Iron (Fe) is an essential micro-nutrient that regulates marine primary productivity over large areas of the ocean, particularly in high-nutrient, low-chlorophyll regions. The GEOTRACES program has greatly advanced our understanding of basin-scale Fe distributions and the processes controlling them. However, temporal variability in Fe distributions, especially over interannual to decadal timescales, remains poorly constrained. In this study, we compiled the Japanese-GEOTRACES dataset, with our compliant dataset, to examine the key processes controlling Fe distributions and their temporal variability in the subarctic Pacific. Temporal variability was investigated using repeated time-series observations in both the western and eastern subarctic Pacific. In the western basin, full-depth observations were conducted 11 times between 2008 and 2023 at time-series Station K2, located at 47°N, 160°E. In addition, meridional vertical sections of dissolved Fe along 155°E, extending from subarctic to subtropical waters, were obtained in 2008 and 2022 to evaluate basin-scale changes. In the eastern basin, five vertical profile observations were conducted between 1997 and 2025 at Ocean Station Papa, located at 50°N, 145°W. All samples were collected using trace-metal clean techniques, generally following GEOTRACES protocols. Vertical profiles of dissolved Fe and labile particulate Fe were determined using FIA with chemiluminescence detection. The full-depth time-series observations reveal a marked contrast in Fe variability between the western and eastern subarctic Pacific. At Station K2, Fe concentrations show pronounced temporal variability, particularly in the intermediate layer, suggesting variable Fe supply and redistribution associated with intermediate-water circulation and marginal-sea processes. In contrast, relatively stable vertical Fe distributions were observed at Ocean Station Papa in the eastern subarctic Pacific, indicating more persistent background conditions and weaker temporal variability in Fe supply. These results suggest that the western subarctic Pacific is strongly influenced by dynamic Fe transport processes, whereas the eastern basin is characterized by comparatively stable Fe distributions. In this presentation, we discuss the mechanisms responsible for the observed temporal variability and how the variability in Fe supply may influence marine productivity.
 

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