Widespread signals of Southern Hemisphere ocean cooling (and AMOC heat piracy)

In the background behind the ongoing drumbeat of global warming doom, evidence is accumulating of Southern Hemisphere ocean cooling centered, of course, on Antarctica. The frigid Antarctica is hugely important in the global ocean system and dominates climate, leading glaciation and deglaciation transitions for instance. Think of it as the “Grand Central Station” of the global ocean circulation system – what is technically called the THC – thermohaline circulation.

Southern Oceans in general

“Much of the Southern Ocean surface south of 55° S cooled and freshened between at least the early 1980s and the early 2010s.”

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019AV000132

Zhang and Deser 2019 also demonstrate southern ocean cooling, most pronounced in the Pacific Ocean sector:

https://ui.adsabs.harvard.edu/abs/2019AGUFM.A43N3089Z/abstract

Humboldt current is cooling

Salvacetti et al 2018 showed from historic proxy measurements of ocean temperatures that the Humboldt current (running from Antarctica north up the coasts of Chile and Peru) is now at its coldest in the entire Holocene, having sharply cooled in the last century:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080634

Antarctic cold downwelling

Much has been said about warm water flow to Antarctica from the surrounding Southern Ocean. However this study shows that this warm inflow is drawn poleward in response to downwelling flows of super-cold Antarctica deep water, down the ocean floor canyons around Antarctica and northward to the general ocean circulation. Multi-layer circulation is happening driven apparently be deep water spread of cold water from Antarctica:

https://advances.sciencemag.org/content/6/18/eaav2516.full

Antarctica cooling 0.02 C/yr for 40+ years

Now a new study by Hsu et al 2021 finds Eastern Antarctica to have been cooling at 0.02 C per year since 1979. 

https://advances.sciencemag.org/content/7/26/eabf9903.full

That’s approaching half a century.

Antarctica is leading the world into glacial inception.

Chilean coast cold upwelling

Off the coast of Chile, a recent increase of upwelling and resultant cooling has been reported in 2017:

https://www.sciencedirect.com/science/article/pii/S0079661116300325

South African costal upwelling-cooling

The same is happening off South Africa:

https://www.tandfonline.com/doi/abs/10.2989/1814232X.2019.1656105

Southern Indian Ocean

Ghadi et al 2016 find the Southern deep Indian Ocean to be 2 degrees C colder than at the early warm part of the Holocene – showing a temperature more usual for glacial than for interglacial conditions:

https://www.sciencedirect.com/science/article/abs/pii/S0377839819301380

AMOC slowing

And to round off – pronounced North Atlantic cooling is now being observed, as a predictable result of weakening of the AMOC (Atlantic Meridional Overturning Circulation) and associated decrease in warm water transport from equator to Arctic in the Atlantic:

https://journals.ametsoc.org/jcli/article/33/5/1677/347129/Reduction-in-Ocean-Heat-Transport-at-26-N-since

Live-link between NH and SH via North Atlantic Deep Water

Thomas Crowley in 1992 showed a direct connection between North Atlantic Deep Water (NADW) formation and Southern Hemisphere temperatures. NADW formation by cold downwelling around the Norwegian Sea in the far north Atlantic, is the downward and southward arm of the AMOC (Atlantic Meridional Overturning Circulation). The Atlantic ocean, practically from pole to pole, is “meridionally bounded”, that is, it is walled in to the east and west by the continents of Africa, Eurasia and South and North America. This constrains the 3D deep ocean circulation, such that if water flows in either north or south at one depth, then it must flow in the opposite direction at another depth, to conserve volume and prevent the ocean bunching up in a way contrary to gravity. As Crowley explained:

“In order to conserve volume, southward export of NADW across the equator is accompanied by import of an equivalent volume of considerably warmer water from shallower oceanic layers in the South Atlantic. The southern hemisphere loses heat as a result of this exchange. The hemispherically averaged net heat loss may be as high as 4 W/m² …”

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/92PA01058

This siphoning of warm tropical surface Atlantic water from the Sh to the NH has a name – it’s called “heat piracy”! Seriously! And what’s even better – it happens in the vicinity of the Caribbean, via the Caribbean current. This Piracy in the Caribbean is responsible for the teleconnection of oceanographic changes in Antarctica and the Arctic.

Crowley also pointed out what many others have, that big changes in glaciation globally, such as glacial inception and termination, are initiated and led from Antarctica, where the respective cooling and warming start first, thousands of years before manifesting elsewhere. To quote Crowley again:

“It is suggested that this more comprehensive view of the role of NADW may explain both decadal‐scale variations in South Atlantic sea surface temperatures in this century and two significant problems in Pleistocene climatology: why southern hemisphere temperatures decreased before CO₂ levels decreased at the end of the last interglacial and why southern hemisphere temperature changes precede changes in northern hemisphere ice volume. It is shown that when NADW production was reinitiated during the last interglacial (120,000 B.P.), high‐latitude southern hemisphere temperatures decreased. The estimated magnitude of altered southern hemisphere heat export is comparable to the ice‐age CO₂ signal and may be able to account for the observed cooling even when CO₂ levels were high. When cast into a frequency domain framework, this interpretation may also help explain why southern hemisphere temperatures lead global ice volume changes.”

Cyclones are cooling the tropics

Tropical cyclones (otherwise known as hurricanes or typhoons depending on location) are claimed to be examples of extreme weather caused by the only thing that causes anything in climate – CO2. (Despite the fact that a warmer world has less equator-pole temperature gradient and thus less – not more – thermodynamic potential energy but never mind that for now.) However another overlooked fact is that tropical cyclones cool the ocean surface due to the vertical mixing they induce. Cold deep water is brought to the surface. This mixing also fertilises the sea surface with upwelled nutrients, increasing plankton primary production. First year oceanography.

This new paper shows that in the last three decades, increasing tropical cyclones have (a) cooled the tropical sea surface by 0.05 C per decade and (b) increased surface concentration of chlorophyll a by 3.7 e-3 mg/m2/decade.

Looks like a negative feedback to me. As a result tropical SST is falling not rising and plankton primary production is rising not falling.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021GL092574

Southern Indian and Pacific oceans turn from warming to cooling

Another recent study revisits two ocean sites where surface warming was prominent during 2003-2013, namely, the southeast Indian Ocean and southern Pacific Ocean. During 2013-2019 this warming has reversed to cooling:

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090889

It’s looking increasingly like the recent warming phenomenon is a north hemisphere thing, driven largely by interhemispheric heat piracy occurring in the Atlantic, connected with the AMOC. But even that is weakening now.