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  • richardmitnick 11:08 am on January 4, 2020 Permalink | Reply
    Tags: "The Complicated Role of Iron in Ocean Health and Climate Change", , , Paleoclimatology,   

    From smithsonian.com: “The Complicated Role of Iron in Ocean Health and Climate Change” 

    smithsonian
    From smithsonian.com

    January 3, 2020
    Emily Underwood

    Iron dust may have played a significant role in the last ice age, and it could be an important factor in mitigating future global temperature increases.

    1
    Iron-rich dust launched into the air by winds swirls around the Southern Ocean. Understanding how iron’s chemistry shifts during its journey from earth to air to sea will be important for developing better climate models. (William Putnam and Arlindo da Silva, NASA / Goddard Space Flight Center)

    One brisk day in April 2013, as he drove with colleagues along the southern coast of Patagonia, Mike Kaplan spotted a geologist’s treasure trove—an active gravel pit with freshly exposed walls. He pulled over, grabbed the backpack full of digging tools stowed in the car trunk and walked into the large hole.

    To Kaplan’s south lay the Southern Ocean, stretching toward Antarctica. Strewn around him was evidence of Earth’s most recent ice age: heaps of crushed rock and gravel released by one of the many glaciers that had once covered North and South America. Standing in the pit, Kaplan spotted what he was looking for: a layer of fine gray silt deposited by ice sheets roughly 20,000 years ago.

    A geologist at Columbia University in New York, Kaplan has spent over a decade collecting the sediments that make dust, and studying how that dust, launched from earth to air to sea, influences Earth’s climate, past and present. Dozens of intriguing samples have made their way home with him, stowed in his suitcase or shipped in a duct-taped cardboard box. As he scraped the dark gray sediment into a plastic bag, he felt a rush of anticipation. Given the sample’s location, he thought that it might be just what he needed to test an aspect of a controversial idea known as the iron hypothesis.

    Proposed in 1990 by the late oceanographer John Martin, the hypothesis suggests that flurries of dust — swept from cold, dry landscapes like the glacial outwash where Kaplan now stood, trowel in hand — played a crucial role in the last major ice age. When this dust landed in the iron-starved Southern Ocean, Martin argued, the iron within it would have fertilized massive blooms of diatoms and other phytoplankton. Single-celled algae with intricate silica shells, diatoms photosynthesize, pulling carbon from the atmosphere and transforming it to sugar to fuel their growth. Going a step further, Martin proposed that using iron to trigger diatom blooms might help combat global warming. “Give me half a tanker of iron and I’ll give you an ice age,” he once said half-jokingly at a seminar, reportedly in his best Dr. Strangelove accent.

    Thirty years after Martin’s bold idea, scientists are still debating just how much iron dust contributed to the ice age, and whether geoengineering of the oceans—a prospect still lobbied for by some—might actually work. Although it’s now well-established that an uptick in iron fertilization occurred in the Southern Ocean during the last major ice age, for example, scientists still argue about how much it reduced carbon dioxide levels in the atmosphere. And while Martin’s hypothesis inspired 13 large iron fertilization experiments that boosted algae growth, only two demonstrated removal of carbon to the deep sea; the others were ambiguous or failed to show an impact, says Ken Buesseler, a marine radiochemist at the Woods Hole Oceanographic Institution in Massachusetts.

    In 2008, concerns about possible environmental impacts of iron fertilization, such as toxic algal blooms and damaged marine ecosystems, prompted the United Nations Convention on Biological Diversity to place a moratorium on all large-scale ocean fertilization experiments. The ban “put the kibosh” on such activity, says Buesseler. The problem with that, many scientists now contend, is that the most fundamental questions about iron fertilization—if it can sequester enough carbon to alter climate, and what its environmental consequences would be—remain unanswered.

    As atmospheric carbon levels soar past 400 parts per million, some researchers believe that the freeze on iron fertilization experiments should be reconsidered, Buesseler among them. “I’m not a supporter of geoengineering, but I think it is our responsibility to look” at ways of actively removing carbon from the atmosphere, including iron fertilization, he says.

    Whether people ever decide to pursue iron fertilization to combat climate change or not, scientists still need to understand the environmental impacts of iron-rich dust and ash from natural sources like volcanoes, and from manmade pollutants, says Vicki Grassian, a physical chemist at the University of California, San Diego. To meet that challenge, labs around the world are studying how iron affects climate and ocean health. Their work spans the scales, from the tiny crystalline structure of iron-peppered nanoparticles to large-scale simulations of global climate. Ultimately, scientists hope to understand the role of iron dust in marine systems, says Kristen Buck, a chemical oceanographer at the University of South Florida. “When you add iron to a system, how does that trigger the system to change?”

    In ancient seas, iron aplenty

    To learn how iron fertilization might work in the future, some researchers are looking at the past, in paleoclimate records such as ice cores and deep-sea sediments. From that perspective, many of the natural iron fertilization experiments have already been run, says Gisela Winckler, a climate scientist at the Lamont-Doherty Earth Observatory at Columbia, and Kaplan’s colleague.

    Three billion years ago the ocean was chock-full of iron, ancient mineral deposits show. Iron was plentiful when life first evolved, and the metal was incorporated into a long list of essential cellular functions. Animals need iron to transport oxygen in their blood and to break down sugar and other nutrients for energy. Plants need iron to transfer electrons during photosynthesis and to make chlorophyll. Phytoplankton need it to “fix” nitrogen into a usable form.

    2
    Ancient layers of iron oxides, typically magnetite or hematite, separated by chert (a type of quartz), form sedimentary rocks called banded iron formations. (One shown here from Fortescue Falls in Western Australia.) It’s thought that iron, once abundant in the oceans, began to form such deposits on the ocean floor between 2.5 billion and 1.9 billion years ago, as oxygen levels rose. (Graeme Churchard via Wikipedia Commons under CC BY 2.0)

    Despite being the fourth most abundant element in the Earth’s crust, iron is vanishingly scarce in the modern ocean. It started disappearing from the seas more than 2.4 billion years ago, when cyanobacteria evolved and started to breathe in carbon dioxide and exhale oxygen. When this happened, dissolved iron rapidly linked up with the newly plentiful oxygen atoms, forming iron oxides such as hematite, a common mineral that contains a form of the element known as iron(III). Most phytoplankton and other living organisms can’t use iron in this state. They require a different form, iron(II), which more readily dissolves and is absorbed by cells.

