Archives par mot-clé : Geology

Hematite reconstruction of Late Triassic hydroclimate over the Colorado Plateau

by Lepre, J & Olsen P.E., Feb 21, 2021 PNAS


Significance

Hematite provides much of the color for the classic Triassic–Jurassic “red beds” of North America and elsewhere. Measuring the spectrum of visible light reflected and absorbed by the red beds, we demonstrate that the hematite concentrations faithfully track 14.5 million years of Late Triassic monsoonal rainfall over the Colorado Plateau of Arizona and use this information to assess interrelationships between environmental perturbations, climate, and the evolution of terrestrial vertebrates. The research challenges conventional ideas that the hematite has limited use for interpreting the ancient past because it is a product of natural chemical alterations that occurred long after the beds were initially deposited.

Abstract

Hematite is the most abundant surficial iron oxide on Earth resulting from near-surface processes that make it important for addressing numerous geologic problems. While red beds have proved to be excellent paleomagnetic recorders, the early diagenetic origin of hematite in these units is often questioned. Here, we validate pigmentary hematite (“pigmentite”) as a proxy indicator for the Late Triassic environment and its penecontemporaneous origin by analyzing spectrophotometric measurements of a 14.5-My–long red bed sequence in scientific drill core CPCP-PFNP13-1A of the Chinle Formation, Arizona. Pigmentite concentrations in the red beds track the evolving pattern of the Late Triassic monsoon and indicate a long-term rise in aridity beginning at ∼215 Ma followed by increased oscillatory climate change at ∼213 Ma. These monsoonal changes are attributed to the northward drift of the Colorado Plateau as part of Laurentia into the arid subtropics during a time of fluctuating CO2. Our results refine the record of the Late Triassic monsoon and indicate significant changes in rainfall proximal to the Adamanian–Revueltian biotic transition that thus may have contributed to apparent faunal and floral events at 216 to 213 Ma.

Scientists Discover Plate Tectonics… Again

by D. Middleton, Feb 5, 2021 in WUWT


An upwelling of rock beneath the Atlantic may drive continents apart
The Mid-Atlantic Ridge may play a more active role in plate tectonics than thought

By Maria Temming

FEBRUARY 4, 2021

An upsurge of hot rock from deep beneath the Atlantic Ocean may be driving the continents on either side apart.

The Americas are moving away from Europe and Africa by a few centimeters each year, as the tectonic plates underlying those continents drift apart. Researchers typically think tectonic plates separate as the distant edges of those plates sink down into Earth’s mantle, creating a gap (SN: 1/13/21). Material from the upper mantle then seeps up through the rift between the plates to fill in the seafloor.

But new seismic data from the Atlantic Ocean floor show that hot rock is welling up beneath a seafloor rift called the Mid-Atlantic Ridge from hundreds of kilometers deep in Earth’s mantle. This suggests that material rising up under the ridge is not just a passive response to tectonic plates sliding apart. Rather, deep rock pushing toward Earth’s surface may be driving a wedge between the plates that helps separate them, researchers report online January 27 in Nature.

A better understanding of plate tectonics — which causes earthquakes and volcanic eruptions — could help people better prepare for these natural disasters (SN: 9/3/17).

The role of megacontinents in the supercontinent cycle

by Wang et al. 2020 in GeolSocAmerica OPEN ACCESS.pdf


ABSTRACT
Supercontinent Pangea was preceded by the formation of Gondwana, a “megacontinent”

about half the size of Pangea. There is much debate, however, over what role the assembly of the precursor megacontinent played in the Pangean supercontinent cycle. Here we dem- onstrate that the past three cycles of supercontinent amalgamation were each preceded by ∼200 m.y. by the assembly of a megacontinent akin to Gondwana, and that the building of a megacontinent is a geodynamically important precursor to supercontinent amalgamation. The recent assembly of Eurasia is considered as a fourth megacontinent associated with future supercontinent Amasia. We use constraints from seismology of the deep mantle for Eurasia and paleogeography for Gondwana to develop a geodynamic model for megacontinent assembly and subsequent supercontinent amalgamation. As a supercontinent breaks up, a megacontinent assembles along the subduction girdle that encircled it, at a specific location where the downwelling is most intense. The megacontinent then migrates along the girdle where it collides with other continents to form a supercontinent. The geometry of this model is consistent with the kinematic transitions from Rodinia to Gondwana to Pangea.

