Mercury concentrations in Antarctic krill from South Georgia, South Orkney Islands, and West Antarctica Peninsula (2013-2019)

This data set presents total mercury (Hg) concentrations measured from Antarctic krill (Euphausia superba) sampled between December 2013 and September 2019 from South Georgia, the South Orkney Islands, and the West Antarctic Peninsula. The data were produced to support a more thorough understanding of how Hg concentration varies in krill and how that might affect the krill-reliant Antarctic food web, especially in the context of a changing climate. Long-term data sets are needed for these purposes but are missing from Southern Ocean environments, given the difficulty and costs of accessing these remote regions. To fulfill this gap, we collaborated with AkerBiomarine, a Norwegian krill fishing and biotech company, to obtain a unique and almost contiguous data set, with fortnightly samples for most months (except October and November) throughout the collection period. We aimed to establish a baseline against which past and future studies could be compared for Hg concentrations in Antarctic krill, and to investigate any potential influence of biological (krill size, sex, and life stage) and abiotic (geographic location and temporal variation) variables in these concentrations.\nLineage: Study sites and sample collection\nKrill were collected by the vessel FV Saga Sea (Aker BioMarine, Oslo, Norway) during December 2013 - September 2014, December 2014 - September 2015, December 2015 - September 2016, January - August 2017, December 2017 - August 2018, and January - September 2018. The vessel predominantly fished at the West Antarctica Peninsula (WAP) and South Orkney Islands (SOI) during summer and autumn, and at South Georgia (SG) in winter and early spring. \nA continuous catch system (Eco-Harvesting® technology, Aker BioMarine) was used to steadily pump live krill for 24 h from a mid-water trawl net onto FV Saga Sea. Twenty individuals were randomly sampled from the catch every day by a fisheries observer, packaged into a vacuum-sealed transparent plastic packet stored inside a dark package, and immediately frozen at -20 oC for 4 h, being subsequently transferred to -80 oC storage until shipping. Packages were transported on dry ice to the Institute for Marine and Antarctic Studies (Hobart, Australia), where they were stored in freezers at either -80 oC or -20 oC until analysis.\n\nMercury analysis\nAn average of three krill samples per sex (male and female) were chosen per fortnight for total Hg analysis, together with a few samples of juveniles. Thawed individuals were sexed, freeze-dried for 24 h, and subsequently weighed. Most samples pooled two to four individuals of the same sex and life stage, but a few samples pooled adults and subadults of the same sex.\nSamples were homogenised to a fine powder (20 -100 µm) for mercury analyses, which were conducted using a Milestone Direct Mercury Analyzer (DMA-80 Tri-Cell; Milestone, Bergamo, Italy). The instrument was calibrated with an aqueous Hg standard for AAS (1000 mg/LHg in nitric acid; Sigma Aldrich TraceCERT®). A calibration curve was constructed by plotting the absorbances of standards against Hg concentrations in nanograms with an R2 value of 0.99 or higher. Samples were analysed using the USEPA method 7473 (U.S. EPA 1998); two blanks and three reference materials were analysed for every 40 samples. Approximately 100 mg of the sample was weighed in nickel boats. After every tenth sample, a replicate sample was analysed. When replicate recovery exceeded a variance of 10% compared to the original sample, a third replicate was run.\n\nMore details on the methodology for data production can be found in the related link (published article).\n\n