The Real Limits to Marine Life: a Further Critique of the Respiration Index
The recently proposed "Respiration Index" (RI = log PO2/PCO2) suggests that aerobic metabolism is limited by the ratio of reactants (oxygen) to products (carbon dioxide) according to the thermodynamics of cellular respiration. Here, we demonstrate further that, because of the large standar...
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ftunisfloridatam:oai:digitalcommons.usf.edu:msc_facpub-3393 2023-05-15T17:51:28+02:00 The Real Limits to Marine Life: a Further Critique of the Respiration Index Seibel, B. A. Childress, J. J. 2013-01-01T08:00:00Z application/pdf https://digitalcommons.usf.edu/msc_facpub/2355 https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=3393&context=msc_facpub unknown Digital Commons @ University of South Florida https://digitalcommons.usf.edu/msc_facpub/2355 https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=3393&context=msc_facpub http://creativecommons.org/licenses/by/3.0/ CC-BY Marine Science Faculty Publications Life Sciences article 2013 ftunisfloridatam 2022-04-07T17:43:29Z The recently proposed "Respiration Index" (RI = log PO2/PCO2) suggests that aerobic metabolism is limited by the ratio of reactants (oxygen) to products (carbon dioxide) according to the thermodynamics of cellular respiration. Here, we demonstrate further that, because of the large standard free energy change for organic carbon oxidation (ΔG° = −686 kcal mol−1), carbon dioxide can never reach concentrations that would limit the thermodynamics of this reaction. A PCO2 to PO2 ratio of 10503 would be required to reach equilibrium (equilibrium constant, Keq = 10503), where ΔG = 0. Thus, a Respiration Index of −503 would be the real thermodynamic limit to aerobic life. Such a Respiration Index is never reached, either in the cell or in the environment. Moreover, cellular respiration and oxygen provision are kinetically controlled such that, within limits, environmental oxygen and CO2 concentrations have little to do with intracellular concentrations. The RI is fundamentally different from the aragonite saturation state, a thermodynamic index used to quantify the potential effect of CO2 on calcification rates, because of its failure to incorporate the equilibrium constant of the reaction. Not only is the RI invalid, but its use leads to incorrect and misleading predictions of the threat of changing oxygen and carbon dioxide to marine life. We provide a physiological framework that identifies oxygen thresholds and allows for synergistic effects of ocean acidification and global warming. Article in Journal/Newspaper Ocean acidification Digital Commons University of South Florida (USF) |
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Life Sciences |
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Life Sciences Seibel, B. A. Childress, J. J. The Real Limits to Marine Life: a Further Critique of the Respiration Index |
topic_facet |
Life Sciences |
description |
The recently proposed "Respiration Index" (RI = log PO2/PCO2) suggests that aerobic metabolism is limited by the ratio of reactants (oxygen) to products (carbon dioxide) according to the thermodynamics of cellular respiration. Here, we demonstrate further that, because of the large standard free energy change for organic carbon oxidation (ΔG° = −686 kcal mol−1), carbon dioxide can never reach concentrations that would limit the thermodynamics of this reaction. A PCO2 to PO2 ratio of 10503 would be required to reach equilibrium (equilibrium constant, Keq = 10503), where ΔG = 0. Thus, a Respiration Index of −503 would be the real thermodynamic limit to aerobic life. Such a Respiration Index is never reached, either in the cell or in the environment. Moreover, cellular respiration and oxygen provision are kinetically controlled such that, within limits, environmental oxygen and CO2 concentrations have little to do with intracellular concentrations. The RI is fundamentally different from the aragonite saturation state, a thermodynamic index used to quantify the potential effect of CO2 on calcification rates, because of its failure to incorporate the equilibrium constant of the reaction. Not only is the RI invalid, but its use leads to incorrect and misleading predictions of the threat of changing oxygen and carbon dioxide to marine life. We provide a physiological framework that identifies oxygen thresholds and allows for synergistic effects of ocean acidification and global warming. |
format |
Article in Journal/Newspaper |
author |
Seibel, B. A. Childress, J. J. |
author_facet |
Seibel, B. A. Childress, J. J. |
author_sort |
Seibel, B. A. |
title |
The Real Limits to Marine Life: a Further Critique of the Respiration Index |
title_short |
The Real Limits to Marine Life: a Further Critique of the Respiration Index |
title_full |
The Real Limits to Marine Life: a Further Critique of the Respiration Index |
title_fullStr |
The Real Limits to Marine Life: a Further Critique of the Respiration Index |
title_full_unstemmed |
The Real Limits to Marine Life: a Further Critique of the Respiration Index |
title_sort |
real limits to marine life: a further critique of the respiration index |
publisher |
Digital Commons @ University of South Florida |
publishDate |
2013 |
url |
https://digitalcommons.usf.edu/msc_facpub/2355 https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=3393&context=msc_facpub |
genre |
Ocean acidification |
genre_facet |
Ocean acidification |
op_source |
Marine Science Faculty Publications |
op_relation |
https://digitalcommons.usf.edu/msc_facpub/2355 https://digitalcommons.usf.edu/cgi/viewcontent.cgi?article=3393&context=msc_facpub |
op_rights |
http://creativecommons.org/licenses/by/3.0/ |
op_rightsnorm |
CC-BY |
_version_ |
1766158622193090560 |