In “Nonlinear increase in seawater ⁸⁷Sr/⁸⁶Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering” Stoll et al., present newly generated ⁸⁷Sr/⁸⁶Sr data for (I)ODP Sites 1168, 1218, and U1406. Especially the work on Site 1218 is very valuable in my opinion, because Sr ratios can be directly compared to the benthic foraminiferal d¹⁸O climate/cryosphere proxy from the same site. The authors find that the gradual increase in ⁸⁷Sr/⁸⁶Sr ratios stalls or even decreases when d¹⁸O is high and that the increase in ⁸⁷Sr/⁸⁶Sr accelerates when d¹⁸O is low. These findings are interpreted to reflect ITCZ related and/or Antarctic weathering related controls on Sr transport to the oceans.

The paper is well written, and well-illustrated. I am not fully convinced by the ITCZ hypothesis, but it can stay in the paper. I have one major comment on the use of the CCSF-A scale for U1406. This would require the authors to transpose the biostratigraphy from the Site U1406 CSF-A to CCSF-A depths, but I think that is worth the effort. Overall, I strongly recommend this manuscript for publication, and would like to congratulate the authors with their nice study.

Major comment:

• Extraordinary effort has gone into generating the best available depth model for Site U1406, and I strongly advise to use the composite CCSF-A scale, and against using the Hole A specific CSF-A scale. There is no benefit to it, and mixing depth models only serves to confuse the reader.

Some smaller comments, which the authors may address at their discretion:

• General comment: Perhaps add a little map with site locations?
• Perhaps state where ODP Site 1168 and IODP Site 1406 are from?
• 4 million years, seems like a very large uncertainty, even for biostratigraphic age control from the 1980s. Million is abbreviated by a big M.
• I would say “astrochronology” instead of “cyclostratigraphy” in this context. The former refers to, in my mind, the alignment of cyclic stratigraphic records (in the depth domain) to an astronomical solution (in the age domain). The latter is, as I understand it, thus a description of cyclically alternating lithologies/proxy records in the stratigraphic depth domain.
• Please make sure the Westerhold et al., 2020 age model is used. At 26.5 Ma a hundred-thousand-year correction of the Pälike et al., 2006 ages is included in Westerhold et al., 2020.
• van Peer et al. 2017a, shows this hiatus in the age domain. van Peer is with a small v.
• Astrochronologic. (See previous comment).
• Delete “GTS”. The Westerhold et al., 2020 CENOGRID record is separate from the GTS2020. (NB: The G(P)TS2020 should not be used, due to incorrect incorporation of several chron boundary reversal ages. Most notably the Liebrand et al., 2016 ages, which were not all being considered reliable or deviant from GTS2012 outside of error, their Supp. Fig. S6.)
• This is an “old” ODP site that probably used the mbsf terminology, instead of CSF-A scale. Perhaps clarify this point in the text?
• L120/121. Sigma and SD are used. Perhaps standardize?
• L135-137. This is the same hiatus identified in van Peer et al., 2017a.
• This definition of the MOGI deviates from the original (Liebrand et al., 2017), which is defined as lasting from 28.0 to 26.3 Ma. Perhaps explain why a longer lasting MOGI is defined. I have no problem with a longer lasting MOGI, it is just an arbitrary definition, but still good to be clear how and why it differs.
• Is an inverted increase not a decrease?
• In Fig. 3a and b this looks like a decrease, not a reduction in the increase. Confusing language.
• I think it is important to redefine the MOGI as used in this study. (See previous comment)
• “Warming” refers to deep-sea (and potentially high latitudes). Perhaps clarify.
• L183-184. Also looks like a modest decrease, not a “slowing of increase”.
• Looks like a decrease to me.
• L212-L215. I do not understand this sentence.
• L241-244. This finding of Oslick can now be reflected on using the new data and age model. Just stating it seems a bit odd. To me it seems that the increase in Sr ratios follows d¹⁸O maxima much quicker, compared to the 1 M.y. lag Oslick found.
• L279-282. Independent Sr age control is great. However, I would mention–also in writing–that for Site U1406 a magnetostratigraphic age model is publicly available (van Peer, 2017a). Are Sr and PMAG age models for Site U1406 in agreement with one another? Or are there any large discrepancies?
• Middle Miocene (25 to 27 Ma). Do the authors mean Oligocene?
• LP = LDP?. Who is PG?

