Chemical analysis of sea ice vein μ-environments using Raman spectroscopy

• Published in: Polar Record
• Main Authors: Barletta, Robert E., Dikes, Heather M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2014
• Subjects: General Earth and Planetary Sciences; Ecology; Geography, Planning and Development; Palmer Station; Palmer-Station; Antarc*; Antarctica; Polar Record; Sea ice
• Online Access: http://dx.doi.org/10.1017/s0032247413000922; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0032247413000922

ABSTRACT Sea ice is a unique environment providing a vast habitat for a variety of life, including microscopic organisms. It accounts for roughly 5–6% of the surface area of the oceans. It is a complex porous structure of crystalline water, gas bubbles, and pockets of brine, as well as a connected structure composed of macro- and micro-porosity filled with concentrated aqueous liquids. Using micro-Raman spectroscopy, it is possible to characterise features of ice at a spatial resolution of a few to tens of micrometers, the scale of relevance to trapped microorganisms, by providing information concerning the presence and amount of molecular species present in the trapped liquids. We have applied this technique to determine the spatial distribution of sulphate, phosphate and carbonate anions in sea-ice veins using ice obtained from the vicinity of the Palmer Station, Antarctica. The observed sulphate concentrations were approximately 20–30% higher than nominal surface seawater concentrations, consistent with the concentration of brine in vein and inclusion liquids during the ice formation process. This concentration was lower than that in veins present in laboratory-prepared ice. Carbonate and dibasic phosphate anions were also observed in the sea ice. This speciation is consistent with an alkaline environment in the sea-ice aqueous system. The mean dibasic phosphate concentration found throughout the sample was 648 mM, while, for carbonate, it was 485 mM. However, these anions showed extremely high spatial variability. The high phosphate and carbonate enhancements observed relative to sulphate point to the influence of processes other than brine formation controlling the chemistry of these anions in sea ice.