Sampling and analytical procedures:
The chemical procedure for the analysis of Po-210 and Pb-210 in aerosols, water samples, snow, ice core, melt ponds and ice-rafted sediments are given in Sampling and Sample-handling Protocols for GEORACES Cruises (known as "Cookbook"): http://geotraces.org/science/intercalibration/222-sampling-and-sample-handling-protocols-for-geotraces-cruises; Baskaran et al., 2013).

Samples for Po-210/Pb-210 analysis were collected from 4 super stations, 3 shelf stations, 1 full station, 1 pacific end member station, 6 ice stations, 2 dirty ice events, and from 14 aerosol deployments. The number of water samples ranged from 16-24 depths for super stations and 3-6 depths for shelf/end member stations. These samples were collected from the ODF rosette and filtered using 0.2um Acropack filters. Two additional filtered water samples were taken from 8L niskins attached atop the multicorer instrument at two separate shelf stations. Four unfiltered water samples were collected for intercalibration between the Wayne State University and Louisiana State Laboratory (collected from 1 full station and 1 super station (original GT 15)). The particulate samples collected by McLane pumps for associated dissolved water samples will be sent to the participating labs for analysis upon completion of the cruise. Samples collected at ice stations included snow, melt pond water, under ice water, and ice cores. All samples were collected unfiltered and subsequently filtered in the onboard lab for analysis of both particulate and dissolved phases. The 2 dirty ice events were conducted between stations using a man basket and each event included a community sample which was divided among other groups. Aerosol deployments were conducted every three or four days, depending on the total run time of the pumps. Dissolved water samples from the shelf stations and 2 of the 4 super stations (original GT13, 15) were acidified and stored for shipment to Dr. Maiti's laboratory where they will be processed. All of the remaining samples were processed onboard by Wayne State personal (Katie Krupp). Dissolved seawater/melted ice station samples were processed by co-precipitation using an iron carrier followed by electroplating to silver planchets. Particle samples and aerosols were leached with acids and plated in the same manner. A known amount of Po-209 spike was added to each sample for determination of Po-210 recovery. These planchets and sample solutions were brought back to Wayne State University for alpha counting and further processing in order to measure Pb-210 and thus determine the Po-210/Pb-210 ratio for each sample collected. In summary, approximately 310 samples were collected for polonium- 210 and lead-210 analysis on the 2015 Arctic GEOTRACES cruise.

Meltpond sampling:
Melt ponds were sampled at Stations 33, 38, 42, 43 and 46. A battery-powered peristaltic pump and silicone tubing were used to fill a carboy for shipboard filtration (Acropak-200, <0.2 um). At each station, the melt ponds were frozen over, so a hole was drilled using the TM-clean corer. Salinity was measured at each melt pond following sampling.

Aerosol sampling:
Aerosol samples were collected over periods of three to five days using five high-volume aerosol
samplers. Three samplers were used to collect aerosols on acid-cleaned Whatman-41 (cellulose) filters for analysis of inorganic trace elements and isotopes (TEIs).

Sea Ice operations:
Snow, ice cores and water under the ice was collected from the six sea ice stations (Table 1).
Ice stations were constricted north of 88.4o N on the northward leg, and north of 82.5o N on the southward leg of the cruise. This narrow latitudinal range resulted from a combination of ice conditions, weather conditions, and available time.

Ice Station Longitude Latitude (samples include snow, ice core, melt ponds and ice-rafted sediment)
Station 31: 183.33W 88.42N
Station 33: 3.529E 89.96N
Station 39: 149.61W 87.78N
Station 42: 150.54W 85.74N
Station 43: 150.00W 85.16N
Station 46: 149.83W 82.49N

Bulk Snow:
Bulk snow for Po-210 and Pb-210 was collected with an acid clean high density polyethylene shovel into a low density polyethylene drum liner. Discrete snow samples were also collected in community provided containers. The bulk snow was melted on board, filtered through a Supor 0.2 um filter membrane and subsampled.

Sea Ice Cores:
Discrete ice cores were collected at all stations. Cores were collected with the Kovaks corer. A total of two Twelve to fifteen cores were taken at each station for a total of 85 sea ice community cores.

Problem report:
We had analyzed a total of 43 water samples, 43 small particle size and 43 large particle size. Out of these, two batches (3 dissolved and 4 particulate (both large and small)) were lost during analysis onboard.