200 meters of the SPRESSO ice core were melted using the University of Maine continuous melting system yielding a resolution of 60 to 110 samples per meter. Melting was performed in a Class 100 clean room. Clean suits, booties and polypropylene gloves were worn during melting and ice core preparation to prevent contamination of the core. The ends of each ice core were scraped using a pre-cleaned (with DI water from a MilliQ-Element system (>18.2 MO)) ceramic knife before melting to prevent contamination. DI water was pumped through the entire melter system between melting sessions to keep the system clean. DI water blanks were collected before and after every melting session to confirm the system is clean. A nickel 270 (>99.99% Ni) melting disk with an inner diameter of 26 mm and an outer diameter of 65 mm was employed. The melter head was heated to a constant temperature of 12-18 °C (depending on ice/firn density).
A total of 18,570 co-registered samples were collected each for IC (ion chromatography), ICP MS (inductively coupled plasma sector field mass spectrometry) and stable water isotope analysis. Sample resolution changed from 1.8 to 0.88 cm from the shallow to the deeper part of the core (average 1.12 cm) yielding 8-9 samples per year on average. Samples were collected from the inner and outer parts of the core. To avoid contamination only the inner portion of each core was sampled for IC (each sample 2 ml volume) and ICP-MS analysis (each sample 2 ml volume). The meltwater from the potentially contaminated outer part was collected for stable isotope analysis (16 ml sample volume). Pump speeds for the melter system were 5, 5.2 and 26.5-27.5 cpm for collection of IC, ICP MS and isotopes, respectively..
All samples for major ion analyses (IC) were collected into LDPE bottles cleaned by successive soaking and rinsing in DI water, and re-frozen. Samples for stable isotope analysis were collected into dried LDPE vials, and re-frozen. Samples for trace element analysis (ICP-MS) were collected into acid-cleaned (Optima HNO3) LDPE vials. ICP-SMS samples were acidified to 1% with double-distilled HN03 under a class-100 HEPA clean bench and allowed to react with the acid for approximately 1 week before being frozen
IC Analyses. A Dionex ion chromatograph with chemical suppression and conductivity detectors was used. Anions (Cl-, NO3-, SO4-) were measured using an AS-11 column, 400µL sample loop, and a Dionex Reagent Free Controller producing a KOH eluent gradient of 1 mM to 8 mM. Two ion chromatographs were paired to a Gilson Liquid Handler autosampler for simultaneous anion and cation analysis. Calibration curves bracket the expected concentration range with correlation coefficients of >0.99. Calibration results were verified using Environment Canada's ION-92 standard diluted to bring the reported values within range.
ICP MS Analyses. Trace element analyses (Na, Mg, Ca, Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Al, S, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Li and K) were performed with the UMaine Thermo Electron Element2 ICP-MS. The use of an ESI Apex high-sensitivity inlet system increased instrument sensitivity and reduced oxide formation in the plasma, lowering detection limits and allowing less abundant isotopes to be measured. A Cetac (Omaha, NE) Model ASX- 260 autosampler is located within our class-100 HEPA clean bench adjacent to the instrument to further reduce contamination. The ICP MS is calibrated daily with five standards that bracket the expected sample concentration range. Certified water reference material, SLRS-4 (Environment Canada) was used to verify the calibration. We used Thermo Electron’s auto lock mass software routine to compensate for mass drift. In an effort to minimize sample handling and possible contamination no internal standard was used.