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

summarized by Marcus Thomas Kirchner Sept. 01 2025
mk@nbri.info

This is a preliminary, non–peer-reviewed manuscript submitted for open discussion

NBRI climate research

Exploring, Documenting, and Preserving Northern Biodiversitythern Biodiversity Resea

Current North Pacific Ocean Heat Anomaly (September 2025)

The North Pacific Ocean is currently experiencing one of the most severe marine heatwaves ever recorded.

·         Regional averages (NOAA, Mercator Ocean International) show +2 to +3 °C above normal in broad zones of the mid-latitude Pacific and the Sea of Japan.

·         Local hotspots, as visualized by Nullschool (NOAA OI SST data), exceed +5 °C above normal, particularly off Japan, around Hokkaidō, and in the western Pacific gyre.

This combination of widespread warming and extreme local peaks highlights the extraordinary intensity of the present anomaly.

Impacts:

·         Ecosystems: Deoxygenation, plankton regime shifts, fish mortality, and jellyfish blooms.

·         Weather: Amplified evaporation drives stronger typhoons, senjō kōsuitai (linear rainbands), and prolonged humid heatwaves in East Asia.

·         Teleconnections: Altered jet stream patterns influence weather extremes in North America and Europe.

·         Climate feedbacks: Persistent marine heatwaves point to long-term changes in circulation (Kuroshio Extension, Aleutian Gyre) and amplify global warming through additional water vapor.

Sources and Monitoring:

·         NOAA Marine Heatwave Tracker (California Current & NE Pacific “Blob”): https://www.integratedecosystemassessment.noaa.gov/regions/california-current/california-current-marine-heatwave-tracker-blobtracker

·         NOAA Coral Reef Watch – Global Daily SST Anomaly Maps: https://coralreefwatch.noaa.gov/product/5km/index_5km_ssta.php

NOAA Data Aug. 27 2025 - northern pacific - in some areas more than +5° C anomaly.


 

 

Northern Pacific

Sea Surface Temperature Anomaly SSTA Data 09 Sept. 2025
Source: OI SST V2.1 / PSL / NOAA

 

“Data: NOAA GFS 0.25°, visualization by Cameron Beccario, earth.nullschool.net, accessed 09 Sept 2025.”




Japan and Sakhalin NOAA Data Aug. 27 2025

 



Sea Surface Temperature Anomaly SSTA Data 09 Sept. 2025
Source: OI SST V2.1 / PSL / NOAA

 

Interpreting the Graphic: North Pacific Sea Surface Temperature Anomalies

The image shows sea surface temperature anomalies (SSTA) in the Northwest Pacific, covering Japan, Sakhalin, the Kuril Islands, Kamchatka, and the Aleutian–Alaska region. Data source: NOAA OISST v2.1, visualized on earth.nullschool.net.

Color scale:

·         Yellow / orange / red = warmer than average (+ anomalies, up to > +5 °C).

·         Blue / turquoise = cooler than average (– anomalies).

Streamlines: White lines show surface currents, including swirling eddies.

Key Patterns

1.    Warm hotspot east of Japan

o    Broad yellow–red zones mark +3 to +5 °C anomalies along the Kuroshio Extension.

o    Numerous eddies trap and redistribute warm water, creating localized peaks above +5 °C.

2.    Sharp frontal contrasts

o    South of Hokkaidō and the Kurils, warm Kuroshio waters meet cold Oyashio waters.

o    This explains the striking juxtaposition of warm anomalies (red/yellow) next to cooler patches (blue).

3.    Japan Sea and Sakhalin region

o    Mixed anomalies (warm and cool) reflect strong local dynamics, wind forcing, and exchanges through narrow straits (e.g., Sōya/La Pérouse Strait).

4.    Bering Sea and Gulf of Alaska

o    Large red fields show persistent positive anomalies, reminiscent of past “Blob” events (2013–2016).

Physical Interpretation

·         Heat transport & eddies: The Kuroshio carries large heat volumes eastward; eddies store and recirculate this heat, delaying cooling.

·         Frontal dynamics: The Kuroshio–Oyashio boundary creates sharp thermal gradients, easily shifted by winds and currents.

·         Air–sea coupling: Reduced heat loss to the atmosphere under stable weather patterns allows anomalies to accumulate; localized upwelling produces cooler spots.