    Hematite has another downside: It sinks. Over billions of years, layer upon layer fell to the sea floor, forming iron ore deposits hundreds to thousands of feet deep. Meanwhile, iron in the waters above diminished to barely detectable levels—an average liter of seawater contains roughly 35 grams of salt, but only on the order of a billionth of a gram of iron. In roughly a third of the ocean, iron is so rare that its absence can hinder the growth of diatoms and other phytoplankton. The Southern Ocean, where Martin developed his hypothesis, is one of the most “iron-limited” oceans in the world. Even with an abundance of other crucial nutrients such as nitrogen and phosphorus, it’s the availability of iron that matters for diatoms and other organisms.

    Unless, of course, a gust of wind delivers a plume of iron particles. Standing in the freshly excavated gravel pit in Patagonia, Kaplan was directly upwind of the Southern Ocean—close to where Martin proposed that ice age dust had helped to fertilize the ocean some 20,000 years ago. It was the perfect place to test whether those iron-rich glacial sediments would have made a good fertilizer for diatoms. Researchers already knew that there was more dust-borne iron during the last ice age, much of it freed by melting glaciers. But no one had yet rigorously tested whether the iron was in the form that diatoms can absorb, Kaplan says.

    Kaplan scraped up the dark gray silt and brought it back to Columbia, where he handed it off to then-graduate student Elizabeth Shoenfelt Troein, who is now a postdoctoral fellow at the Massachusetts Institute of Technology. Shoenfelt Troein flew out to the Stanford Synchrotron Radiation Lightsource in Menlo Park, California. There, along with her adviser Benjamin Bostick and fellow graduate student Jing Sun, she spent many long nights zapping the sediment with high-powered X-rays to reveal its mineral composition.

    Kaplan scraped up the dark gray silt and brought it back to Columbia, where he handed it off to then-graduate student Elizabeth Shoenfelt Troein, who is now a postdoctoral fellow at the Massachusetts Institute of Technology. Shoenfelt Troein flew out to the Stanford Synchrotron Radiation Lightsource in Menlo Park, California. There, along with her adviser Benjamin Bostick and fellow graduate student Jing Sun, she spent many long nights zapping the sediment with high-powered X-rays to reveal its mineral composition.

    Only certain types of minerals yield dust that is rich in soluble forms of iron, including iron(II), the kind that diatoms can easily digest, as Grassian and colleagues described in 2008 in the Annual Review of Physical Chemistry. Clay minerals containing iron, for example, yield iron(II) more easily than hematite, as they’ve found in experiments on dust from around the world, including Africa’s Sahara Desert, Chinese loess and Saudi Arabian beach sand. Winds blowing off the Sahara are one of the most important sources of iron dust in the ocean, supplying more than 70 percent of dissolved iron to the Atlantic, another group has found. But there are several other paths by which iron(II) makes its way to the oceans, including rivers, hydrothermal vents, volcanoes and glacial outwash plains like the one where Kaplan found his sample in Patagonia.

    Iron is among the most common elements on Earth, but is rarely found in its pure metallic form (Fe). Instead, it readily reacts with oxygen to form various iron oxides, and with other elements to form a wide array of minerals. Hematite is the main source of iron used to make steel but living organisms can more readily use iron in the +2 oxidation state. Adding water to an iron oxide can create rust in what’s termed a hydrated iron oxide. (A. Murugan / New Castle University 2011)

    The glacial sediment contained far more iron(II) than samples deposited during non-glacial periods from the same region, Shoenfelt Troein found. When glaciers grind down bedrock, the resulting freshly ground sediments tend to contain more iron(II) than sediments produced from weathering by wind and water, which are richer in iron(III), Winckler says. Back at Columbia, Shoenfelt Troein fed the iron(II)–rich, glacial sediment to a common species of diatom, Phaeodactylum tricornutum, and the diatoms reproduced 2.5 times as fast as they did on weathered sediment, the team reported in Science Advances in 2017. This would translate into a roughly fivefold increase in carbon uptake compared with the non-glacial sediment, the team calculated.

    When the team looked at marine sediment cores from several glacial and interglacial periods spanning 140,000 years, Winckler, Shoenfelt Troein and colleagues found that dust from the glacial periods contained 15 to 20 times more iron(II) than did dust from the current interglacial period. That suggests that the potency of glacial sediment led to a self-reinforcing cycle, in which higher rates of iron fertilization in the oceans reduced carbon in the air, leading to colder temperatures, which in turn, grew glaciers, the team reported in the Proceedings of the National Academy of Sciences in 2018. It also suggests that not all iron is equal when it comes to fertilization, and that freshly mined, fine-ground iron might be more effective than other forms, Winckler says.

    In most of the geoengineering experiments in the 1990s and early 2000s, scientists mixed a powdered form of iron called ferrous sulfate with acidic water and fed the liquid off the back of a ship, says David Emerson, a geomicrobiologist at the Bigelow Laboratory for Ocean Sciences in Maine. The fate of ferrous sulfate once it enters the oceans is not fully known, he says, but it’s reasonable to assume that some of it oxidizes to the diatom-disdained iron(III) and sinks, even if some persists in the upper water column for days. Emerson recently proposed using aircraft to distribute a fine iron dust produced by iron-eating bacteria, called biogenic oxide. This form is composed of iron nanoparticles bound to organic compounds, and would likely stay suspended longer than ferrous sulfate in the sunlit surface waters where diatoms grow, he says.

