Cross-slope volume transport

[adele-morrison]

Compute the cross-1000m isobath transport. Plots:

• circumpolar integrated transport, cumulatively integrated as a function of density from bottom up
• time series of maximum offshore transport in dense layers
• transport distribution along the contour in different density classes (DSW, CDW, AASW)

Note, the old issue with the old simulations is here.

[claireyung]

Across the 1000 isobath contour:

Circumpolar Integrated Transport

The circumpolar integrated transport, cumulatively integrated as a function of density from bottom up is

Bottom water export decreases over time, and moves to lighter densities. CDW flows appear to move to heavier densities?

Time series of bottom water transport

We can plot the maximum transport of bottom water as a function of time, which is decreasing (though seasonal):

We can also see that the density of this maximum in the streamfunction is decreasing in time (though also seasonal, and dependent on finite sigma_1 bin size)

Cumulative integrals of transport in different density classes According to Morrison (2020) paper sigma_1 density classes. Note that the cumulative integrals getting further apart means the transport changed in that location.

DSW: Generally decreasing northward transport in source regions, as seen in circumpolar analysis above

CDW: Generally decreasing southward transport, but increases near 140-100W (cumulative integrals get closer together again) near Amundsen Sea?

AASW: Southward transport increasing near Ross?

Vertically integrated heat transport: HT relative to 0degC. Increasing approximately uniformly around the continent

See the notebooks in my branch https://github.com/pedrocol/basal_mom5-collaborative-project/tree/claire/notebooks/cross_contour

[adele-morrison]

Nice one Claire! That’s a pretty dramatic drop in the DSW export, consistent with the increase in bottom age in the abyss.

Is the heat transport relative to 0degC or the freezing point temperature?

On Mon, Oct 24, 2022 at 10:48 PM, claireyung @.***> wrote:

Across the 1000 isobath contour: [image: Screen Shot 2022-10-24 at 10 29 06 pm] https://user-images.githubusercontent.com/61528379/197516030-3c6742fe-14b2-41fe-bfd2-8b389b29a209.png

Circumpolar Integrated Transport

The circumpolar integrated transport, cumulatively integrated as a function of density from bottom up is [image: Screen Shot 2022-10-24 at 10 29 21 pm] https://user-images.githubusercontent.com/61528379/197516106-15a3fcdd-2241-4297-bcf8-bf58157a90a4.png Bottom water export decreases over time, and moves to lighter densities. CDW flows appear to move to heavier densities?

Time series of bottom water transport

We can plot the maximum transport of bottom water as a function of time, which is decreasing (though seasonal): [image: Screen Shot 2022-10-24 at 10 29 35 pm] https://user-images.githubusercontent.com/61528379/197516307-c9924d83-83fe-4c83-9d16-a7182b8e1a85.png

We can also see that the density of this maximum in the streamfunction is decreasing in time (though also seasonal, and dependent on finite sigma_1 bin size) [image: Screen Shot 2022-10-24 at 10 29 43 pm] https://user-images.githubusercontent.com/61528379/197516411-ab61e9eb-7040-4db1-8562-b0eb04454afe.png

Cumulative integrals of transport in different density classes According to Morrison (2020) paper sigma_1 density classes. Note that the cumulative integrals getting further apart means the transport changed in that location.

DSW: Generally decreasing northward transport in source regions, as seen in circumpolar analysis above [image: Screen Shot 2022-10-24 at 10 29 55 pm] https://user-images.githubusercontent.com/61528379/197516719-ab20f5e4-784b-4ba1-a2a0-3e43fa0ff3ed.png

CDW: Generally decreasing southward transport, but increases near 140-100W (cumulative integrals get closer together again) near Amundsen Sea? [image: Screen Shot 2022-10-24 at 10 30 01 pm] https://user-images.githubusercontent.com/61528379/197516782-a30e73c9-e5d5-418d-ab3e-493e349c91c4.png

AASW: Southward transport increasing near Ross? [image: Screen Shot 2022-10-24 at 10 30 08 pm] https://user-images.githubusercontent.com/61528379/197516810-419b8d55-c764-476e-8104-c3d1b212c467.png

Vertically integrated heat transport: Increasing approximately uniformly around the continent [image: Screen Shot 2022-10-24 at 10 36 16 pm] https://user-images.githubusercontent.com/61528379/197516964-4bde02d3-0e82-4007-9718-b7ea947e4be0.png

See the notebooks in my branch https://github.com/pedrocol/basal_mom5-collaborative-project/tree/claire/notebooks/cross_contour

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[claireyung]

Heat transport is now relative to -5 degrees C -- agrees with Morrison et al. (2020) supp. material? (Would be better to have the actual minimum freezing point instead of something arbitrary though)

[claireyung]

Updated Gade line formulation overturning has less weakening in overturning than the heat balance formulation

[adele-morrison]

This last plot is great! Nice to see we still have overturning with the Gade line formulation - the impact of the extra freshening at depth on density is being compensated by cooling relative to the GPC13 simulation.

