[MITgcm-support] Passive tracer decoupling from convection

Fri Sep 3 01:52:00 EDT 2021

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.png
>
> However, oxygen still didn't change much:
> 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 
> <mailto: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 <mailto: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.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.png
>
>         Here is the oxygen concentration of the AMOC cross-section in
>         equilibrium:
>         image.png
>
>         Here is the oxygen concentration after the hosing:
>         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://www.ldeo.columbia.edu/~yzhou/>
>
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-- 
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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