Feedback processes modulating the sensitivity of atlantic thermohaline circulation to freshwater forcing timescales

Hyo Jeong Kim, Soon Il An, Soong Ki Kim, Jae Heung Park

Research output: Contribution to journalArticlepeer-review

Abstract

Paleoproxy records indicate that abrupt changes in thermohaline circulation (THC) were induced by rapid meltwater discharge from retreating ice sheets. Such abrupt changes in theTHChave been understood as a hysteresis behavior of a nonlinear system. Previous studies, however, primarily focused on a near-static hysteresis under fixed or slowly varying freshwater forcing (FWF), reflecting the equilibrated response of the THC. This study aims to improve the current understanding of transient THC responses under rapidly varying forcing and their dependency on forcing time scales. The results simulated by an Earth system model suggest that the bifurcation is delayed as the forcing time scale is shorter, causing the Atlantic meridional overturning circulation collapse and recovery to occur at higher and lower FWF values, respectively. The delayed shutdown/recovery occurs because bifurcation is determined not by the FWF value at the time but by the total amount of freshwater remaining over the THC convection region. The remaining freshwater amount is primarily determined by the forcing accumulation (i.e., timeintegrated FWF), which is modulated by the freshwater/salt advection by ocean circulations and freshwater flux by the atmospheric hydrological cycle. In general, the latter is overwhelmed by the former.When the forced freshwater amount is the same, the modulation effect is stronger under slowly varying forcing because more time is provided for the feedback processes.

Original languageEnglish
Pages (from-to)5081-5092
Number of pages12
JournalJournal of Climate
Volume34
Issue number12
DOIs
Publication statusPublished - 2021 Jun 15

Bibliographical note

Funding Information:
Acknowledgments This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF-2017K1A3A7A03087790, NRF-2018R1A5A1024958). Author H.-J. Kim is grateful for financial support from the Hyundai Motor Chung Mong Koo Foundation. The authors also thank the editor and anonymous reviewers for providing insightful suggestions.

Publisher Copyright:
© 2021 American Meteorological Society. All rights reserved.

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

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