Early-Warning Signals for Marine Anoxic Events

Rick Hennekam*, Bregje van der Bolt*, Egbert H. van Nes, Gert J. de Lange, Marten Scheffer, Gert Jan Reichart

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

20 Citations (Scopus)


Predicting which marine systems are close to abrupt transitions into oxygen-deficient conditions (“anoxia”) is notoriously hard but important—as rising temperatures and coastal eutrophication drive many marine systems toward such tipping points. Rapid oxic-to-anoxic transitions occurred regularly within the eastern Mediterranean Sea on (multi)centennial time scales, and hence, its sedimentary archive allows exploring statistical methods that can indicate approaching tipping points. The here presented high-resolution reconstructions of past oxygen dynamics in the Mediterranean Sea reveal that early-warning signals in these deoxygenation time series occurred long before fast transitions to anoxia. These statistical indicators (i.e., rise in autocorrelation and variance) are hallmarks of so-called critical slowing down, signaling a steady loss of resilience of the oxygenated state as the system approaches a tipping point. Hence, even without precise knowledge of the mechanisms involved, early-warning signals for widespread anoxia in marine systems are recognizable using an appropriate statistical approach.

Original languageEnglish
Article numbere2020GL089183
JournalGeophysical Research Letters
Issue number20
Publication statusPublished - 28 Oct 2020


  • anoxia
  • early-warning signals
  • Mediterranean Sea
  • sapropels
  • sedimentary trace metals
  • tipping points


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