Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”

Aerial view of the Archipelago Sea Kari Mattila, The Archipelago Research Institute

According to the researchers, human-induced pollution, from fertilisers and sewage running off the countries surrounding the Baltic into the sea, is the main driver of recent oxygen loss in the region’s coastal waters. The spread of low-oxygen areas can have dire consequences for the environment and for local populations as it can reduce fish yields and even lead to massive mortality of marine animals.

“The Baltic was strongly impacted by human nutrient inputs in the 20th century and is still experiencing the legacy of those inputs today,” says Tom Jilbert, an assistant professor at the University of Helsinki, Finland, who took part in the research. But despite recent measures to reduce the release of polluting nutrients, the researchers write in the new study that they found “no evidence of recovery” from oxygen depletion in the Archipelago Sea, a coastal area between mainland Finland and Sweden that is part of the Baltic.

A reason, they say, may be climate change. Since warm waters are less effective at holding oxygen, “global warming is likely to exacerbate oxygen depletion,” says Sami Jokinen, a researcher at the University of Turku, Finland, and lead-author of the Biogeosciences study. Jilbert adds: “Climate change was not the main cause of the current dead zone, but it is an important factor delaying the recovery.”

To find out what fuelled oxygen loss in the past and what role climate played, the team drilled and studied a 4-metre-long sediment core from the seafloor in the Archipelago Sea. This allowed them to see, for the first time, how oxygen levels changed in this area over the past 1500 years. This period includes the Medieval Climate Anomaly, a time of warmer climate but low nutrient pollution from 900 to around 1350, as well as modern times.

“The interesting finding from our study is that, in the coastal areas, oxygen loss in the modern period really stands out, due to the strong signal of recent human nutrient inputs,” says Jilbert. The team found that oxygen levels were also low during the warmer medieval period, but they write in their study that the present oxygen loss is “unprecedentedly severe,” showing how excess pollution and warmer temperatures can combine to make dead zones thrive.

The team also found that this recent oxygen loss started in the early 1900s, decades before it had been previously thought and prior to regular water-quality monitoring. “This is surprising because the 1950s is often regarded as the period of rising oxygen depletion in the Baltic Sea, which has been linked to the substantial increase in human-induced nutrient loading around that time,” says Jokinen. Landmass in the Baltic Sea area has been rising since the end of the Ice Age removed weighty ice sheets from the region, and this uplift makes some coastal areas more sensitive to oxygen loss. “On top of this, we found evidence of marked human-induced nutrient loading already at the turn of the 20th century, which likely stimulated oxygen depletion in coastal areas,” he continues.

This nutrient loading has long-term effects, making it hard to stop the ongoing spread of dead zones. Rivers in the inhabited coastlines of the Baltic carry nutrients into the sea, triggering algal blooms. As the algae die, they sink to the seafloor and are decomposed by bacteria, which use up oxygen in this process. “If human nutrient inputs are reduced, this might be expected to reduce the blooms and shrink the dead zone,” explains Jilbert. But, in dead zones, the decaying algae release phosphorus more efficiently, which then flows back to surface waters where it leads to the growth of cyanobacteria (blue-green bacteria), which, in turn, capture nitrogen from the atmosphere. “As a result, the total amount of nutrients – phosphorus and nitrogen – in the water remains high even after human inputs have been reduced,” says Jilbert. “It is a self-sustaining vicious circle that can take decades to reverse,” adds Jokinen.

“Nowadays, and likely in the future, oxygen loss in the Archipelago Sea is sustained by the continued leakage of nutrients from the agricultural land, the release of phosphorus from the sediments to the water column due to low oxygen levels, and by the ongoing global warming.” says Jokinen. “Hopefully our study will contribute to the better recognition of climate change as a substantial driver of oxygen loss in the Baltic alongside human-induced nutrient loading. To achieve good ecological status in coastal areas under the projected global warming, the required reduction in nutrient input might be higher than previously thought,” concludes Jokinen.

“The good news is that many countries in the Baltic catchment have taken significant steps towards nutrient loading reductions,” says Jilbert. “In some coastal regions we are already seeing improvements. Better understanding of the balance between nutrient inputs and climate change will therefore help to guide management of the Baltic in the future.”

###

Please mention the name of the publication (Biogeosciences) if reporting on this story and, if reporting online, include a link to the paper (https://doi.org/10.5194/bg-15-3975-2018) or to the journal website (https://www.biogeosciences.net). The link to the paper will be active once the embargo lifts.

MORE INFORMATION
This research is presented in the paper ‘A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century’ to appear in the EGU open access journal Biogeosciences on 5 July 2018.

