Scheduled Downtime
On Tuesday 24 October 2023 @ 5pm MT the forums will be in read only mode in preparation for the downtime. On Wednesday 25 October 2023 @ 5am MT, this website will be down for maintenance and expected to return online later in the morning.
Normal Operations
The forums are back online with normal operations. If you notice any issues or errors related to the forums, please reach out to

Understanding this strange looking MOC output


Shown below are two MOC diagnostics which directly plot the Atlantic MOC streamfunction generated by POP2. The one on the left is a PI MOC while the one on the right is for a LGM-like simulation in which the Bering Strait and the Canadian Archipelago are closed and small coastline changes are made throughout the world, but in any cell where the there is a common ocean between PI and LGM (i.e. anything away from coastlines) the bathymetry is kept the same as PI.

The problem consuming me is that I don't understand what the second figure means, or it is even meaningful. A few questions that I am specifically trying to wrap my head around are:
  1. Why is there this strange circulation in the high-latitudes?
  2. Why does the POP calculation does not show the sill at 60N (as seen in the PI) even though the bathymetries are the same? In both figures the bottom topography is just masked cells where the MOC is ~0. The sill is always there, so why is the computation showing a flow at depths below 3000m?
  3. Is this suggestive of an error in POP's calculation of the MOC? How accurate is MOC calculation at those high latitudes where the dipole grid experiences significant departures from a standard spherical grid?
Any help understanding this feature would be very appreciated.