See also  What might Earth’s next supercontinent look like? New study provides clues

Rocks show Mars once felt like Iceland

by Rice University, Jan 21, 2021 in ScienceDaily


Crater study offers window on temperatures 3.5 billion years ago

Once upon a time, seasons in Gale Crater probably felt something like those in Iceland. But nobody was there to bundle up more than 3 billion years ago.

The ancient Martian crater is the focus of a study by Rice University scientists comparing data from the Curiosity rover to places on Earth where similar geologic formations have experienced weathering in different climates.

Iceland’s basaltic terrain and cool weather, with temperatures typically less than 38 degrees Fahrenheit, turned out to be the closest analog to ancient Mars. The study determined that temperature had the biggest impact on how rocks formed from sediment deposited by ancient Martian streams were weathered by climate.

The study by postdoctoral alumnus Michael Thorpe and Martian geologist Kirsten Siebach of Rice and geoscientist Joel Hurowitz of State University of New York at Stony Brook set out to answer questions about the forces that affected sands and mud in the ancient lakebed.

Data collected by Curiosity during its travels since landing on Mars in 2012 provide details about the chemical and physical states of mudstones formed in an ancient lake, but the chemistry does not directly reveal the climate conditions when the sediment eroded upstream. For that, the researchers had to look for similar rocks and soils on Earth to find a correlation between the planets.

Volcanic eruptions directly triggered ocean acidification during Early Cretaceous

by Northwestern University, Dec 21, 2020 in ScienceDaily


Around 120 million years ago, the earth experienced an extreme environmental disruption that choked oxygen from its oceans.

Known as oceanic anoxic event (OAE) 1a, the oxygen-deprived water led to a minor — but significant — mass extinction that affected the entire globe. During this age in the Early Cretaceous Period, an entire family of sea-dwelling nannoplankton virtually disappeared.

By measuring calcium and strontium isotope abundances in nannoplankton fossils, Northwestern earth scientists have concluded the eruption of the Ontong Java Plateau large igneous province (LIP) directly triggered OAE1a. Roughly the size of Alaska, the Ontong Java LIP erupted for seven million years, making it one of the largest known LIP events ever. During this time, it spewed tons of carbon dioxide (CO2) into the atmosphere, pushing Earth into a greenhouse period that acidified seawater and suffocated the oceans.

In Geological Terms, Today’s Atmospheric CO2 Concentrations Are Still Uncomfortably Low

by P. Gosselin, Dec 5, 2020 in NoTricksZone


Under 180 ppm atmospheric CO2 concentration, life on earth begins to die.

The earth came very close to that point not long ago during the Ice Ages (20,000 years ago). Then the planet warmed naturally, and an increase in atmospheric CO2 to over 200 ppm followed (new study here).

The earth saw CO2 levels of close to 8000 ppm in the past, i.e. about 20 times more than today. The following chart shows the earth’s atmospheric CO2 concentrations for the past 600 million years.

Today, thanks in large part to mankind, concentrations have risen to over 400 ppm, yet historically this remains at the very low end of the scale compared to the thousands of ppm seen naturally earlier in history.

Greening planet

Today, definitely a safer level would be near 1000 ppm. Studies unanimously show plant growth at these higher levels is far enhanced. Already today we see clear evidence the planet is greening Zhu et al. (2016), in part due to the fertilizations taking place through human emissions:

Editorial: Deep Carbon Science

by D. Cardace et al., Nov 12, 2020 in Front.Earth.Sci.


Editorial on the Research Topic
Deep Carbon Science

Our understanding of the slow, deep carbon cycle, key to Earth’s habitability is examined here. Because the carbon cycle links Earth’s reservoirs on nano- to mega-scales, we must integrate geological, physical, chemical, biological, and mathematical methods to understand objects and processes so small and yet so vast. Here, we profile current research in the physical chemistry of carbon in natural and model systems, processes ongoing in the deepest portions of planets, and observations of carbon utilization by the deep biosphere. The relationships between the carbon cycle and planetary habitability are undeniable, forming a conceptual anchor to all work in deep carbon science.

Carbon minerals respond to changing pressures, temperatures, and geochemical conditions. The geologic record preserves evidence of transitional periods at the submicroscopic to regional landscape scales, and demonstrates interplay between carbon-bearing phases and the biosphere. In a new review, Morrison et al. (2020) cast a retrospective look through deep time and call for emerging approaches to clarify the coevolution of the biosphere and geosphere.

