OSNAP: subpolar overturning peaks in spring
A 6-year OSNAP record shows the subpolar AMOC maximum in spring and minimum in winter, mostly from the eastern subpolar gyre.
Source
Seasonality of the Meridional Overturning Circulation in the subpolar North Atlantic
Inspect source passages
OSNAP: subpolar overturning peaks in spring
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
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.
What they did
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.
What they found
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.
The limits
What it doesn't show
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.
Key terms
- OSNAP
- Overturning in the Subpolar North Atlantic Program observing array since 2014.
- MOC
- Meridional Overturning Circulation: northward upper / southward deep volume transport.
- OSNAP East / West
- Greenland–Scotland versus Labrador sections of the array.
- MHT / MFT
- Meridional heat and freshwater transports across the array.
- Sv
- Sverdrup, 10^6 m³ s−1.
Flashcards
0 of 11 answers reviewed
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
Most subpolar OSNAP overturning occurs at:
Common questions
Does the Labrador Sea dominate subpolar overturning?
No; OSNAP East carries most of the mean and variability.
When is the seasonal MOC maximum?
Spring (May), not in midwinter convection.
How much monthly variance is seasonal?
About 40% across the full array.
Is one boundary current enough?
No DWBC alone captured most MOC variability in earlier OSNAP years.
More on Ocean circulation