[MITgcm-support] Passive tracer decoupling from convection

Tue Sep 7 17:47:24 EDT 2021

Hi Yuxin,

First of all, I agree with all the suggestions from Christoph.

Furthemore, normally during the experiments of climate change (climate
warming I mean) you see the tracers distribution changinging
on a centennial time scale  in the upper/mid ocean because the perturbation
of climate continues and it also increases with time.

In your case, it seems that you are applying a perturbation for a blink of
an eye and you expect the system
to change. The timescale of your climate perturbation is way too short.
I doubt that the change in advection scheme will do something on a short
run.

What you use is a cheap set-up to run  as far as computing time is concerned
so you coud/shoud run it for long(er) time with the same
perturbation (adding fresh water in the NA)
applied each year (on the order of centuries) and then look at  the results
as physical and bgc tracer distribution.

Also try to look at other papers that have done some paleo experiments
relative to ocean oxygenation
with models and see if you get similar results or which kind of time scale
they deal with to perturb the 3D tracer distribution.

I hope what I said here helps and makes sense.

Cheers
Manfredi

On Fri, Sep 3, 2021 at 5:45 PM Yuxin Zhou <yzhou at ldeo.columbia.edu> wrote:

> Dear Christoph,
> Your suggestions make a lot of sense. Thanks for pointing them out!
>
> Cheers,
> Yuxin
>
> On Fri, Sep 3, 2021 at 1:52 AM Christoph Voelker <christoph.voelker at awi.de>
> wrote:
>
>> Dear Yuxin,
>>
>> in both of your setups I would not expect much response in the deep
>> oxygen. In the first, AMOC recovers probably quickly, so there is not much
>> reason to change. In the second, ten years is still fairly short, for
>> changing tracer distributions in the deeper parts of the ocean. The
>> timescale of ventilation of intermediate waters is on the order of several
>> decades, in the deep ocean it is centuries to millenia. So I expect yo will
>> at least have to run 1000 years with continuously changed overtrning to see
>> some larger effects in the deep North Atlantic. Maybe have a look at the
>> distribution of CFCs or anthropogenic carbon in the North Atlantic from the
>> GLODAP data base; then you see observations of how far a signal from the
>> surface penetrates within the deep Atlantic within a few decades.
>>
>> Cheers, Christoph
>> Am 03.09.21 um 02:45 schrieb Yuxin Zhou:
>>
>> Hi Spencer,
>> Thanks for the reply. I tested out two of your ideas. After hosing for
>> one year, I first let the AMOC recover for 100 years. Oxygen
>> basically remained the same. Then I hosed with 5Sv of freshwater for ten
>> years. AMOC is basically gone at this point:
>> [image: image.png]
>>
>> However, oxygen still didn't change much:
>> [image: image.png]
>>
>> Going forward, I might test out the different advection schemes and other
>> ptracer parameters to see if that helps. Again, I appreciate your help.
>>
>> Best,
>> Yuxin
>>
>> On Wed, Sep 1, 2021 at 10:29 PM Spencer Jones <spencerjones at tamu.edu>
>> wrote:
>>
>>> Dear Yuxin,
>>> It seems to me that maybe you just didn't run for long enough to see any
>>> change in the oxygen concentration. From your email it seems like you only
>>> ran for 1 year. Is that right? I wouldn't expect the oxygen concentration
>>> to change until several years (maybe even decades) after hosing has taken
>>> place, and only to change if the reduction in the AMOC continues (i.e. you
>>> might want to continue hosing, rather than switching it off).
