Geoscientists from the Warnemünde Leibniz Institute for Baltic Sea Research, the universities of Oldenburg and Hannover as well as the Rutgers University (USA) succeeded now in reconstructing the depositional environment of the last interglacial (Eemian, 128,000 years ago) in the Black Sea with unprecedented details. This enabled for the first time a direct comparison between the current oxygen-depleted conditions in the deep water with those during the Eemian when the water temperatures in summer were 3° higher. It shows that the dead zones of the Black Sea will most probably expand by a future global warming leading to a significant shrinking of the productive zone in the surface water.
Oxygen deficiency together with the occurrence of toxic hydrogen sulphide below water depths of 100 – 150 m are the most prominent features of the Black Sea, the world´s largest brackish basin. Today, up to 90 % of the Black Sea water body is a harsh and hostile oxygen-free environment where no higher life can survive.
It is critical to understand how these dead zones will develop in response to the ongoing global warming and sea level rise. The detailed analyses of sediments from the last interglacial (Eemian) in the Black Sea, recently published in the international journal “Palaeogeography, Palaeoclimatology, Palaeoecology“ offer insights into a potential future.
Oxygen depletion in the bottom waters of the Black Sea causes a decelerated decomposition of the organic matter sinking to the seafloor. These organic-rich muds form the so-called sapropels that are quite common among both recent and Eemian deposits.
By means of detailed analyses of redox-sensitive chemical elements in these sapropels, the team succeeded in reconstructing a differentiated picture of the deep-water conditions during the Holocene and Eemian periods in the Black Sea.
As environmental witnesses (so-called proxies) the geoscientists used, for example, the trace elements molybdenum and rhenium, which react differently and specifically on oxygen deficiency and the presence of sulphide. In total, the analysis of more than 10 of such proxies enabled the reconstruction of a complex picture.
IOW geologist Antje Wegwerth summarizes the results: ”During the Eemian period the deep water of the Black Sea showed a significantly higher concentration of sulphide and, thus, was more toxic than today. The hostile conditions expanded over thousands of years and finally reached the so called photic zone, the highly productive surface water layer exposed to light.”
In such a resolution and quality, no Eemian sediments have been investigated so far, because these deep lying deposits are normally accessible only by expensive deep-sea drillings. However, during a cruise on R/V METEOR sediments from both Holocene and Eemian periods could be retrieved by conventional gravity coring from a prominent bathymetric ridge structure. Thus, the direct comparison of both interglacials became possible.
Postglacial warming during the Eemian and the Holocene caused significant changes in the Black Sea. The large polar ice sheets disappeared, the global sea level rose, and once flooding the shallow Bosporus sill, the salty and dense water masses of the Mediterranean Sea intruded the formerly Black Sea “Lake”. This led to a strong stratification with saline deep waters below the brackish surface waters.
At the same time, elevated sea surface temperatures resulted in an increased productivity and flux of organic matter, ultimately exhausting oxygen in the basin during its decomposition. The interaction of these processes finally lead to the generation of enormous “dead zones” in the Black Sea.
Wegwerth, A., Eckert, S., Dellwig, O., Schnetger, B., Severmann, S., Weyer, S., Brüske, A., Kaiser, J., Köster, J., Arz, H.W., Brumsack, H.-J. Redox evolution during Eemian and Holocene sapropel formation in the Black Sea. Palaeogeography, Palaeoclimatology, Palaeoecology (2018) 489, 249-260
Dr. Antje Wegwerth, +49 381 5197 3481, Antje.Wegwerth@io-warnemuende.de
Press and public relation:
Dr. Barbara Hentzsch | +49 381 5197-102 | Barbara.Hentzsch@io-warnemuende.de
IOW is a member of the Leibniz Association with currently 91 research institutes and scientific infrastructure facilities. The focus of the Leibniz Institutes ranges from natural, engineering and environmental sciences to economic, social and space sciences as well as to the humanities. The institutes are jointly financed at the state and national levels. The Leibniz Institutes employ a total of 18.100 people, of whom 9.200 are scientists. The total budget of the institutes is 1.6 billion Euros. (http://www.leibniz-association.eu)
Dr. Barbara Hentzsch | idw - Informationsdienst Wissenschaft
Life on land and tropical overheating 250 million years ago
10.01.2018 | MUSE Museo delle Scienze
New study reveals strong El Niño events cause large changes in Antarctic ice shelves
09.01.2018 | University of California - San Diego
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
Scientists at Helmholtz Zentrum München have discovered a mechanism that amplifies the autoimmune reaction in an early stage of pancreatic islet autoimmunity prior to the progression to clinical type 1 diabetes. If the researchers blocked the corresponding molecules, the immune system was significantly less active. The study was conducted under the auspices of the German Center for Diabetes Research (DZD) and was published in the journal ‘Science Translational Medicine’.
Type 1 diabetes is the most common metabolic disease in childhood and adolescence. In this disease, the body's own immune system attacks and destroys the...
Researchers from LMU/MPQ implement a dynamical version of the 4D quantum Hall effect with ultracold atoms in an optical superlattice potential
In literature, the potential existence of extra dimensions was discussed in Edwin Abbott’s satirical novel “Flatland: A Romance of Many Dimensions” (1884),...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
10.01.2018 | Earth Sciences
10.01.2018 | Materials Sciences
10.01.2018 | Physics and Astronomy