{"id":15458,"date":"2018-07-05T06:00:54","date_gmt":"2018-07-05T06:00:54","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=15458"},"modified":"2020-06-09T12:57:40","modified_gmt":"2020-06-09T12:57:40","slug":"study-oxygen-loss-in-the-coastal-baltic-sea-is-unprecedentedly-severe","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/study-oxygen-loss-in-the-coastal-baltic-sea-is-unprecedentedly-severe\/","title":{"rendered":"Study: oxygen loss in the coastal Baltic Sea is \u201cunprecedentedly severe\u201d"},"content":{"rendered":"

The Baltic Sea is home to some of the world\u2019s largest dead zones, areas of oxygen-starved waters where most marine animals can\u2019t survive.\u00a0But while parts of this sea have long suffered from low oxygen levels, a new study by a team in Finland and Germany shows that oxygen loss in coastal areas over the past century is unprecedented in the last 1500 years.<\/span><\/p>\n

The research is published in the European Geosciences Union journal\u00a0Biogeosciences<\/a>.<\/span><\/p>\n

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\nAccording 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\u2019s 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 animaAls.<\/span><\/p>\n

\u201cThe Baltic was strongly impacted by human nutrient inputs in the 20th century and is still experiencing the legacy of those inputs today,\u201d 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 \u201cno evidence of recovery\u201d from oxygen depletion in the Archipelago Sea, a coastal area between mainland Finland and Sweden that is part of the Baltic.<\/span><\/p>\n

A reason, they say, may be climate change. Since warm waters are less effective at holding oxygen, \u201cglobal warming is likely to exacerbate oxygen depletion,\u201d says Sami Jokinen, a researcher at the University of Turku, Finland, and lead-author of the Biogeosciences study. Jilbert adds: \u201cClimate change was not the main cause of the current dead zone, but it is an important factor delaying the recovery.\u201d<\/span><\/p>\n

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.<\/span><\/p>\n

\u201cThe 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,\u201d 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 \u201cunprecedentedly severe,\u201d showing how excess pollution and warmer temperatures can combine to make dead zones thrive.<\/span><\/p>\n

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. \u201cThis 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,\u201d 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. \u201cOn 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,\u201d he continues.<\/span><\/p>\n

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. \u201cIf human nutrient inputs are reduced, this might be expected to reduce the blooms and shrink the dead zone,\u201d 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. \u201cAs a result, the total amount of nutrients \u2013 phosphorus and nitrogen \u2013 in the water remains high even after human inputs have been reduced,\u201d says Jilbert. \u201cIt is a self-sustaining vicious circle that can take decades to reverse,\u201d adds Jokinen.<\/span><\/p>\n

\u201cNowadays, 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.\u201d says Jokinen. \u201cHopefully 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,\u201d concludes Jokinen.<\/span><\/p>\n

\u201cThe good news is that many countries in the Baltic catchment have taken significant steps towards nutrient loading reductions,\u201d says Jilbert. \u201cIn 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.\u201d<\/span><\/p>\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

The Baltic Sea is home to some of the world\u2019s largest dead zones, areas of oxygen-starved waters where most marine animals can\u2019t survive.<\/p>\n","protected":false},"author":2,"featured_media":15461,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-15458","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july-150x150.jpg",150,150,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july-300x146.jpg",300,146,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",600,292,false],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",600,292,false],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",550,267,false],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",95,46,false],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",617,300,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",96,47,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2018\/07\/revoscience_uw-news_2018-july.jpg",150,73,false]},"author_info":{"info":["RevoScience"]},"category_info":"Research<\/a>","tag_info":"Research","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/15458","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=15458"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/15458\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/15461"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=15458"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=15458"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=15458"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}