At a Glance

The Baltic has the most dead zones of any seas in the world and the situationcontinues to worsen.Nutrient-rich runoff from countries that surround the Baltic Seais the main driver of recentoxygenlossin the region's coastal waters, researchers say.

Oxygen loss in coastal areas of the Baltic Sea over the past century is unprecedented in the last 1,500 years,a new study says.

Nutrient-rich runoff from countries that surround the Baltic Seais the of recentoxygenlossin the region's coastal waters,German and Finnish researchers in a study published Thursday in theEuropean Geosciences Union journalBiogeosciences say

"The Baltic was strongly impacted by in the 20th century and is still experiencing the legacy of those inputs today," Tom Jilbert, an assistant professor at the University of Helsinki, Finland, said in a press release.

Despite efforts to reduce nitrogen-rich runoff that comes from fertilizer and sewage, the areas experiencing oxygen loss appears to be widening, while current dead zones are not recovering. The scientists say this is likely due to climate change.

"Climate change was not the main cause of the current dead zone, but it is an important factor delaying the recovery," said lead author of the study, Sami Jokinen, of theUniversity of Turku, Finland.

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The researcherscame to theirconclusions after drilling and analyzing a 13-foot-long sediment core from the seafloor, capturing the oxygen footprint over the past 1,500 years.

They found that oxygen levels were also low during the warmMedieval Climate Anomaly from 900 to 1300, but the levels detected during this ancient period is nothing compared to the "unprecedented" loss of oxygen over the past century.

"The interesting finding from our study is that, in thecoastal areas, oxygen loss in the modern period really stands out, due to the strong signal of recent human nutrient inputs," Jilbert said.

Although the 1950s is when low oxygen levels were first detected in coastal areas, the researchers say their findings suggestthe loss began in the early 1900s.

"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," Jokinen said.

The scientists notethatnutrient loading has long-term effects and makes it increasingly difficult to stop the spread of dead zones that are triggered by oxygen-consuming algal blooms.

Oxygen loss is further exacerbated by phosphorus released from the decaying algae.

"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," said Jokinen. "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."