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Anoxia/high temperature double whammy during the Permian-Triassic marine crisis and its aftermath.

Song H, Wignall PB, Chu D, Tong J, Sun Y, Song H, He W, Tian L - Sci Rep (2014)

Bottom Line: The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery.Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters.Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.

ABSTRACT
The Permian-Triassic mass extinction was the most severe biotic crisis in the past 500 million years. Many hypotheses have been proposed to explain the crisis, but few account for the spectrum of extinction selectivity and subsequent recovery. Here we show that selective losses are best accounted for by a combination of lethally warm, shallow waters and anoxic deep waters that acted to severely restrict the habitable area to a narrow mid-water refuge zone. The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery. Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters. In contrast, hypoxia tolerant but temperature intolerant small foraminifers were driven from shallow-waters but thrived on dysoxic slopes margins. Only those mollusc groups, which are tolerant of both hypoxia and high temperatures, were able to thrive in the immediate aftermath of the extinction. Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.

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PTB mass extinction dead water model showing the only refuge zone for the crisis lay in a narrow refuge zone of intermediate water depths.The chemocline separated anoxic and sulfidic deep waters from oxygenated surface waters and could move up and down during the Permian-Triassic interval14, causing the refuge zone to shift vertically following the chemocline. Bulk parameters in the water column are based on modern Black Sea1516.
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f2: PTB mass extinction dead water model showing the only refuge zone for the crisis lay in a narrow refuge zone of intermediate water depths.The chemocline separated anoxic and sulfidic deep waters from oxygenated surface waters and could move up and down during the Permian-Triassic interval14, causing the refuge zone to shift vertically following the chemocline. Bulk parameters in the water column are based on modern Black Sea1516.

Mentions: Both anoxia and high temperature can significantly impact marine ecosystems and they often act in lethal synergy because oxygen requirements increase with temperature13. However, the effects of these two variables vary within marine ecosystems allowing the role of each to be evaluated. Generally, seawater temperature declines with increasing water depth and thus the most severe temperatures are experienced in the shallowest waters. In contrast, anoxia develops in the mid-water column or the deepest waters of restricted seas and is unlikely to have a direct or prolonged affect in surface water because of the rapid exchange of oxygen with the atmosphere. The double whammy of anoxia and lethal temperatures, proposed for the PTB mass extinction, therefore predict there will be a potential refuge zone at intermediate water depths (Fig. 2).


Anoxia/high temperature double whammy during the Permian-Triassic marine crisis and its aftermath.

Song H, Wignall PB, Chu D, Tong J, Sun Y, Song H, He W, Tian L - Sci Rep (2014)

PTB mass extinction dead water model showing the only refuge zone for the crisis lay in a narrow refuge zone of intermediate water depths.The chemocline separated anoxic and sulfidic deep waters from oxygenated surface waters and could move up and down during the Permian-Triassic interval14, causing the refuge zone to shift vertically following the chemocline. Bulk parameters in the water column are based on modern Black Sea1516.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3928575&req=5

f2: PTB mass extinction dead water model showing the only refuge zone for the crisis lay in a narrow refuge zone of intermediate water depths.The chemocline separated anoxic and sulfidic deep waters from oxygenated surface waters and could move up and down during the Permian-Triassic interval14, causing the refuge zone to shift vertically following the chemocline. Bulk parameters in the water column are based on modern Black Sea1516.
Mentions: Both anoxia and high temperature can significantly impact marine ecosystems and they often act in lethal synergy because oxygen requirements increase with temperature13. However, the effects of these two variables vary within marine ecosystems allowing the role of each to be evaluated. Generally, seawater temperature declines with increasing water depth and thus the most severe temperatures are experienced in the shallowest waters. In contrast, anoxia develops in the mid-water column or the deepest waters of restricted seas and is unlikely to have a direct or prolonged affect in surface water because of the rapid exchange of oxygen with the atmosphere. The double whammy of anoxia and lethal temperatures, proposed for the PTB mass extinction, therefore predict there will be a potential refuge zone at intermediate water depths (Fig. 2).

Bottom Line: The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery.Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters.Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.

ABSTRACT
The Permian-Triassic mass extinction was the most severe biotic crisis in the past 500 million years. Many hypotheses have been proposed to explain the crisis, but few account for the spectrum of extinction selectivity and subsequent recovery. Here we show that selective losses are best accounted for by a combination of lethally warm, shallow waters and anoxic deep waters that acted to severely restrict the habitable area to a narrow mid-water refuge zone. The relative tolerance of groups to this double whammy provides the first clear explanation for the selective extinction losses during this double-pulsed crisis and also the fitful recovery. Thus, high temperature intolerant shallow-water dwellers, such as corals, large foraminifers and radiolarians were eliminated first whilst high temperature tolerant ostracods thrived except in anoxic deeper-waters. In contrast, hypoxia tolerant but temperature intolerant small foraminifers were driven from shallow-waters but thrived on dysoxic slopes margins. Only those mollusc groups, which are tolerant of both hypoxia and high temperatures, were able to thrive in the immediate aftermath of the extinction. Limited Early Triassic benthic recovery was restricted to mid-water depths and coincided with intervals of cooling and deepening of water column anoxia that expanded the habitable mid-water refuge zone.

Show MeSH
Related in: MedlinePlus