March 31st, 2026

---

Key Findings

• Sea surface temperature variations in the Gulf Stream (GS) and Kuroshio–Oyashio Extension (KOE) regions vary together, with the strongest relationship occurring during boreal summer.
• Representing a unified mid-latitude climate mode across the North Atlantic and North Pacific, the summertime linkage between the GS and KOE has strengthened in the historical record.
• A high-resolution configuration of GFDL’s SPEAR climate model reproduces the observed seasonal characteristics of the GS-KOE relationship.
• Model results reveal that earlier changes in Arctic sea ice influence the GS–KOE relationship, suggesting that the summertime GS–KOE linkage may evolve in a changing climate.

---

Youngji Joh, Sang-Wook Yeh, Thomas L. Delworth, Zachary M. Labe, Andrew T. Wittenberg, William F. Cooke, Jiale Lou, and Young-Gyu Park. Science Advances DOI: 10.1126/sciadv.adx6366

The Gulf Stream in the North Atlantic and the Kuroshio–Oyashio Extension in the North Pacific are western boundary current systems that transport heat and shape regional ocean conditions. Variations in sea surface temperature in these regions can interact with atmospheric circulation and affect climate variability across the Northern Hemisphere.

The authors examine observations and climate model simulations to investigate how variability in these two ocean regions is connected. The analysis shows that sea surface temperatures in the Gulf Stream and Kuroshio–Oyashio Extension vary together, with the strongest relationship occurring during boreal summer. The strength of their observed relationship has increased over time, indicating a growing synchronization between the two regions.

Simulations using a high-resolution configuration of GFDL’s Seamless System for Prediction and EArth System Research (SPEAR) climate model reproduce the observed synchronization and its seasonal characteristics. The model experiments indicate that earlier changes in Arctic Sea ice may influence the development of this connection through changes in large-scale climate circulations affecting both ocean basins.

The results describe a connection between two mid-latitude ocean regions and their evolving relationship in a changing climate. The study also illustrates how interbasin interactions among the ocean, atmosphere, and sea ice contribute to climate variability across the Northern Hemisphere.

Spatiotemporal evolution of summertime synchronization between the Gulf Stream and Kuroshio-Oyashio ExtensionTop: Sea surface temperature (SST) anomalies regressed onto the time series of summertime synchronization between the Gulf Stream (GS) and the Kuroshio–Oyashio Extension (KOE).
Bottom: Temporal evolution of seasonal GS–KOE synchronization calculated as a 30-year running correlation between GS and KOE SST indices using ERA5 reanalysis. Linear warming trends are removed to isolate internal variability.