"No ACC slowdown has actually been observed yet in the real world, but the study shows a concerning trend."
The paper this article is about is actually from March https://news.mongabay.com/short-article/2025/04/melting-antarctic-ice-could-weaken-worlds-strongest-ocean-current-study-warns/
A prose summary by the authors: https://theconversation.com/melting-antarctic-ice-will-slow-the-worlds-strongest-ocean-current-and-the-global-consequences-are-profound-251053
paper https://iopscience.iop.org/article/10.1088/1748-9326/adb31c
ACC = Antarctic circumpolar current. It races around the continent, mixes warm surface water with deeper cold water , hides our CO2 in the process, is also a driver in the AMOC.
So, reading that sentence, I misunderstood it to mean that it never slowed in #paleoclimate either. But if it is in part salinity-driven and if meltwater influx slows it down as the authors found in their super-high-resolution model, then surely it did happen in the past, as well.
And in a past from when ~reliable proxies would exist, if one knows what to look for, of course.
If the ACC didn't slow down during the last 1mio years, okay. Maybe, salinity and cold temperature stayed suitable then.
But from #sealevel reconstructions like Miller et al 2020, it is known that Antarctica shed and regrew a lot of ice when temperatures were higher than in the last 1mio years.
And 15mio years ago, the continent was ice free for the last time. Between then and 3mio years ago, lotsa melt & regrowth occurred, meaning lotsa periods with a potentially slow ACC in salty but too-warm waters.
What to look for tho? What else does occur and leave a footprint when ACC slows?
Ah! The mixing between ocean basins is slowed or paused.
A temperature spike in the Indian #ocean for example takes longer to propagate into the Pacific, longer than a comparable spike takes in a ACC at full-speed. Maybe a stupid example because such a spike would be too short... something else then...
ah! The Southern Annular Mode would change with a slow ACC, I bet. Maybe going from annual changes to decadal changes or such like.
And the SAM should be detectable in lake sediment in Australia. Maybe even sediment from that dry salt lake North of Adelaide that gets flooded every 50yrs or so . Maybe, with a slow ACC, that salt lake is flooded permanently - or never.
Cool.
Did researchers drill a 3-15mio year sediment core in an Australian lake?
La 
