Samples were collected according to Cutter and Bruland 2012, utilizing a trace metal clean rosette (GT-C rosette). Samples above 20 m were pumped from a hole drilled in the ice far away from the ship, using clean sampling techniques.
Sample bottles were cleaned according to Hammerschmidt et al. 2012.
Dissolved mercury analyses were performed at sea, with the exception of monomethylmercury. The full methodology may be found in the Hg Cook Book, and more detailed method descriptions can be found in Lamborg et al. 2012, Hammerschmidt and Bowman 2012, Bowman et al. 2015, Bowman et al. 2016.
All dissolved species of mercury were measured with a Tekran Model 2500 CVAFS Mercury Detector. Analysis of total mercury (HgT; Fitzgerald and Gill 1979, Bloom and Fitzgerald 1988, Bloom 1989) has a method detection limit of 0.10 pM, and procedural duplicates varied by 11 ± 5% (n = 17).
Elemental mercury (Hg0) was analyzed according to Fitzgerald and Gill (1979), Bloom and Fitzgerald (1988) and Bloom (1989). The method detection limit was 0.04 pM and procedural duplicates varied by 11 ± 14% (n = 8).
Monomethylmercury (MMHg) was analyzed according to Bowman and Hammerschmdit (2011), Tseng et al. (2004) and Munson et al. (2014). The method detection limit was 0.020 pM, and procedural duplicates averaged 11 ± 8% (n =5).
Dimethylmercury (DMHg) was analyzed according to Bowman and Hammerschmidt (2011), Tseng et al. (2004) and Baya et al. (2013). The method detection limit was 0.012 pM.