Oceanic dissolved oxygen(DO)in the ocean has an indispensable role on supporting biological respiration,maintaining ecological balance and promoting nutrient cycling.According to existing research,the total DO has dec...Oceanic dissolved oxygen(DO)in the ocean has an indispensable role on supporting biological respiration,maintaining ecological balance and promoting nutrient cycling.According to existing research,the total DO has declined by 2%of the total over the past 50 a,and the tropical Pacific Ocean occupied the largest oxygen minimum zone(OMZ)areas.However,the sparse observation data is limited to understanding the dynamic variation and trend of ocean using traditional interpolation methods.In this study,we applied different machine learning algorithms to fit regression models between measured DO,ocean reanalysis physical variables,and spatiotemporal variables.We demonstrate that extreme gradient boosting(XGBoost)model has the best performance,hereby reconstructing a four-dimensional DO dataset of the tropical Pacific Ocean from 1920 to 2023.The results reveal that XGBoost significantly improves the reconstruction performance in the tropical Pacific Ocean,with a 35.3%reduction in root mean-squared error and a 39.5%decrease in mean absolute error.Additionally,we compare the results with three Coupled Model Intercomparison Project Phase 6(CMIP6)models data to confirm the high accuracy of the 4-dimensional reconstruction.Overall,the OMZ mainly dominates the eastern tropical Pacific Ocean,with a slow expansion.This study used XGBoost to efficiently reconstructing 4-dimensional DO enhancing the understanding of the hypoxic expansion in the tropical Pacific Ocean and we foresee that this approach would be extended to reconstruct more ocean elements.展开更多
We investigated dissolved iodine species in seawater from the northern South China Sea Shelf.Iodide concentrations were determined by cathodic stripping square wave voltammetry,and iodate was measured by spectrophotom...We investigated dissolved iodine species in seawater from the northern South China Sea Shelf.Iodide concentrations were determined by cathodic stripping square wave voltammetry,and iodate was measured by spectrophotometry.Dissolved organic iodine(DOI)was measured with reference to reduced iodide.R-TDI(R-X or rationalized-X is the concentration of X normalized to a salinity of 35,TDI represents total dissolved iodine)was in the range of 0.43–0.46μmol/L,showing a relatively conservative behavior,while iodate,iodide,and DOI showed non-conservative behaviors.Distribution characteristics in the surface waters showed R-iodate values in the 0.28–0.32μmol/L range and an offshore>inshore trend,while R-iodide was in the 0.11–0.19μmol/L range and R-DOI in the 0–0.07μmol/L range,reflecting an inshore>offshore trend for both.The vertical distribution showed the highest R-iodide concentrations in the surface waters and decreased values with depth,reaching less than0.01μmol/L at depths>200 m.R-iodate increased with depth with a measured peak value of 0.43μmol/L.Seawater with high iodate/iodide ratio(up to 2.9)was found in the central upwelling region and gradually decreased to 2.0 far from this center.The relationship between R-iodide and R-iodate among all samples followed the 1:1 relationship with a slope slightly less than 1,indicating that the conversion between iodate and iodide species could not account for the observed changes.This finding also suggests that DOI may be an important participant in the mass balance.A box model was applied to calculate the input and output of iodine species,and the result showed that approximately 8%of iodate(1.50×10~8 mol/a)imported to the shelf sea was reduced.Concomitantly,the amount of iodide and DOI produced in the shelf amounted to 1.07×10~8 mol/a,roughly 14%higher than the input iodide.展开更多
基金The National Natural Science Foundation of China under contract Nos T2421002, 623B2071,and 42125601the National Key R&D Program of China under contract No. 2023YFF0805300
文摘Oceanic dissolved oxygen(DO)in the ocean has an indispensable role on supporting biological respiration,maintaining ecological balance and promoting nutrient cycling.According to existing research,the total DO has declined by 2%of the total over the past 50 a,and the tropical Pacific Ocean occupied the largest oxygen minimum zone(OMZ)areas.However,the sparse observation data is limited to understanding the dynamic variation and trend of ocean using traditional interpolation methods.In this study,we applied different machine learning algorithms to fit regression models between measured DO,ocean reanalysis physical variables,and spatiotemporal variables.We demonstrate that extreme gradient boosting(XGBoost)model has the best performance,hereby reconstructing a four-dimensional DO dataset of the tropical Pacific Ocean from 1920 to 2023.The results reveal that XGBoost significantly improves the reconstruction performance in the tropical Pacific Ocean,with a 35.3%reduction in root mean-squared error and a 39.5%decrease in mean absolute error.Additionally,we compare the results with three Coupled Model Intercomparison Project Phase 6(CMIP6)models data to confirm the high accuracy of the 4-dimensional reconstruction.Overall,the OMZ mainly dominates the eastern tropical Pacific Ocean,with a slow expansion.This study used XGBoost to efficiently reconstructing 4-dimensional DO enhancing the understanding of the hypoxic expansion in the tropical Pacific Ocean and we foresee that this approach would be extended to reconstruct more ocean elements.
基金The Zhangzhou National Science Foundation of Fujian under contract No.JJ2020J29。
文摘We investigated dissolved iodine species in seawater from the northern South China Sea Shelf.Iodide concentrations were determined by cathodic stripping square wave voltammetry,and iodate was measured by spectrophotometry.Dissolved organic iodine(DOI)was measured with reference to reduced iodide.R-TDI(R-X or rationalized-X is the concentration of X normalized to a salinity of 35,TDI represents total dissolved iodine)was in the range of 0.43–0.46μmol/L,showing a relatively conservative behavior,while iodate,iodide,and DOI showed non-conservative behaviors.Distribution characteristics in the surface waters showed R-iodate values in the 0.28–0.32μmol/L range and an offshore>inshore trend,while R-iodide was in the 0.11–0.19μmol/L range and R-DOI in the 0–0.07μmol/L range,reflecting an inshore>offshore trend for both.The vertical distribution showed the highest R-iodide concentrations in the surface waters and decreased values with depth,reaching less than0.01μmol/L at depths>200 m.R-iodate increased with depth with a measured peak value of 0.43μmol/L.Seawater with high iodate/iodide ratio(up to 2.9)was found in the central upwelling region and gradually decreased to 2.0 far from this center.The relationship between R-iodide and R-iodate among all samples followed the 1:1 relationship with a slope slightly less than 1,indicating that the conversion between iodate and iodide species could not account for the observed changes.This finding also suggests that DOI may be an important participant in the mass balance.A box model was applied to calculate the input and output of iodine species,and the result showed that approximately 8%of iodate(1.50×10~8 mol/a)imported to the shelf sea was reduced.Concomitantly,the amount of iodide and DOI produced in the shelf amounted to 1.07×10~8 mol/a,roughly 14%higher than the input iodide.
