Collaborative Research: GEOTRACES particulate intercalibration

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Large sampling and methodological biases, with reported differences as large as 200%, continue to confound the marine geochemical research community involved in water-column particulate sampling. When the GEOTRACES Intercalibration Cruise (IC) program was designed, the extent and reality of reported differences had not been fully appreciated. The resolution of this problem remains an urgent priority. In this project, researchers at the University of California Berkeley - Lawrence Berkeley National Laboratory and the Woods Hole Oceanographic Institution will participate in the US-GEOTRACES IC study. The UCB/LBNL team will deploy Multiple Unit Large Volume in-situ Filtration System (MULVFS) as part of the IC study. MULVFS is a unique, highly flexible, and reliable system with an unparalleled and globally tested ability for collection of particulate and dissolved species from the sea. MULVFS collects size fractionated particulate samples from 10000 L volumes of seawater at 12 depth horizons in the upper 1000 m. Subsamples will be provided to other IC experiment participants. LBNL/UCB will analyze particulate samples from bottle and McLane pumps as part of the IC experiment. MULVFS will also be used for simultaneous comparison of different particle capture and size separation devices (e.g. McLane, Challenger, Kiel pump filter holders), filter types, and adsorber systems. This work has been highly coordinated with the GEOTRACES IC PIs and participants as well as with members of the GEOTRACES Science Steering Committee. The work that will be carried out through this award is designed to eliminate investigator and sampling approach dependency for GEOTRACES particulate sampling and will reconcile the various sampling approaches to be used in this program. Work will support multi-investigator particulate matter IC studies using MULVFS in both the environmentally easy locations such as the BATS and SAFe site and in physically dynamic and biologically variable locations such as in the Gulf Stream and California Current. MULVFS was designed to retain particles in strong current flows of the Gulf Stream. Comparison with other particle sampling methodologies in both challenging and non-challenging environments will lead to understanding and resolution of biases /differences that are both substantial, documented in published literature, and further documented in this proposal. Such an inter calibration has never been done before. Furthermore, MULVFS greatly improves the efficiency of the IC experiment by providing high resolution baseline profiles of trace metals and nuclides in the upper water column. GEOTRACES places high priority on particulate matter samples being representative in composition and size distribution of the particulates naturally occurring in the water column whether or not the water column is warm, cold, quiescent or physically dynamic or biologically variable. Broader Impacts: The proposed work tackles the very real problems of method-dependent particle sampling and pre analysis biases (large particle loss from some pumps, large particle settling loss before filtration in bottles, poor sample preservation, etc.). It will be of relevance to all members of the oceanography community who engage in particle studies.