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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, Interesting) by Anonymous Coward on Tuesday February 06, @10:12PM (2 children)

    by Anonymous Coward on Tuesday February 06, @10:12PM (#1343395)

    Along your lines, I've managed to make some compromises, seems a lot more practical than an all-or-nothing commitment to "green" living that some friends have tried (they mostly failed). For example, here in the USA northeast:

      I have some clothes that shrink in the dryer, so they either go in for 10-15 minutes to get some of the moisture out and then hang, or they may hang straight from the spin cycle. But I don't say anything about *her* clothes, just mine. They are spread out enough that we don't have mold problems in the winter (in fact, this adds some useful humidity to the dry indoor air). I might use the dryer all the way to full dry on the most humid summer days.

      While I used to be hard core about cycling year round for local errands, that was before I fell on black ice one sunny/chilly day. Didn't break anything but took the warning to heart. Now that I'm approaching 70, I'm a fair weather cyclist (in the winter I use a stationary bike, just enough so I have some muscle tone when it gets nicer out).

      Most of the time I'm able to combine car trips to minimize miles driven, but the biggest part of keeping miles down is working from home (which I've been fortunate to do for many years).

      Bought this house a few years before cheap fracking gas came in from the next state over. Gas (for heating) was getting pricey back then, so added an extra foot of fiberglass batt insulation to the attic floor, in addition to the ~6 inches that was already there. It made a noticeable difference in comfort in the winter, with ceiling temp (IR temp) essentially the same as room air temp. We run the house at 71F day (wearing two layers) and 68 night in winter. In summer we don't turn on the AC until it gets into the upper 70s (depending on humidity), and almost always turn the AC off when we go to bed.

      It's a brick ranch, not about to tear down the wall board to insulate the walls. We did add plastic film inside many of the windows, making the old thermopane double glass into triple layer. While the 3M instructions say to replace every year, we've left it up, seems to be good for 5+ years before it starts to come off.

      On food waste, with no kids around, we can cook just enough that we rarely have any wasted edible food. All the vege scraps go into a composter outside--and the raspberry plants seem to really love the compost every few years. We're not vegetarian or on any other strict diet, but we tend to have a couple of vege meals a week, and beef only once or twice a week.

      While curbside recycling doesn't take as much as it used to, we still recycle about as much paper, plastic(1&2 only) and clear glass as we have trash (landfill). There's been a plastic grocery bag ban here for years now. Re-usable grocery bags have become standard and no big deal.

      Started out with a gas lawn mower but when that broke we replaced it with a little battery electric which has been fine (Black & Decker 40V). While it takes a little longer, the extra steps are not bad and the bonus is that it's quiet and doesn't buzz my hands. It's so light that self-propelled would hardly make a difference in the effort to push it.

    There's more little tweaks like these and I like to think that they add up...but I also recognize that my "footprint" on the planet is much higher than a true primitive life style.

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  • (Score: 2) by JoeMerchant on Tuesday February 06, @11:28PM (1 child)

    by JoeMerchant (3937) on Tuesday February 06, @11:28PM (#1343415)

    >so added an extra foot of fiberglass batt insulation to the attic floor, in addition to the ~6 inches that was already there.

    I had a house with an easy access attic that had 6" of fiberglass batt installed when it was new in 1972... Around about 2008 I added 6 more inches of encapsulated batt on top and I swear it was like a tripling or more of the actual insulation value - that old paper-down glass up insulation seemed to have degraded from its R-19 rated value when new to something more akin to R-6 maybe R-9 30+ years later.

    --
    🌻🌻 [google.com]
    • (Score: 0) by Anonymous Coward on Wednesday February 07, @02:18AM

      by Anonymous Coward on Wednesday February 07, @02:18AM (#1343440)

      Might have been an actual tripling, since (I assume) the initial batt insulation was between the ceiling joists, so there was heat conduction through the joists in parallel with the fiberglass. 1.5" thick joints and ~15" between joists full of the initial fiberglass, so about 10% of the ceiling was wood.

      The extra layer(s) of batt on top of the joists block the heat loss through the wood.

      In my case (added two layers of 6" batt), the installer was happy to run the two layers at 90 degrees to each other, so air gaps between the batts in each layer were mostly covered by the other crossed layer.

      Initially I had planned to diy, but when I priced the insulation, it turned out that installed was nearly the same price...the insulation contractor got a truckload price on the product.