    4
    Not all iron is equal when it comes to fertilizing diatoms. When scientists fed this common diatom species, Phaeodactylum tricornutum, a glacier-made sediment rich in soluble iron(II), the phytoplankton reproduced 2.5 times as fast as they did when fertilized with sediment that contained a less soluble form of iron. The higher growth rate would translate into a roughly fivefold increase in carbon uptake, the team calculated. (Alessandra De Martino, Ecole Normale Superieure, Paris / NSF)

    Getting iron to linger in surface waters won’t necessarily ensure that the carbon absorbed by diatoms actually reaches the deep sea, however. Roughly 90 percent of the organic carbon that diatoms create during photosynthesis is released back into the ocean in dissolved form as the algae dies, rots and is consumed by bacteria, zooplankton and fish, Buesseler says. Just 10 percent of the carbon produced by the ocean’s creatures migrates to the depths where it may remain for hundreds to thousands of years—the length of time relevant for climate mitigation. A mere 1 percent gets permanently buried on the seafloor. Critically, no iron fertilization experiment has yet lasted long enough to track how much of the carbon that diatoms do capture actually gets sequestered to the deep ocean, he says.

    Location also plays a vital role in whether iron fertilization is effective, Winckler says. Based on marine sediment cores, Winckler and her colleagues have reconstructed a 500,000-year record of iron dust levels throughout the Pacific to see if—and where—notable spikes of iron fertilization occurred in the past. The team knows how much the dust level has changed, and in parallel measures the biological responses to the dust to determine if the phytoplankton “actually cares about the change,” she says. She concludes that the iron hypothesis appears to apply only to some parts of the Southern Ocean—and not other low-iron regions the such as equatorial Pacific, where past iron fertilization experiments have boosted phytoplankton growth but failed to show the degree of carbon capture scientists had expected.

    There are many complex factors involved in determining where iron fertilization might work, including upwelling currents that deliver iron from deeper waters and the availability of other vital nutrients. Yet “people often just look at one piece of this puzzle, and then make big conclusions,” Winckler says.

    6
    Before the GEOTRACES effort to map the global sources of iron, the metal’s path was somewhat unclear. In a 2019 paper, scientists used data from GEOTRACES to “fingerprint” the origins of soluble iron in particles of dust that fall on the ocean. Human activities such as burning coal or gasoline contributed as much as 80 percent of the soluble iron that landed on the sea surface throughout the world’s oceans—far more than a previous model (shown on the left) had suggested. Mineral dust swept from dry regions like the Sahara made up a smaller portion of the ocean’s iron. (T.M. Conway et al / Nature Communications 2019 under CC BY 4.0)

    Grassian studies yet another factor that can influence iron fertilization in unexpected ways: the chemical reactions that transform particles containing iron as they fly through the sky, exposed to air, water and sunlight. At her lab in San Diego, she simulates the effects of water vapor and airborne pollutants on iron particles. She and her colleagues have discovered that chemicals like sulfur dioxide and nitric acid make iron more soluble—and thus easier for diatoms to absorb—by coating them in acid.

    Iron particles produced by manmade pollution are also potent fertilizers, she and others have found. Iron flecks in coal fly ash, for example, are amorphous globs that dissolve more easily than the crystals found in mineral dust. The result is that even if you have less overall iron in coal fly ash, its impact on algae could be just as important as that of mineral dust, Grassian says.

    Iron can rapidly alter its molecular composition or state as it moves from the Earth’s crust to the ocean, and such changes determine whether iron is in a chemical form that diatoms and other photosynthetic algae can use—and thus, how much carbon they capture. Yet, for decades, climate and atmospheric chemistry models have overlooked iron’s complexity, which includes the many forms of iron present in dust as well as how dust is altered by aging and chemical exposures. “As physical chemists, we’re trying to understand the details … to get away from thinking about things in a too-simplistic fashion,” Grassian says.

    Other researchers are studying what happens when dust-borne iron dissolves into the ocean. When water molecules come up against the abrupt transition to air, many can no longer find partners for all their hydrogen bonds. As a result, one of every four water molecules has something akin to a grasping limb—a single hydroxyl (OH) group—pointing up into the air with nothing to bind to, creating an uneven chemical landscape. That variability can affect how iron transforms into one of its myriad chemical identities, and then how organisms such as diatoms interact with the metal, says Heather Allen, a physical chemist at Ohio State University.

    Sometimes iron doesn’t interact only with the water, but also encounters a millimeter-thick gel of carbohydrates, proteins and lipids known as the sea surface microlayer, or the ocean’s “skin.” This layer can concentrate trace metals such as iron, particularly when oily pollutants common along shipping routes, such as hydraulic fluids, are present, says Allen.

    Iron is so scarce in the ocean that even a bit of rust flaking off a ship’s hull can throw measurements off by a factor of 10. The instruments used to detect iron are sensitive: “If a whale poops, there goes your whole experiment,” Buck says. Through a project called GEOTRACES, Buck and an international consortium of other scientists have examined more than 20,000 measurements to map where iron comes from in the ocean, where it goes and how it changes. To avoid contamination, scientists process seawater samples in plastic-enclosed bubble labs that appear more suited to studying deadly microbes than one of Earth’s most abundant elements.

    They’ve found that most naturally produced iron dust blows off the Sahara and other deserts, but large amounts are also released in plumes of hot dissolved minerals from hydrothermal vents. Volcanoes, which can spew thousands of kilograms of iron into the atmosphere in a single eruption, are another important source. Although the evidence is circumstantial, iron fertilization from volcanic ash may have contributed to the brief hiatus in carbon buildup in the atmosphere after the 1991 eruption of the Philippines’ Mt. Pinatubo, says Emerson. Unfortunately, there was no monitoring at the time to determine if this led to a large-scale iron fertilization event, he says.

    The ocean’s iron miners

    Given how quickly iron rusts and sinks, there should be very little dissolved iron in seawater, including the highly soluble iron(II). Yet GEOTRACES has detected more of it than scientists predicted. Buck and others believe that some of these scant traces of dissolved iron can be explained by an active effort made by living things to scavenge it. In addition, they point to the presence of organic molecules called ligands, which lock up iron in a soluble, diatom-friendly form. One common example of a ligand is found in siderophores, chemical compounds that bacteria secrete to break down iron particles.

    Some organisms actively mine iron from dust. On the northernmost end of the Red Sea, for example, marine biogeochemist Yeala Shaked of the Hebrew University of Jerusalem is studying how a stringlike, reddish kind of phytoplankton called Trichodesmium takes advantage of iron-rich dust that blows in from the Sahara. This Trichodesmium species assembles into puffball-shaped colonies, each composed of tens to thousands of individual filaments. When this dust lands, the colonies shuttle the iron-rich mineral particles into the center of the colony and start extracting iron(II). A colony can transform a pool of iron(III) into iron(II) in 30 minutes, Shaked and her colleagues have found in lab experiments.

