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prokaryotes

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Past Extinction Events, as an Analog for Today
« on: July 15, 2019, 09:03:38 PM »
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Study the parallels between hyperthermals and current climate change is by finding a suitable analogue – that is, the hyperthermal that was most similar to the kind of global warming that we’re seeing today.

Carbon input during the PETM was likely still 10 times as slow as in the modern era. Indicators of PETM ocean acidification demonstrate strong dissolution, but modern rates are faster.

The build up period that led to the PETM, in which around 3tn tonnes of CO2 was released into to the atmosphere, may have taken thousands of years. In comparison, the onset of current climate change has taken less than two centuries.

Research suggests that the rate of carbon release as a result of human-driven climate change, and its resultant effect on the world’s oceans, could be “completely unprecedented”.[3]

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The Paleocene–Eocene Thermal Maximum has become a focal point of considerable geoscience research because it probably provides the best past analog by which to understand impacts of global climate warming and of massive carbon input to the ocean and atmosphere, including ocean acidification.
https://en.wikipedia.org/wiki/Paleocene–Eocene_Thermal_Maximum

Killing models during the Permian–Triassic mass extinction
[2]

STRESSORS
Temperature
Ocean acidification (Reduced PH)
Deoxygenation (extreme condition in Ocean, leading to hydrogen sulfide production)
Mercury loading
Increased dissolved seawater CO2

Multiple stressors can have synergistic impacts For example, high temperatures increase an organism’s oxygen demand and reduce its aerobic scope, while lower pH may reduce the oxygen-carrying capacity of blood pigments and seasonal hypoxia can reduce oxygen availability.

Likewise, temperature can have variable effects on susceptibility to metal pollution, and metal pollution can in turn reduce thermal tolerance.[1]

EVENTS

Flood Basalts and Mass Extinctions - Assessing volatile release, environmental change, and biological extinction at finer temporal resolution should be a top priority to refine ancient hyperthermals as analogs for anthropogenic climate change
   
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  • Flood basalts, the largest volcanic events in Earth history, triggered dramatic environmental changes on land and in the oceans.

    Rapid volcanic carbon emissions led to ocean warming, acidification, and deoxygenation that often caused widespread animal extinctions.

    Animal physiology played a key role in survival during flood basalt extinctions, with reef builders such as corals being especially vulnerable.

    The rate and duration of volcanic carbon emission controlled the type of environmental disruption and the severity of biological extinction.
[1]


[1]

THRESHOLDS / AMPLIFYING FEEDBACKS
A new model from MIT indicates that previous consensus climate models have underestimated the atmospheric CO2 levels required to push the ocean beyond a tipping point that would lead to mass extinction in the coming millenia:

Title: "Breaching a “carbon threshold” could lead to mass extinction"

http://news.mit.edu/2019/carbon-threshold-mass-extinction-0708

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We find that the observed pink noise behavior is intrinsic to Earth’s climate dynamics, which suggests a range of possible implications, perhaps the most important of which are ‘resonances’ in which processes couple and amplify warming https://news.yale.edu/2018/09/04/think-pink-better-view-climate-change

QUESTIONS

1. What role played hydrogen sulfide in past extinction events?

2. What can we exactly conclude about the rate of emissions today vs past events? What does it mean for ecosystem resilience, and planetary boundaries?

3. How will Earth's geomorphology respond to uptake in weathering, deglaciation - mass balance changes at the poles?

4. Why were some events characterized by extensive anoxia and widespread black shale deposition whereas other events were dominated by warming and acidification?[1]

5. What were the most important environmental kill mechanisms responsible for eliminating marine and terrestrial organisms?[1]


ANSWERS

1. The hydrogen sulfide at the Permian (and other extinctions) likely reflects an extreme development of the coastal "dead zones" that we see today. In terms of the cause, the consensus appears to have shifted somewhat towards nutrient runoff (and eutrophication) as the primary driver, rather than slowing ocean circulation as might have been proposed 10-15 years ago.

2. The rate of emission, and therefore the rate of environmental disruption, likely provides a first-order constraint for extinctions/adaptation - modulated by duration.

5. Species extinction and survival were likely rooted in their physiological responses to temperature, pH, oxygen, and related stressors, and a growing understanding from extant organisms provides clues to understand biotic vulnerability during hyperthermals.

[1]

TERMINOLOGY
Oceanic Anoxic Event (OAE) and mass extinctions are considered to be hyperthermals - usually associated with flood basalt eruptions.[1]. Phases of rapid global warming, known collectively as hyperthermals.[3]

Flood basalts are a subset of large igneous provinces (LIPs), the terms flood basalt and LIP are often used interchangeably, although the former should be reserved for the extrusive component of an LIP. Flood basalts are giant volcanic eruptions or series of eruptions that cover large stretches of land or the ocean floor with basalt lava.

RELATED

Hydrogen sulfide and environmental stresses / H2S is produced in response to numerous plant stresses, including heavy metal exposure, temperature, drought and salt stress. https://www.sciencedirect.com/science/article/abs/pii/S0098847218311146

Ammonium intoxication is a previously unexplored killing mechanism for extinctions. https://www.sciencedirect.com/science/article/pii/S0012821X19302407



REFERENCES

1. Flood Basalts and Mass Extinctions, Matthew E. Clapham and Paul R. Renne 2019 https://www.annualreviews.org/doi/pdf/10.1146/annurev-earth-053018-060136

2. Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction, Michael J. Benton 2018 https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0076

3. Hyperthermals: What can they tell us about modern global warming? https://www.carbonbrief.org/hyperthermals-what-can-they-tell-us-about-modern-global-warming
« Last Edit: July 16, 2019, 04:52:41 PM by prokaryotes »
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prokaryotes

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Re: Past Extinction Events, as an Analog for Today
« Reply #1 on: July 16, 2019, 09:32:00 PM »
Made a video.
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