to previously reported values from the deep Atlantic. Finally,
we find that seawater dissolved δ60Ni in regions with hydrothermal input
can be either higher or lower than background deep ocean δ60Ni,
depending on vent geochemistry and proximity.