Radium as a tracer of benthic trace element inputs from the Peruvian continental margin (2013 U.S. Pacific GEOTRACES cruise)

Abstract:

The Peruvian coast hosts one of the largest upwelling systems leading to a zone of high productivity. The combination of nutrient inputs from upwelled waters and iron input from the continental shelf sediments facilitates phytoplankton growth. However, the high chlorophyll areas are sporadic within the Peruvian zone with alternating iron-replete to iron-limited conditions leading to High Nutrient Low Chlorophyll zones. The lack of iron relative to the high nutrient concentration in these areas of the upwelling system is mainly due to the narrowing of the continental shelf which reduces the supply of sedimentary iron and thus, impacts the biological productivity. During the 2013 U.S. GEOTRACES Eastern Pacific Zonal Transect (EPZT), sediment inputs from the Peruvian continental shelf were traced by radium, a natural radionuclide produced by the decay of sediment-bound thorium isotopes. In situ pumps were deployed to collect large volumes of seawater to map the distribution of radium isotopes in concert with a wide range of trace elements and isotopes (TEIs) across the Peruvian upwelling area. Here, we report vertical profiles of radium (²²³Ra, ²²⁴Ra, ²²⁶Ra, ²²⁸Ra) along a transitional zone between the coastal and central oceanic waters of the South Pacific up to 110 °W to investigate benthic Ra isotope inputs and the implications for shelf sediment-derived TEI fluxes to the phytoplankton bloom in offshore waters.