Critical to transformations of Earth’s carbon inventory over time are indomitable tectonics – which influence Earth’s surface environment, weathering, metamorphism, magmatism, and volcanism. The slow, deep (endogenous) carbon cycle refines and re-distributes carbon within Earth. In fact, over the 200-million-year-long time scale, important tectonic controls on carbon cycling emerge (Wong et al., 2019). Wong et al. (2019) document the spatiotemporal evolution of fluxes inferred from plate tectonic reconstructions, and highlight CO2 fluxes from continental rift settings post-Pangea. The volcanic flux of CO2 has been successfully reconstructed by direct study of CO2 flux through lakes and adjacent soils (Hughes et al., 2019), an important and often overlooked CO2 valve linking lithosphere, atmosphere, and hydrosphere. From perspectives rooted deeper in the tectonic system, the important roles that serpentinites play in the carbon cycle are evaluated in two senses: 1) serpentinite as a carbon vector to the deep mantle (Merdith et al., 2019), and 2) serpentine mud volcanoes as sites of carbon mobilization through organic acid release (Eickenbusch et al., 2019), in a Mariana Trench case study.

Continuer la lecture de Editorial: Deep Carbon Science

East African Rift System is slowly breaking away, with Madagascar splitting into pieces

by Virginia Tech, Nov 13, 2020 in ScienceDaily


The African continent is slowly separating into several large and small tectonic blocks along the diverging East African Rift System, continuing to Madagascar — the long island just off the coast of Southeast Africa — that itself will also break apart into smaller islands.

These developments will redefine Africa and the Indian Ocean. The finding comes in a new study by D. Sarah Stamps of the Department of Geosciences for the journal Geology. The breakup is a continuation of the shattering of the supercontinent Pangea some 200 million years ago.

Rest assured, though, this isn’t happening anytime soon.

“The rate of present-day break-up is millimeters per year, so it will be millions of years before new oceans start to form,” said Stamps, an assistant professor in the Virginia Tech College of Science. “The rate of extension is fastest in the north, so we’ll see new oceans forming there first.”

Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations

by Jurikova, H. et al., Oct 19, 2020 in NatureGeoscience


Abstract

The Permian/Triassic boundary approximately 251.9 million years ago marked the most severe environmental crisis identified in the geological record, which dictated the onwards course for the evolution of life. Magmatism from Siberian Traps is thought to have played an important role, but the causational trigger and its feedbacks are yet to be fully understood. Here we present a new boron-isotope-derived seawater pH record from fossil brachiopod shells deposited on the Tethys shelf that demonstrates a substantial decline in seawater pH coeval with the onset of the mass extinction in the latest Permian. Combined with carbon isotope data, our results are integrated in a geochemical model that resolves the carbon cycle dynamics as well as the ocean redox conditions and nitrogen isotope turnover. We find that the initial ocean acidification was intimately linked to a large pulse of carbon degassing from the Siberian sill intrusions. We unravel the consequences of the greenhouse effect on the marine environment, and show how elevated sea surface temperatures, export production and nutrient input driven by increased rates of chemical weathering gave rise to widespread deoxygenation and sporadic sulfide poisoning of the oceans in the earliest Triassic. Our findings enable us to assemble a consistent biogeochemical reconstruction of the mechanisms that resulted in the largest Phanerozoic mass extinction.

A New Mass Extinction Event Has Been Discovered, And It Triggered The Rise of Dinosaurs

by M. Benton, Sep 25, 2020 in ScienceAlert


Huge volcanic eruptions 233 million years ago pumped carbon dioxide, methane, and water vapour into the atmosphere. This series of violent explosions, on what we now know as the west coast of Canada, led to massive global warming.

Our new research has revealed that this was a planet-changing mass extinction event that killed off many of the dominant tetrapods and heralded the dawn of the dinosaurs.

The best known mass extinction happened at the end of the Cretaceous period, 66 million years ago. This is when dinosaurs, pterosaurs, marine reptiles and ammonites all died out.

This event was caused primarily by the impact of a giant asteroid that blacked out the light of the sun and caused darkness and freezing, followed by other massive perturbations of the oceans and atmosphere.

Geologists and palaeontologists agree on a roster of five such events, of which the end-Cretaceous mass extinction was the last. So our new discovery of a previously unknown mass extinction might seem unexpected.

