Dataset: Total water-column Thorium-234 measurements collected during January cruises of the Palmer LTER program along the Western Antarctic Peninsula from 2016-2020

This dataset has not been validatedData not availableVersion 1 (2024-12-04)Dataset Type:Cruise Results

Principal Investigator: Michael R. Stukel (Florida State University)

BCO-DMO Data Manager: Shannon Rauch (Woods Hole Oceanographic Institution)


Project: Quantifying Processes Driving Interannual Variability in the Biological Carbon Pump in the Western Antarctic Peninsula (WAP Carbon export)


Abstract

This dataset includes total water-column Thorium-234 measurements collected during January cruises of the Palmer LTER program along the Western Antarctic Peninsula. 238U-234Th disequilibrium is used as a proxy for sinking particle flux out of the upper ocean. Vertical profiles of 234Th were measured using standard small-volume techniques on 5 Palmer LTER cruises on ARSV Laurence M. Gould during 2016-2020. Measurements typically spanned from the surface to a depth of ~200 meters, although the dee...

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Total 234Th was measured using standard small volume techniques (Benitez-Nelson et al., 2001; Pike et al., 2005). 4-liter (L) samples for total 234Th were sampled using a CTD Niskin rosette (typically from eight depths spanning the epipelagic). Samples were acidified to a pH of <2 with HNO3. A tracer addition of 230Th was added and samples were mixed vigorously. Samples were allowed to equilibrate for 4-9 hours and then adjusted to a pH of 8-9 with NH4OH. KMnO4 and MnCl2 were added and samples were mixed and allowed to sit for ~12 hours as Th co-precipitated with manganese oxide. Samples were then vacuum-filtered at high pressure onto QMA filters, dried, and mounted in RISO sample holders.

Samples were beta counted on a RISO low-level background beta counter at Palmer Station and re-counted >6 half-lives later. Samples for water-column 234Th were then dissolved in HNO3/H2O2 solution and 229Th tracer was added. Samples were evaporated and reconstituted in dilute nitric acid / hydrofluoric acid. They were then analyzed by inductively-coupled plasma mass spectrometry at the Woods Hole Oceanographic Institution Analytical Lab to determine the ratio of 229:230Th to determine the initial yield of the 234Th filtration. 238U activity (for estimating 238U-234Th deficiency) was estimated from a linear relationship with salinity (Owens et al., 2011).


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General

Ducklow, H. W., Stukel, M. R., Eveleth, R., Doney, S. C., Jickells, T., Schofield, O., Baker, A. R., Brindle, J., Chance, R., & Cassar, N. (2018). Spring–summer net community production, new production, particle export and related water column biogeochemical processes in the marginal sea ice zone of the Western Antarctic Peninsula 2012–2014. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 376(2122), 20170177. https://doi.org/10.1098/rsta.2017.0177
General

Stukel, M. R., & Ducklow, H. W. (2017). Stirring Up the Biological Pump: Vertical Mixing and Carbon Export in the Southern Ocean. Global Biogeochemical Cycles, 31(9), 1420–1434. Portico. https://doi.org/10.1002/2017gb005652
General

Stukel, M. R., Asher, E., Couto, N., Schofield, O., Strebel, S., Tortell, P., & Ducklow, H. W. (2015). The imbalance of new and export production in the western Antarctic Peninsula, a potentially “leaky” ecosystem. Global Biogeochemical Cycles, 29(9), 1400–1420. Portico. https://doi.org/10.1002/2015gb005211
General

Stukel, M. R., Schofield, O. M. E., & Ducklow, H. W. (2022). Seasonal variability in carbon:234thorium ratios of suspended and sinking particles in coastal Antarctic waters: Field data and modeling synthesis. Deep Sea Research Part I: Oceanographic Research Papers, 184, 103764. https://doi.org/10.1016/j.dsr.2022.103764
Methods

Benitez-Nelson, C. R., Buesseler, K. O., van der Loeff, M. R., Andrews, J., Ball, L., Crossin, G., & Charette, M. A. (2001). Journal of Radioanalytical and Nuclear Chemistry, 248(3), 795–799. https://doi.org/10.1023/a:1010621618652