 

Key Takeaways

·         Extremely warm surface waters dominate the Northwest Pacific, with regional anomalies of +2 to +3 °C and local hotspots exceeding +5 °C.

·         Frontal zones around Japan, Sakhalin, and the Kurils display strong contrasts, driven by Kuroshio–Oyashio interactions.

·         Such anomalies are not absolute temperatures, but deviations from the climatological mean (1982–2010 baseline).

·         Local peaks vs. averages: While NOAA and Mercator report +2 to +3 °C regional means, this visualization reveals localized extremes above +5 °C.



NOAA Data Aug. 27 2025


 

Sea Surface Temperature Anomaly SSTA Data 09 Sept. 2025
Source: OI SST V2.1 / PSL / NOAA

“Data: NOAA GFS 0.25°, visualization by Cameron Beccario, earth.nullschool.net, accessed 09 Sept 2025.”


 

NOAA Data Aug. 27 2025

 

 

Sea Surface Temperature Anomaly SSTA Data 09 Sept. 2025
Source: OI SST V2.1 / PSL / NOAA



 

This visualizations highlight an extraordinary contrast in global sea surface temperature anomalies (SSTA):

·         Equatorial Pacific (La Niña):
A continuous blue band across the tropical Pacific shows –1 to –2 °C anomalies. This is the clear signature of a La Niña event, driven by stronger trade winds and the upwelling of cold subsurface water.

·         North Pacific Hotspot:
In sharp contrast, the North Pacific (Japan, Bering Sea, Gulf of Alaska) displays vast red and yellow zones, with anomalies reaching +3 to +5 °C. Warm water displaced westward by La Niña accumulates in the western and northern Pacific, fueling unprecedented marine heatwaves.

·         North Atlantic “Cold Blob”:
South of Greenland, cooler-than-average waters signal a weakened Atlantic Meridional Overturning Circulation (AMOC), reducing heat transport into northern Europe.

Why this matters

·         Energy shift: Heat removed from the equatorial Pacific during La Niña is redistributed to the western Pacific and North Pacific mid-latitudes, creating regional hotspots.

·         Atmosphere–ocean feedback: The La Niña cooling plus the North Pacific warming destabilize large-scale circulation (Walker cell, jet stream), driving weather extremes.

·         Regional impacts:

o    East Asia: stronger monsoons, typhoons, and record-breaking heat.

o    North America: altered storm tracks, droughts, and heat domes.

o    Europe: the Atlantic cold anomaly increases the risk of colder winters.

Summary Statement

This images capture a triple anomaly pattern rarely observed:

·         Cold tropics (La Niña)

·         Hot North Pacific (+5 °C hotspots)

·         Cold North Atlantic (AMOC “cold blob”)

Together, these signals indicate that the global ocean–atmosphere system is shifting into an unstable state, with far-reaching impacts on ecosystems, regional climates, and extreme weather.

New Research Spotlight – Atlantic–Pacific Link

A 2025 study by Yamagami et al. (Gulf Stream drives Kuroshio behind the recent abnormal ocean warming) demonstrates that variability in the North Atlantic Gulf Stream region drives ocean warming in the North Pacific Kuroshio Extension.

·         Atlantic → Pacific coupling: Positive SST anomalies in the Gulf Stream trigger a Northern Annular Mode-like circulation, weakening the Aleutian Low. This shifts the Kuroshio Extension northward, enhancing warm water transport and generating positive SST anomalies across the North Pacific.

·         One-way influence: The study found no significant reverse effect from the Kuroshio back to the Gulf Stream.

·         High-resolution models: Climate models with fine ocean resolution reproduce this coupling best, underscoring the role of mesoscale eddies.

These findings identify the North Atlantic as a key pacemaker of mid-latitude climate variability, with direct implications for understanding the current extreme North Pacific marine heatwaves observed in 2025.

Source: Yamagami et al., 2025 – Gulf Stream drives Kuroshio behind the recent abnormal ocean warming






What the graphic shows (NOAA OISST v2.1, 27 August 2025)

·         North Atlantic

o    Strong red/orange anomalies along the U.S. East Coast and Gulf Stream extension → +2 to +4 °C.

o    A persistent “cold blob” south of Greenland (blue patch), again reflecting weakened heat transport by the Atlantic Meridional Overturning Circulation (AMOC).

