|« Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model » by Crichton et al.|
Revised version of the manuscript by Crichton et al. has been largely improved since the original one. Details on model and experiments setup have been moved to appendix, which is a good point. I appreciate the introduction of new simulations with closed CAS so conclusions are better justified. I also acknowledge the effort that have been done to make the manuscript clearer especially in the results and discussion parts. I therefore believe that the manuscript is ready for publication. I however still have minor comment on one point that I feel might still be made clearer for the reader.
Paragraph referring to CO2 concentration (l. 41 and following) during the Miocene in the Introduction is not clear.
First, is not straightforward to understand about which part of the Miocene the authors are referring to when stating “Climate modelling studies have tended to apply a forcing of around 400ppm, based on later estimates (Londoño et al 2018 references therein) » (l. 41-42) as they do not provide references for such modeling studies and also because multiple paleoclimate simulations have been performed both for the late and the middle Miocene for which most of the groups used different pCO2 concentration (see Burls et al., 2021, https://doi.org/10.1029/2020PA004054 for compilation).
I addition, I do not really understand the few lines on pCO2 that seems to focus on the mid-Miocene, while the paper provide simulation from 15 Ma onward. I do not think this part is really needed, because the authors then discuss pCO2 concentration needed to reproduce Miocene climate state in the discussion and compare it with the same references. I feel like one sentence on pCO2 decrease since MMCT providing appropriate reference(s) (in which the recent review by Rae et al., 2021, https://doi.org/10.1146/annurev-earth-082420-063026 could be cited for example) would probably have been enough and would make the introduction more synthetic and clearer.
List of specific comment :
l.56 : I do not think Hamon et al. (2013) is the appropriate reference as they "only" test the impact of closing the eastern Tehtys seaway on climate/ocean. As there are many references focusing on eastern Tethys seaway closure it would be better to cite paleogeography paper such as Rögl et al. 1999 (or the many others that studies on the paleogeographic evolution of the region during the Miocene) or at least papers suggesting switch off of the Mediterranean / Atlantic connection based on geochemistry (such Bialik et al. 2019 or others).
l. 110 “ noting that these proxies, like any proxy, are subject to uncertainties and limitations” is a pretty vague statement and do not help the reader to identify potential weakness of the model-data comparison. I still think that kind of point is very important to clarified especially when the paper target a broad audience from both modeling and data researchers. Short sentence listing mains limitations of such proxies would be more useful.
Fig 9-11 - I think you should provide de regression coefficients.
Technical correction :
l. 37-38 « Marine data also indicate a significantly warmer-than-present Miocene climate with global surface ocean temperatures 6 °C warmer than present (Stewart et al., 2004; Herbert et al., 2016), global deep ocean temperature 4 to 6 °C warmer (Cramer et al., 2011). » — This sentence sounds grammatically incorrect.
l. 51 Correct reference is Sepulchre et al. 2014 (as in the reference list)
l. 475 & 481 - Modestou (as in the reference list) or Modestu (as in the Text) ?
l. 514 : Tethyan instead of Tethian ?
l.538 ‘Bell et al. (2015) found that an early Pliocene (4.7 to 4.2 Ma) shoaling of CAS was had no profound impact’
Mid-Miocene or mid-Miocene ? Please keep in consistent in the paper
Overuse of brackets make some part of the paper difficult to read and most of the time they can be removed as the text content within the brackets perfectly fits within the sentence.
In paragraph 3.4 you start using ‘benthic T’ instead of ‘benthic temperature’ but the T abbreviation is never defined in the paper and I am not sure it is very useful. It might be bette to keep using ‘benthic temperature’ everywhere
Burls et al., 2021, https://doi.org/10.1029/2020PA004054
Rae et al., 2021, https://doi.org/10.1146/annurev-earth-082420-063026
Rögl et al. 1999 - Mediterranean and Paratethys. Facts and hypotheses of an Oligocene to Miocene paleogeography (short overview). Geologica carpathica, 50(4), 339-349.
Bialik et al. 2019, https://doi.org/10.1038/s41598-019-45308-7