The speciation of water in sea water and in gelatinous marine animals

Abstract

Abstract Raman spectra provide important information on the speciation of water in sea water, and its relationship to temperature, pressure, and salinity. These spectra reveal two primary water bands: a bending mode doublet peak at 1640 cm −1 , and a dominant water stretching mode band with Raman shifts in the 2900–3800 cm −1 region. Early laboratory work revealed the presence of an ‘isosbestic point’ within the water spectra, which is consistent with a two component structure. Ocean scientists working with aircraft based pulsed time gated laser systems used the temperature dependence of the two component water structure observed within the water stretching band to determine upper ocean temperature profiles. We find that our results are consistent with the Walrafen water pentamer as the primary structure in rapid exchange with H 2 O monomers, and we have deconvoluted the stretching band into 5 peaks. From laboratory pressure cell data very clear trends in water structure with temperature, pressure, and to a lesser degree salinity can be observed, and a plot of the natural log of the water peak amplitudes versus the inverse of the absolute temperature permits estimation of the strength of the hydrogen bond. While there is no definitive way to distinguish between a fully “intact” and a fully “broken” hydrogen bond and the hydrogen bonded water structures are evanescent, our observations are consistent with ΔH = 2.48 kcal/mol. From our compiled expeditionary data (primarily from Monterey Bay, California) from ~ 280 m to 2740 m depth we find strong compensation of the opposing temperature and pressure effects such that the observed water peaks show a remarkable consistency throughout the deep water column. In situ Raman observations of the gelatinous mass (mesoglea) of many deep-sea animals show that liquid water there is absent, and essentially all salts are excluded. Within the mesoglea the water bending modes are eliminated and the O H stretching modes are composed of only 3 bands.