Featured Research

from universities, journals, and other organizations

Oxygen depletion in the Baltic Sea is ten times worse than a century ago

Date:
March 31, 2014
Source:
Aarhus University
Summary:
The Baltic Sea is suffering from a lack of oxygen. Poor oxygen conditions on the seabed are killing animals and plants, and experts are now sounding the alarm -- releasing fewer nutrients into the Baltic Sea is absolutely necessary. The deepest areas of the Baltic Sea have always had a low oxygen content. The inflow of fresh water is actually limited by low thresholds at the entrance to the Baltic Sea. At the same time, there is a relatively fresh layer above the denser and saltier water in the deep layer of the sea. This results in an effective stratification of the water column, which prevents the mixing of water masses necessary to transfer oxygen to the water at the bottom.

When the oxygen content in the bottom water reaches a low point, the only survivors are ultimately bacteria that live on and in the seabed. Here the patches of white sulfur bacteria form a shroud.
Credit: Photo: Peter Bondo Christensen

The Baltic Sea is suffering from a lack of oxygen. Poor oxygen conditions on the seabed are killing animals and plants, and experts are now sounding the alarm -- releasing fewer nutrients into the Baltic Sea is absolutely necessary. After several years of discussions, researchers from Aarhus University (Denmark), Lund University (Sweden) and Stockholm University (Sweden) have determined that nutrients from the land are the main cause of widespread areas of oxygen depletion. The results were published on 31 March in the journal Proceedings of the National Academy of Sciences.

Nutrients are the villain

The deepest areas of the Baltic Sea have always had a low oxygen content. The inflow of fresh water is actually limited by low thresholds at the entrance to the Baltic Sea. At the same time, there is a relatively fresh layer above the denser and saltier water in the deep layer of the sea. This results in an effective stratification of the water column, which prevents the mixing of water masses necessary to transfer oxygen to the water at the bottom.

During the last century, the areas of oxygen depletion have increased drastically from approximately 5,000 km2 in around 1900 to the present day, where they extend to 60,000 km2 -- or about one and a half times the total area of Denmark.

"We analysed data for the water temperature, oxygen content and salinity stretching back for 115 years. On the basis of this analysis, we can determine that the many nutrients from the land are the main cause of the widespread oxygen depletion," says Professor Jacob Carstensen, Department of Bioscience, Aarhus University.

Seabed without oxygen

Oxygen depletion occurs when the oxygen uptake at the bottom exceeds the amount of oxygen brought to the deeper water layers via currents and mixing by the wind.

During the last twenty years, climate change has also played a role in the poor oxygen situation. Warmer conditions reduce the solubility of oxygen from the atmosphere and increase oxygen consumption because the biological respiration processes are boosted.

"The water temperature has risen and will continue to rise in the years ahead. It's therefore extra important that all the countries surrounding the Baltic Sea are committed to the Baltic Sea action plan they joined, and that they comply with the necessary efforts to reduce the release of nutrients into the Baltic," emphasises Professor Carstensen, who is also director of the Baltic Nest Institute in Denmark.

Oxygen depletion on the seabed has a negative impact on the entire ecosystem. This is partly because the seabed turns into a 'desert' inhabited only by bacteria that can survive without or with very low amounts of oxygen. Some bacteria produce methane, which can bubble up to the water and tear large areas of the toxic, hydrogen sulphide-rich seabed with it. This involves sediment disturbances that can kill fish high up in the water column.

Studies show that it takes decades before benthic fauna once more return to a dead seabed when the oxygen conditions improve.


Story Source:

The above story is based on materials provided by Aarhus University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jacob Carstensen, Jesper H. Andersen, Bo G. Gustafsson, and Daniel J. Conley. Deoxygenation of the Baltic Sea during the last century. PNAS, March 31, 2014 DOI: 10.1073/pnas.1323156111

Cite This Page:

Aarhus University. "Oxygen depletion in the Baltic Sea is ten times worse than a century ago." ScienceDaily. ScienceDaily, 31 March 2014. <www.sciencedaily.com/releases/2014/03/140331153616.htm>.
Aarhus University. (2014, March 31). Oxygen depletion in the Baltic Sea is ten times worse than a century ago. ScienceDaily. Retrieved September 17, 2014 from www.sciencedaily.com/releases/2014/03/140331153616.htm
Aarhus University. "Oxygen depletion in the Baltic Sea is ten times worse than a century ago." ScienceDaily. www.sciencedaily.com/releases/2014/03/140331153616.htm (accessed September 17, 2014).

Share This



More Earth & Climate News

Wednesday, September 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Scientists Examine Colossal Squid

Raw: Scientists Examine Colossal Squid

AP (Sep. 16, 2014) — Squid experts in New Zealand thawed and examined an unusual catch on Tuesday: a colossal squid. It was captured in Antarctica's remote Ross Sea in December last year and has been frozen for eight months. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Man Floats for 31 Hours in Gulf Waters

Man Floats for 31 Hours in Gulf Waters

AP (Sep. 16, 2014) — A Texas man is lucky to be alive after he and three others floated for more than a day in the Gulf of Mexico when their boat sank during a fishing trip. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Researchers Explore Shipwrecks Off Calif. Coast

Researchers Explore Shipwrecks Off Calif. Coast

AP (Sep. 16, 2014) — Federal researchers are exploring more than a dozen underwater sites where they believe ships sank in the treacherous waters west of San Francisco in the decades following the Gold Rush. (Sept. 16) Video provided by AP
Powered by NewsLook.com
Isolated N. Korea Asks For International Help With Volcano

Isolated N. Korea Asks For International Help With Volcano

Newsy (Sep. 16, 2014) — Mount Paektu volcano in North Korea is showing signs of life and there's not much known about it. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

    Technology News



    Save/Print:
    Share:  

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile iPhone Android Web
    Follow Facebook Twitter Google+
    Subscribe RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins