September 25, 2022

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New technology shows ancient temperatures were much hotter than thought

New technology shows ancient temperatures were much hotter than thought

Zoom / Isotopes in sediment cores such as these can provide indications of past temperatures.

In a recent paper Posted in Sciences, Professor Nellie Meckler of the University of Bergen and colleagues argue that the climate between about 35 and 60 million years ago may have been much warmer than we thought. Their findings indicate the presence of a certain level of carbon dioxide2 This may result in more warming than previous work indicated, and it hints that the ocean circulated differently during that warm, ice-free climate.

Their conclusions came from new measurements of carbon and oxygen isotopes found in the shells of tiny creatures called benthic foraminifera, or “holes,” that lived on the sea floor at the time. Previous work with similar samples had estimated temperatures using Oxygen isotopes—a technique that can be confused with changes in the amount of water trapped in ice at the poles and, to a lesser extent, with differences in ocean salinity. The new study used technology that records temperatures more reliably and produces warmer numbers.

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Benthic oxygen isotopes were a mainstay of ancient global climate studies, with the most recent detailed record stretching far back 60 million years. Deep ocean temperatures reflect ocean surface temperatures on time scales longer than about 1,000 years because “conveyor belt“Ocean circulation flips over on this time scale. Oxygen isotopes In that water it reflects the ocean surface temperature, and thus the global climate, because water containing the heavier isotope oxygen-18 is slightly more difficult to evaporate than water containing oxygen-16; When the sea is warmer and there is more evaporation, oxygen-18 accumulates in the oceans.

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This isotopic buildup is calibrated according to temperature, but this calibration requires knowledge of the ocean’s salinity and how much water is trapped in the ice caps. “Globalism [oxygen isotope] The curve… has always had a near-hidden uncertainty due to the dual effects of temperature and ice volume that we can now solve using agglomerated isotopes, said Sierra Petersen of the University of Michigan, who was not involved in Meckler’s study.

The aggregated isotope method removes the need to make this assumption about the amount of water sequestered in the ice because it simultaneously measures the levels of carbon-13 present in the same calcium carbonate sample in the crust of a hole. Thermodynamics favors the “clumping” of heavy isotopes of calcium carbonate in cold water, but as the water temperature rises, entropy increasingly exerts its influence, and heavier isotopes become scattered in the shell material. . degree The isotope clump is calibrated for temperature In the laboratory for a variety of materials, allowing aggregated isotope measurements to obtain temperature measurements in deep time.

The new method indicates that between 57 and 52 million years ago, the North Atlantic Abyss was about 20 °C. This is a significant difference from the oxygen isotope data, which yielded temperatures between 12 and 14 degrees Celsius. “It’s much warmer,” Meckler said. For comparison, today’s equivalent is about 1-2 ° C.