the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Limited exchange between the deep Pacific and Atlantic oceans during the warm mid-Pliocene and MIS M2 "glaciation"
Kim A. Jakob
Sze Ling Ho
Oliver Friedrich
Eirik Vinje Galaasen
Stijn De Schepper
Paul A. Wilson
Anna Nele Meckler
Abstract. The mid-Pliocene (3.3–3.0 Ma) is the most recent period in Earth’s history of sustained, global warmth analogous to predicted near-future climates. Despite considerable efforts to characterize and understand the climate dynamics of the mid-Pliocene, the deep ocean and its response to this warming remains poorly understood. Here we present new mid-Pliocene Mg/Ca and Δ47 (“clumped isotope”) temperatures from the deep Pacific and North Atlantic oceans. These records cover the transition from Marine Isotope Stage (MIS) M2 — considered the most pronounced “glacial” stage of the mid-Pliocene — to the warm KM5 interglacial. We find that a large (>4 °C) temperature gradient existed between these two basins throughout that interval, with the deep North Atlantic considerably warmer and likely saltier than at present. We interpret our results to indicate that the deep Pacific and North Atlantic oceans were bathed by water masses with very different physical properties during the mid-Pliocene, and that only limited deep oceanic exchange occurred between the two basins. Our results point to a fundamentally different mode of ocean circulation or mixing compared to the present, where heat and salt is distributed from the North Atlantic into the Pacific. The amplitude of cooling observed at both sites during MIS M2 suggests that changes in benthic δ18O associated with this cold stage were mostly driven by temperature change in the deep ocean rather than ice volume.
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Anna Hauge Braaten et al.
Status: open (until 05 Jul 2023)
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CC1: 'Comment on cp-2023-13', Harry Dowsett, 27 Apr 2023
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Mid Pliocene is not the correct terminology anymore (the Pliocene is divided into the Zanclean and Piacenzian). The interval you are writing about would be correctly termed Late Pliocene or mid Piacenzian (see GTS2020).
Citation: https://doi.org/10.5194/cp-2023-13-CC1 -
RC1: 'Comment on cp-2023-13', Anonymous Referee #1, 15 May 2023
reply
Hauge Braaten et al. present a combination of thermometers (Mg/Ca and D47) applied to benthic foraminifera from 2 sites (in the Pacific Ocean and in the Atlantic Ocean) to reconstruct the bottom water interaction between the 2 oceans during the mid Piacenzian. This article presents a significant amount of measurements and high quality conclusions. It deserves to be published. I have a few suggestions, mostly on salinity reconstructions and minor comments.
Regarding the salinity reconstruction, I would suggest being more critical of your methodology. The relationship between d18Osw and salinity changes over time. Assuming that the relationship during the mid Piacenzian is similar to today's is probably wrong. Although the authors mentioned it, they assume that their reconstructions of salinity is correct and I suggest being more careful in interpreting your data. Additionally, the authors should add a discussion of the uncertainties in thier estimated salinity. Is a change of 2 PSU, using this methodology, really significant? (Line 377). Same question for a salinity difference of 0.2 between the Atlantic Ocean and the Pacific Ocean (Line 391). Finally, did the authors take into account the global changes during this period (based on sea level change for example) in order to obtain the local salinity signal?
The preservation and contamination tests presented in supplementary material are not mentioned in the text. I found it confusing to only read that the foraminifera are well preserved without any justification, until I read the supplementary material. I would suggest, at least, mentionning the supplementary material.
Lines 209, 254 and 255: do the authors have uncertainties at 1 or 2 sigma?
Line 281: I would mention that the author are still talking about Mg/Ca derived temperature in this paragraph.
Line 295: MIS not MI2
Figure 2 and 3: It would be great if the authors could also add the uncertainties on the Mg/Ca temperatures
Lines 395-396: Can the authors expand on this sentence, please?
Line 410: What are the authors referring to? Model, data? References are missing
Lines 458-462: How did the authors conclude on the ice volume proportion of thier d18Osw parameters? How did they remove the salinity part of the d18Osw, as explaining previously?
Citation: https://doi.org/10.5194/cp-2023-13-RC1
Anna Hauge Braaten et al.
Anna Hauge Braaten et al.
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