DOI: 10.1002/2014GB004986
Scopus记录号: 2-s2.0-85027936341
论文题名: The effects of secular calcium and magnesium concentration changes on the thermodynamics of seawater acid/base chemistry: Implications for Eocene and Cretaceous ocean carbon chemistry and buffering
作者: Hain M ; P ; , Sigman D ; M ; , Higgins J ; A ; , Haug G ; H
刊名: Global Biogeochemical Cycles
ISSN: 8866236
出版年: 2015
卷: 29, 期: 5 起始页码: 517
结束页码: 533
语种: 英语
英文关键词: acidification
; carbon chemistry
; carbon dioxide
; ion pairing
; seawater buffering
; seawater calcium
Scopus关键词: acidification
; buffering
; carbon dioxide
; Cretaceous
; Eocene
; ion
; seawater
; secular variation
; thermodynamics
英文摘要: Reconstructed changes in seawater calcium and magnesium concentration ([Ca2+], [Mg2+]) predictably affect the ocean's acid/base and carbon chemistry. Yet inaccurate formulations of chemical equilibrium "constants" are currently in use to account for these changes. Here we develop an efficient implementation of the MIAMI Ionic Interaction Model to predict all chemical equilibrium constants required for carbon chemistry calculations under variable [Ca2+] and [Mg2+]. We investigate the impact of [Ca2+] and [Mg2+] on the relationships among the ocean's pH, CO2, dissolved inorganic carbon (DIC), saturation state of CaCO3 (Ω), and buffer capacity. Increasing [Ca2+] and/or [Mg2+] enhances "ion pairing," which increases seawater buffering by increasing the concentration ratio of total to "free" (uncomplexed) carbonate ion. An increase in [Ca2+], however, also causes a decline in carbonate ion to maintain a given Ω, thereby overwhelming the ion pairing effect and decreasing seawater buffering. Given the reconstructions of Eocene [Ca2+] and [Mg2+] ([Ca2+]∼20 mM; [Mg2+]∼30 mM), Eocene seawater would have required essentially the same DIC as today to simultaneously explain a similar-to-modern Ω and the estimated Eocene atmospheric CO2 of ∼1000 ppm. During the Cretaceous, at ∼4 times modern [Ca2+], ocean buffering would have been at a minimum. Overall, during times of high seawater [Ca2+], CaCO3 saturation, pH, and atmospheric CO2 were more susceptible to perturbations of the global carbon cycle. For example, given both Eocene and Cretaceous seawater [Ca2+] and [Mg2+], a doubling of atmospheric CO2 would require less carbon addition to the ocean/atmosphere system than under modern seawater composition. Moreover, increasing seawater buffering since the Cretaceous may have been a driver of evolution by raising energetic demands of biologically controlled calcification and CO2 concentration mechanisms that aid photosynthesis. ©2015. American Geophysical Union. All Rights Reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/77978
Appears in Collections: 气候变化事实与影响
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作者单位: Ocean and Earth Sciences, University of Southampton, Southampton, United Kingdom; Department of Geosciences, Princeton University, Princeton, NJ, United States; Geologisches Institut, ETH, Zürich, Switzerland
Recommended Citation:
Hain M,P,, Sigman D,et al. The effects of secular calcium and magnesium concentration changes on the thermodynamics of seawater acid/base chemistry: Implications for Eocene and Cretaceous ocean carbon chemistry and buffering[J]. Global Biogeochemical Cycles,2015-01-01,29(5)