Increasing ocean stratification over the past half-century

Guancheng Li, Lijing Cheng, Jiang Zhu, Kevin E. Trenberth, Michael E. Mann, John P. Abraham

Research output: Contribution to journalArticlepeer-review

229 Scopus citations


Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down to depths of 2,000 m using the squared buoyancy frequency N2 and newly available ocean temperature/salinity observations. We find that stratification globally has increased by a substantial 5.3% [5.0%, 5.8%] in recent decades (1960–2018) (the confidence interval is 5–95%); a rate of 0.90% per decade. Most of the increase (~71%) occurred in the upper 200 m of the ocean and resulted largely (>90%) from temperature changes, although salinity changes play an important role locally.

Original languageEnglish (US)
Pages (from-to)1116-1123
Number of pages8
JournalNature Climate Change
Issue number12
StatePublished - Dec 2020

All Science Journal Classification (ASJC) codes

  • Environmental Science (miscellaneous)
  • Social Sciences (miscellaneous)


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