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posted by janrinok on Tuesday February 06, @01:21PM   Printer-friendly

Arthur T Knackerbracket has processed the following story:

Marine anoxia is characterized by the oceans being severely depleted in dissolved oxygen, making them toxic and thus having devastating impacts on the organisms inhabiting them. One such event, known as Oceanic Anoxic Event 2 (OAE2), occurred ~93.5 million years ago across the Cenomanian-Turonian boundary of the Upper Cretaceous and lasted for up to 700,000 years.

During such scenarios, organic matter is buried at an elevated rate, producing distinctive layers of black shale in the geological record, which are depleted in the isotopically-heavier carbon-13, therefore generating a positive carbon isotope excursion of ~6‰ for this study period.

The specific factors triggering OAE2 are still debated, but the most widely supported is volcanism from the Caribbean Large Igneous Province and High Arctic Large Igneous Province, increasing atmospheric carbon dioxide and therefore warming the planet.

Among the plethora of impacts from a warmer planet is increased weathering of land, with fluvial processes transporting this material to the oceans, providing key nutrients to primary producers in the surface ocean. Enhanced primary productivity produces more oxygen, but trophic food chains ultimately use up more of this oxygen in their metabolic processes.

Compounded by decreased solubility of oxygen in warmer oceans, this results in widespread deoxygenation of Earth's marine realm, the focus of new research published in Climates of the Past.

[...] Revealing the significance of the work, Dr. Abraham said, "Our research delves into the ancient oceans' secrets, specifically a period 93.5 million years ago when much of the ocean was devoid of oxygen. By studying natural chemical fingerprints preserved in marine sediments, we uncover how volcanic activities and climate warming in the past led to drastic ocean deoxygenation. Understanding this in deep time is crucial, as they mirror the challenges we face today with the ongoing climate crisis, helping us predict and mitigate future consequences."

Taking samples of organic matter from the drilled cores, the research team isolated compounds of biological origin that are stable over geological time periods of millions of years, known as biomarkers. Dr. Abraham explains that biomarkers are known as "molecular fossils," adding, "Biomarkers are chemical compounds found in sedimentary rocks that originated from living organisms millions of years ago. Think of them as molecular fossils that, unlike bones or shells, are not easily visible to the naked eye. These compounds, once part of living organisms, have remained chemically stable over vast geological timescales.

"We extract them carefully using a series of chemical procedures and a technique known as gas chromatography–mass spectrometry in the lab to isolate these compounds from the drilled sediments and to avoid contamination.

"Analyzing these biomarkers helps us reconstruct past environmental conditions, such as temperature and oxygen levels in the oceans, but linking their presence to specific historical environmental conditions requires meticulous laboratory work and a profound understanding of geochemical processes."

The scientists found that the percentage of total organic carbon content of the samples increased through the study period (3.8 million years), peaking at ~28 weight % at OAE2 from initial levels of 1–17 weight %. This occurred alongside a ~5-8°C increase in sea surface temperature up to ~43°C.

Key biomarkers of 28,30-dinorhopane and lycopane are indicative of this warming and decline in oxygen, forming an oxygen minimum zone in the Cenomanian, similar to those observed in the Black Sea today. This data is coupled with a noticeable reduction in the abundance of benthic foraminifera (bottom ocean-dwelling single-celled microorganisms) in the late Cenomanian, as they were not able to survive in the depleted-oxygen environment.

Such persistent low-oxygen layers increase in number and size with enhanced warming of the oceans, forming a thick zone at depth below a highly productive thin surface layer that is oxygen-rich. Biomarkers of C35 hopanoid thiophene and isorenieratane reveal this water-column euxinia (both anoxic and sulphidic) expanded to finally reach the surface photic zone through the Cenomanian-Turonian boundary at OAE2.

[...] Looking ahead to the future of Earth's oceans with the expansion of oxygen minimum zones, Dr. Abraham says, "In today's world, oceanic conditions are generally hypoxic but have not yet reached anoxic levels in open oceans. However, closed basins or seas are more prone to becoming anoxic.

"With ongoing global warming, it is predicted that oxygen minimum zones will expand both horizontally and vertically. Warmer water holds less oxygen, and increased surface temperatures can lead to stronger stratification of ocean layers, thereby reducing the mixing that normally replenishes oxygen in deeper waters.

"Additionally, global warming can enhance biological activity in surface waters, resulting in more organic matter sinking to the depths, where it consumes oxygen as it decomposes, a process evident during OAE2.

"Today, oxygen minimum zones are primarily found in the Pacific and Indian Oceans, with conditions making life hard for many marine species. With the current trends of global warming, these zones are expected to expand, reducing habitable marine space and adversely affecting marine biodiversity and fisheries.

"By the end of this century, if the current trajectory of warming and nutrient runoff continues, we might see a significant increase in anoxic and euxinic conditions in our oceans, threatening marine ecosystems and the services they provide to humanity."

Journal information: Climate of the Past


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  • (Score: 3, Interesting) by gnuman on Tuesday February 06, @10:28PM (1 child)

    by gnuman (5013) on Tuesday February 06, @10:28PM (#1343401)

    Insulation has gotten better, and yet it's still a far cry from what a primitive mud hut can do.

    Do I dare to say you've never lived in a mud hut before? You know, maybe you wouldn't complain about deficiencies of insulation when your potty-water froze at night. My grandma used to sleep on top of the stove to keep warm at night. You could fit a hand in the "cracks" in her house walls, but at least it was nowhere close to living in a mud hut you dream of. She had to live in a mud hut during the war when the house burned down during occupation. It was the worse year of her life, she says. I believe her.

    We've designed our cities to be quite hostile to walking and bicycling.

    Ah yes, American cities. You are spot on how hostile to living they are. Then Americans come to places in Europe and wonder what wonderland we have here -- can walk anywhere you need in 15 minutes. Then they go back home, and enjoy their freedoms in 2h jams. Mind you, locals here enjoy their jam-freedoms too. I pass them on my bike everyday going to work.

    I plan on going back to North America but I never plan on living in an urban setting there ever again.

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  • (Score: 2) by JoeMerchant on Tuesday February 06, @11:32PM

    by JoeMerchant (3937) on Tuesday February 06, @11:32PM (#1343416)

    >You could fit a hand in the "cracks" in her house walls

    The CCC built stone cabins on the Cheaha mountain in Alabama in the 1930s. The State Park there still rents them out and we have stayed several times around New Year... the stone itself transmits heat not-quite as well as aluminum plate - you can actually heat the stones near the gigantic fireplace (using a pickup truck full of wood in 3-4 nights) and they will radiate nicely for a couple of hours after the fire dies down, but the real killer is the cracks between the rocks where the wind blows through. One year we saw a neighbor in the next cabin stuffing the worse cracks with paper - it helps, but not a lot.

    --
    🌻🌻 [google.com]