    Even small changes in the abundance and productivity of phytoplankton could have a significant impact on marine life and the rate of global warming, so organisms such as Trichodesmium are key to global climate models. An ambitious effort at MIT, for example, is attempting to incorporate many different phytoplankton species into their simulations.

    Despite iron’s assumed influence over climate, climate models still don’t currently include much detailed information about the element, says Andreas Schmittner, a climate scientist at Oregon State University. Although it’s now well-established that iron fertilization occurred in the ancient Southern Ocean, for example, there’s still lively debate over how much it affected past carbon dioxide levels. Some scientists have argued that iron fertilization wasn’t particularly important, and that most of the roughly 100 ppm drop in carbon dioxide during the last ice age can be explained by changes in ocean currents and sea ice.

    But in June 2019, Schmittner and colleagues published a different take in Science Advances, calculating that cooler temperatures and iron fertilization were responsible for most of the decrease, and ocean circulation and sea ice had “close to zero” impact, he says. Iron fertilization alone accounted for a 25 to 35 ppm decrease in atmospheric carbon during that period, “a larger effect than we expected,” he says.

    Once scientists have pieced together more about iron’s complex chemistry, they will still have to learn when to turn certain factors off and on in these climate models to accurately simulate reality, Grassian says. Better models will also depend on fine-tuning countless other factors that could affect how much carbon dioxide sequestration occurs in response to a phytoplankton bloom, including how layers of ocean water mix, and the presence of zooplankton, tiny marine organisms that graze on algae.

    Several iron fertilization experiments favored certain phytoplankton species over others, a consequence that could inadvertently reorganize marine food webs. Large algal blooms both natural and manmade have also been known to deplete oxygen in the water, creating dead zones. One risk is that iron fertilization could damage ecosystems downstream, by depriving them of nutrients that normally would have reached them, Buesseler says. “What happens when that water upwells somewhere else and [a] fishery collapses because … you’ve kind of stripped away all the juicy nutrients in one part of the ocean?”

    Meanwhile, the controversy over iron fertilization as a geoengineering approach rages on. As the vision of a climate-tweaking tool has waned, some companies have attempted to apply the idea to revitalize fisheries. In a highly controversial 2012 example, American businessman Russ George persuaded members of the Haida Nation to fund the dumping of roughly 100 tons of iron sulfate off the coast of Canada, fertilizing a 10,000-square-kilometer algae bloom. George sold the controversial project as a way to boost salmon populations and sequester carbon, but follow-up studies failed to find conclusive evidence that it worked.

    In 2013, the London Protocol, an international treaty that prevents ocean dumping, adopted amendments allowing researchers to apply for exceptions to the moratorium on iron fertilization experiments. Winckler does not advocate using iron fertilization as a geoengineering tool, but she is among those who think that more rigorous experiments are necessary to establish the approach’s efficacy and potential risks and benefits, even if people decide never to use it. “We are in a climate crisis, and we’ve got to think about these questions,” she says.

    See the full article here .

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  • richardmitnick 9:24 am on December 27, 2019 Permalink | Reply
    Tags: , , , , , Paleoclimatology   

    From Eos: “Reconstructing 150 Million Years of Arctic Ocean Climate” 

    From AGU
    Eos news bloc

    From Eos

    18 December 2019
    David Shultz

    1
    The drillship Vidar Viking, operated by the European Consortium for Ocean Research Drilling, sits amid Arctic sea ice during the International Ocean Discovery Program’s Arctic Coring Expedition in 2004. Sediment cores collected during the expedition were used in a recent study to shed light on Arctic climate over the past 150 million years. Credit: Martin Jakobsson ECORD/IODP

    The high northern latitudes of the Arctic—seen as the canary in the coal mine for modern climate change—are warming at an outsized rate compared with elsewhere on the planet. Already, experts predict that the Arctic Ocean might be ice free during summer months in as little as 40–50 years. The trend has researchers concerned that resulting feedbacks, especially reductions in Earth’s albedo as ice increasingly melts, may lead to rapid changes in the global climate.

    To understand how the future could play out, scientists look back to other warm periods in Earth’s history. Despite the Arctic’s critical role in Earth’s climate, however, data about the sea ice and climate history of the region are limited. Here Stein compiles a review of the existing literature on Arctic climate from the late Mesozoic era (about 150 million to 66 million years ago) through the ongoing Cenozoic era [Paleoceanography and Paleoclimatology].

    In the late Mesozoic, Earth’s atmosphere was characterized by much higher atmospheric greenhouse gas concentrations and much higher average temperatures than today. Then, during the past 50 million years or so, the planet experienced a dramatic long-term cooling trend, culminating in the glacial and interglacial cycles of the past 2.5 million years and the most recent ongoing interglacial period, in which rapid anthropogenic warming is occurring.

    Much of the data presented in the review are from the International Ocean Discovery Program’s Expedition 302, called the Arctic Coring Expedition (ACEX), which was the first scientific drilling effort in the permanently ice covered Arctic Ocean. Examining geological records from sediment cores offers insights into previous climates on Earth and helps scientists disentangle natural and human-caused effects in the modern climate. The author combines and compares grain size, marine microfossil, and biomarker data from the ACEX sediment cores with information from terrestrial climate data, other Arctic and global marine climate records, and plate tectonic reconstructions to create a history of Arctic conditions reaching back into the Cretaceous period.

    The results reveal numerous periods of warming and cooling, but overall, the planet’s temperature has mirrored trends in atmospheric carbon dioxide, with the transition from the warm Eocene to the cooler Miocene coinciding with a drop in carbon dioxide concentrations from above 1,500 to below 500 parts per million over a period of roughly 25 million years.

    Although late Miocene climate and sea ice conditions might have been similar to those proposed to be in our near future, the rate of change in the late Miocene was very different from today. Whereas the ongoing change from permanent to seasonal sea ice cover in the central Arctic Ocean, strongly driven by anthropogenic forcing, is occurring over a timescale of decades, the corresponding change in the late Miocene probably occurred over thousands of years.