>>>
>>> I'm not sure why tutorial_global_oce_biogeo doesn't match with
>>> observations, but usually the tutorial experiments are set up to
>>> demonstrate the model functionality, not to provide a very realistic
>>> simulation. You might need to put more work into improving the forcing
>>> fields and/or resolution in order to get realistic output.
>>> Good luck ,
>>> Spencer
>>>
>>> On Tue, Aug 31, 2021 at 9:28 PM Yuxin Zhou <yzhou at ldeo.columbia.edu>
>>> wrote:
>>>
>>>> Hi all,
>>>> I'm running the tutorial_global_oce_biogeo experiment and analyzing the
>>>> oxygen results and I found some weird behaviors. Any help would be
>>>> appreciated.
>>>>
>>>> Here is the AMOC stream function in equilibrium, which looks normal:
>>>> [image: image.png]
>>>>
>>>> Here is the AMOC stream function after a hosing of 5 Sv for one year
>>>> (by increasing precipitation in the 50-70N North Atlantic region), which
>>>> looks normal too. It shows a weakened NADW:
>>>> [image: image.png]
>>>>
>>>> Here is the oxygen concentration of the AMOC cross-section in
>>>> equilibrium:
>>>> [image: image.png]
>>>>
>>>> Here is the oxygen concentration after the hosing:
>>>> [image: image.png]
>>>>
>>>> Firstly, the oxygen concentration of the AMOC in equilibrium does not
>>>> reflect modern observations such as the World Ocean Atlas, which shows
>>>> oxygenated water closely following the presence of the NADW. Secondly,
>>>> oxygen basically doesn't change even though circulation changed
>>>> dramatically. It seems convection processes barely impact oxygen at all.
>>>>
>>>> Has anyone else seen this behavior? Any suggestions for tests I can run
>>>> to figure out what's wrong?
>>>>
>>>> Thanks,
>>>> Yuxin
>>>> --
>>>> Yuxin Zhou
>>>> https://www.ldeo.columbia.edu/~yzhou/
>>>> <https://urldefense.com/v3/__https://www.ldeo.columbia.edu/*yzhou/__;fg!!KwNVnqRv!XGV-_ZoSHtQ8Iafno1yNILLkNCN6MaDMwIwpWla_Ftn5cl116QSs05k-WzMaoC6wDGs$>
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>>
>>
>> --
>> Yuxin Zhou
>> https://www.ldeo.columbia.edu/~yzhou/
>> <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.ldeo.columbia.edu_-7Eyzhou_&d=DwMFaQ&c=-35OiAkTchMrZOngvJPOeA&r=igpxhFyItwkD6Vnn8g54Ybzj3kX5f-S1LY9JKm2YT1c&m=5RRKYrzBx0Ip12mHGJEGgcA7HZwj22DeGL2yqzP45xw&s=2PWwsb3Wd06-6UTA59-cjHS6zgYgdOO_wwZosqjdTdc&e=>
>>
>> _______________________________________________
>> MITgcm-support mailing listMITgcm-support at mitgcm.orghttp://mailman.mitgcm.org/mailman/listinfo/mitgcm-support <https://urldefense.proofpoint.com/v2/url?u=http-3A__mailman.mitgcm.org_mailman_listinfo_mitgcm-2Dsupport&d=DwMFaQ&c=-35OiAkTchMrZOngvJPOeA&r=igpxhFyItwkD6Vnn8g54Ybzj3kX5f-S1LY9JKm2YT1c&m=5RRKYrzBx0Ip12mHGJEGgcA7HZwj22DeGL2yqzP45xw&s=qVTFFzLPKT4fGMLWEycvKMFSJWV497LFejrmUkxBM1s&e=>
>>
>> --
>> Christoph Voelker
>> Alfred Wegener Institute
>> Helmholtz Centre for Polar and Marine Research
>> Am Handelshafen 12
>> 27570 Bremerhaven, Germany
>> e: Christoph.Voelker at awi.de
>> t: +49 471 4831 1848
>>
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>
>
> --
> Yuxin Zhou
> https://www.ldeo.columbia.edu/~yzhou/
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-- 

Dr. Manfredi Manizza
Geosciences Research Division
Scripps Institution of Oceanography
University of California San Diego
9500 Gilman Drive La Jolla, CA 92093-0244
email : mmanizza at ucsd.edu
tel   : +1-858-534-7094
web   : http://bluemoon.ucsd.edu/mmanizza/

web   : https://mmanizza.scrippsprofiles.ucsd.edu/
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