Annual Cycle Changes in the Vertical Structure of Ocean Temperature:A Fingerprint of Human Influence on Climate

Shi, Jia Rui, Santer, Benjamin D., Kwon, Young Oh and Wijffels, Susan E. (2025) Annual Cycle Changes in the Vertical Structure of Ocean Temperature:A Fingerprint of Human Influence on Climate. Journal of Climate, 38 (7). pp. 1595-1610. ISSN 0894-8755

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Abstract

We investigate changes in the vertical structure of the ocean temperature annual cycle amplitude (TEMPAC) down to a depth of 300 m, providing important insights into the relative contributions of anthropogenic and natural influences. Using observations and phase 6 of the Coupled Model Intercomparison Project (CMIP6) simulations, we perform a detection and attribution analysis by applying a standard pattern-based “fingerprint” method to zonal-mean TEMPAC anomalies for three major ocean basins. In all model historical simulations and observational datasets, TEMPAC increases significantly in the surface layer, except in the Southern Ocean, and weakens within the subsurface ocean. There is a decrease in TEMPAC below the annual-mean mixed layer depth, mainly due to a deep-reaching winter warming signal. The temporal evolution of signal-to-noise (S/N) ratios in observations indicates an identifiable anthropogenic fingerprint in both surface and interior ocean annual temperature cycles. These findings are consistent across three different observational datasets, with variations in fingerprint detection time likely related to differences in dataset coverage, interpolation method, and accuracy. Analysis of CMIP6 single-forcing simulations reveals the dominant influence of greenhouse gases and anthropogenic aerosols on TEMPAC changes. Our identification of an anthropogenic TEMPAC fingerprint is robust to the selection of different analysis periods. S/N ratios derived with model data only are consistently larger than ratios calculated with observational signals, primarily due to model versus observed TEMPAC differences in the Atlantic. Human influence on the seasonality of surface and subsurface ocean temperature may have profound consequences for fisheries, marine ecosystems, and ocean chemistry.

Item Type:	Article
Additional Information:	Publisher Copyright: © 2025 American Meteorological Society.
Uncontrolled Keywords:	climate,climate change,ocean,ocean dynamics,pattern detection,atmospheric science,sdg 13 - climate action,sdg 14 - life below water ,/dk/atira/pure/subjectarea/asjc/1900/1902
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Related URLs:	http://www.scopus.com/inward/record.url?...
Depositing User:	LivePure Connector
Date Deposited:	19 Mar 2026 09:33
Last Modified:	23 Mar 2026 01:21
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102477
DOI:	10.1175/JCLI-D-24-0418.1

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