    The author also highlights that as much as the sediment data reveal, there are also gaps in the understanding of the record. A long interval in which sedimentation rates slowed to a crawl during the early Cenozoic era, for example, presents challenges to scientists analyzing the Arctic climate history during the Miocene, Oligocene, Eocene, and Paleocene epochs. The cause of this slowdown remains a mystery to researchers, which, the author notes, emphasizes the importance of securing additional sediment cores from the Arctic on future scientific drilling expeditions to help fill the holes in the timeline.

    See the full article here .

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  • richardmitnick 9:15 am on December 26, 2019 Permalink | Reply
    Tags: "The Climate Learning Tree", Anthropogenic climate change, Catastrophists are not patient people., , Paleoclimatology   

    From Nautilus: “The Climate Learning Tree” 

    Nautilus

    From Nautilus

    December 26, 2019
    Summer Praetorius

    Why we need to branch out to solve global warming.

    As a paleoclimatologist, I often find myself wondering why more people aren’t listening to the warnings, the data, the messages of climate woes—it’s not just a storm on the horizon, it’s here, knocking on the front door. In fact, it’s not even the front door anymore. You are on the roof, waiting for a helicopter to rescue you from your submerged house.

    The data is clear: The rates of current carbon dioxide release are 10 times greater than even the most rapid natural carbon catastrophe [1] in the geological records, which brought about a miserable hothouse world of acidic oceans lacking oxygen, triggering a pulse of extinctions.[2]

    Despite the evidence for anthropogenic climate change, views about the severity and impact of global warming diverge like branch points on a gnarly old oak tree (below).

    1

    The first split is between deniers and acceptors; only the denial branch doesn’t go anywhere—it’s just a dead stump, no longer sustained by the nutrients of evidence. The next bifurcation is on the root cause of climate change. Naturalists say “the climate has always changed,” which aside from ignoring evidence that the recent increase in carbon dioxide is from burning fossil fuels,[3] is a diversion tactic for derailing meaningful conversations by stating the obvious. Of course, the climate is always changing; the relevant variable is the rate at which it does so.

    If we follow the branch line that accepts the evidence for human-induced climate change, the next major split is between those who see global warming as a good thing and those who view it as a bad one. The former view an ice-free Arctic as a business boon for oil extraction or sweltering cities as an expanding market for air conditioners, or they are your clueless uncle joking about his property going up in value because it will suddenly be beachfront property.

    This view is perched on a naïve premise that stability still prevails even amid the progressive undercutting of the systems that make it possible. It neglects the fact that accelerating the rates of change makes the probability of crossing thresholds far more likely.

    If you keep following the branch points higher and higher, you come to a split in the messaging around the outlook for the future. This might even be between two climate scientists with similar backgrounds—some of whom are struggling with ecological grief[4] and depression over dying coral reefs and the world their children will inherit, while others seem to always keep their chin up, adamant that the only way to communicate and solve the problem is to make sure it is wrapped in a bow of positivity.

    The divergent outlook of the future is like the old geological battle of gradualism versus catastrophism. Gradualists asserted that it was slow and steady processes like erosion that shaped the earth. Catastrophists pointed to extinction events in the fossil record as evidence for episodic events that punctuated the status quo and completely altered Earth’s bio and geo-spheres—events like asteroid impacts or volcanism-induced carbon catastrophes. Both, it would turn out, were right. They were just pointing to different periods in Earth’s history—different slopes on the graph—adamant that they had the proof to back up their claim.

    If we were to consider this dualism in terms of personality, we would all fall somewhere on the spectrum of gradualist to catastrophist. Gradualists expect more or less steady rates of change. They have money in the stock market; trust in stability. They are inclined to believe science will engineer a solution to climate change. Catastrophists have a healthy respect for the unexpected. They store their money in gold and bury it under the apple tree, viewing any day as ripe for collapse: earthquake, stock market, tsunami, bolide. Catastrophists are not patient people.

    The fact is, climate change will come both slow and steady as well as fast and furious, reflecting the long-term average changes in global temperature and the short-term extremes that will continue to get more and more outrageous as the system absorbs energy. The last five decades have been to some extent slow and steady because the oceans have absorbed so much of the excess heat energy,[5] buffering us from the brunt of it. This has likely contributed to a false sense of security for those who don’t know the climate system is riddled with thresholds and tipping points,[6] thinking that future changes will unfold just as gradually as the past.

    But all that heat is now fueling massive storms and generating marine heatwaves that can take down entire ecosystems in shockingly abrupt timescales. Slow erosion can give way to sudden failure. The last five years have given us a taste of the fast and furious. In these fives year, we have witnessed the collapse of coral reefs,[7] the collapse of the California kelp forest,[8] wildfires[9] and hurricanes[10] of unprecedented proportions. These are local catastrophes unfolding in real time to the occupants of these regions, their lives already divided into before and afters, much like a geological timeline.

    If there is one lesson we should heed from Earth history, it’s that thresholds become far more likely as the rates and magnitude of change increase. And the danger of thresholds is that they are effectively one-way doors: easily walked through and closed to re-entry. This is the time-asymmetry of instability: It takes much longer to establish stability than it does to unravel it.

    Rates may be the simplest and most critical aspect of climate change to understand, and yet it is not something that most people likely see on a regular basis. When I talk about rate, I take for granted that I am conjuring an image in my mind the whole time, in part because I stare at graphs of climate history every day. All those stories of ecological catastrophe are compactly folded up into a single near-vertical line on a graph. That’s when you know you’re in trouble: when the slope suddenly goes vertical (below).

    2
    DANGER AHEAD: Temperature anomalies for the Holocene period (green)[11] compared with recent global warming (blue)[12] and future projections of a low carbon emission scenario (RCP2.6, pink) and high emission scenario (RCP8.5, black) from the IPCC AR5 report.[13] The Holocene exhibits relatively gradual rates of change, whereas rates of modern and projected temperature increase are many times greater. We still have agency on whether we choose to take the double-black diamond route or an intermediate slope.