*Apologies for posting this again. Something went wrong with the upload last time. The line numbers dissapeared*

In “Nonlinear increase in seawater 87Sr/86Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering” Stoll et al., present newly generated 87Sr/86Sr data for (I)ODP Sites 1168, 1218, and U1406. Especially the work on Site 1218 is very valuable in my opinion, because Sr ratios can be directly compared to the benthic foraminiferal d18O climate/cryosphere proxy from the same site. The authors find that the gradual increase in 87Sr/86Sr ratios stalls or even decreases when d18O is high and that the increase in 87Sr/86Sr accelerates when d18O is low. These findings are interpreted to reflect ITCZ related and/or Antarctic weathering related controls on Sr transport to the oceans. 

The paper is well written, and well-illustrated. I am not fully convinced by the ITCZ hypothesis, but it can stay in the paper. I have one major comment on the use of the CCSF-A scale for U1406. This would require the authors to transpose the biostratigraphy from the Site U1406 CSF-A to CCSF-A depths, but I think that is worth the effort. Overall, I strongly recommend this manuscript for publication, and would like to congratulate the authors with their nice study. 

Major comment:

•    L93. Extraordinary effort has gone into generating the best available depth model for Site U1406, and I strongly advise to use the composite CCSF-A scale, and against using the Hole A specific CSF-A scale. There is no benefit to it, and mixing depth models only serves to confuse the reader.

Some smaller comments, which the authors may address at their discretion:

•    General comment: Perhaps add a little map with site locations?

•    L27. Perhaps state where ODP Site 1168 and IODP Site 1406 are from?

•    L55. 4 million years, seems like a very large uncertainty, even for biostratigraphic age control from the 1980s. Million is abbreviated by a big M. 

•    L55. I would say “astrochronology” instead of “cyclostratigraphy” in this context. The former refers to, in my mind, the alignment of cyclic stratigraphic records (in the depth domain) to an astronomical solution (in the age domain). The latter is, as I understand it, thus a description of cyclically alternating lithologies/proxy records in the stratigraphic depth domain.

•    L63. Please make sure the Westerhold et al., 2020 age model is used. At 26.5 Ma a hundred-thousand-year correction of the Pälike et al., 2006 ages is included in Westerhold et al., 2020. 

•    L71. van Peer et al. 2017a, shows this hiatus in the age domain. van Peer is with a small v.

•    L79. Astrochronologic. (See previous comment).

•    L81. Delete “GTS”. The Westerhold et al., 2020 CENOGRID record is separate from the GTS2020. (NB: The G(P)TS2020 should not be used, due to incorrect incorporation of several chron boundary reversal ages. Most notably the Liebrand et al., 2016 ages, which were not all being considered reliable or deviant from GTS2012 outside of error, their Supp. Fig. S6.)

•    L101. This is an “old” ODP site that probably used the mbsf terminology, instead of CSF-A scale. Perhaps clarify this point in the text?

•    L120/121. Sigma and SD are used. Perhaps standardize?

•    L135-137. This is the same hiatus identified in van Peer et al., 2017a.

•    L147. This definition of the MOGI deviates from the original (Liebrand et al., 2017), which is defined as lasting from 28.0 to 26.3 Ma. Perhaps explain why a longer lasting MOGI is defined. I have no problem with a longer lasting MOGI, it is just an arbitrary definition, but still good to be clear how and why it differs. 

•    L173. Is an inverted increase not a decrease?

•    L180. In Fig. 3a and b this looks like a decrease, not a reduction in the increase. Confusing language. 

•    L181. I think it is important to redefine the MOGI as used in this study. (See previous comment) 

•    L183. “Warming” refers to deep-sea (and potentially high latitudes). Perhaps clarify.

•    L183-184. Also looks like a modest decrease, not a “slowing of increase”. 

•    L186. Looks like a decrease to me.

•    L212-L215. I do not understand this sentence. 

•    L241-244. This finding of Oslick can now be reflected on using the new data and age model. Just stating it seems a bit odd. To me it seems that the increase in Sr ratios follows 18O maxima much quicker, compared to the 1 M.y. lag Oslick found.

•    L279-282. Independent Sr age control is great. However, I would mention–also in writing–that for Site U1406 a magnetostratigraphic age model is publicly available (van Peer, 2017a). Are Sr and PMAG age models for Site U1406 in agreement with one another? Or are there any large discrepancies?

•    L305. Middle Miocene (25 to 27 Ma). Do the authors mean Oligocene?

•    L353. LP = LDP?. Who is PG?