Presentation Information
[P01-043]Ventilated-Driven Variability of Dissolved Oxygen
in North Pacific Central Mode Water
○Tatsuki Ueyama1 (1. Graduate School of Science, Tohoku University (Japan))
Keywords:
North Pacific Central Mode water (CMW),Dissolved oxygen
[Purpose] Mode water plays an important role in transporting physical and biogeochemical signals acquired during ventilation into the ocean interior. North Pacific Central Mode Water (CMW) is formed in the western mid-latitude of the North Pacific, where a deep mixed layer develops in winter and ventilation to great depth. After spring, this ventilated water is subducted into ocean interior as CMW and transported by the subtropical gyre. In this study, we investigate the relationship between CMW volume and dissolved oxygen within the CMW density range.
[Methode] To investigate this relationship, we use observation data, including BGC Argo floats, and Hawaii Ocean Time-series (HOT), as well as a gridded product, Gridded Ocean Biogeochemistry from Artificial Intelligence (GOBAI), which estimates the dissolved oxygen using machine-leaning algorithms. We focus two regions: (1) a large CMW volume is observed, and (2) near the Hawaiian island, which represents a downstream region of CMW.
[Results]In region (1), dissolved oxygen shows significant variability corresponding to variations in CMW volume. In contrast, in region (2), we don't observe interannual variability in dissolved oxygen that corresponds to variations in CMW volume. Nevertheless, long-term decline in both CMW volume and dissolved oxygen are observed.
[Consideration] These results suggest that the formation rate of CMW influences dissolved oxygen concentrations within the CMW distribution region. Furthermore, the results from the vicinity of Hawaii indicate that a reduction in the formation and subsequent transport of ventilated waters as CMW likely contributes to the long-term decline in dissolved oxygen. Particularly, pronounced declining trends in both dissolved oxygen and CMW volume are found in the denser isopycnal class (26.3- 26.4 kg/m3), indicating reduced ventilation of denser CMW. An increase in sea surface temperature (SST) due to global warming has been observed, leading to lower surface density. We suggest that this surface density decrease has reduced the formation of denser CMW, resulting in a decline in well-ventilated water dissolved oxygen within this density layer.
[Conclusion]Decreasing the ventilated water such as CMW might be one of the factor which decreasing dissolved oxygen in the ocean interior.
[Methode] To investigate this relationship, we use observation data, including BGC Argo floats, and Hawaii Ocean Time-series (HOT), as well as a gridded product, Gridded Ocean Biogeochemistry from Artificial Intelligence (GOBAI), which estimates the dissolved oxygen using machine-leaning algorithms. We focus two regions: (1) a large CMW volume is observed, and (2) near the Hawaiian island, which represents a downstream region of CMW.
[Results]In region (1), dissolved oxygen shows significant variability corresponding to variations in CMW volume. In contrast, in region (2), we don't observe interannual variability in dissolved oxygen that corresponds to variations in CMW volume. Nevertheless, long-term decline in both CMW volume and dissolved oxygen are observed.
[Consideration] These results suggest that the formation rate of CMW influences dissolved oxygen concentrations within the CMW distribution region. Furthermore, the results from the vicinity of Hawaii indicate that a reduction in the formation and subsequent transport of ventilated waters as CMW likely contributes to the long-term decline in dissolved oxygen. Particularly, pronounced declining trends in both dissolved oxygen and CMW volume are found in the denser isopycnal class (26.3- 26.4 kg/m3), indicating reduced ventilation of denser CMW. An increase in sea surface temperature (SST) due to global warming has been observed, leading to lower surface density. We suggest that this surface density decrease has reduced the formation of denser CMW, resulting in a decline in well-ventilated water dissolved oxygen within this density layer.
[Conclusion]Decreasing the ventilated water such as CMW might be one of the factor which decreasing dissolved oxygen in the ocean interior.
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