And yet this event, termed the Carnian Pluvial Episode (CPE), seems to have killed as many species as the giant asteroid did. Ecosystems on land and sea were profoundly changed, as the planet got warmer and drier.

On land, this triggered profound changes in plants and herbivores. In turn, with the decline of the dominant plant-eating tetrapods, such as rhynchosaurs and dicynodonts, the dinosaurs were given their chance.

Curved rock etchings reveal which way dangerous faults ruptured—and how they might again

by P. Voosen, Sep 23, 2020 in AAAS Science


Many of the world’s most dangerous earthquake faults are a silent menace: They have not ruptured in more than a century. To gauge the hazard they pose to buildings and people, geologists cannot rely on the record of recent strikes, captured by seismometers. Instead, they must figure out how the faults behaved in the past by looking for clues in the rocks themselves, including slickenlines, scour marks along the exposed rock face of a fault that can indicate how much it slipped in past earthquakes.

Earthquakes don’t happen all at once. Rather, the slip between rocks begins at one spot on the face of the fault—the hypocenter—and travels along it, like a zipper being unzipped. As the rupture advances, the earthquake waves it generates pile up and intensify, like the siren of an approaching ambulance. Los Angeles lies at the northern terminus of the southern San Andreas fault, Ampuero notes. “If it breaks north, toward LA, that would be pretty bad.”

Life on Earth may have begun in hostile hot springs

by Jack L. Lee, Sep 245, 2020 in Sciencenews


At Bumpass Hell in California’s Lassen Volcanic National Park, the ground is literally boiling, and the aroma of rotten eggs fills the air. Gas bubbles rise through puddles of mud, producing goopy popping sounds. Jets of scorching-hot steam blast from vents in the earth. The fearsome site was named for the cowboy Kendall Bumpass, who in 1865 got too close and stepped through the thin crust. Boiling, acidic water burned his leg so badly that it had to be amputated.

Some scientists contend that life on our planet arose in such seemingly inhospitable conditions. Long before creatures roamed the Earth, hot springs like Bumpass Hell may have promoted chemical reactions that linked together simple molecules in a first step toward complexity. Other scientists, however, place the starting point for Earth’s life underwater, at the deep hydrothermal vents where heated, mineral-rich water billows from cracks in the ocean floor.

As researchers study and debate where and how life on Earth first ignited, their findings offer an important bonus. Understanding the origins of life on this planet could offer hints about where to search for life elsewhere, says Natalie Batalha, an astrophysicist at the University of California, Santa Cruz. “It has very significant implications for the future of space exploration.” Chemist Wenonah Vercoutere agrees. “The rules of physics are the same throughout the whole universe,” says Vercoutere, of NASA’s Ames Research Center in Moffett Field, Calif. “So what is there to say that the rules of biology do not also carry through and are in place and active in the whole universe?”

A global-scale data set of mining areas

by Maus, V. Sep 8, 2020 in ScientificData OPEN ACCESS


Abstract

The area used for mineral extraction is a key indicator for understanding and mitigating the environmental impacts caused by the extractive sector. To date, worldwide data products on mineral extraction do not report the area used by mining activities. In this paper, we contribute to filling this gap by presenting a new data set of mining extents derived by visual interpretation of satellite images. We delineated mining areas within a 10 km buffer from the approximate geographical coordinates of more than six thousand active mining sites across the globe. The result is a global-scale data set consisting of 21,060 polygons that add up to 57,277 km2. The polygons cover all mining above-ground features that could be identified from the satellite images, including open cuts, tailings dams, waste rock dumps, water ponds, and processing infrastructure. The data set is available for download from https://doi.org/10.1594/PANGAEA.910894 and visualization at www.fineprint.global/viewer.

SANGAY VOLCANO ERUPTS TO 40,000 FT (12.2 KM)

by Cap Allon, Sep 21, 2020 in Electroverse


Ecuador’s active Sangay Volcano exploded in dramatic fashion over the weekend, firing volcanic ash high into the atmosphere — the explosion was a number of times stronger than those previously observed during the volcano’s recent uptick.

The ‘high-level’ eruption occurred at 04:20 local time on Sunday, September 20 and generated a dense, dark ash plume, but the ‘biggie’ was sandwiched between numerous other powerful blasts that occurred throughout the weekend:

More crucially though, particulates ejected to around 32,800 ft (10 km) –and into the stratosphere– can have a direct cooling effect across the planet.

