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Juan C. García

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Ocean oxygen levels
« on: February 28, 2019, 07:51:01 AM »
Widespread and sometimes drastic marine oxygen declines are stressing sensitive species—a trend that will continue with climate change
In the past decade ocean oxygen levels have taken a dive—an alarming trend that is linked to climate change, says Andreas Oschlies, an oceanographer at the Helmholtz Center for Ocean Research Kiel in Germany, whose team tracks ocean oxygen levels worldwide. “We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are,” he says.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.


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Re: Ocean oxygen levels
« Reply #1 on: March 28, 2019, 03:00:13 PM »
In Ancient Oceans that Resembled Our Own, Oxygen Loss Triggered Mass Extinction

Roughly 430 million years ago, during the Earth's Silurian Period, global oceans were experiencing changes that would seem eerily familiar today. Melting polar ice sheets meant sea levels were steadily rising, and ocean oxygen was falling fast around the world.

At around the same time, a global die-off known among scientists as the Ireviken extinction event devastated scores of ancient species. Eighty percent of conodonts, which resembled small eels, were wiped out, along with half of all trilobites, which scuttled along the seafloor like their distant, modern-day relative the horseshoe crab.

Now, for the first time, a Florida State University team of researchers has uncovered conclusive evidence linking the period's sea level rise and ocean oxygen depletion to the widespread decimation of marine species. Their work highlights a dramatic story about the urgent threat posed by reduced oxygen conditions to the rich tapestry of ocean life.

... The experiments revealed significant global oxygen depletion contemporaneous with the Ireviken event. Compounded with the rising sea level, which brought deoxygenated waters into shallower and more habitable areas, the reduced oxygen conditions were more than enough to play a central role in the mass extinction. This was the first direct evidence of a credible link between expansive oxygen loss and the Ireviken extinction event.

Only about 8 percent or less of the global oceans experienced significantly reducing conditions with very little to no oxygen and high levels of toxic sulfide, suggesting that these conditions didn't need to advance to whole-ocean scale to have an outsized, destructive effect. 

Seth A. Young et al. Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction, Earth and Planetary Science Letters (2019)
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late


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Re: Ocean oxygen levels
« Reply #2 on: March 28, 2019, 05:29:32 PM »
Add to this the follow on effects of hydrogen sulfide emission from the oceans and lowering atmospheric oxygen levels.

Some speculate that these were major factors in the extinctions on land.

These effects are apparently short lived in geologic terms (thousands of years). That is no consolation to those killed by them.