Major reversal in ocean circulation detected in the Southern Ocean

The article says that deep water is warmer, afaik deep water is colder and surface water is hotter (https://en.wikipedia.org/wiki/Upwelling)?

A 2023 study https://www.sciencedaily.com/releases/2023/03/230330102327.h... observed slowdown in Antarctic overturning, in which cold water sinks down at the south pole and then spreads north in the deeper parts of the ocean.

The slowing of this process would cause deep ocean water to become warmer.

edit: the publication linked in the article https://www.pnas.org/doi/epub/10.1073/pnas.2500440122 makes this a bit clearer:

"In the polar Southern Ocean, cold, fresh surface waters overlay warmer, saltier deep waters (Fig. 2A). During winter, surface cooling and sea ice formation reduce stratification, allowing vertical mixing to transport heat upward, either melting sea ice from below or limiting its growth (8). However, decades of surface freshening strengthened stratification, trapping subsurface heat at depth, sustaining expanded sea ice coverage (7, 9) and limiting deep convection along with open-ocean polynyas (10). Here, we show that since 2015, these conditions have reversed: Surface salinity in the polar Southern Ocean has increased, upper-ocean stratification has weakened, sea ice has reached multiple record lows, and open-ocean polynyas have reemerged."

Also this link explains the warmer deep water:

https://en.m.wikipedia.org/wiki/Circumpolar_deep_water

In general at high enough depth the ocean temperature is constant[0]. At high latitude like the southern ocean it's constant at whatever depth. I think the surface ambient temperature is below(cooler) the temperature where the water density is the highest around 4 degrees for pure water(water has negative thermal expansion which causes it to expand and float!), for southern ocean salinity is between 33-34 and maximum density is below 0[1] but still ambient might be lower which means the colder water is lighter.

https://en.wikipedia.org/wiki/File:ThermoclineSeasonDepth.pn...

https://en.wikipedia.org/wiki/File:T-S_diagram.pdf

That trapped warmth doesn't mean the deep water is "hot" in an absolute sense, just that it's saltier and denser and relatively warmer than the surface

I’m reminded of how small changes in temperature can greatly effect the metabolism of things like crabs: https://www.globalseafood.org/advocate/noaa-confirms-link-be...