Cooling in the Deep South

Several papers report four decades of Southern Ocean cooling from the early 1980’s till 2020, as posted by NoTricksZone (Pierre Gosselin). This reinforces a general picture of ongoing cooling – not warming – in the Southern Ocean and Antarctica. Here’s the link to this NTZ article:

https://notrickszone.com/2022/06/27/a-significant-and-robust-cooling-trend-in-the-southern-ocean-from-1982-2020-defies-climate-models/

This robust Southern Ocean cooling was reported by Xu et al. this year in 2022, who showed that the Southern Ocean (50°S–70°S) has continued to cool for the last 40 years, with amplitudes ranging from -0.1°C to -0.3°C per decade in different regions:

Click to access 1653459783138717.pdf

Setting this cooling in the longer term context of the whole Holocene, three authors show that the Southern Ocean is currently 1-2 whole degrees C cooler now than at any time over the Holocene interglacial. Here are the three papers:

Shuttleworth et al 2021:

https://www.sciencedirect.com/science/article/abs/pii/S0012821X20305938

Civel-Mazens et al 2021:

https://www.sciencedirect.com/science/article/abs/pii/S0921818121001119

Ghadi et al 2020:

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

Cooling of the Deep South means downwelling supply of more cold bottom water to the world’s deep ocean circulation

As a consequence of this ongoing Southern Ocean cooling, two papers indicate that in the last decade or so, formation of highly saline cold deep water formation around the margin of Antarctica has increased and strengthened. In the long term more cold deep water supply from Antarctica will result in a cooling effect on global climate. Antarctica is the biggest global source of cold saline bottom water which drives the Thermo Haline Circulation.

https://www.nature.com/articles/s41598-020-71290-6

https://www.science.org/doi/10.1126/sciadv.aav2516

Antarctic bottom water (AABW) is one of the major deep water compartments of the global oceans. In the last half century or so the supply of AABW from its source in Antarctica had been observed to decline; however Alessandro Salvini et al 2020 reported in Nature Geosciences that this decline has reversed. Now the supply of AABW from the Ross Sea is increasing:

https://www.nature.com/articles/s41561-020-00655-3

The same observation was made in the Weddell Sea by Kerr et al. 2018. In that Antarctic Sea the supply of bottom water (Weddell Sea Bottom Water, WSBW) also turned around from decline to increase, around 2005:

https://www.sciencedirect.com/science/article/abs/pii/S0967064517301261

Thus several lines of evidence point to strengthening supply of deep cold water from Antarctica, to the global ocean circulation. Which might put a crimp in global warming – eventually.