Here we present current research topics of our section.
A sensational discovery: Traces of rainforests in West Antarctica
[01. April 2020] An international team of researchers led by geoscientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, have now provided a new and unprecedented perspective on the climate history of Antarctica. In a sediment core collected in the Amundsen Sea, West Antarctica, in February 2017, the team discovered pristinely preserved forest soil from the Cretaceous, including a wealth of plant pollen and spores and a dense network of roots. These plant remains confirm that, roughly 90 million years ago, the coast of West Antarctica was home to temperate, swampy rainforests where the annual mean temperature was ca. 12 degrees Celsius – an exceptionally warm climate for a location near the South Pole. The researchers surmise that this warmth was only possible because there was no Antarctic ice sheet and because the atmospheric carbon dioxide concentration was significantly higher than indicated by climate models to date. The study, which provides the southernmost directly assessable climate and environmental data from the Cretaceous and poses new challenges for climate modellers around the globe, was released today in the journal NATURE.
Johann P. Klages, Ulrich Salzmann, Torsten Bickert, Claus-Dieter Hillenbrand, Karsten Gohl, Gerhard Kuhn, Steven M. Bohaty, Jürgen Titschack, Juliane Müller, Thomas Frederichs, Thorsten Bauersachs, Werner Ehrmann, Tina van de Flierdt, Patric Simões Pereira, Robert D. Larter, Gerrit Lohmann, Igor Niezgodzki, Gabriele Uenzelmann-Neben, Maximilian Zundel, Cornelia Spiegel, Chris Mark, David Chew, Jane E. Francis, Gernot Nehrke, Florian Schwarz, James A. Smith, Tim Freudenthal, Oliver Esper, Heiko Pälike, Thomas A. Ronge, Ricarda Dziadek, and the Science Team of Expedition PS104: Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature. doi:10.1038/s41586-020-2148-5
Major wind-driven ocean currents are shifting toward the poles
[24. February 2020] In the course of the past 40 years, the major wind-driven current systems in the ocean have steadily shifted toward the poles. Experts at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), came to this conclusion after analysing long-term global satellite data on the ocean surface temperature and sea level height. Both datasets offer insights into the evolution of large-scale surface currents, and indicate that, in the Northern and Southern Hemisphere alike, the borders of the ocean gyres and their boundary currents are moving closer to the poles, at a rate of over 800 metres per year. This displacement of tremendous water masses is chiefly driven by global warming, as e.g. calculations using a new AWI climate model confirm. According to the AWI researchers, the consequences of this change can already be felt by human beings and the environment alike: in affected regions, the sea level is rising, indigenous species are migrating, and storms are now following new courses. The study was released today in the journal Geophysical Research Letters.
Hu Yang, Gerrit Lohmann, Uta Krebs-Kanzow, Monica Ionita, Xiaoxu Shi, Dmitry Sidorenko, Xun Gong, Xueen Chen, and Evan J. Gowan: Poleward Shift of the Major Ocean Gyres Detected in a Warmin Climate. Geophysical Research Letters. doi: 10.1029/2019GL085868
Melting triggers melting
[11. July 2018] The melting of glaciers on one side of the globe can trigger disintegration of glaciers on the other side of the globe, as has been presented in a recent paper by a team of AWI scientists, who investigated marine microalgae preserved in glacial deposits and subsequently used their findings to perform climate simulations. The study highlights a process with alerting consequences for modern ice sheets: continuous warming of the ocean can result in a massive loss of polar ice mass, and consequently to rapid sea level rise.
Edith Maier, Xu Zhang, Andrea Abelmann, Rainer Gersonde, Stefan Mulitza, Martin Werner, Maria Méheust, Jian Ren, Bernhard Chapligin, Hanno Meyer, Rüdiger Stein, Ralf Tiedemann and Gerrit Lohmann: North Pacific freshwater events linked to changes in glacial ocean circulation. Nature, 2018. doi: 10.1038/s41586-018-0276-y
Signs of tipping point for oxygen minimum zone in the ocean
[08. May 2018] When ocean temperatures change, the natural variability of the oxygen supply and the associated biogeochemical cycles don’t respond in a lineal manner. Instead, circa 6,000 years ago a tipping point was reached relatively suddenly. This was the key finding of a study by group of researchers led by geologists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), which has now been published in the journal PNAS.
Lester Lembke-Jene, Ralf Tiedemann, Dirk Nürnberg, Xun Gong, and Gerrit Lohmann: A Rapid Shift and Millennial-scale Variations in Holocene North Pacific Intermediate Water Ventilation. Proceedings of the National Academy of Sciences of the United States of America (PNAS). doi:10.1073/pnas.1714754115
New findings on the past and future of sea ice cover in the Arctic
[29. August 2017] Temperatures in the Arctic are currently climbing two to three times faster than the global average. The result – and, thanks to feedback effects, also the cause – is dwindling sea ice. In a study published in the actual volume of Nature Communications, geo- and climate researchers at the Alfred-Wegener Institute, Helmholtz Centre for Polar- and Marine Research (AWI) show that, in the course of our planet’s history, summertime sea ice was to be found in the central Arctic in periods characterised by higher global temperatures – but less CO2 – than today.
