Ocean circulation
OSNAP: subpolar overturning peaks in spring
Open access · cc by · source: Europe PMC
A 6-year OSNAP record shows the subpolar AMOC maximum in spring and minimum in winter, mostly from the eastern subpolar gyre.
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OSNAP: subpolar overturning peaks in spring
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The record spans 71 months from August 2014 to June 2020.
The retrieval of mooring data in 2020 extended the OSNAP observation time series to 71 months, covering the period from August 2014 to June 2020 (Fig.
Seasonal variability explains about 40% of monthly MOC variance.
Overall, seasonal variability explains about 40% of the total variability of the monthly MOC time series across the full OSNAP array over the 6-year observational period.
Key findings
Full-array MOC ranges ~10–25 Sv (mean East 16.3 Sv vs West 3.0 Sv). Seasonal MOC is 21.1 Sv in spring versus 12.3 Sv in winter (8.8 Sv peak-to-trough) and explains ~40% of monthly variance. Overturning peaks in May, 3–5 months after maximum transformation. East still dominates; West strengthened in 2019–2020.
Methodology
Authors extended the OSNAP mooring array (60 moorings, West and East sections) to 71 months (August 2014–June 2020) and computed seasonal cycles of MOC, meridional heat transport, and freshwater transport versus winter water-mass transformation and Ekman transport.
Limitations
Six years cannot define the decadal AMOC. Seasonality is not identical every year (East missed a 2019 spring peak). Ekman transport is a small mean but can matter seasonally, and Labrador Sea convection is not the main mean MOC source.
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