[adele-morrison]

Just to add that the rapid reduction in overturning in GPC13 (but relatively modest decrease in GPC15) is consistent with:

• the overall large shelf freshening in GPC13 compared to GPC15
• more shelf cooling in GPC15 compared with GPC13.

[claireyung]

Updated 10 year results for Gade line basal melt experiment showing reduction in overturning of ~2Sv that stabilises after 5 ish years

[adele-morrison]

Nice! I'm excited to see how this changes again once we implement the iceberg runoff. I predict it will increase again.

On Fri, 16 Dec 2022 at 11:54, claireyung @.***> wrote:

Updated 10 year results for Gade line basal melt experiment showing reduction in overturning of ~2Sv that stabilises after 5 ish years

[image: Screenshot 2022-12-16 at 11 39 38 am] https://user-images.githubusercontent.com/61528379/207995870-feffc09b-9b9e-4e9a-8481-f628746b9d59.png

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[pedrocol]

Hi Claire,

Is the one in the plot GPC013 or GPC015? The gade line one is 15.

Cheers,

Pedro.

Get Outlook for iOShttps://aka.ms/o0ukef

---

From: Adele Morrison @.> Sent: Thursday, December 15, 2022 9:56:52 PM To: pedrocol/basal_mom5-collaborative-project @.> Cc: Subscribed @.***> Subject: Re: [pedrocol/basal_mom5-collaborative-project] Cross-slope volume transport (Issue #28)

Nice! I'm excited to see how this changes again once we implement the iceberg runoff. I predict it will increase again.

On Fri, 16 Dec 2022 at 11:54, claireyung @.***> wrote:

Updated 10 year results for Gade line basal melt experiment showing reduction in overturning of ~2Sv that stabilises after 5 ish years

[image: Screenshot 2022-12-16 at 11 39 38 am] https://user-images.githubusercontent.com/61528379/207995870-feffc09b-9b9e-4e9a-8481-f628746b9d59.png

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[claireyung]

It's GPC015!

The GPC013 (for 5 years) is up in a higher comment and has greater reduction of overturning.

[claireyung]

Interestingly, with another 10 years of data, the overturning seems to grow slightly again (dotted lines are 10-20 years) to have a new overturning maximum at a lighter density:

[adele-morrison]

Interesting. Maybe some time series would be handy to see the rate of adjustment. Could do a few versions:

• time series of transport at fixed density (perhaps the control peak density value would work)
• Time series of peak transformation rate
• Time series of density of peak transformation

[claireyung]

Time series of transport at fixed density:

Time series of peak transport:

Time series of density of peak transport:

[adele-morrison]

Nice time series Claire! Will be interesting to see how the icebergs change it again. From the age plot it looks like we might get an increase in bottom water in the Weddell with icebergs, but maybe a decrease elsewhere.

Actually, that make me think, maybe it would be useful to do these transport plots (maybe just the top one with transport against density) for the 4 different DSW sectors in case they are changing differently.

[claireyung]

Transport Plots by DSW sector

Main transport reduction from Ross/Adelie, Weddell has lightening of peak transport. Note Weddell sector includes the peninsula.

Note no iceberg run plots yet but will compute soon :)

[claireyung]

Iceberg (GPC018) results - even stronger decrease in DSW export than the basal run

Cumulative cross-contour transport in density classes:

Change in DSW export locations for iceberg run. Also suggests strong lightening of Prydz export as no longer appears in DSW density class? Confirmed by regional integrals:

[adele-morrison]

Interesting! We expected it to increase again. Any ideas why DSW decreases further in the iceberg experiment?

[PaulSpence]

So icebergs decrease DSW and the MOC. Maybe we need to look at the salt balance on the shelf - like in the easterlies project.

[claireyung]

Adele pointed out that in the density class sigma_1 > 32.56, DSW export is bigger in the iceberg run than in the basal-only run, which may be the relevant DSW for export into deeper ocean/AABW/MOC (see figures above with black, pink and blue lines showing transport across isobath contour cumulatively integrated)

So the southward export is slightly bigger in the basal-only run, but it's in a lighter density class so may not get into the abyss. @PaulSpence how does the iceberg MOC look at year 15?

[adele-morrison]

Closing this issue because it uses the old simulations. See new cross-slope transport issue https://github.com/pedrocol/basal_mom5-collaborative-project/issues/65.