In the case of coastal upwelling zones, yes! In the offshore gyres acidification tracks the atmosphere, but this water is then subducted & gets additional carbon from remineralisation, pushing it into CO2 chemistry space where the acidification from that initial CO2 uptake is amplified

Sure! And great work @jfarmersalmanac.bsky.social and @oceanandclimate.bsky.social for the fascinating paper and threads!

Kudos to Maddie for leading this work and many thanks to @willerstorfi.bsky.social @gmacgilchrist.bsky.social @oceanicandrea.bsky.social Casimir de Lavergne & Laurie Menviel for all their help and input, @uniofstandrews.bsky.social for funding Maddie’s PhD, and all of you for reading!

We are psyched about this as the ice ages are cool (sorry!) - but also as figuring out these processes by which the ocean took up 100s of gigatonnes of CO2 from the atmosphere in the past may help us better understand the controls on its capacity for carbon uptake in the future… 📈🌊

This likely acted in concert with other processes (changes in winds, circulation, sea ice, iron) to draw down CO2 during the ice ages.
It can also explain why biogeochemical records from the North Pacific and Southern Ocean share similar structure (Haug & Sigman‘s “polar twins” 👯)

Notably, this is achieved without any change in Southern Ocean upwelling, sea ice or iron supply - it’s simply the result of having less carbon in the upwelled water.

The consequence - shown here - is that less CO2 would be delivered to the Southern Ocean. This by itself reduces Southern Ocean CO2 outgassing by as much as 50%.

In previous papers we and others have shown that these intermediate depth N Pacific waters were better ventilated during glacial periods (e.g. figure here from Rae 2020 and see also Rafter 2022 and Keigwin 1998 among others!) www.science.org/doi/full/10....

Part of the inspiration for this study was an interesting paper by Haidi Chen showing that much of the CO2 outgassed in the Southern Ocean today is sourced from the intermediate depth North Pacific. As these waters are old and CO2 rich they have huge outgassing potential (red colours below).

Nice one John - see also additional notes in thread below: bsky.app/profile/mudw...

More relevant for fossil fuel CO2 are rapid external carbon additions from large igneous provinces and the organic material they often burn up - consistently linked to mass extinction in the geological record www.nature.com/articles/s41...

These sorts of relatively slow reshufflings of carbon around the ocean also aren’t a relevant analogue for very rapid addition of carbon from an external source: in former case saturation state changes are muted, while with FF addition saturation state drops sharply www.science.org/doi/10.1126/...

It’s a pretty basic misrepresentation- they use our paper to suggest ice age ocean was more acidic, but we show this was only true for deep Southern Ocean, while upper ocean (much more relevant for OA-sensitive ecosystems) had higher pH! www.nature.com/articles/s41...

Add me to the list! Rae 2018 misrepresented on page 7: we show deep ocean pH rose out of the ice - but surface ocean pH (the more relevant property for the vast majority of marine life) fell!

Please see thread below on catastrophic impact of geological pH change: bsky.app/profile/mudw...

Finally for anyone needing a boost on climate progress in light of record temperatures and an acidifying ocean, please check out this wonderful article by @billmckibben.bsky.social - the challenge is huge, but so is our progress www.newyorker.com/news/annals-... 🧪💡🔌⚡️☀️