Ordovician mass extinction second wave - deep sea anoxia

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SUMMARY

The discussion centers on the second wave of the Ordovician mass extinction, approximately 445 million years ago, driven by deep-sea anoxia. The Nature paper highlights that changes in ocean currents led to vertical decoupling, disrupting the flow of oxygenated water from shallow to deep waters. This resulted in anoxic conditions in deep-sea sediments, significantly impacting eukaryotic life. Key evidence includes the use of iodine as an oxygen proxy, demonstrating the relationship between sediment data and historical oxygen levels.

PREREQUISITES
  • Understanding of sedimentology and its role in paleoclimatology
  • Familiarity with thermohaline circulation and ocean currents
  • Knowledge of biogeochemical cycles, specifically iodine cycling
  • Basic concepts of mass extinction events in Earth's history
NEXT STEPS
  • Research the role of iodine as an oxygen proxy in marine environments
  • Study the mechanisms of thermohaline circulation and its impact on ocean ecosystems
  • Examine case studies of vertical decoupling in modern oceanography
  • Explore the implications of deep-sea anoxia on historical biodiversity
USEFUL FOR

Paleontologists, marine biologists, geologists, and environmental scientists interested in mass extinction events and oceanographic processes.

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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