 

·         Caribbean & Gulf of Mexico

o    Almost uniformly +2 to +3 °C above normal, providing record-high ocean heat content.

o    These waters act as “fuel” for hurricanes → more intense tropical cyclones possible in late 2025 season.

·         South Atlantic (near Brazil, West Africa)

o    Alternating warm and cool anomalies, linked to changes in the Atlantic Niño and cross-equatorial wind stress.

·         Equatorial Pacific & Eastern Pacific

o    Clear blue anomaly band (–1 to –2 °C) along the equator = La Niña signature.

o    Off Peru/Ecuador → cold upwelling intensified, while just north/south of the equator the water remains warmer.

·         Eastern Pacific (off California)

o    Strong positive anomalies, linked to regional upwelling changes and ongoing marine heatwave activity in the Northeast Pacific.

Why this matters

·         Dual Atlantic signal:

o    Warm along U.S. East Coast → stronger hurricane potential.

o    Cold blob south of Greenland → linked to AMOC slowdown, affecting European climate and winter patterns.

·         La Niña + Atlantic warm pool:

o    This combination typically shifts the Walker circulation and jet streams, altering rainfall in South America, Africa, and Asia.

o    Increases likelihood of heavier hurricanes in the Atlantic and drier conditions in parts of South America.

·         Global coupling:

o    The Atlantic anomalies (warm + cold blob) interact with the Pacific (La Niña), producing large-scale atmospheric wave trains that reshape global climate extremes.

In summary:
This map shows how the Atlantic and Pacific anomalies are locked into a coupled pattern:

·         La Niña cooling in the Pacific,

·         North Atlantic cold blob near Greenland,

·         Extreme warm pools in the Gulf of Mexico and along the U.S. East Coast.

Together, these signals strongly influence hurricane activity, monsoon rainfall, and Europe’s upcoming winter climate.





Regional Cold Anomalies – South Atlantic & Northern Australia

In addition to the dramatic warming in the North Pacific, several regions of the global ocean currently show significant cold anomalies:

·         South Atlantic (west of southern Africa):
Cooler-than-average waters (–0.5 to –2 °C) are linked to enhanced Benguela upwelling and the Atlantic Niño pattern. These anomalies influence rainfall across West Africa, with potential impacts on the Sahel rainy season.

·         Northern Australia and the Maritime Continent:
Cold anomalies (–0.5 to –1.5 °C) in the Timor and Arafura Seas reflect the influence of the ongoing La Niña. Stronger trade winds drive warm water westward into the Indonesian seas, while local upwelling cools the northern Australian margins. The result: wetter conditions over Indonesia but a tendency toward drier climate in northern Australia.

Global Context

These cold pools are part of a broader three-pole anomaly pattern:

·         Tropical Pacific: La Niña cooling.

·         North Pacific: Extreme marine heatwaves (+3 to +5 °C).

·         North Atlantic: Persistent “cold blob” south of Greenland.

·         South Atlantic & Northern Australia: Secondary cold anomalies tied to regional upwelling and ENSO dynamics.

Together, these hotspots and cold pools highlight the highly disrupted state of the global ocean–atmosphere system in 2025, with cascading effects on monsoons, storm tracks, and regional climates.




“Data: NOAA GFS 0.25°, visualization by Cameron Beccario, earth.nullschool.net, accessed 09 Sept 2025.”

 

NOAA Data Aug. 27 2025

 

 

 

Sea Surface Temperature Anomaly SSTA Data 09 Sept. 2025
Source: OI SST V2.1 / PSL / NOAA

 

“Data: NOAA GFS 0.25°, visualization by Cameron Beccario, earth.nullschool.net, accessed 09 Sept 2025.”

Arctic marine heatwaves have reached extraordinary levels, with average sea surface temperatures in August 2023 spiking 5–7 °C above normal, and absolute readings surpassing 11 °C in the Barents, Kara, Laptev, and Beaufort Seas—a clear signal of Arctic Amplification driven by sea-ice loss and solar heat uptake. These extremes have moderated somewhat by August 2024 (2–4 °C anomalies), yet long-term warming trends remain significant. This warming not only destabilizes Arctic ecosystems but also disrupts global climate systems through feedbacks into ice cover, ocean heat storage, and atmospheric circulation.

