A paper analyzing changes in Ocean Heat Content (OHC) since 2000 was published at University of Auckland, summarized here:  Unexpected ocean heat patterns show NZ in extreme zone.  Excerpts in italics with my bolds and added images.

The world’s oceans are heating faster in two bands stretching around the globe and New Zealand is in one of them, according to new research led by climate scientist Dr Kevin Trenberth.

In both hemispheres, the areas are near 40 degrees latitude. The first band at 40 to 45 degrees south is heating at the world’s fastest pace, with the effect especially pronounced around New Zealand, Tasmania, and Atlantic waters east of Argentina.  The second band is around 40 degrees north, with the biggest effects in waters east of the United States in the North Atlantic and east of Japan in the North Pacific.

“This is very striking,” says Trenberth, of the University of Auckland and the National Center of Atmospheric Research (NCAR) in Boulder, Colorado. “It’s unusual to discover such a distinctive pattern jumping out from climate data,” he says. “What is unusual is the absence of warming in the subtropics, near 20 degrees latitude, in both hemispheres.”

The heat bands have developed since 2005 in tandem with poleward shifts in the jet stream, the powerful winds above the Earth’s surface that blow from west to east, and corresponding shifts in ocean currents, according to Trenberth and his co-authors in the Journal of Climate.

Besides the two key zones, sizeable increases in heat took place in the area from 10 degrees north to 20 degrees south, which includes much of the tropics. However, the effect was less distinct because of variations caused by the El Niño-Southern Oscillation climate pattern, Trenberth says.

The scientists processed an “unprecedented” volume of atmospheric and ocean data to assess 1 degree latitude strips of ocean to a depth of 2000m for the period from 2000 to 2023, Trenberth says. Changes in heat content, measured in zettajoules, were compared with a 2000-04 baseline.

The AMS paper is Distinctive Pattern of Global Warming in Ocean Heat Content by Trenberth et al (2025). Excerpts in italics with my bolds and added images.

The focus of this paper is from 2000 through 2023, as 2000 is when reliable TOA radiation data became available. Accordingly, the OHC for the 0–2000-m depth is shown not only for the global mean but also as spatial trends over the 2000–23 period (Fig. 1); see methods in section 2. The global values from 1980 show increased confidence after 2005 or so, when Argo data became available globally (Cheng et al. 2017, 2024b). The spatial patterns of trends are of considerable interest because, although the ocean is warming nearly everywhere, by far the greatest increases are in the midlatitudes: in western boundary currents east of Japan in the Kuroshio Extension region of the Pacific and in the Gulf Stream extension in the Atlantic, and nearly everywhere from 35° to 50°S in the Southern Hemisphere (SH). Wu et al. (2012) earlier noted that the warming rate in subtropical western boundary currents in all ocean basins far exceeds the globally averaged surface ocean warming rate. Of particular interest is why the midlatitudes are warming the most.

Conclusions

Heating in the climate system from 2000 to 2023 is most clearly manifested in zonal mean OHC for 0–2000-m depth. It occurs primarily in the top 300 m and is evident in SSTs. The SST changes emphasize surface warming in the NH, but the strongest energy increases are in the SH, where ocean area and volume are greater. In the NH, heating occurs at all latitudes in the Atlantic with some modulation and slightly reduced MHT from the south, but in the North Pacific, strong warming near 40°N is countered by cooling near 20°N. The zonal mean across all oceans is more robust than a focus on any particular ocean basin.

Estimates of TOA radiation, atmospheric energy transports, surface fluxes of energy, and redistribution of energy by surface winds and ocean currents reveal that the patterns of OHC warming are mostly caused by systematic changes in the atmospheric circulation, which alters ocean currents. The coupled atmospheric changes have resulted in a striking pattern of changes in the vertically integrated atmospheric energy divergence which is strongly reflected in surface wind stress and anomalous net surface heat fluxes into and out of the ocean.

In response to the wind changes, the ocean redistributes heat meridionally, especially in western boundary currents in the NH. Hence, the patterns are not directly related to TOA radiation imbalances but arise primarily from coupled atmosphere–ocean changes. In turn, those influence storms and cloudiness, and thus TOA radiation. Changes in atmospheric aerosols and associated clouds may have played a role in the North Pacific and North Atlantic, likely in amplifying SST anomalies, although, because land is warming a lot more than the oceans, advection of warmer air from continents over the northern oceans may also be in play.

In the NH, changes are associated with the western boundary currents, but the associated atmospheric changes require analysis of more than a zonal mean framework, as continents play a major role. Nonetheless, it is clear that the atmosphere and ocean currents are systematically redistributing heat from global warming, profoundly affecting local climates.

My Comment:

The final sentence read literally refers to heat released by oceanic activity under the influence of solar radiation and atmospheric circulations such as jet streams.  However, the term “global warming” can taken by some to mean planetary higher temperatures due to humans burning hydrocarbons.  The leap of faith to attribute human agency to natural processes serves an agenda against society’s traditional energy platform.

Further, the graph showing zettajoules can be misleading.  Ocean heat graphs labelled in Zettajoules make it look scary, but the actual temperature changes involved are microscopic, and impossible to measure to such accuracy in pre-ARGO days.

Since 2004, for instance, ARGO data shows an increase of about two hundredths of a degree.