Antarctic Circumpolar Current: How Earth’s most powerful ocean current changed over the past 5.3 million years

Recommendable, but you have to discount the climate change garbage contained in the article!

Fact is we still know so very little about what goes on in our vast oceans not to mention its effects on climate over time! It is actually shocking how little we know about our oceans in the 21st century, it is like terra incognita! This reason alone disqualifies already any Global Warming and Climate Change propaganda and demagoguery!

This study also only scratches in tiny ways the surface of our understanding of oceanology! Anything else is pretense of knowledge!

"The Antarctic Circumpolar Current is the most powerful current system on Earth. It moves 100 times as much water as all the Earth’s rivers combined in a circular current that flows clockwise around Antarctica.

In recent decades the ACC has been speeding up, but scientists have been unsure whether this increase is connected to human-induced global warming.

Now, new research indicates that the ACC slowed down during cold glacial periods in the past and gained speed during warm interglacial times – these speedups also correlate with major losses of Antarctica’s ice.
“The ACC has a major influence on heat distribution and CO2 storage in the ocean,” ..."

"... The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets. An international research team led by the Alfred Wegener Institute and the Lamont-Doherty Earth Observatory have now used sediments taken from the South Pacific to reconstruct the flow speed in the last 5.3 million years. Their data show that during glacial periods, the current slowed; during interglacials, it accelerated. Consequently, if the current global warming intensifies in the future, it could mean that the Southern Ocean stores less CO2 and that more heat reaches Antarctica. The study was just released in the journal Nature. ..."

From the abstract:

"The Antarctic Circumpolar Current (ACC) represents the world’s largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial–interglacial cycles, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling and increasing global ice volume. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO2 during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming."

Earth’s most powerful ocean current changed with the climate

Evolution of the most powerful ocean current on Earth (original press release) Ocean sediment cores reveal climate-related fluctuations in the Antarctic Circumpolar Current in past epochs

Five million years of Antarctic Circumpolar Current strength variability (open access)

Driven by powerful winds, the Antarctic Circumpolar Current swirls clockwise around the southern continent. Hotter colors represent higher velocities; red dots are drill sites.

Fig. 2: ACC strength changes over the past three glacial cycles (records along north–south transects from the SAZ to the AZ and west–east across the EPR in the SAZ) compared with Antarctic ice-core temperature and atmospheric CO2 records.

Fig. 5: Schematic illustrating key atmospheric and oceanic processes influencing million-year trends in ACC strength.