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 July 23, 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 July 23, 2014).

Share This




More Earth & Climate News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

New Orleans Plans to Recycle Cigarette Butts

New Orleans Plans to Recycle Cigarette Butts

AP (July 21, 2014) — New Orleans is the first U.S. city to participate in a large-scale recycling effort for cigarette butts. The city is rolling out dozens of containers for smokers to use when they discard their butts. (July 21) Video provided by AP
Powered by NewsLook.com
Shark Sightings a Big Catch for Cape Tourism

Shark Sightings a Big Catch for Cape Tourism

AP (July 21, 2014) — A rise in shark sightings along the shores of Chatham, Massachusetts is driving a surge of eager vacationers to the beach town looking to catch a glimpse of a great white. (July 21) Video provided by AP
Powered by NewsLook.com
Spectacular Lightning Storm Hits London

Spectacular Lightning Storm Hits London

AFP (July 19, 2014) — A spectaCular lightning storm struck the UK overnight Friday. Images of lightning strikes over the Shard and Tower Bridge in central London. Duration: 00:23 Video provided by AFP
Powered by NewsLook.com
A Centuries' Old British Tradition Is Far from a Swan Song

A Centuries' Old British Tradition Is Far from a Swan Song

AFP (July 19, 2014) — As if it weren't enough that the Queen is the Sovereign of the UK and 15 other Commonwealth realms, she is also the owner of all Britain's unmarked swans. Duration: 02:18 Video provided by AFP
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