Ordovician mass extinction second wave - deep sea anoxia

[jim mcnamara]

https://www.nature.com/articles/s41561-021-00843-9
Popular science version:
https://scitechdaily.com/uncovering...s-behind-Earth's-first-major-mass-extinction/

Nature paper discusses causes of the second "wave" of mass extinction at the end of the Ordovician (~445mya)
Really cool aspect - the page has a link to the code, data sets, and support files. Yes!
Models using sediment data show, using iodine as an oxygen proxy:
Shallow warmer waters seem to have stayed at then current oxygen levels, but models show that ocean currents apparently changed. This caused deep sea deposits to show anoxic conditions in sediments formed deep in ocean basins. Which would kill off eucaryotic organisms.

The term vertical decoupling refers to lost flow from shallow waters into deeper waters. The Earth's modern global conveyor belt currents have vertical coupling:
https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-currents (lots of pictures for tl;dr folks).
There are also links for primary and secondary schools - see "Adopt a drifter program"

Thermohaline circulation drives the "global conveyor belt". This moves warmer surface water with oxygen down into lower depths.
The main claim in the paper is that the movement of oxygenated water into the depths turned off.
Conveyor Belt details:
https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html

 

[jim mcnamara]

RE: iodine as a proxy for oxygen levels -
The best I can find is an abstract behind a paywall which is slightly helpful:
https://www.sciencedirect.com/science/article/abs/pii/S0009254117301419

 

[jim mcnamara]

Another better graphic on iodine:
https://www.bing.com/images/search?...0F1D157&selectedIndex=2&ajaxhist=0&ajaxserp=0