Biogeochemical controls on dissolved micronutrient (Ni, Cu, Zn, Cd) distributions in the Equatorial Pacific Ocean

durch Dr. Namann Deep Singh (FB2/CH)

Mittwoch 15.10.2025, 13:15 → 14:30 Europe/Berlin

8A-002 - Hörsaal Ostufer / Lecture Hall East (GEOMAR - Standort Ostufer / GEOMAR - East Shore)

The Equatorial Pacific Ocean (EPO) is one of the most productive regions in the ocean with strong outgassing of CO₂, and thereby plays a prominent role in the global carbon cycle with a strong coupling between the supply of trace nutrients to the surface ocean and primary production. We report distributions of nutrient-type dissolved trace metals (dTM) including Ni (dNi), Cu (dCu), Zn (dZn) and Cd (dCd), and supporting particulate trace metal (pTM) data along the GEOTRACES transect GP11, during a developing El Nino in early 2023. The section covers the entire EPO zonal stretch representing diverse biogeochemical regimes including the highly productive eastern and central EPO, and oligotrophic western EPO warm pool. Surface waters (<100 m) show dTMs minima and significant correlations between pTM and particulate phosphorus (pP), indicating phytoplankton uptake of TMs. Large fractions (64-97%) of dNi, dZn and dCd in the surface mixed layer (10-90 m) were supplied by vertical upwelling, strongly influenced by the west-east shoaling of the thermocline and transport of sub-surface waters by the Equatorial Undercurrent. Moreover, spatial variability in upwelling fluxes controlled biological Cd uptake in the EPO. In subsurface waters (>200 m), water mass mixing and organic matter (OM) remineralization largely governed the dCd distribution. The partial scavenging of remineralized Ni and Zn and/or their retention (slower remineralization) to particles determined the dNi and dZn distributions and their relationships with macronutrients in the thermocline depths (200-500 m). Observed dCu in the thermocline and intermediate waters (200-1000 m) was lower than levels calculated using our water mass mixing model with literature dCu endmembers, indicating net scavenging removal along the advective pathways of the water masses. Strong enrichments in dNi and dCu were observed in deep waters (>2500 m) of the eastern and central EPO, which could not be explained by water mass mixing and OM remineralization. Particulate data indicate a limited influence of reversible scavenging and deep water remineralization, with the supply from sediments likely supporting dNi and dCu increases in deep waters. The study has implications for the supply of trace nutrients to surface waters and its impact on biological production in the EPO, and provides new perspectives on the inter-basin variability in trace metal biogeochemical cycling in the Pacific Ocean.