<div dir="ltr"><div dir="ltr">Hi Kaushai,<div><br></div><div>I would say that if your PO4 conc. increases it means that your sink term in the equation is either zero or almost zero.</div><div><br></div><div>One possibility could be that there is a problem in the term of PO4 equation of biological </div><div>drawdown of PO4 (that mimics the uptake by phytoplankton).</div><div>In this case first you might want to check if the model reads correctly the light fields from surface to<br></div><div>depth (top 200 m). Normally the seasonal cycle of PO4 at the surface should follow the the opposite of light availability</div><div>especially in the polar oceans (I assume you work in that environment if you use shelfice...)</div><div><br></div><div>Furthermore, normally the buildup of nutrients is at depth where the POP gets remineralized and then it gets </div><div>converted into inorganic PO4 and then winter convection replenished the values in the top boxes of the model.</div><div><br></div><div><br></div><div>At which depth do you see this problem? At all the depths? Surface ? Bottom?</div><div><br></div><div>> Somehow the parametrization for remineralization of particulate organic matter (POP) does not work well in the offline mode (<span class="gmail_default">MITgcm/</span>pkg/dic/phos_flux.F)<br></div><div>IF you have no remineralization of POP you could not have an increase in PO4, for instance.</div><div><br></div><div>I hope this helps to make some progress on your debugging. </div><div><br></div><div>Cheers</div><div>Manfredi</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Aug 11, 2020 at 1:19 PM Kaushal Gianchandani <<a href="mailto:Kaushal.G@mail.huji.ac.il">Kaushal.G@mail.huji.ac.il</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div style="font-family:arial,helvetica,sans-serif">Hello everyone</div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">I am currently using MITgcm to model the biogeochemistry in the context of paleoclimate. For the same, I have created an offline 2d model that uses the packages: dic, gchem, ptracers in conjunction with shelfice. </div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">I am facing a problem with the concentration of the nutrient (phosphate - PO4) in the model --- the concentration does not reach a steady-state. After just a few years of integration, the concentration deviates significantly from what it should be. In fact, the initial concentration of PO4 increases well beyond what I initially start with. </div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">I have gone through many threads provided in [MITgcm-support] dealing with similar problems but none of the solutions listed there worked for my problem. I have already tried the following:<br></div><div><div style="font-family:arial,helvetica,sans-serif">1. Used the model with only dissolved organic phosphorus (DOP) and PO4 --- no problem in this case. The net Phosphorus is conserved and both PO4 and DOP concentrations reach a steady-state. <span style="font-family:Arial,Helvetica,sans-serif">Somehow the parametrization for remineralization of particulate organic matter (POP) does not work well in the offline mode (</span><span class="gmail_default" style="font-family:Arial,Helvetica,sans-serif">MITgcm/</span><span style="font-family:Arial,Helvetica,sans-serif">pkg/dic/phos_flux.F</span><span style="font-family:Arial,Helvetica,sans-serif">)</span></div><div style="font-family:arial,helvetica,sans-serif">2. Running the model without the shelfice package --- the problem persists. </div><div style="font-family:arial,helvetica,sans-serif">3. Verified that the PTRACERS_EvPrRn is unset.</div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">Please note that the online model with the same configuration works well. I'd really appreciate any help in this regard. </div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">Thank you,</div><div style="font-family:arial,helvetica,sans-serif"><br></div><div style="font-family:arial,helvetica,sans-serif">Regards,</div><div style="font-family:arial,helvetica,sans-serif">Kaushal.</div></div><div><br></div>-- <br><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div style="font-size:small;color:rgb(0,0,0);font-family:Helvetica"><div style="font-size:12.8px;letter-spacing:0.2px"><font size="2"><b>Kaushal Gianchandani<br></b>Ph.D. Student in Oceanography<br>Fredy & Nadine Herrmann Institute of Earth Sciences</font></div><div style="font-size:12.8px;letter-spacing:0.2px"><font size="2">Hebrew University of Jerusalem, Israel</font></div><div style="font-size:12.8px;letter-spacing:0.2px"><font size="2">Phone: +972-50-471-4621<br>web: <a href="https://urldefense.com/v3/__https://kaushalgianchandani.github.io/__;!!Mih3wA!TGi9JaQBzVj1MhGt5VmVDIsa8L5ryHlldY8FoA1Yh0WPfE3mxo1UkaFHGJOx1rxX$" target="_blank">https://kaushalgianchandani.github.io</a></font></div></div></div></div></div></div></div></div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><pre cols="72">Dr. Manfredi Manizza
Geosciences Research Division
Scripps Institution of Oceanography
University of California San Diego
9500 Gilman Drive La Jolla, CA 92093-0244
email : <a href="mailto:mmanizza@ucsd.edu" target="_blank">mmanizza@ucsd.edu</a>
tel : +1-858-534-7094
web : <a href="http://bluemoon.ucsd.edu/mmanizza/" target="_blank">http://bluemoon.ucsd.edu/mmanizza/</a> </pre></div></div></div></div></div>