Continental margin sources of iron, aluminum, and manganese to the Pacific Equatorial Undercurrent: A data and modeling approach

The distribution of dissolved, total acid soluble and particulate iron, aluminum and manganese in the southern source region of the Equatorial Undercurrent (EUC) and western and central equatorial Pacific are presented here. Trace element concentrations were elevated along the slope of Papua New Guinea and within the New Guinea and New Ireland Coastal Undercurrents (NGCU, NICU). Within the upper EUC, a dissolved aluminum maxima extended across the western and central Pacific. Within the lower EUC, maxima in total acid soluble iron, manganese, and particulate aluminum persisted across most of the study region (145°E - 140°W), consistently 25 - 75 m deeper than the local dissolved aluminum maximum. Trace element concentrations along the equator were greatest in the west and decreased eastward, with the exception of particulate manganese, which showed elevated concentrations near the dateline. The strong oceanic currents of the EUC source region appear to mobilize trace elements and transport them eastward via the lower EUC.;Biogeochemical model simulations of this western equatorial thermocline source of iron were conducted to assess the fate, transport, and cycling of a similar dissolved iron source. Two data-based simulated thermocline sources of iron were transported across the equatorial Pacific to the equatorial upwelling region and significantly impact primary productivity and community structure. These simulations indicate that not all of the observed particulate iron source in the west is likely to be bioavailable. They also confirmed and quantified the decoupling of iron, nitrate and silicate due primarily to the rapid scavenged and localized sinking of iron.