DataSheet_1_Reconstruction of the marine carbonate system at the Western Tropical Atlantic: trends and variabilities from 20 years of the PIRATA program.csv

The Western Tropical Atlantic Ocean (WTAO) is crucial for understanding CO2 dynamics due to inputs from major rivers (Amazon and Orinoco), substantial rainfall from the Intertropical Convergence Zone (ITCZ), and CO2-rich waters from equatorial upwelling. This study, spanning 1998 to 2018, utilized sea surface temperature (SST) and sea surface salinity (SSS) data from the PIRATA buoy at 8°N 38°W to reconstruct the surface marine carbonate system. Empirical models derived total alkalinity (TA) and dissolved inorganic carbon (DIC) from SSS, with subsequent estimation of pH and fCO2 from TA, DIC, SSS, and SST data. Linear trend analysis showed statistically significant temporal trends: DIC and fCO2 increased at a rate of 0.7 µmol kg-1 year-1 and 1.539 µatm year-1, respectively, and pH decreased at a rate of -0.001 pH units year-1, although DIC did not show any trend after data was de-seasoned. Rainfall analysis revealed distinct dry (July to December) and wet (January to June) seasons, aligning with lower and higher freshwater influence on the ocean surface, respectively. TA, DIC, and pH correlated positively with SSS, exhibiting higher values during the dry season and lower values during the wet season. Conversely, fCO2 correlated positively with SST, showcasing higher values during the wet season and lower values during the dry season. This emphasizes the influential roles of SSS and SST variability in CO2 solubility within the region. Finally, we have analysed the difference between TA and DIC (TA-DIC) as an indicator for ocean acidification and found a decreasing trend of -0.93 ± 0.02 μmol kg-1 year-1, reinforcing the reduction in the surface ocean buffering capacity in this area. All trends found for the region agree with data from other stations in the tropical and subtropical Atlantic Ocean. In conclusion, the use of empirical models proposed in this study has proven to help filling the gaps in marine carbonate system data in the Western Tropical Atlantic.

西热带大西洋（Western Tropical Atlantic Ocean, WTAO）因受亚马逊河、奥里诺科河等大型河流的物质输入，热带辐合带（Intertropical Convergence Zone, ITCZ）带来的强降雨，以及赤道上升流（equatorial upwelling）输送的富二氧化碳水体影响，成为研究二氧化碳动态（CO2 dynamics）的关键区域。本研究覆盖1998年至2018年，利用位于8°N 38°W的PIRATA浮标（PIRATA buoy）获取的海表温度（sea surface temperature, SST）与海表盐度（sea surface salinity, SSS）数据，重建了该区域的海洋表层碳酸盐系统（surface marine carbonate system）。研究通过经验模型（empirical models）从海表盐度反演得到总碱度（total alkalinity, TA）与溶解无机碳（dissolved inorganic carbon, DIC），随后结合总碱度、溶解无机碳、海表盐度与海表温度数据，进一步估算得到pH与二氧化碳分压（fCO2）。线性趋势分析（linear trend analysis）结果显示存在统计显著的时间变化趋势：溶解无机碳与二氧化碳分压分别以0.7 μmol·kg⁻¹·year⁻¹与1.539 μatm·year⁻¹的速率上升，pH则以-0.001 pH单位·year⁻¹的速率下降；不过在对数据进行去季节化处理（de-seasoned）后，溶解无机碳未呈现显著趋势。降雨分析揭示了该区域分明的旱季（7月至12月）与雨季（1月至6月），分别对应海洋表层受到的淡水影响（freshwater influence）较弱与较强的时期。总碱度、溶解无机碳与pH均与海表盐度呈正相关，在旱季数值更高，雨季则更低。与之相反，二氧化碳分压与海表温度呈正相关，在雨季数值更高，旱季更低，这凸显了海表盐度与海表温度的变化对该区域二氧化碳溶解度（CO2 solubility）的关键调控作用。此外，本研究以总碱度与溶解无机碳的差值（TA-DIC）作为海洋酸化（ocean acidification）的指示指标，分析发现其以-0.93 ± 0.02 μmol·kg⁻¹·year⁻¹的速率呈下降趋势，进一步证实了该区域表层海洋缓冲能力（buffering capacity）的减弱。本研究得到的该区域变化趋势，与热带及亚热带大西洋（subtropical Atlantic Ocean）其他观测站的监测数据一致。综上，本研究提出的经验模型有效填补了西热带大西洋海洋碳酸盐系统数据的空白。