Dataset: Concentrations of size-fractionated particulate thorium and protactinium isotopes (Th-232, Th-230, Pa-231) in seawater collected during the U.S. GEOTRACES Arctic cruise (HLY1502, GN01) on USCGC Healy from August to October 2015

This dataset contains concentrations of size-fractionated particulate thorium and protactinium isotopes (Th-232, Th-230, Pa-231) in seawater collected during the U.S. GEOTRACES Arctic cruise (HLY1502, GN01) on USCGC Healy from August to October 2015. This is compiled data produced by two laboratories with the following associations: Lamont-Doherty Earth Observatory of Columbia University (LDEO) and the University of Minnesota (UMN). All data have been deemed intercalibrated by the International GEOTRACES Standards and Intercalibration (S&I) Committee.

Naming Conventions:
Parameter names in the form such as "Th_232_SPT_CONC_PUMP" are adopted based on a recommendation from the GEOTRACES community (https://www.geotraces.org/parameter-naming-conventions/).

The "small particulate" (SPT) data refers to the particle size class 0.8-51 µm and is sometimes also called the "suspended" size fraction. The "large particulate" (LPT) data refers to particles greater than 51 µm and is sometimes referred to as the "sinking" size fraction. The particulate samples were collected by in-situ pumping over two loaded filter holders/flowpaths. One filter holder/flowpath was loaded with paired 0.8 µm Pall Supor800 polyethersulfone filters behind a 51 µm Sefar polyester mesh prefilter ("Supor-side") and the other filter holder/flowpath was loaded with paired 1 µm Whatman QMA quartz fiber filters behind a 51 µm Sefar polyester mesh prefilter ("QMA-side") (see Xiang and Lam, 2020 for particulate sampling methodology). Analysis of the paired Supor filters represents a particle size class approximating 0.45-51 µm (Bishop et al., 2012), while the top filter alone represents 0.8-51 µm and it is this size class referred to here as the "small particulate" fraction. We measured a select number of top and bottom Supor filters separately for radionuclides and found that the bottom filters had radionuclide levels that were indistinguishable from procedural blanks ("dipped" filter blanks). Therefore, whether or not samples were analyzed as paired Supor filters, or the top Supor filter alone, we infer the "small particulate" data to represent the 0.8-51 µm particle size class or "suspended" size fraction. The "large particulate" data is based on the analysis of the QMA-side 51 µm Sefar polyester mesh prefilters. Only a selection of "large particulate" samples were analyzed and those analyses were all performed at the University of Minnesota (UMN).

Units of Measurement:
Radionuclide concentrations are given as micro-Becquerel (10e-6 Bq, µBq or micro-Bq) per kilogram seawater for Th-230 and Pa-231, and picomole (10e-12 mol, pmol) per kilogram seawater for Th-232. A Becquerel is the SI unit for radioactivity and is defined as 1 disintegration per second. These units are recommended by the GEOTRACES community.