Volcanic eruptions are one of the key forcings driving Earth into its next bout of global cooling. Their worldwide uptick (along with a seismic uptick) is tied to low solar activity, coronal holes, a waning magnetosphere, and the influx of Cosmic Rays penetrating silica-rich magma.

A 500-million-year survey of Earth’s climate reveals dire warning for humanity

by P. Voosen, May 22, 2019 in AAAS/Science


When it opens next month, the revamped fossil hall of the Smithsonian Institution’s National Museum of Natural History in Washington, D.C., will be more than a vault of dinosaur bones. It will show how Earth’s climate has shifted over the eons, driving radical changes in life, and how, in the modern age, one form of life—humans—is, in turn, transforming the climate.

To tell that story, Scott Wing and Brian Huber, a paleobotanist and paleontologist, respectively, at the museum, wanted to chart swings in Earth’s average surface temperature over the past 500 million years or so. The two researchers also thought a temperature curve could counter climate contrarians’ claim that global warming is no concern because Earth was much hotter millions of years ago. Wing and Huber wanted to show the reality of ancient temperature extremes—and how rapid shifts between them have led to mass extinctions. Abrupt climate changes, Wing says, “have catastrophic side effects that are really hard to adapt to.”

But actually making the chart was unexpectedly challenging—and triggered a major effortto reconstruct the record. Although far from complete, the research is already showing that some ancient climates were even more extreme than was thought.

Volcanic ash may have a bigger impact on the climate than we thought

by University of Colorado at Boulder, Sep 11, 2020 in ScienceDaily


“They saw some large particles floating around in the atmosphere a month after the eruption,” Zhu said. “It looked like ash.”

She explained that scientists have long known that volcanic eruptions can take a toll on the planet’s climate. These events blast huge amounts of sulfur-rich particles high into Earth’s atmosphere where they can block sunlight from reaching the ground.

Researchers haven’t thought, however, that ash could play much of a role in that cooling effect. These chunks of rocky debris, scientists reasoned, are so heavy that most of them likely fall out of volcanic clouds not long after an eruption.

Zhu’s team wanted to find out why that wasn’t the case with Kelut. Drawing on aircraft and satellite observations of the unfolding disaster, the group discovered that the volcano’s plume seemed to be rife with small and lightweight particles of ash — tiny particles that were likely capable of floating in the air for long periods of time, much like dandelion fluff.

Journal Reference:

  1. Yunqian Zhu, Owen B. Toon, Eric J. Jensen, Charles G. Bardeen, Michael J. Mills, Margaret A. Tolbert, Pengfei Yu, Sarah Woods. Persisting volcanic ash particles impact stratospheric SO2 lifetime and aerosol optical properties. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-18352-5

Meteorite study suggests Earth may have been wet since it formed

by Washington University in St. Louis, Aug 27, 2020 in ScienceDaily


Enstatite chondrite meteorites, once considered ‘dry,’ contain enough water to fill the oceans — and then some

A new study finds that Earth’s water may have come from materials that were present in the inner solar system at the time the planet formed — instead of far-reaching comets or asteroids delivering such water. The findings published Aug. 28 in Science suggest that Earth may have always been wet.

Researchers from the Centre de Recherches Petrographiques et Geochimiques (CRPG, CNRS/Universite de Lorraine) in Nancy, France, including one who is now a postdoctoral fellow at Washington University in St. Louis, determined that a type of meteorite called an enstatite chondrite contains sufficient hydrogen to deliver at least three times the amount of water contained in the Earth’s oceans, and probably much more.

Enstatite chondrites are entirely composed of material from the inner solar system — essentially the same stuff that made up the Earth originally.

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water,” said lead author Laurette Piani, a researcher at CPRG. “Hydrogen-bearing material was present in the inner solar system at the time of the rocky planet formation, even though the temperatures were too high for water to condense.”

Le Précambrien : les bactéries, la tectonique des plaques et l’oxygène

by A. Préat (.pdf), 21 août 2020 in Bull.Séanc.Acad.R.Sci.OutreMer


 Mots-clés. — Écosystèmes microbiens; Isotopes du carbone et du soufre; Oxydoréduction; Oxygène; Océans et atmosphère. 

