Assessing the impact of landwater on the Northwest Pacific using normalized Total Alkalinity

Abstract. The impact of landwater was assessed using salinity-normalized Total Alkalinity observations. The observational data included surface carbonate parameters from decades of surveys conducted by volunteer cargo ships and research vessels in the Northwest Pacific. Statistical processes, such as re-gridding and Fourier regression, used in a previous study were also applied in this study to improve the spatiotemporal resolution. First, the seawater area affected by landwater was identified using an Empirical Orthogonal Function analysis of normalized Total Alkalinity. The differences in normalized Total Alkalinity and Dissolved Inorganic Carbon from the surrounding area were then analysed to evaluate the causes such as landwater supply, advection effects, and biological activities. In addition, the impact of landwater on oceanic CO₂ uptake and acidification in the study area was assessed. The analysis showed that landwater was the main source of total coastal Alkalinity but was not the dominant cause of Dissolved Inorganic Carbon. The supply of landwater had little effect on oceanic CO₂ uptake throughout the year. The supply of by landwater was a factor in coastal acidification; however, the supplied Total Alkalinity reduced the overall acidification trend by 65 %. The results of this study are expected to be further improved by enhancing observations, such as the vertical profiles of carbonate parameters, and are expected to expand to other sea areas and be applied to global budgets.