Interactive freshwater stretches AMOC’s slow beat
Fixing freshwater flux in CESM1 inserts a ~30-year AMOC peak; coupling precipitation, evaporation, and ice melt lengthens the cycle via Labrador Sea salinity.
Source
Freshwater Flux Variability Lengthens the Period of the Low-Frequency AMOC Variability
What they did
Authors compared a 1400-year preindustrial CESM1 control with a 350-year partially coupled run that prescribes daily-climatology freshwater flux, then diagnosed AMOC PC-1 spectra and Labrador Sea density budgets.
What they found
Coupled AMOC power sits in a 50–100-year band. Without interactive FWF a sharp ~30-year peak appears and density anomalies reverse in ~15 years. Interactive FWF lengthens positive Labrador density by ~50% (17 to 25 years) via evaporation and Irminger salinity advection.
The limits
What it doesn't show
This is one model’s internal variability under preindustrial forcing, not an observational AMOC spectrum; the first 50 FWFIX years are spin-up; periods <15 years were filtered.
Key terms
- AMOC
- Atlantic Meridional Overturning Circulation.
- FWF
- Freshwater flux from precipitation, evaporation, and melt.
- FWFIX
- Partially coupled run with FWF prescribed as a daily climatology.
- Labrador Sea
- Key deep-water formation region for low-frequency AMOC.
- PC-1
- First principal component of the overturning streamfunction, the AMOC index.
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Interactive FWF does what to AMOC period?
Common questions
What does interactive FWF do to AMOC period?
Lengthens multidecadal variability and suppresses a ~30-year peak.
Where is the density source?
Labrador Sea interior deeper than 2000 m.
Local FWF mechanism?
Warmth-driven evaporation that salinifies the mixed layer.
Remote mechanism?
Advection of Irminger/southeast Greenland salinity anomalies.
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