Résumé. — L’oxygène n’est pas apparu aussi brutalement qu’on le pensait sur notre planète. Malgré un apport en oxygène lié aux cyanobactéries dès l’archéen, ce ne sont pas ces microorganismes qui sont à la base de la première grande «révolution» de l’oxygène qui a eu lieu à la limite archéen/paléoprotérozoïque (il y a deux milliards et demi d’années) dans l’atmosphère, lors du Grand Événement d’Oxydation. Ce sont les processus liés au cycle de la tectonique des plaques (activité mantellique et périodes intenses d’érosion/altération) qui ont contribué de manière déterminante à l’augmentation de la concentration de l’oxygène atmosphérique voici deux milliards et demi d’années. Les deux principaux processus responsables de cette augmentation sont liés à l’enfouissement de la matière organique et de la pyrite. L’altération des séries riches de ces deux composants conditionnera ensuite pendant près d’un milliard d’années la composition chimique des océans en oxygène, soufre et fer. Au cours du temps, l’oxygène proviendra de l’activité des cyanobactéries et l’atmosphère réductrice du début de l’archéen sera remplacée par une atmosphère oxydante à la fin du précambrien. 

Keywords. — Microbial Ecosystems; Carbon and Sulfur Isotopes; Oxidation Reduction; Oxygen; Oceans and Atmosphere. 

Summary. — The Precambrian: Bacteria, Plate Tectonics and Oxygen. — Oxygen did not appear as abruptly as we thought on our planet. Despite an oxygen supply related to cyanobacteria since the Archean, these microorganisms are not at the origin of the first great oxygen revolution that took place at the Archean/Paleoproterozoic boundary (two and a half billion years) in the atmosphere during the Great Oxidation Event. Two processes related to the cycle of plate tectonics (mantle activity and intense periods of erosion/weathering) were mostly involved in the increase of the atmospheric oxygen concentration two and a half billion years ago. These two main processes are related to the burial of organic matter and pyrite. The alteration of series with high contents of these two elements will then condition for nearly one billion years the oxygen, sulfur and iron chemical composition of the oceans. Oxygen will finally come from the activity of cyanobacteria and the early Archean reducing atmosphere will be replaced by an oxidizing atmosphere at the end of the Precambrian. 

Fig. 3. — Évolution des compositions chimiques et des organismes des océans en trois phases majeures. À l’archéen, les océans contiennent peu d’oxygène et sont relativement riches en fer (colonne de gauche), alors que dans les océans modernes (colonne de droite) l’oxygène est abondant et le fer en quantité limitée. Entre ces deux phases, un long intervalle d’un peu plus d’un milliard d’années est caractérisé par des océans avec des concentrations modérées d’oxygène en surface et des eaux plus profondes riches en H2S en présence de quantités limitées de fer, de molybdène et d’autres éléments en traces importants dans les cycles biologiques. La colonne centrale représente l’«Océan de Canfield» et caractérise le Boring Billion. L’H2S produit (suite à la présence des sulfates, cf. texte) réagit avec le fer ferreux pour former la pyrite. Le fer ferreux n’est donc pas consommé par l’oxygène durant cet intervalle de temps, mais par l’H2S. L’Événement Lomagundi-Jatuli a lieu à environ 2,1 Ga dans le GOE (Great Oxidation Event), marqué par une très forte production d’oxygène. Le début du GOE est marqué par l’oxydation de la pyrite sur les cratons et la disparition des minéraux détritiques sensibles aux conditions d’oxydoréduction des éléments chalcophiles ou sidérophiles (uraninite, sidérite, pyrite, molybdénite, etc.). Les deux grands épisodes «Terre Boule de Neige» à 2,3 Ga («Glaciation Makganyena») et 0,635 («Glaciation Marinoenne»), et d’autres événements glaciaires moins importants ne sont pas reportés ni discutés dans le texte (modifié d’après Knoll 2003). 

 

More Proof That Geologic Forces Are Melting Thwaites and Pine Island Glaciers

by J.E. Kamis, July 20, 2020 in ClimateChangeDispatch


As previously explained before, increased melting/ice loss of Antarctica’s Pine Island and Thwaites glaciers is the result of geologically induced heat flow emitted from underlying bedrock “hotspots,” not climate change (Figure 1).

All but a very minor amount of Antarctica’s glacial ice melting occurs in the western portion of this continent. The most rapid and greatest ice mass loss areas are in West Antarctica.

They are positioned directly above geographically extensive and high heat flow geological features. This association is thought to be strong evidence of a cause and effect relationship.

