Baltic Sea oxygen levels at '1,500-year low due to human activity'. Earlier this year a study revealed that ocean dead zones have quadrupled in size since the 1950s, and are found the world over in coastal regions of high population, from Europe to North America and China.

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Baltic Sea oxygen levels at '1,500-year low due to human activity'. Earlier this year a study revealed that ocean dead zones have quadrupled in size since the 1950s, and are found the world over in coastal regions of high population, from Europe to North America and China.