Inter-Basin SST Contrasts during a North Pacific Marine Heatwave: Co-occurring Mid-Latitude Pacific Cooling and North Atlantic Cold Anomaly

This preliminary discussion paper synthesizes global observational datasets and recent 2025 literature to document and interpret simultaneous ocean–atmosphere anomalies across three key regions: a persistent North Pacific marine heatwave affecting waters around Japan and the Sea of Okhotsk, a subpolar North Atlantic cold anomaly (“cold blob”), and exceptional Arctic warming north of Siberia with 2-m air-temperature anomalies locally exceeding +10 °C. Using operational products (NOAA OISST v2.1, Copernicus ERA5, Mercator Ocean International marine-heatwave bulletins, NSIDC Arctic sea-ice analyses) and peer-reviewed studies—including Yamagami et al. 2025, which identifies a Gulf-Stream-to-Kuroshio atmospheric bridge—the paper highlights inter-basin coupling mechanisms that explain the coherence of extratropical SST anomalies observed in 2025. The text includes plain-text references with stable URLs for all datasets and sources to facilitate reproducibility and citation.