Contrasting Scavenging Intensities of 210Po and 210Pb at Key Interfaces of the East Pacific Zonal Transect, GEOTRACES

Abstract:

The ²¹⁰Po - ²¹⁰Pb pair has been widely utilized in quantification of particulate scavenging and cycling of biogenic and lithogenic particulate matter in marine systems. Samples were collected and vertical profiles of particulate (>51 µm and 0-51 µm) and dissolved (< 0.45 µm) phases from six Super Stations along the East Pacific Zonal Transect of the GEOTRACES cruise were analyzed. The primary objectives of this investigation include: i) to compare the scavenging intensity of ²¹⁰Po and ²¹⁰Pb at the high-productivity Peru margin to that in the Oxygen Minimum Zones (OMZs) in the upper 300 m to the mesopelagic waters; ii) to quantify the differences in the scavenging intensity of ²¹⁰Po and ²¹⁰Pb between the bottom waters at the East Pacific Rise (EPR) to those in other stations including the station where OMZ were found; and iii) to evaluate the preferential scavenging of ²¹⁰Po and/or ²¹⁰Pb, if any, from the dissolved and particulate concentrations of ²¹⁰Po, ²¹⁰Pb, Fe, and Mn within the plume of the EPR. From preliminary ²¹⁰Po results, we report the following: i) both dissolved and particulate ²¹⁰Po concentrations in the South Pacific appear to be significantly higher than those of the North Atlantic; ii) the maximum concentration of ²¹⁰Po is generally found between 100 and 200 m, likely due to remineralization of sinking particulate matter with ²¹⁰Po/²¹⁰Pb activity ratio of >1.0; and iii) in one third of stations, we observed active scavenging near the sediment-water interface, indicating removal of ²¹⁰Po (and likely ²¹⁰Pb) by suspended particulate matter in the bottom nepheloid layer. The preliminary modeling of the particulate and dissolved ²¹⁰Po and ²¹⁰Pb, the relative importance of Mn- and Fe-oxides in the EPR plume, differences in the scavenging intensity of these nuclides at critical interfaces such as mesopelagic waters at OMZ, highly productive waters at the Peru margin, and near the sediment-water interface will be presented.