A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere?
Seasonal oscillations in the partial pressure of carbon dioxide (<i>p</i>CO<sub>2</sub>) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the <i>p</i>CO<sub>...
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MDPI AG
2022-11-01
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| Series: | Thermo |
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| Online Access: | https://www.mdpi.com/2673-7264/2/4/28 |
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| author | Ivan R. Kennedy John W. Runcie Shuo Zhang Raymond J. Ritchie |
| author_facet | Ivan R. Kennedy John W. Runcie Shuo Zhang Raymond J. Ritchie |
| author_sort | Ivan R. Kennedy |
| collection | DOAJ |
| description | Seasonal oscillations in the partial pressure of carbon dioxide (<i>p</i>CO<sub>2</sub>) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the <i>p</i>CO<sub>2</sub> in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the <i>p</i>CO<sub>2</sub> in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO<sub>3</sub><sup>2−</sup>) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO<sub>3</sub> (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO<sub>2</sub> emission to air. Paradoxically, the increasing CO<sub>2</sub> concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric <i>p</i>CO<sub>2</sub> by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO<sub>2</sub> from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO<sub>2</sub> per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO<sub>3</sub> in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater. |
| first_indexed | 2024-03-09T15:47:20Z |
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| institution | Directory Open Access Journal |
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| last_indexed | 2024-03-09T15:47:20Z |
| publishDate | 2022-11-01 |
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| spelling | doaj.art-06e137468330416184265596897dbf222023-11-24T18:23:46ZengMDPI AGThermo2673-72642022-11-012440143410.3390/thermo2040028A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere?Ivan R. Kennedy0John W. Runcie1Shuo Zhang2Raymond J. Ritchie3School of Life and Environmental Sciences, Sydney Institute of Agriculture, University of Sydney, Sydney, NSW 2006, AustraliaAquation Pty Ltd., P.O. Box 3146, Woy Woy, NSW 2257, AustraliaState Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, ChinaFaculty of Technology and Environment, Prince of Songkla University, Phuket Campus, Phuket 83120, ThailandSeasonal oscillations in the partial pressure of carbon dioxide (<i>p</i>CO<sub>2</sub>) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the <i>p</i>CO<sub>2</sub> in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the <i>p</i>CO<sub>2</sub> in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO<sub>3</sub><sup>2−</sup>) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO<sub>3</sub> (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO<sub>2</sub> emission to air. Paradoxically, the increasing CO<sub>2</sub> concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric <i>p</i>CO<sub>2</sub> by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO<sub>2</sub> from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO<sub>2</sub> per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO<sub>3</sub> in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater.https://www.mdpi.com/2673-7264/2/4/28CO<sub>2</sub>Keeling curveMauna Loacarbonatesocean pHchemical potential |
| spellingShingle | Ivan R. Kennedy John W. Runcie Shuo Zhang Raymond J. Ritchie A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? Thermo CO<sub>2</sub> Keeling curve Mauna Loa carbonates ocean pH chemical potential |
| title | A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? |
| title_full | A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? |
| title_fullStr | A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? |
| title_full_unstemmed | A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? |
| title_short | A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere? |
| title_sort | new look at physico chemical causes of changing climate is the seasonal variation in seawater temperature a significant factor in establishing the partial pressure of carbon dioxide in the earth s atmosphere |
| topic | CO<sub>2</sub> Keeling curve Mauna Loa carbonates ocean pH chemical potential |
| url | https://www.mdpi.com/2673-7264/2/4/28 |
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