Assessment and improvement of the sea ice processing for dissolved inorganic carbon analysis

Abstract

Dissolved inorganic carbon (DIC) is an important parameter to characterize the biogeochemical processes in sea ice and across the ocean-sea ice-atmosphere interface. The main challenge in bulk sea ice processing for DIC analysis is to melt the ice core without exposure to the air, which otherwise might contaminate the sample. A common practice is to seal the ice core in a gas-tight plastic bag and remove the air gently using a syringe or a hand pump. However, this procedure is time-consuming and the uncertainty in DIC concentration processed in this way has not been fully accessed. In this study, we modified the method by using a vacuum sealer and evaluated this procedure by examining the impact of ice sample processing, biological activity, gaseous CO 2 initially present in sea ice, and the presence of ikaite (CaCO 3 Á6H 2 O) crystals. The results show that no loss or gain in DIC occurs during the evacuation and ice melting process and that it might not be necessary to pre-poison the ice samples during the ice melting process. In addition, gaseous CO 2 initially present in sea ice has a negligible impact on DIC analysis. If detectable ikaite crystals are present in sea ice, the measurement results should be referred to total inorganic carbon instead of DIC. The field test at Station Nord in Greenland demonstrates that the modified method is simple and quick to use even under the most remote and extreme environments.When sea ice grows, most of the brine is expelled to the under-ice seawater due to gravity drainage, while a small portion stays trapped in the ice matrix (Niedrauer and Martin 1979). The chemical composition of brine is primarily a function of salinity and temperature, but can be modified by biological activity and abiotic processes such as gas exchange and mineral formation (Papadimitriou et al. 2007).Dissolved inorganic carbon (DIC) in sea ice, the measurement of which could include gaseous CO 2 in the bubbles of the ice, is an important parameter to describe the ocean-sea ice-atmosphere CO 2 flux. As described in Tison et al. (2002), sea ice was for many years considered as a lid over seawater preventing CO 2 exchange between the atmosphere and ocean. Some observations suggest that sea ice can be an active source or sink for CO 2 (e.g., Nomura et al. 2010;Miller et al. 2011). A more recent study shows that the effective gas velocity decreases in proportion to sea ice cover, suggesting that CO 2 flux through sea ice could be minor (Butterworth and Miller 2016). However, direct measurements of the CO 2 flux on sea ice based on the chamber method and eddy covariance tend to largely disagree as pointed out in Geilfus et al. (2013). Since the ice-atmosphere CO 2 flux is limited by the DIC stocks in sea ice (Moreau et al. 2015), improved measurements of DIC in sea ice are needed to better understand the air-ice CO 2 flux. Rysgaard et al. (2011) proposed a conceptual model describing the role of sea ice in controlling air-sea CO 2 exchange (i.e., sea ice carbon pump), and noted that a large data...

Reproducing Arctic springtime tropospheric ozone and mercury depletion events in an outdoor mesocosm sea ice facility

“…All ice cores were taken from outside of the acrylic tubes within a few metres from where the tubes were located and cut into 3 cm sections immediately after the retrieval. Ice sections were stored in gas-tight plastic bags (Nylon/poly, Cabela's) and vacuumsealed (Hu et al, 2018), followed by melting at 4 • C in the dark until further analysis. Under-ice water was sampled for ion composition analysis by submerging 50 mL polypropylene tubes (Falcon) completely underwater from the hole where the ice core was taken, after manually clearing off floating ice.…”

“…Once sea ice melted, meltwa-ter, and seawater were transferred to gas-tight vials (12 mL Exetainers, Labco High Wycombe, UK), preserved with 12 µL saturated HgCl 2 solution, and stored at room temperature in the dark until analysis. Total alkalinity was determined by Gran titration (Gran, 1952) on a TIM 840 titration system (Radiometer Analytical, ATS Scientific) (Hu et al, 2018). The sample (12 mL) was titrated with a standard 0.05 M HCl solution (Alfa Aesar).…”

Reproducing springtime Arctic tropospheric ozone depletion events in an outdoor mesocosm sea-ice facility

“…Ice cores were taken from outside of the acrylic tubes within a few meters from where the tubes were located and cut into 3-cm sections immediately after the retrieval. Ice sections were stored in gas-tight plastic bags (Nylon/poly, Cabela's) and vacuum-sealed (Hu et al, 2018), followed by melting at 4 °C in the dark until further analysis. Under-ice water was sampled for major ion analysis by submerging 50-mL polypropylene tubes (Falcon) completely underwater from the hole where the ice core was taken, after manually clearing off floating ice.…”

“…Once sea ice melted, meltwater and seawater were processed similarly by transferring to gas-tight vials (12-mL Exetainers, Labco High Wycombe, UK), preserved with 12 µL solution of saturated HgCl2, and stored at room temperature in the dark until analysis. Total alkalinity was determined by Gran titration (Gran, 1952) on a TIM 840 titration system (Radiometer Analytical, ATS Scientific) (Hu et al, 2018). A 12-mL sample was titrated with a standard 0.05 M HCl solution (Alfa Aesar).…”

Landfast sea ice in the Bothnian Bay (Baltic Sea) as a temporary storage compartment for greenhouse gases

“…Directly after extraction of the core, the temperature profile was measured in situ using a calibrated temperature probe (Testo 720 1 , +0.1 C precision) inserted into predrilled holes (5-cm intervals), perpendicular to core sides. Cores were then cut into 5-10 cm sections, stored in sealed plastic containers, and vacuum-sealed in a gas-tight plastic bag (nylon/poly, Cabela's, Sidney, NE, USA; Hu et al, 2018) directly in the field. Back in the laboratory, samples were melted in the dark at 4 C to minimize the possible dissolution of ikaite crystals.…”