    For many climate scientists, the awareness of being on the knife’s edge of the graph, plotting steeper and steeper every day is like learning to live with vertigo, partitioning off a deep sense that we are no longer on stable ground while simultaneously trying to get on with the day, show up to work, laugh with our kids.

    Those who warn about potential instability have always been labeled “Cassandras of doom.” There’s an irony to this because Cassandra was right. She was just ignored as an “alarmist”— that dirty word now cleverly used to emasculate anyone concerned about climate change into the category of “hysterical woman.”

    The thing about alarms is that they turn out to be useful. The canary in the coalmine, smoke detectors, tornado sirens, cell phone alerts; we generally agree that instruments to detect and convey impending threats are a step in the right direction. In fact, we require them in most buildings. The inconvenience of an occasional false alarm is far outweighed by the benefit of not dying in your sleep by a raging fire.

    So while catastrophists may get the eye-roll of hyperbole, gradualists warrant an occasional head-slap of naivete. Their apparent inability to conceive a fundamentally different world leads them into a default mode of complacency, one that ironically makes it much more likely to provoke the thing they aren’t expecting. On the flip side, catastrophists are more prone to expect disaster, and might be more motivated to prevent the potential threats. So each will unwittingly prove the other one right, if they have their way of things.

    What if instead of feeling threatened by differences in opinion, we were to reconceptualize them in much the same way a tree will distribute a canopy to collect as much sunlight as possible—as a multi-pronged approach to getting the job done? In the same sense that both fast and slow processes contribute to Earth change, both steady progress and immediate local action will contribute to climate solutions. Let’s take stock of our pace and work together, thankful there is someone else to fill the space we can’t. After all, we are not lone trees, but a living, connected forest, and balance is essential for stability.

    References

    1. Cui, Y., et al. Slow release of fossil carbon during .the Palaeocene-Eocene thermal maximum Nature Geoscience 2, 481-485 (2011).

    2. McInerney, F.A. & Wing, S.L. The Paleocene-Eocene thermal maximum: A perturbation of carbon cycle, climate, and biosphere with implications for the future. Annual Review of Earth and Planetary Sciences 39, 489–516 (2011).

    3. “How Do We Know That Recent CO2 Increases Are Due to Human Activities?” RealClimate.org (2004).

    4. Cunsolo, A. & Ellis, N.R. Ecological grief as a mental health response to climate change-related loss. Nature Climate Change 8, 275–281 (2018).

    5. Cheng, L., Abraham, J., Hausfather, Z., & Trenberth, K.E.How fast are the oceans warming? Science 363, 128-129 (2019).

    6. Lenton, T.M. Climate tipping points—too risky to bet against. Nature.com (2019).

    7. Hughes, T.P., et al. Global warming impairs stock–recruitment dynamics of corals. Nature 568, 387–390 (2019).

    8. Rogers-Bennett, L. & Catton, C.A. Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens. Scientific Reports 9, 1–9 (2019).

    9. Park, W.A., et al. Observed impacts of anthropogenic climate change on wildfire in California. Earth’s Future 7, 892–910 (2019).

    10. Trenberth, K.E., et al. Hurricane Harvey links to ocean heat content and climate change adaptation. Earth’s Future 6, 730–744 (2018).

    11. Marcott, S.A., Shakun, J.D., Clark, P.U., & Mix, A.C. A reconstruction of regional and global temperature for the past 11,3000 years. Science 339, 1198-1201 (2013).

    12. GISTEMP Team. GISS Surface Temperature Analysis (GISTEMP), version 4. NASA Goddard Institute for Space Studies (2019).

    13. IPCC Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change Stocker, T.F., et al. (Eds.) Cambridge University Press (2013).

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 12:38 pm on December 6, 2019 Permalink | Reply
    Tags: "Antarctic Ice Cores Offer a Whiff of Earth’s Ancient Atmosphere", , , , Paleoclimatology   

    From Eos: “Antarctic Ice Cores Offer a Whiff of Earth’s Ancient Atmosphere” 

    From AGU
    Eos news bloc

    From Eos

    27 November 2019
    Katherine Kornei

    Bubbles of greenhouse gases trapped in ice shed new light on an important climate transition that occurred about a million years ago.

    1
    A slice of an ice core containing hundreds of tiny bubbles, each a whiff of Earth’s atmosphere. Credit: Yuzhen Yan

    To determine how Earth’s climate has varied over time, scientists are constantly on the lookout for the oldest whiffs of our planet’s atmosphere. The current record holders, recently extracted from Antarctic ice cores and dated to over 2 million years old, reveal concentrations of gases like carbon dioxide (CO2) and methane in ancient Earth’s atmosphere.

    Researchers have now shown that levels of these greenhouse gases fluctuated less millions of years ago than they did in more recent times. That discovery has implications for how Earth transitioned between two climatic periods roughly a million years ago, the team reported.

    Two Worlds

    The climatic history of Earth has been far from constant: For the past 800,000 years, continental-scale ice sheets have repeatedly grown and retreated in glacial-interglacial cycles occurring roughly every 100,000 years (the “100K world”). (The current interglacial period, which has persisted for about the past 11,000 years, is known as the Holocene.)

    But records stretching back further in time—to between 2.8 million and 1.2 million years ago—suggest that glacial-interglacial cycles were shorter and lasted only about 40,000 years (the “40K world”). However, there have been no direct observations of atmospheric greenhouse gases from that long ago. Until now.

    Yuzhen Yan, a geoscientist at Princeton University when this research was conducted, and his collaborators spent 7 weeks in Antarctica during the 2015–2016 austral summer collecting ice cores. They worked in the Allan Hills, about 200 kilometers northwest of McMurdo Station. The area, famous for its ice, is also a mecca for meteorite hunters: ALH84001, a potato-sized meteorite originally blasted off of Mars, was found in the Allan Hills and made headlines in the 1990s when scientists announced that it contained microbial fossils.

    Follow the Blue

    Yan and his colleagues drilled into “blue ice,” a rare type of ice that’s been compressed over time. Scientists value it because it’s often very old, even when relatively near the surface. In the Allan Hills, blue ice is being pushed toward a mountain and is slowly uplifting, Yan said. “What used to be buried very deep…is progressively getting closer to the surface.” At the same time, strong winds ablate the ice from the top, progressively removing younger material.

