Permian-Triassic mass extinction was caused by ocean acidification

New findings of scientists from several universities published in Science show that the Permian-Triassic mass extinction (~ 252 million years ago), the greatest extinction event of all time, was caused by ocean acidification. The researchers studied boron isotopes from marine sediments in order to reconstruct seawater pH and subsequently combined these data with quantitative modeling techniques to develop a scenario for the mass extinction. Their results show that seawater pH remained relatively stable during the first phase of the extinction, but rapidly shifted to more acidic values during the second phase, which lasted ~ 10 thousand years. This acidification of the oceans had dramatic consequences for life on Earth and is thought to be associated with the release of massive amounts of carbon, related to the volcanism of the Siberian Traps. Up to 96 % of living marine species became extinct during the Permian-Triassic mass extinction and now, it has been shown for the first time that ocean acidification was the responsible mechanism.

Journal reference: Clarkson, M. O., Kasemann, S. A., Wood, R. A., Lenton, T. M., Daines, S. J., Richoz, S., … & Tipper, E. T. (2015). Ocean acidification and the Permo-Triassic mass extinction. Science348(6231), 229-232.

Image: Eruption of the Tavurvur volcano on February 13, 2009 near Rabaul, New Britain, Papua New Guinea. Source: Taro Taylor, Wikimedia Commons.

Emperor penguins on Antarctica forced into refugia during last glacial maximum

Research of biologists published in Global Change Biology indicates that emperor penguins on Antarctica were forced into refugia by extreme cold during the last glacial maximum (~ 19.5 – 16 thousand years ago). By comparing the DNA of fossil emperor penguins with the DNA of living individuals and colonies, the scientists were able to reconstruct the population dynamics of emperor penguins on Antarctica through time. Their results show three mitochondrial clades within emperor penguins at the time of the last glacial maximum, which suggests that these birds were isolated in three small, separate populations and may have survived in refugia such as the Ross Sea. The population sizes of emperor penguins are related to the balance between sea ice available for breeding and open water available for foraging. Sea ice extent around Antarctica was much greater during the last glacial maximum than at present and therefore, reduced food availability resulted in severe losses among populations of emperor penguins.

Journal reference: Younger, J. L., Clucas, G. V., Kooyman, G., Wienecke, B., Rogers, A. D., Trathan, P. N., … & Miller, K. J. (2015). Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum. Global change biology21(6), 2215-2226.

Image: Emperor penguin colony foraging along the Weddell Sea, Antarctica. Source: Christopher Michel, Wikimedia Commons.

Rise of animals on Earth delayed by insufficient oxygen

Geologists of different universities have found that insufficient levels of atmospheric oxygen during the mid-Proterozoic (~ 1.8 billion to 800 million years ago) delayed the evolutionary rise of animals on Earth. They studied chromium isotope data from shallow marine Proterozoic sediments and compared them to younger Phanerozoic sediments deposited in similar environments. Their findings suggest that chromium oxidation in the Proterozoic was very limited and that oxygen levels were at most 0.1 % of present atmospheric levels. Previous estimates of atmospheric concentrations have varied greatly, but it was generally accepted that oxygen existed at Earth’s surface during the Proterozoic. The late appearance and diversification of metazoans was therefore long thought to be limited by genetic advancements and ecological innovation, but now it appears that their evolution was instead delayed by low levels of oxygen.

Journal reference: Planavsky, N. J., Reinhard, C. T., Wang, X., Thomson, D., McGoldrick, P., Rainbird, R. H., … & Lyons, T. W. (2014). Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals. Science346(6209), 635-638.

Image: Cirrus clouds above Warsaw, Poland. Source: Przemyslaw Idzkiewicz, Wikimedia Commons.

Sahara desert may be older than previously thought

New findings of climatologists published in Nature reveal that the formation of the Sahara desert may have started up to 7 million years ago, more than twice as long ago as previously thought. Following the discovery of aeolian dune deposits that challenged the widely accepted age of approximately 2 – 3 million years for the Sahara desert, the scientists have used climate models to simulate the mechanisms behind the onset of aridification in northern Africa. Their results show that the origination of the Sahara desert may be related to shrinking of the Tethys Sea and the uplift of the Arabian Peninsula, associated with the northward movement of the African tectonic plate towards the Eurasian tectonic plate during the late Miocene. This reorganization of landmasses is thought to have significantly weakened the African summer monsoon, resulting in a reduced flow of moisture from the Atlantic Ocean and increasingly arid conditions in northern Africa. Until now, it was long believed that the desertification of northern Africa was related to the onset of glaciation on the Northern Hemisphere during the Pliocene and Pleistocene.

Journal reference: Zhang, Z., Ramstein, G., Schuster, M., Li, C., Contoux, C., & Yan, Q. (2014). Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene. Nature, 513(7518), 401-404.

Image: Sand dunes of the Sahara desert at sunset in Fezzan, Libya. Source: Luca Galuzzi, Wikimedia Commons.

New details on the uplift history of the Tibetan Plateau

Research of geologists published in GSA Bulletin has revealed new information regarding the uplift history of the Tibetan Plateau, at present the highest elevated mountain range on Earth (~ 4.5 km). The scientists have reconstructed lake paleotemperatures for the Miocene and Pliocene by using clumped isotope thermometry, based on carbonate shells from gastropods in two well-studied basins in central and southwestern Tibet. Their results show that between the late Miocene and early Pliocene, paleotemperatures were up to 9 °C colder than during the mid-Pliocene and younger. Since paleotemperature records reflect changes in both climate and elevation, the scientists estimate that the Tibetan Plateau must have reached an even higher paleoelevation (~ 5.4 km) than at present. This fits well with paleontological and isotopic data from the Miocene-Pliocene indicating the presence of cold-adapted mammals in a cold, high-elevation climate.

Journal reference: Huntington, K. W., Saylor, J., Quade, J., & Hudson, A. M. (2015). High late Miocene–Pliocene elevation of the Zhada Basin, southwestern Tibetan Plateau, from carbonate clumped isotope thermometry. Geological Society of America Bulletin127(1-2), 181-199.

Image: North face of Mount Everest as seen from Tibet, China. Source: Luca Galuzzi, Wikimedia Commons.

Antarctic sea level rising faster than global sea level

Climatologists at the University of Southampton have discovered that over the past 19 years, sea level around the coast of Antarctica has risen 2 cm more than the global average rise of 6 cm. They have detected this rapid sea level rise by studying detailed satellite images of an area spanning over a million square kilometers and have attributed it to the melting of fresh water from the Antarctic glaciers and ice shelves, which is further supported by a decrease in the salinity of the surrounding ocean waters. In order to explain these observations, the scientists estimate that a total discharge of approximately 430 Gt of fresh water to the surrounding ocean is required. Furthermore, global ocean circulation model simulations of the effects of melting ice on the Antarctic Ocean closely match their findings.

Journal reference: Rye, C. D., Garabato, A. C. N., Holland, P. R., Meredith, M. P., Nurser, A. G., Hughes, C. W., … & Webb, D. J. (2014). Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge. Nature Geoscience7(10), 732-735.

Image: Melting icebergs along the Antarctic Peninsula, Antarctica. Source: Christopher Michel, Wikimedia Commons.