 

Summary

In boreal summer–autumn 2025, the North Pacific maintained a large, persistent marine heatwave (MHW) with moderate to locally severe–extreme categories—including the Sea of Okhotsk and waters adjacent to Japan—against a background of record-high global ocean warmth. At the same time, the subpolar North Atlantic retained a cool anomaly (“cold blob”) embedded within a warm Atlantic. The Siberian Arctic (Kara–Laptev shelf seas) saw exceptionally warm summer conditions, closely tied to low sea-ice cover and strong surface fluxes over newly open water. Recent work by Yamagami et al. (2025) provides a dynamical Atlantic→Pacific teleconnection—from Gulf Stream SSTs via a Northern-Annular-Mode–like atmospheric pattern to a northward-shifted Kuroshio Extension—that helps explain coherent extratropical SST anomalies across the basins in 2025.

Mercator Ocean International data portal: https://www.mercator-ocean.eu

 

 

1) North Pacific and waters around Japan (2025): persistent MHW with Okhotsk intensification

Operational bulletins through late September show the North Pacific (120°W–120°E) MHW “stable in extent and intensity”, with moderate to strong and locally severe categories; in the Sea of Okhotsk, the affected area expanded with severe to extreme pockets. In Japanese marginal seas, typhoon-mixed, short-lived cool pulses did not overturn the positive mean SST anomaly regime. In the longer context, SST around Japan has warmed +1.33 °C per century, roughly twice the global ocean rate, preconditioning the region for frequent, persistent warm seasons and MHWs.

Mercator Ocean International bulletin (20 September 2025): https://www.mercator-ocean.eu/bulletin/marine-heatwave-bulletin-20-september-2025/

 

2) North Atlantic “cold blob” (2025): structure, drivers, and Pacific relevance

Weekly anomaly summaries in July–September 2025 continued to show a subpolar gyre cool pool south of Greenland (typical −2 °C to +3 °C weekly anomalies basin-wide, with negative departures in the cold-blob core), superimposed on otherwise warm North Atlantic backgrounds. Mechanistically, the cold blob reflects heat-transport divergence associated with AMOC variability and subpolar gyre dynamics, partly offset by anomalous ocean heat uptake.

Recent 2025 studies highlight key drivers:

 

3) A 2025 Atlantic→Pacific bridge: Gulf Stream → NAM-like pattern → Kuroshio Extension

Yamagami et al. (2025) demonstrate a causal link from Gulf Stream SST variability to the Kuroshio region in multi-model ensembles: positive Gulf Stream anomalies excite a NAM-like atmospheric pattern, weaken the Aleutian Low, shift the Kuroshio Extension northward, and enhance warm-water advection into the Northwest Pacific. Roughly 16 % of internal SST variance in the Kuroshio sector is explained by internal Gulf Stream variability; the reverse (Pacific→Atlantic) influence is not significant.

Yamagami Y., Tatebe H., Kohyama T., Kido S., Okajima S. (2025). “Gulf Stream drives Kuroshio behind the recent abnormal ocean warming.” arXiv preprint. URL: https://arxiv.org/abs/2503.01117

 

 

4) Siberian Arctic (Kara–Laptev shelf): why local 2-m air-temperature anomalies ≥ +10 °C can occur in summer 2025

Authoritative 2025 diagnostics show very low summer sea-ice along the Eurasian shelf (Kara–Laptev), with Arctic daily extent ranking third lowest at end-July and large areas of open water along the Northern Sea Route. Satellite commentary in mid-July highlighted “frigid air meeting warmer open water” over the Laptev Sea, consistent with strong surface heat fluxes and cloud-street formation. UK Met Office briefings singled out Kara/Laptev as warmest relative to average in July 2025. ERA5 anomaly maps for July show strong positive 2-m air-temperature departures over newly ice-free waters; synoptic analyses in late summer show 925-hPa anomalies of +5 to +7 °C under persistent ridging over the Siberian coast. Over short time/space scales where ridge-induced warm advection passes over newly opened, dark ocean, local 2-m anomalies ≥ +10 °C (and occasionally higher) are physically expected—monthly means are lower but still markedly positive.

 

Sources:

 

 

5) Integrated Perspective

 

 

Conclusion and Outlook

The year 2025 highlights the importance of inter-basin ocean–atmosphere coupling.

 

 

Outlook

 

 

This synthesis underscores that future marine extremes around Japan, the North Atlantic, and the Arctic cannot be treated in isolation. The 2025 event suite demonstrates how regional anomalies are connected through large-scale dynamics, and how climate-driven teleconnections are likely to intensify.