    Working in temperatures of around –15°C, the researchers drilled down to nearly bedrock and extracted roughly 300 meters of ice from three sites. Back in the laboratory, they age dated sections of the 8-centimeter-diameter (3-inch) ice cores using argon isotopes.

    However, the ages they recovered didn’t march smoothly from youngest to oldest—there were discontinuities, probably caused by the ice folding as it uplifted, the team suggests. Dating blue ice is a “key difficulty” in ice core analysis, given its jumbled stratigraphy, said John Moore, a climate scientist at the University of Lapland and Beijing Normal University not involved in the research. But there’s still “huge potential” to studying blue ice, he said.

    Pesky Microbes

    Given the discontinuous ages of the cores they recovered, Yan and his colleagues interpreted their measurements as “snapshots” of the ancient climate rather than a continuous record. They divided their 40K-world samples into three bins with average ages of 1.5 million, 2.0 million, and 2.7 million years. However, it wasn’t possible to accurately measure the concentration of carbon dioxide in air bubbles from the oldest ice.

    Blame the microbes, the team concluded. Millions of years ago, tiny organisms were probably consuming organic matter near the ice-bedrock interface and emitting carbon dioxide. The tip-off? A carbon dioxide concentration of over 1,600 parts per million in the oldest ice, roughly fourfold higher than present-day levels. “That’s very high,” said Yan.

    Younger ice—farther away from the ice-bedrock interface—wasn’t as affected by contributions of this “respiratory CO2,” the scientists concluded. After correcting for their discrete sampling, Yan and his collaborators estimated that carbon dioxide concentrations in the 40K world ranged from 204 to 289 parts per million.

    By comparing these data with those from other ice core records, researchers concluded that carbon dioxide levels were similar in the 40K and 100K worlds during interglacial periods. However, the picture changed during glacial periods: Carbon dioxide levels were about 20 parts per million higher, on average, in the 40K world compared with the 100K world. That’s consistent with a number of other proxy reconstructions, said Yan, but now “we can tell this with a very high level of confidence.”

    Dust Fertilization?

    These results contradict the idea that a long-term decline in carbon dioxide levels during both glacial and interglacial periods drove the transition between the 40K and 100K worlds, the researchers suggest. “We’re against the notion that long-term cooling was the cause of the Mid-Pleistocene Transition,” said Yan.

    Instead, these data are consistent with another hypothesis involving airborne dust. The concept is that winds deposited dust containing iron and other micronutrients near Antarctica around 800,000 years ago. This “fertilization” of the Southern Ocean boosted biological productivity because marine organisms such as phytoplankton rely on iron for growth. As these organisms died, their carbon-rich shells and skeletons sank to the seafloor and were incorporated, over millions of years, into rocks like limestone. This drawdown of carbon lowered atmospheric carbon dioxide levels during glacial periods, researchers have hypothesized [Nature].

    Getting even older samples of ice will allow scientists to dig further back into Earth’s climate history, said Yan. Right now, several of his colleagues are back in Antarctica, drilling again in the Allan Hills. And they’ve got the really big equipment with them, said Yan. “This time, they’re bringing a 10-inch drill.”

    See the full article here .

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  • richardmitnick 4:40 pm on November 26, 2019 Permalink | Reply
    Tags: , , , , Paleoclimatology   

    From Eos: “Sea Caves Hold Clues to Ancient Storms” 

    From AGU
    Eos news bloc

    From Eos

    22 November 2019
    Lakshmi Supriya

    1
    To collect sediment cores, the team’s rig anchored on the Thatch Point blue hole in the Bahamas. Credit: Jeffrey Donnelly

    Sediments deposited in ocean caves are not all the same. Sediments deposited when a storm passes are different from those deposited in normal weather.

    This difference is helping scientists unravel when hurricanes blew by various points in the Atlantic Ocean, going back about 1,500 years. Figuring out the timelines of old cyclones may help validate computer models and provide insights into future hurricanes.

    Records of old hurricanes go back only about 150 years, and such intense storms are relatively rare, making it difficult to obtain statistically significant data. “The real value of using geological records to go back further in time [is that it] allows us to look at a lot more storms,” said Amy Frappier, a paleoclimatologist at Skidmore College in Saratoga Springs, N.Y., who was not involved in the study.

    Sediments deposited in lakes or seas make up one such record. During normal weather, the sediments deposited are soft, with almost cold cream–like consistency. But when a big storm passes by, it rakes up and deposits coarse sediments that normal tides can’t move. Thus, if one digs up sediments without disturbing the layers, by looking where the coarse material was dumped, one can figure out when large storms passed by.

    Go Blue

    In a new study published in Paleoceanography and Paleoclimatology, Jeffrey Donnelly of the Woods Hole Oceanographic Institution in Massachusetts targeted blue holes. Blue holes are ocean caves that formed when sea levels were much lower. The roofs of the caves collapsed, and when the sea level rose much higher, they formed big holes at the bottom of the ocean.

    “It’s sort of the perfect sediment trap for the sorts of records we are after,” said Donnelly. “Hurricane sediments can get in but can’t get out.”

    2
    Sediment cores from blue holes were analyzed for coarse grains, which indicate hurricane activity. Credit: Lakshmi Supriya

    So Donnelly and his team dug about 20 meters into blue holes off South Andros Island, Bahamas, to bring up sediment cores comprising a record going back to about 1,500 years. (Radiocarbon dating of organic matter like leaves trapped in the sediments indicated the age of the sediments.) The team also collected shorter sediment cores from two other blue holes to corroborate the results. The cores were analyzed in the lab for coarse grains, indicating hurricane activity.

    The analysis revealed that the frequency of hurricane landfall on South Andros in the past 1,500 years varied between quiet periods and periods of intense storms. Periods of powerful storms occurred when the Intertropical Convergence Zone, a low-pressure belt near the equator, was far north, suggesting it influenced tropical storms. Researchers also noted the early part of the 13th century was uncharacteristically quiet. They think the reason may be unusually high volcanic activity.

