Heat Dissipation And Energetic Efficiency In Animal Anoxibiosis - Economy Contra Power

This survey on calorimetry and thermodynamics of anoxibiosis applies classical and irreversible thermodynamics to interpret experimental, direct calorimetric results in order to elucidate the sequential activation of various biochemical pathways. First, the concept of direct and indirect calorimetry is expanded to incorporate the thermochemistry of aerobic and anoxic metabolism in living cells and organisms. Calorimetric studies done under normoxia as well as under physiological and environmental anoxia are presented and assessed in terms of ATP turnover rate. Present evidence suggests that unknown sources of energy in freshwater and marine invertebrates under long-term anoxia may be important. During physiological hypoxia, thermodynamically grossly inefficient pathways sustain high metabolic rates for brief periods. On the contrary, under long-term environmental anoxia, low steady-state heat dissipation is linked to the more efficient succinate, propionate, and acetate pathways. In the second part of this paper these relationships are discussed in the context of linear, irreversible thermodynamics. The calorimetric and biochemical trends during aerobic-anoxic transitions are consistent with thermodynamic optimum functions of catabolic pathways. The theory predicts a decrease of rate with an increase of thermodynamic efficiency; therefore maximum rate and maximum efficiency are mutually exclusive. Cellular changes of pH and adenylate phosphorylation potential are recognized as regulatory mechanisms in the energetic switching to propionate production. While enzyme kinetics provides one key for understanding metabolic regulation, our insight remains incomplete without a complementary thermodynamic analysis of kinetic control in energetically coupled pathways.

Air-sea exchange of methanol and acetone during HiWinGS: Estimation of air phase, water phase gas transfer velocities

The air-sea fluxes of methanol and acetone were measured concurrently using a proton-transfer-reaction mass spectrometer (PTR-MS) with the eddy covariance (EC) technique during the High Wind Gas Exchange Study (HiWinGS) in 2013. The seawater concentrations of these compounds were also measured twice daily with the same PTR-MS coupled to a membrane inlet. Dissolved concentrations near the surface ranged from 7 to 28 nM for methanol and from 3 to 9 nM for acetone. Both gases were consistently transported from the atmosphere to the ocean as a result of their low sea surface saturations. The largest influxes were observed in regions of high atmospheric concentrations and strong winds (up to 25 m s(-1)). Comparison of the total air-sea transfer velocity of these two gases (K-a), along with the in situ sensible heat transfer rate, allows us to constrain the individual gas transfer velocity in the air phase (k(a)) and water phase (k(w)). Among existing parameterizations, the scaling of k(a) from the COARE model is the most consistent with our observations. The k(w) we estimated is comparable to the tangential (shear driven) transfer velocity previously determined from measurements of dimethyl sulfide. Lastly, we estimate the wet deposition of methanol and acetone in our study region and evaluate the lifetimes of these compounds in the surface ocean and lower atmosphere with respect to total (dry plus wet) atmospheric deposition.