Spatio-temporal Distribution Of Ocean Acidification In The Last Two Decades And Its Potential Trends In The Gulf Of Mexico

Ocean acidification is an important negative effect of atmospheric carbon dioxide(CO2)uptake by the oceans,disrupting the fundamental chemical balance of the ocean and ultimately directly affecting the ocean’s ability to absorb carbon.Coastal ocean acidification is characterized by complex and diverse patterns of change due to frequent human and biological activity.The Gulf of Mexico(GOM)is a global coastal area with complex hydrographic conditions,which is significantly disturbed by anthropogenic activities and shows strong spatio-temporal heterogeneity in the parameters of its ocean carbonate system.Therefore,the study of ocean acidification in the GOM as a representative of the complex sea area is important to investigate the carbon cycle and dynamics of the coastal area in the context of global climate change.Ocean acidification can be characterized by a combination of sea surface total alkalinity(TA),which indicates the ability of seawater to neutralize acid,sea surface partial pressure of carbon dioxide(pCO2),which determines the ocean-atmosphere exchange carbon flux,and ocean pH,which is a key indicator to quantify ocean acidification.The purpose of this study is to estimate the spatio-temporal distribution of sea surface TA,sea surface pCO2 and sea surface pH in the GOM by remote sensing method,providing data support for the current status and future trends of coastal ocean acidification investigation.Analyzing spatio-temporal distribution characteristics of carbonate system parameters based on spatio-temporal data;combining environmental impact factors to analyze acidification-related ocean chemistry quantitative control process and drivers of seasonal changes,and comprehensive multi-source data to comprehensively assess the current status of ocean acidification in the GOM and estimate future acidification trends.The main research contents and results of this study are as follows:(1)Sea surface alkalinity estimation and its main influencing factors sea surface salinity(SSS)inversion.From the perspective of improving the accuracy of SSS data and segmentation modeling,a sea surface TA segmentation multiple linear regression model is constructed to estimate the sea surface TA in the GOM based on the correlation between sea surface temperature(SST),SSS and sea surface TA,obtaining meticulous spatial data of 1 km sea surface TA with high spatial resolution to fills the gap of fine sea surface TA spatio-temporal data in the GOM.Analyzing the spatio-temporal heterogeneity of sea surface TA on the basis of meticulous sea surface TA data,analyzing the seasonal variation of sea surface TA and its influence factors based on the seasonal variation of SSS and SST,providing a reference for the analysis of spatio-temporal heterogeneity of sea surface TA.The inversion and estimation models constructed in this study have high accuracy,with R2 of 0.95 and RMSE of 0.17 psu for the SSS inversion model and R2 of 0.66 and RMSE of 21.00 μmol kg-1 for the sea surface TA estimation model.The results of sea surface TA estimation show that the sea surface TA in the GOM shows a gradient distribution increasing from north to south,and the seasonal variation is mainly influenced by evaporation,deep water upwelling,and anaerobic activity,etc.(2)Sea surface pCO2 estimation and its spatio-temporal heterogeneity analysis in the GOM based on partitioning and semi-mechanical ideas.Combining the idea of zoning and semi-mechanism,the Cubist algorithm is used to divide GOM based on the spatial heterogeneity of sea surface pCO2 environmental variables for the first time and estimate sea surface pCO2 by using the measurement data and MODIS remote sensing data.Analyzing the control process of sea surface pCO2 in each region of the GOM and the main environmental variables that indicate the control process of sea surface pCO2,exploring the drivers of seasonal changes of sea surface pCO2 in the GOM based on the heterogeneity of pCO2 influence factors.This study provides a data basis for explaining the seasonal carbon sink in the GOM,a methodological reference for analyzing the mechanism of sea surface pCO2 in each region of the Gulf of Mexico,and an idea for analyzing the drivers of seasonal changes in sea surface pCO2 in the GOM.The results show that the GOM can be divided into six regions based on the heterogeneity of sea surface pCO2 environmental variables,with a circular distribution of estuarine,inner and outer continental shelf and offshore regions,and the control processes of sea surfacepCO2 also differ greatly in each subregion.Seasonal changes of freshwater input,shelf circulation,plant production effects and ocean temperature affect seasonal changes of sea surface pCO2.(3)Assessment of ocean acidification in the GOM in different perspective and its future trends estimation.The study estimates the spatial distribution of ocean pH in the GOM for the last 20 years,quantifies the ocean acidification in the GOM by sea surface pH,and integrates sea surface TA,pCO2 and pH to assess the current state of ocean acidification in different perspective.Combining future ocean and climate factor data to predict the distribution of sea surface acidification in the GOM in 2100 by using a geographically weighted regression model.This study provides a data basis for quantifying sea surface acidification and analyzing the spatial distribution of sea surface acidification,provides a method reference for quantitatively analyzing the response of ocean acidification to climate change in the GOM.The results of the study show that the sea surface pH decreases fluctuate,with large differences in the decreasing trend among regions,and the shelf area shows seasonal cyclical changes.The future sea surface pH acidification is mainly concentrated in the estuary and the southwest semi-enclosed offshore area.This study provides data support for the assessment of the current state of ocean acidification from three aspects:acidification buffering capacity,atmospheric CO2 absorption capacity,and acidification quantification;the application of the zonal estimation method provides methodological reference for the analysis of acidification heterogeneity in complex coastal areas;the study of current state assessment and future trend estimation provides a new perspective for ocean acidification research and lays the research foundation for future ocean acidification research in coastal areas.