The scientific article is available online, free of charge, from the publication date onwards, at https://doi.org/10.5194/bg-15-3975-2018 (this URL will redirect to the final, peer-reviewed paper after the embargo lifts). While the embargo lasts, a pre-print version of the final paper is available for download at https://www.egu.eu/news/414/new-study-oxygen-loss-in-the-coastal-baltic-sea-is-u… (scroll down to the Media section).

Citation: Jokinen, S. A., Virtasalo, J. J., Jilbert, T., Kaiser, J., Dellwig, O., Arz, H. W., Hänninen, J., Arppe, L., Collander, M., and Saarinen, T.: A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century, Biogeosciences, 15, 3975–4001, 2018.

The study was conducted by Sami Jokinen (Department of Geography and Geology, University of Turku, Finland); Joonas Virtasalo (Geological Survey of Finland); Tom Jilbert (Department of Environmental Sciences, University of Helsinki, Finland); Jérôme Kaiser, Olaf Dellwig and Helge Arz (Leibniz Institute for Baltic Sea Research, Germany); Jari Hänninen (Archipelago Research Institute, University of Turku); Laura Arppe (Finnish Museum of Natural History, University of Helsinki); Miia Collander (Department of Food and Environmental Sciences, University of Helsinki); and Timo Saarinen (Department of Geography and Geology, University of Turku).

The European Geosciences Union (EGU) is Europe’s premier geosciences union, dedicated to the pursuit of excellence in the Earth, planetary, and space sciences for the benefit of humanity, worldwide. It is a non-profit interdisciplinary learned association of scientists founded in 2002 with headquarters in Munich, Germany. The EGU publishes a number of diverse scientific journals, which use an innovative open access format, and organises a number of topical meetings, and education and outreach activities. Its annual General Assembly is the largest and most prominent European geosciences event, attracting over 14,000 scientists from all over the world. The meeting’s sessions cover a wide range of topics, including volcanology, planetary exploration, the Earth’s internal structure and atmosphere, climate, energy, and resources. The EGU 2019 General Assembly is taking place in Vienna, Austria, from 7 to 12 April 2019. For information and press registration, please check https://media.egu.eu, or follow the EGU on Twitter (@EuroGeosciences) and Facebook (European Geosciences Union).

If you wish to receive our press releases via email, please use the Press Release Subscription Form at https://www.egu.eu/news/subscribe/. Subscribed journalists and other members of the media receive EGU press releases under embargo (if applicable) at least 24 hours in advance of public dissemination.

Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on all aspects of the interactions between the biological, chemical, and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere, and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual, and modelling approaches are welcome.

CONTACTS
Scientists

Sami Jokinen
PhD Student, Department of Geography and Geology
University of Turku, Finland
+358(0)443 713 545
sami.jokinen@utu.fi

Tom Jilbert
Assistant Professor in Aquatic Biogeochemistry
University of Helsinki, Finland
+358(0)294 157 923, +358(0)504 480 348
tom.jilbert@helsinki.fi

Press officers

Bárbara Ferreira
EGU Media and Communications Manager
Munich, Germany
+49-89-2180-6703
media@egu.eu
@EuroGeosciences

Tuomas Koivula
Managing Editor, University of Turku Communications
+358(0)50 593 3955, +358(0)29 450 2350
viestinta@utu.fi

http://doi.org/10.5194/bg-15-3975-2018 – Scientific paper (the link will be active after the study is published on 5 July)
http://www.biogeosciences.net/ – Journal
http://www.egu.eu/medialibrary/video/3078/video-summary-oxygen-loss-in-the-coast… – Video summary
http://www.egu.eu/news/414/new-study-oxygen-loss-in-the-coastal-baltic-sea-is-un… – Press release on the EGU website, including paper pre-print, images and video

Media Contact

Dr. Bárbara Ferreira EGU Executive Office European Geosciences Union

Weitere Informationen:

http://www.egu.eu/

Alle Nachrichten aus der Kategorie: Studies and Analyses

innovations-report maintains a wealth of in-depth studies and analyses from a variety of subject areas including business and finance, medicine and pharmacology, ecology and the environment, energy, communications and media, transportation, work, family and leisure.

Zurück zur Startseite

Kommentare (0)

Schreib Kommentar

Neueste Beiträge

High-thermoresistant biopolyimides become water-soluble like starch

This is the first report for the syntheses of water-soluble polyimides which are Interestingly derived from bio-based resources, showing high transparency, tunable mechanical strength and the highest thermoresistance in water-soluble…

Land management in forest and grasslands

How much can we intensify? A first assessment of the effects of land management on the links between biodiversity, ecosystem functions and ecosystem services. Ecosystem services are crucial for human…

A molecular break for root growth

The dynamic change in root growth of plants plays an important role in their adjustment to soil conditions. Depending on the location, nutrients or moisture can be found in higher…

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.

Close