The real limits to marine life: a further critique of the Respiration Index
The recently proposed "Respiration Index" (RI = log P O 2 / P CO 2 ) 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...
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ftcopernicus:oai:publications.copernicus.org:bg17424 2023-05-15T17:51:34+02:00 The real limits to marine life: a further critique of the Respiration Index Seibel, B. A. Childress, J. J. 2018-09-27 application/pdf https://doi.org/10.5194/bg-10-2815-2013 https://www.biogeosciences.net/10/2815/2013/ eng eng doi:10.5194/bg-10-2815-2013 https://www.biogeosciences.net/10/2815/2013/ eISSN: 1726-4189 Text 2018 ftcopernicus https://doi.org/10.5194/bg-10-2815-2013 2019-12-24T09:55:23Z The recently proposed "Respiration Index" (RI = log P O 2 / P CO 2 ) 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 (Δ G ° = −686 kcal mol −1 ), carbon dioxide can never reach concentrations that would limit the thermodynamics of this reaction. A P CO 2 to P O 2 ratio of 10 503 would be required to reach equilibrium (equilibrium constant, K eq = 10 503 ), where Δ G = 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 CO 2 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 CO 2 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. Text Ocean acidification Copernicus Publications: E-Journals Biogeosciences 10 5 2815 2819 |
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Copernicus Publications: E-Journals |
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English |
description |
The recently proposed "Respiration Index" (RI = log P O 2 / P CO 2 ) 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 (Δ G ° = −686 kcal mol −1 ), carbon dioxide can never reach concentrations that would limit the thermodynamics of this reaction. A P CO 2 to P O 2 ratio of 10 503 would be required to reach equilibrium (equilibrium constant, K eq = 10 503 ), where Δ G = 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 CO 2 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 CO 2 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 |
Text |
author |
Seibel, B. A. Childress, J. J. |
spellingShingle |
Seibel, B. A. Childress, J. J. The real limits to marine life: a further critique of the Respiration Index |
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 |
publishDate |
2018 |
url |
https://doi.org/10.5194/bg-10-2815-2013 https://www.biogeosciences.net/10/2815/2013/ |
genre |
Ocean acidification |
genre_facet |
Ocean acidification |
op_source |
eISSN: 1726-4189 |
op_relation |
doi:10.5194/bg-10-2815-2013 https://www.biogeosciences.net/10/2815/2013/ |
op_doi |
https://doi.org/10.5194/bg-10-2815-2013 |
container_title |
Biogeosciences |
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10 |
container_issue |
5 |
container_start_page |
2815 |
op_container_end_page |
2819 |
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1766158759575420928 |