    The team also compared the data to similar data from the Gulf of Mexico and the East Coast of the United States. Increased storm activity in South Andros corresponded to increased landfalls in the Gulf of Mexico. But surprisingly, the East Coast saw more hurricanes when South Andros was relatively quiet. It’s likely that storm tracks have been moving northward in the past millennium, the authors suggest.

    “If we can determine there are natural cycles in hurricane occurrences and strength, this gives researchers some skill in predicting future storms,” said Kristine DeLong, a paleoclimatologist at Louisiana State University in Baton Rouge who was not involved in the study. Computer models can then be refined using all these past data to make better predictions.

    When such reconstructions from different parts of the world are put together, they may help create a map of ancient tropical storms and help us be better prepared for future storms.

    See the full article here .

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  • richardmitnick 1:57 pm on April 23, 2019 Permalink | Reply
    Tags: "Atacama’s Past Rainfall Followed Pacific Sea Temperature", A Lack of Rain and Records, “It seems that ‘wetter’ episodes in the recent past in the Coastal Cordillera between Antofagasta and Arica line up with El Niño–like conditions”, “Our record covers only the first glacial-interglacial cycle”, “Whether this pattern is representative for all glacial­-interglacial times has to be tested with longer paleoclimate records.”, , Paleoclimatology, The abundance of some planktonic diatoms further indicates the existence of an ephemeral water body” meaning the basin may have periodically flooded to become a temporary lake., The researchers are working to see whether the El Niño–like pattern extends further back.   

    From Eos: “Atacama’s Past Rainfall Followed Pacific Sea Temperature” 

    From AGU
    Eos news bloc

    From Eos

    4.23.19
    Kimberly M. S. Cartier

    This is the first paleoclimate record of precipitation near Atacama’s hyperarid core and suggests that its moisture source is different from that of the Andes.

    1
    Past rainfall in the Atacama Desert may have coincided with El Niño–like conditions. The team that discovered this conducted a deep-drilling follow-up expedition in 2017, seen here. Credit: Jan Voelkel

    Even the driest place on Earth, the Atacama Desert in Chile, still sees intermittent rainfall. In the past 215,000 years, these sporadic rainfall events may have coincided with elevated sea surface temperatures nearby that resemble El Niño conditions.

    “The Atacama Desert experienced several interspersed episodes of ‘wetter,’ still arid, conditions,” Benedikt Ritter, a paleoclimatologist at the University of Cologne in Germany, told Eos. “We are exploring…the mutual evolutionary relationship between climate, geomorphology, and biological evolution.”

    Ritter and his team published these results last month in Scientific Reports.

    2
    In 2014, Benedikt Ritter and his team, seen here, used percussion drilling to extract a sediment core from the top 6 meters of a clay pan basin in the Atacama Desert. Credit: Damian Lopez

    A Lack of Rain and Records

    The hyperarid core of the Atacama Desert currently gets less than 2 millimeters of rainfall a year. Scientists don’t know when those conditions began or how often they were interrupted or for how long. The area’s sediment record for the most recent geologic period “appears like a white spot on the map,” Ritter said.

    Water runoff from the Altiplano, or Andean Plateau, to the east confuses sediment records in the hyperarid region, making it difficult to isolate local precipitation records.

    “The mostly barren landscape is almost undiscovered in terms of paleoclimate studies for the younger timescale,” Ritter said.

    Ritter and his team focused on a basin in the coastal mountain range, the Coastal Cordillera, that cuts through the hyperarid region. The basin’s location separates it from the surrounding mountain drainage networks, and its clay pan bottom helps it retain water. Sediment cores collected from this endorheic basin, the researchers hypothesized, should track past precipitation near the hyperarid core of the desert.

    Relatively Wet Periods

    The team used percussion drilling to collect a sediment core from the top 6.2 meters of the clay pan. The rock record spans the past 215,000 years and is the first paleoclimate record of the middle and upper Pleistocene for this region.

    The researchers looked at the size and composition of sediment grains as well as the abundance of fossilized microorganisms at different depths along the core. On the basis of these measures, they identified two significant wet times in the paleoclimate record: one around 200,000 years ago and a shorter period around 120,000 years ago.

    “Wet” is relative in the most arid place on the planet, Ritter said. “What we can tell, based on the sedimentological data, is that there was enough water available to transport coarse-grained sediment from the catchment into this pan.”

    Moreover, “the abundance of some planktonic diatoms further indicates the existence of an ephemeral water body,” meaning the basin may have periodically flooded to become a temporary lake.

    Atlantic Versus Pacific

    The researchers compared the timing of the basin’s wet periods with other nearby climate records and found something pretty surprising, Ritter said.

    “It seems that ‘wetter’ episodes in the recent past in the Coastal Cordillera, between Antofagasta and Arica, line up with El Niño–like conditions,” specifically, higher sea surface temperatures along the Chilean and Peruvian coasts, he explained.

    3
    The researchers extracted a pilot core, part of which is seen here, from a basin in the coastal mountain range of the Atacama. Credit: Tibor Dunai

    “The pattern is totally inverse to the Andes,” said Marco Pfeiffer, a geoscientist at the Universidad de Chile in La Pintana who has studied the Atacama’s paleolakes and paleoclimate. “In this sense, [the study] is extremely novel and without a doubt a great contribution to the local paleoclimatology.” Pfeiffer was not involved with this research

    Because Ritter’s team collected this sediment core from a basin near to, but not within, the hyperarid zone, “there is still the question [of whether] these results could be extrapolated to iconic sites of the hyperarid core such as Yungay,” Pfeiffer cautioned.

    Drilling Down Deeper

    “Our record covers only the first glacial-interglacial cycle,” Ritter said. “Whether this pattern is representative for all glacial­-interglacial times has to be tested with longer paleoclimate records.”

    The researchers are working to see whether the El Niño–like pattern extends further back. In 2017, they conducted a follow-up expedition to this region and drilled deeper into the clay pan. Their new cores reach 8 times deeper than their first, Ritter said.

    “This new deep drilling sediment record extends the published reconstructed paleoclimate in this part of the Atacama Desert to even older times,” he said. The team plans to publish these records in the near future.

    See the full article here .

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