Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21b1222c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P21B-1222
Physics
[0738] Cryosphere / Ice, [0750] Cryosphere / Sea Ice, [5422] Planetary Sciences: Solid Surface Planets / Ices, [6020] Planetary Sciences: Comets And Small Bodies / Ices
Scientific paper
The composition and morphology of the fluid microchannels threading polycrystaline ice affects the integrity of ice core records and the strength of ice-atmosphere interactions. These fluids owe their existence to impurities and curvature depression. Electrolyte impurities induce bulk colligative effects, but also charge ice surfaces, while screening the resulting electrostatic repulsion. A non-monotonic rather than positive dependence of channel width δ on electrolyte concentration has thus been predicted. Herein we report the first time-resolved, confocal microscopy study of freezing water and electrolyte solutions doped with 10 μM of C-SNARF-1, a fluorescent pH probe. The freezing of doped water concentrates the probe into discrete δ = (12 ± 2) μm channels embedded in pristine ice, whereas ice fronts advancing (at < 5 μm/s) into 1 mM electrolytes destabilize and engulf them into < 1 μm fluid occlusions distributed over the sample. These findings are consistent with a non-monotonic dependence of δ on ion concentration. pH increases by less than 0.4 unit within the occlusions formed in freezing NaCl solutions, and by over 1 unit upon subsequent thawing, revealing that hydroxide ion slowly produced via the dissociation of water molecule in ice seeps from ice to relieve the excess charge generated by chloride inclusion. In contrast, the preferential incorporation of the ammonium ions over the acetate anions into ice leads to the acidification of partially frozen ammonium acetate solutions.
Cheng Jipeng
Colussi Agustín J.
Hoffmann Mark R.
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