Discussion of evidence supporting the contention that the melting of Pine Island and Thwaites glaciers is the result of bedrock heat flow begins with a review of the regional geology (refer to Figure 1).

The Pluton Rich “hotspot” is a 61,000-thousand-square-mile area that is home to numerous high-heat-flow lava pockets that are bounded and fueled by deep earth reaching faults.

Several detailed research studies document the existence and configuration of this area. This lies along the West Antarctic Rift.

The Mount Erebus Volcanic Complex “Hotspot” is the most geologically active portion of Antarctica. It is a 25,000-square-mile high-heat-flow area, much of which is absent of glacial ice.

The absence of glacial ice across a huge portion of West Antarctica is extremely unusual and exceedingly difficult to explain by invoking global warming.

Figure 1. NASA map of Antarctica’s ice sheet thickness 1992-2017. Greatest ice thickness losses shaded red. The outline of three regional sub-glacial geological Hotspots” are outlined in red (Image by NASA, most labeling by J. Kamis).

Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation

by de la Vega et al., 2020 in Nature OPEN  ACCESS


Abstract

The Piacenzian stage of the Pliocene (2.6 to 3.6 Ma) is the most recent past interval of sustained global warmth with mean global temperatures markedly higher (by ~2–3 °C) than today. Quantifying CO2 levels during the mid-Piacenzian Warm Period (mPWP) provides a means, therefore, to deepen our understanding of Earth System behaviour in a warm climate state. Here we present a new high-resolution record of atmospheric CO2 using the δ11B-pH proxy from 3.35 to 3.15 million years ago (Ma) at a temporal resolution of 1 sample per 3–6 thousand years (kyrs). Our study interval covers both the coolest marine isotope stage of the mPWP, M2 (~3.3 Ma) and the transition into its warmest phase including interglacial KM5c (centered on ~3.205 Ma) which has a similar orbital configuration to present. We find that CO2 ranged from 389+388389−8+38ppm to 331+1311,331−11+13,ppm, with CO2 during the KM5c interglacial being 371+3229371−29+32ppm (at 95% confidence). Our findings corroborate the idea that changes in atmospheric CO2 levels played a distinct role in climate variability during the mPWP. They also facilitate ongoing data-model comparisons and suggest that, at present rates of human emissions, there will be more CO2 in Earth’s atmosphere by 2025 than at any time in at least the last 3.3 million years.

Carbon dioxide level unprecedented in 15 MY… More evidence it’s not the climate control knob!avid Middl

by David Middleton, July 10, 2020 in WUWT


If the Earth was 3-4 °C warmer with a much higher sea level 3.3 million years ago, with about the same CO2 concentration, what does this say about the potency of it as a climate control knob?

The last time CO2 levels were this low, Earth was in the deepest ice age of the Phanerozoic Eon, the Pennsylvanian (Late Carboniferous)-Early Permian.

Figure 5. Phanerozoic temperatures (pH-corrected) and carbon dioxide. The Miocene is the first epoch of the Neogene Period (Berner et al, 2001 and Royer et al., 2004) (older is toward the left).

Mass spectrometry and climate science. Part I: Determining past climates

by Judith Curry, June 16, 2020 in ChRotter_WUWT


Mass spectrometry is essential for research in climate science.

Understanding climate requires having sufficient knowledge about past climate and about the important factors that are influencing climate today, so that reliable models can be developed to predict future climate.

Analytical chemistry enables measurement of the chemical composition of materials, from the amounts of elements and their isotopes in a sample to the identity and concentrations of substances in the most complex biological organisms.

This two-part series covers the application of a powerful analytical chemistry technology — mass spectrometry — to two important areas in climate science:

  • Obtaining reliable information about past climate
  • Understanding composition and behavior of aerosols, which have a large impact on climate

The examples that are included for each topic were selected out of many published papers on the study of climate using mass spectrometry, partly because they feature a very wide range of types of these instruments. The authors were very helpful in providing me with information on their work.[1]

The technology described in this essay may at times be quite complicated! However, I hope that the results of each study will be understandable.

Part 1: Determining past climate

Figure 1: Age of samples taken at indicated depth below surface of ice core

Giant tectonic plate under Indian Ocean is breaking in two

by Geggel L., May 21, 2020 in LiveScience


The giant tectonic plate under the Indian Ocean is going through a rocky breakup … with itself.

In a short time (geologically speaking) this plate will split in two, a new study finds.

