Ordovician mass extinction second wave - deep sea anoxia

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The discussion centers on a Nature paper that explores the causes of the second wave of mass extinction at the end of the Ordovician period, approximately 445 million years ago. The research highlights the role of ocean currents and sediment data, specifically using iodine as a proxy for oxygen levels. It reveals that while shallow, warmer waters maintained current oxygen levels, changes in ocean currents led to anoxic conditions in deep-sea sediments, adversely affecting eukaryotic life.The concept of vertical decoupling is introduced, referring to the disruption of oxygen flow from shallow to deeper waters, which contrasts with the modern global conveyor belt currents that typically facilitate this exchange. The paper asserts that the thermohaline circulation, responsible for moving oxygenated surface water to deeper ocean layers, was significantly impaired during this period. Overall, the findings underscore the importance of ocean circulation patterns in historical mass extinction events.
jim mcnamara
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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
 
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