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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: 1, Troll) by turgid on Tuesday February 06, @09:44PM (2 children)

    by turgid (4318) Subscriber Badge on Tuesday February 06, @09:44PM (#1343386) Journal

    About the ways that cities are set up, there are proposals to improve that (15 Minute Cities), but the Alt-Wrong/Libertarian/Popular Conservative types have this conspiracy theory that they're an undemocratic Marxist plot to take away our freedom. Don't mention lower speed limits either!

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  • (Score: 3, Insightful) by bzipitidoo on Wednesday February 07, @05:07PM

    by bzipitidoo (4388) on Wednesday February 07, @05:07PM (#1343528) Journal

    Cool, thanks for mentioning 15 minute cities. I hadn't heard of them.

    One thing I remember was the time I went to a city council meeting to propose a slight change to the zoning laws: Permit, just permit but don't require, gaps wide enough for pedestrians in those walls they use to separate the commercial from the residential. No one would have to change a thing if they didn't want to. But that apparently was still asking too much. As I was telling this to one of the councilpersons, a shopkeeper overheard me and went nuts. He started ranting that pedestrians have no business walking through the back areas, and this would force shops to pay more money to neaten up those places, and it would raise his insurance because it's dangerous back there the way delivery trucks barrel through, and it would increase teen loitering and drive away his customers, and blah, blah, blah. No one else could get a word in. Finally when he ran out of steam, the councilperson said, "man, you are on a roll!"

    That experience convinced me that you can't change existing places, there will be too much resistance. Want to build a better city? Got to start a new city.

  • (Score: 3, Informative) by turgid on Wednesday February 07, @09:53PM

    by turgid (4318) Subscriber Badge on Wednesday February 07, @09:53PM (#1343552) Journal

    I think we'd better have some citations. I'm not making it up.

    1 15 minute cities: How they got caught in conspiracy theories [bbc.co.uk]

    Conspiracy theories linking "15-minute cities" to sinister ploys to control people may once have been the preserve of fringe groups on social media, but have they now entered the mainstream of British politics?

    2 What is the '15-minute city' conspiracy theory? [abc.net.au]

    After outlandish claims about lizard people, 5G and COVID-19 vaccines, conspiracy theorists are now targeting the world of urban planning, with protests against the 15-minute city concept springing up around the globe.

    3 ‘This is political expediency’: how the Tories turned on 15-minute cities [theguardian.com]

    The transport secretary, Mark Harper, went further, telling delegates the 15-minute cities concept was “a Labour-backed movement … to remove your freedom to get from A to B how you want.

    “What is sinister, and what we shouldn’t tolerate, is the idea that local councils can decide how often you go to the shops, and that they can ration who uses the roads and when, and that they police it all with CCTV.” The government would look into ways to stop “overzealous” councils restricting road use “if they don’t follow the rules”, he said.

    4 How ‘15-minute cities’ turned into an international conspiracy theory [cnn.com]

    They claimed he wanted to confine people to their neighborhoods and accused him of being part of a malign international plot to control people’s movement in the name of climate action.

    5 The 15-Minute City Conspiracy Theory Goes Mainstream [wired.com]

    Back in February, when a Conservative Party lawmaker in the UK’s House of Commons voiced support for the 15-minute city conspiracy, he was laughed at by his fellow members of Parliament. Now, eight months later, the British government is fully embracing the fringe conspiracy and placing it at the heart of government policy.

    These people call themselves patriots, and they belong to groups with names like the ERG, National Conservatives, Popular Conservatives, Reform UK, various opaque right-wing "think tanks" (see Tufton Street) and they spout forth on highly biased TV "news" channels such as GB News. These people are the Raving Right, the illiberal, authoritarian elite. They are the Alt-Wrong. Unfortunately they are currently in government in the UK.

    In which other country could you see "news" and current affairs programmes on TV hosted by members of the sitting government party interviewing members of that government and no-platforming "lefty" dissenters?