To humans, however, this breakup will take an eternity. The plate, known as the India-Australia-Capricorn tectonic plate, is splitting at a snail’s pace — about 0.06 inches (1.7 millimeters) a year. Put another way, in 1 million years, the plate’s two pieces will be about 1 mile (1.7 kilometers) farther apart than they are now.

“It’s not a structure that is moving fast, but it’s still significant compared to other planet boundaries,” said study co-researcher Aurélie Coudurier-Curveur, a senior research fellow of marine geosciences at the Institute of Earth Physics of Paris.

Related: In photos: Ocean hidden beneath Earth’s surface

For instance, the Dead Sea Fault in the Middle East is moving at about double that rate, or 0.2 inches (0.4 centimeters) a year, while the San Andreas Fault in California is moving about 10 times faster, at about 0.7 inches (1.8 cm) a year.

The plate is splitting so slowly and it’s so far underwater, researchers almost missed what they’re calling the “nascent plate boundary.” But two enormous clues — that is, two strong earthquakes originating in a strange spot in the Indian Ocean — suggested that Earth-changing forces were afoot.

On April 11, 2012, a magnitude-8.6 and magnitude-8.2 earthquake hit beneath the Indian Ocean, near Indonesia. The earthquakes didn’t happen along a subduction zone, where one tectonic plate slides under another. Instead, these quakes originated in a weird place for earthquakes to happen — in the middle of the plate.

Arctique géologique 1/2

by Préat A. & Van Vliet-Lanoë B., 22 mai 2020 in ScienceClimatEnergie


A la grande différence de l’Antarctique, l’Arctique est un océan entouré de plateaux continentaux (Fig. 2). L’océan ou bassin arctique est actuellement constitué par un double bassin, séparé une crête très importante, la ride Lomonosov : le sous-bassin canadien à croûte continentale amincie (3 600 m)  et le sous-bassin eurasiatique à croûte océanique mince, de loin le plus profond (5000 m entre la crête Lomonosov et la ride océanique active de Gakkel). Il est entouré comme le long de l’Atlantique Nord par une plateforme continentale ennoyée, constituée de croûte continentale.  Le bassin arctique  d’abord marin et connecté au Proto-Atlantique au début du Jurassique (voir plus loin), est isolé depuis le Jurassique moyen et essentiellement de nature lacustre, modifiant le régime thermique océanique, amenant un contexte voisin du Glaciaire au Crétacé inférieur (au Valanginien in Dromart et al. 2003 ; Korte et al. 2015 ; Piskarev et al. 2018). Il ne se ré-ouvrira sur le bassin atlantique qu’à partir de l’Eocène, via l’ouverture du détroit de Fram. D’autre part le pôle  magnétique terrestre (Nord) est resté sur le bassin arctique depuis le début du Jurassique, donc en position de déficit énergétique lié à l’obliquité de l’orbite terrestre.

Fig. 2  Image Gebco Arctique : L’océan ou bassin arctique est actuellement constitué par un double bassin, séparé une crête très importante, la ride Lomonossov (voir texte).

Are We Seeing a New Ocean Starting to Form in Africa?

by Klemetti, E., May 8, 2020 in EOS


Although shallow magma storage at Erta Ale volcano hints at a rift-to-ridge transition, the tectonic future of the Afar region is far from certain.

Standing next to a lava lake at the summit of a massive volcano, Christopher Moore, a Ph.D. candidate at the School of Earth and Environment at the University of Leeds in the United Kingdom, could see the red haze of lava flows a few kilometers away. This might seem like a rare sight, but at Ethiopia’s Erta Ale, it’s business as usual.

Are such behaviors the first signs of a tectonic transition? This question is part of what Moore has been studying at Erta Ale. The entire Afar region in eastern Africa finds itself in the middle of changes that could split the continent, forming a new ocean basin. The magmatism at Erta Ale might be offering signs of this switch by mimicking the characteristics of a mid-ocean ridge.

Satellite image of eastern Africa, with the Red Sea and the Gulf of Aden to the east
The East African Rift valley, the Red Sea, and the Gulf of Aden are clearly visible in this Landsat 8 image, taken on 8 November 2019. Credit: NASA/Erik Klemetti

However, there isn’t agreement about how close the Afar region is to this tectonic transition. The geophysical characteristics of magma storage at Erta Ale could point to the region’s conversion to an incipient oceanic spreading center, but the petrology of the erupting lava might be telling us that we aren’t there yet.