Ruediger Stein, Kirsten Fahl, Paul Gierz, Frank Niessen & Gerrit Lohmann: Arctic Ocean sea ice cover during the penultimate glacial and the last interglacial. Nature Communications. doi: 10.1038/s41467-017-00552-1
Falling sea level caused volcanos to overflow
[06. July 2017] Throughout the last 800,000 years, Antarctic temperatures and atmospheric carbon dioxide concentrations showed a similar evolution. However, this was different during the transition to the last ice age: approximately 80,000 years ago, temperature declined, while the carbon dioxide content of the atmosphere remained relatively stable. An international research team led by the GEOMAR Helmholtz Centre for Ocean Research Kiel and the Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research has now discovered that a falling sea level may have caused enhanced volcanic activity in the ocean, which can explain the anomaly. The results are published today in the journal Nature Communications.
Hasenclever, J., G. Knorr, L. H. Rüpke, P. Köhler, J. Morgan, K. Garofalo, S. Barker, G. Lohmann, I. R. Hall: Sea level fall during glaciation stabilized atmospheric CO2 by enhanced volcanic degassing (2017). Nature Communications. doi: 10.1038/NCOMMS15867
How the climate can rapidly change at tipping points
[19. June 2017] During the last glacial period, within only a few decades the influence of atmospheric CO2 on the North Atlantic circulation resulted in temperature increases of up to 10 degrees Celsius in Greenland – as indicated by new climate calculations from researchers at the Alfred Wegener Institute and the University of Cardiff. Their study is the first to confirm that there have been situations in our planet’s history in which gradually rising CO2 concentrations have set off abrupt changes in ocean circulation and climate at “tipping points”. These sudden changes, referred to as Dansgaard-Oeschger events, have been observed in ice cores collected in Greenland. The results of the study have just been released in the journal Nature Geoscience.
Nature Geoscience: Xu Zhang, Gregor Knorr, Gerrit Lohmann, Stephen Barker: Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state. doi: 10.1038/NGEO2974
How the Arctic Ocean became saline
[06. June 2017] The Arctic Ocean was once a gigantic freshwater lake. Only after the land bridge between Greenland and Scotland had submerged far enough did vast quantities of salt water pour in from the Atlantic. With the help of a climate model, researchers from the Alfred Wegener Institute have demonstrated how this process took place, allowing us for the first time to understand more accurately how Atlantic circulation as we know it today came about. The results of the study have now been published in the journal Nature Communications.
Michael Stärz, Wilfried Jokat, Gregor Knorr, Gerrit Lohmann: Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge. Nature Communications. doi: 10.1038/NCOMMS15681
Intensification and poleward shift of oceanic boundary currents
[28. June 2016] Global warming results in fundamental changes to important ocean currents. As scientists from the Alfred-Wegener-Institute show in a new study, wind-driven subtropical boundary currents in the northern and southern hemisphere are not only going to increase in strength by the end of this century. The Kuroshio Current, the Agulhas Current and other oceanic currents are shifting their paths towards the pole and thus carry higher temperatures and thus the risk of storms to temperate latitudes. For this study, researchers evaluated a wealth of independent observational data and climate simulations. They showed the same pattern for all boundary currents, with the Gulf Stream as the only exception. According to the data, the latter will weaken over the next decades. The study has been published today in the Journal of Geophysical Research professional journal.
Hu Yang, Gerrit Lohmann, Wei Wei, Mihai Dima, Monica Ionita, Jiping Liu: Intensification and Poleward Shift of Subtropical Western Boundary Currents in a warming climate, Journal of Geophysical Research. doi: 10.1002/2015JC011513
Six to ten million years ago: Ice-free summers at the North Pole
[04. April 2016] An international team of scientists led by the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) have managed to open a new window into the climate history of the Arctic Ocean. Using unique sediment samples from the Lomonosov Ridge, the researchers found that six to ten million years ago the central Arctic was completely ice-free during summer and sea-surface temperature reached values of 4 to 9 degrees Celsius. In spring, autumn and winter, however, the ocean was covered by sea ice of variable extent, the scientists explain in the current issue of the journal Nature Communications. These new findings from the Arctic region provide new benchmarks for groundtruthing global climate reconstructions and modelling.
Ruediger Stein, Kirsten Fahl, Michael Schreck, Gregor Knorr, Frank Niessen, Matthias Forwick, Catalina Gebhardt, Laura Jensen, Michael Kaminski, Achim Kopf, Jens Matthiessen, Wilfried Jokat, and Gerrit Lohmann: Evidence for ice-free summers in the late Miocene central Arctic Ocean. Nature Communications 7: 11148. doi: 10.1038/ncomms11148
How stable is the West Antarctic Ice Sheet?
[05. February 2016] A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West Antarctic Ice Sheet. The result would be a rise in the global sea level by several metres. A collapse of the West Antarctic Ice Sheet may have occurred during the last interglacial period 125,000 years ago, a period when the polar surface temperature was around two degrees Celsius higher than today. This is the result of a series of model simulations which the researchers of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have published online in the journal Geophysical Research Letters.
Johannes Sutter, Paul Gierz, Klaus Grosfeld, Malte Thoma, Gerrit Lohmann: Ocean temperature thresholds for Last Interglacial West Antarctic Ice Sheet collapse. Geophysical Research Letters 2016. doi: 10.1002/2016GL067818