Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect t...Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect to calcium carbonate(CaCO_(3))minerals are unfavorable for their dissolution,and mediation strategies are thus required to improve the efficiency of OAE-mCDR.In this study,we conducted laboratory incubation experiments using nearshore surface seawater to examine the dissolution dynamics of natural(Iceland spar)and biogenic(Emiliania huxleyi coccolith)calcite minerals.In the experimental group with added bacteria,total alkalinity(TA)and dissolved inorganic carbon(DIC)concentrations markedly increased over the incubation period,corresponding to a notable decline in pH and dissolved organic carbon concentrations.Moreover,the concentration of dissolved calcium ions increased in the coccolith dissolution experiment.However,in the control group without bacteria,all the parameters were nearly constant or changed only slightly over time in both the Iceland spar and coccolith dissolution experiments.Therefore,microbial mediation clearly enhanced calcite mineral dissolution in oversaturated seawater,which likely occurred in the acidic microenvironments produced by bacterial metabolic activity.Linear regression analyses of the DIC and TA revealed that the relative contribution of CaCO_(3)dissolution to organic matter decomposition was 0.18±0.13 and 0.22±0.01,respectively,in the Iceland spar and coccolith experimental groups.The linear regression slope,defined as the OAE-mCDR efficiency indicating the amount of atmospheric CO_(2)absorbed per unit increase in TA,was 3.53±1.87 and 4.36±0.05 for the two groups.Both values exceed a theoretical value of 0.81 under the incubation seawater conditions,primarily driven by DIC increases from organic matter decomposition in the substrate medium.However,microbe-mineral interactions might also improve OAE performance and capabilities.We propose that microbial mediation plays an important role in promoting carbonate mineral dissolution,even in calcite-oversaturated seawater,and can be incorporated into future mCDR implementation strategies.展开更多
基金The National Natural Science Foundation of China under contract No.42421004.
文摘Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect to calcium carbonate(CaCO_(3))minerals are unfavorable for their dissolution,and mediation strategies are thus required to improve the efficiency of OAE-mCDR.In this study,we conducted laboratory incubation experiments using nearshore surface seawater to examine the dissolution dynamics of natural(Iceland spar)and biogenic(Emiliania huxleyi coccolith)calcite minerals.In the experimental group with added bacteria,total alkalinity(TA)and dissolved inorganic carbon(DIC)concentrations markedly increased over the incubation period,corresponding to a notable decline in pH and dissolved organic carbon concentrations.Moreover,the concentration of dissolved calcium ions increased in the coccolith dissolution experiment.However,in the control group without bacteria,all the parameters were nearly constant or changed only slightly over time in both the Iceland spar and coccolith dissolution experiments.Therefore,microbial mediation clearly enhanced calcite mineral dissolution in oversaturated seawater,which likely occurred in the acidic microenvironments produced by bacterial metabolic activity.Linear regression analyses of the DIC and TA revealed that the relative contribution of CaCO_(3)dissolution to organic matter decomposition was 0.18±0.13 and 0.22±0.01,respectively,in the Iceland spar and coccolith experimental groups.The linear regression slope,defined as the OAE-mCDR efficiency indicating the amount of atmospheric CO_(2)absorbed per unit increase in TA,was 3.53±1.87 and 4.36±0.05 for the two groups.Both values exceed a theoretical value of 0.81 under the incubation seawater conditions,primarily driven by DIC increases from organic matter decomposition in the substrate medium.However,microbe-mineral interactions might also improve OAE performance and capabilities.We propose that microbial mediation plays an important role in promoting carbonate mineral dissolution,even in calcite-oversaturated seawater,and can be incorporated into future mCDR implementation strategies.
