Contrasting Scavenging Intensities of 210Po and 210Pb at Key Interfaces of the East Pacific Zonal Transect, GEOTRACES
Tuesday, 16 December 2014
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.