A Texas A&M-led study analyzed ocean floor sediment cores to provide new insights into the relationship between deep ocean oxygenation and atmospheric carbon dioxide levels in the 50,000 years before the last ice age
Why do carbon dioxide levels in the atmosphere wax and wane in conjunction with the warm and cold periods of Earth’s past? Scientists have been trying to answer this question for many years, and thanks to chemical clues left in sediment cores extracted from deep in the ocean floor, they are starting to put together the pieces of that puzzle.
Recent research suggests that there was enhanced storage of respired carbon in the deep ocean when levels of atmospheric carbon dioxide concentrations were lower than today’s levels. But new research led by a Texas A&M University scientist has reached back even further, for the first time revealing insights into atmospheric carbon dioxide levels in the 50,000 years before the last ice age.
From 2008 to 2016 a widespread cooling ranging from 0.6°C to more than 2.0°C has chilled effectively the entire oceanic region from E. Canada to N. Iceland to S. Europe. The cooling persists year-round and extends from the surface down to depths of 800 m.
About 790,000 years ago, a meteor slammed into Earth with such force that the explosion blanketed about 10% of the planet with shiny black lumps of rocky debris. Known as tektites, these glassy blobs of melted terrestrial rock were strewn from Indochina to eastern Antarctica and from the Indian Ocean to the western Pacific. For more than a century, scientists searched for evidence of the impact that created these pitted blobs.
But the crater’s location eluded detection — until now.
Geochemical analysis and local gravity readings told researchers that the crater lay in southern Laos on the Bolaven Plateau; the ancient impact was concealed under a field of cooled volcanic lava spanning nearly 2,000 square miles (5,000 square kilometers), the scientists reported in a new study.
Was the crater buried? On Laos’ Bolaven Plateau, the scientists found a site where fields of volcanic lava might have hidden signs of an older meteor impact. In a region that the researchers targeted as a likely spot for a crater, most of the lava flows were also in the right age range: between 51,000 and 780,000 years old.
The study authors peered below the lava’s surface by taking gravity readings at more than 400 locations. Their resulting gravity map showed one area “of particular interest” with a gravitational anomaly, a subsurface zone less dense than the volcanic rock surrounding it. Their measurements hinted at an elliptical, “elongated crater” about 300 feet (100 m) thick, about 8 miles (13 km) wide and 11 miles (17 km) long, according to the study.
Together, all of these clues suggested that “this thick pile of volcanic rocks does indeed bury the site of the impact,” the scientists wrote.
Dry summers were not rare 1000 years ago. Researchers from the University of Greifswald’s research group ‘Landscape Ecology and Ecosystem Dynamics’ have been able to reconstruct 1000 years of the dry summer period in northern Germany.
Beech forest – photo: Dr. Tobias Scharnweber
The article ‘Removing the no-analogue bias in modern accelerated tree growth leads to stronger medieval drought’ was published in 2019’s February edition of the journal Scientific Reports.
As part of the current collaborative research project BaltRap (The Baltic Sea and its Southern Lowlands: Proxy-Environment interactions in times of rapid changes), the researchers investigated growth rings in nearly 2000 living beech trees – including some from the university’s own Elisenhain forest – and archaeological wood used for construction from around 1000 A.D. The growth rings found in this wood are a unique archive of previous environmental conditions. If the climatic conditions are good, growth rings are wide; in unfavourable years, like in dry 2018, there is little growth. Dendroclimatology uses this correlation to reconstruct past environmental conditions.
by Indriani Roy, September28, 2018 in FrontiersinEarthScience
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom
The puzzle of recent global warming trend slowdown has captured enough attention, though the underlying cause is still unexplained. This study addresses that area segregating the role of natural factors (the sun and volcano) to that from CO2 led linear anthropogenic contributions. It separates out a period 1976–1996 that covers two full solar cycles, where two explosive volcanos erupted during active phases of strong solar cycles. The similar period also matched the duration of abrupt global warming. It identifies that dominance of Central Pacific (CP) ENSO and associated water vapor feedback during that period play an important role. The possible mechanism could be initiated via a preferential alignment of NAO phase, generated by explosive volcanos. Inciting extratropical Rossby wave to influence the Aleutian Low, it has a modulating effect on CP ENSO. Disruption of Indian Summer Monsoon and ENSO during the abrupt warming period and a subsequent recovery thereafter can also be explained from that angle. Interestingly, CMIP5 model ensemble, and also individual models, fails to comply with such observation. It also explores possible areas where models miss important contributions due to natural drivers.
La géologie, une science plus que passionnante … et diverse