Dataset: Suspended particle total mercury and monomethylmercury in the California Current Ecosystem (CCE) determined from samples collected on R/V Roger Revelle cruise RR2105 (P2107) in July to August 2021

Final no updates expectedDOI: 10.26008/1912/bco-dmo.926959.1Version 1 (2024-05-14)Dataset Type:Cruise Results

Principal Investigator: Carl Lamborg (University of California-Santa Cruz)

Principal Investigator: Amina T. Schartup (University of California-San Diego Scripps)

Student: Hannah M. Adams (University of California-San Diego Scripps)

Student: Xinyun Cui (University of California-Santa Cruz)

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


Program: Ocean Carbon and Biogeochemistry (OCB)

Program: Long Term Ecological Research network (LTER)

Project: California Current Ecosystem Long Term Ecological Research site (CCE LTER)

Project: Collaborative Proposal: Unravelling the Oceanic Dimethylmercury Cycle (DMHg in the Ocean)


Abstract

This dataset includes concentrations of suspended particulate total mercury and monomethylmercury from 8 upwelling stations and 5 offshore stations (13 stations in total, 2-4 depths per station), during the 2021 CCE LTER Process Cruise (P2107), from July 17th to Aug 9th. Suspended particle samples (1 and 51 micrometers (µm)) were collected with a multiple-unit large-volume in situ filtration system. Sampling depths were from the surface (10 meters) to the deep ocean as deep as 1000 meters.

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Suspended particles were collected using McLane Research in-situ pumps (WTS-LV) using modified, two-layer filter holders. The top filter holder layer was loaded with a 51-micrometer (μm) polyester mesh filter to collect large-size fraction particles (LSF). The other filter holder layer was loaded with a pre-combusted GF/F glass microfiber filter (Whatman) to collect small-size fraction particles (SSF, 1-51 μm). Filter holders were acid-leached before use, and GF/F filters were additionally combusted at 450 degrees Celsius (°C) for 4 hours. Sinking particles were collected by sediment traps.

Total mercury (THg) and monomethylmercury (MMHg) in suspended and sinking particles were determined by digesting filter portions in nitric acid (2N, trace mental grade, Fisher) for 4 hours at 60°C constant water bath with intermittent sonication. For THg determination, digestates were oxidized with bromine monochloride for at least 2 hours and pre-reduced with hydroxylamine hydrochloride. Subsamples were then reduced with stannous chloride, and the evolved Hg0 concentrations were determined by dual gold amalgamation cold vapor atomic fluorescence spectrometry (CVAFS) with a Tekran 2600 against both gaseous Hg0 and aqueous Hg2+ standards. MMHg determination used a direct ethylation method. Digestates were treated with ascorbic acid, buffered with acetate, and neutralized with potassium hydroxide (KOH; 45%) to pH between 4 and 5. Sodium tetraethylborate (1%, in 2% KOH) was added in digestates reacting for 20 minutes prior to analysis by CVAFS. The method detection limits for THg and MMHg were 26.5 femtomolar (fM) and 3.3 fM in the SSF, and 0.75 fM and 0.24 fM in the LSF, respectively.

For carbon (C) mass determination in the SSF and LSF, filters were packed into a tin capsule and analyzed for particulate carbon mass and measured using Carlo Erba 1108 elemental analyzer coupled to a Thermo Finningan Delta Plus XP IRMS at University of California, Santa Cruz. The analytical precision of C % is 0.65% in the SSF and 1.1% in the LSF based on the organic standards IU Acetanilide and USGC41.


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Results

Cui, X., Adams, H. M., Song, Y., Stukel, M. R., Schartup, A. T., & Lamborg, C. H. (2024). Upwelling Enhances Hg Particle Scavenging in the California Current Ecosystem. https://doi.org/10.21203/rs.3.rs-4102885/v1
Methods

Bowman, K. L., Hammerschmidt, C. R., Lamborg, C. H., & Swarr, G. (2015). Mercury in the North Atlantic Ocean: The U.S. GEOTRACES zonal and meridional sections. Deep Sea Research Part II: Topical Studies in Oceanography, 116, 251–261. doi:10.1016/j.dsr2.2014.07.004
Methods

Munson, K. M., Babi, D., & Lamborg, C. H. (2014). Determination of monomethylmercury from seawater with ascorbic acid-assisted direct ethylation. Limnology and Oceanography: Methods, 12(1), 1–9. doi:10.4319/lom.2014.12.1