the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Pelagic ecosystem responses to changes in seawater conditions during the Middle Pleistocene Transition in the Eastern Mediterranean
Abstract. We present a multiproxy, ecosystem-level assessment of paleoenvironmental change and its impacts on marine organisms in the Eastern Mediterranean during the Middle Pleistocene Transition, between 923 and 756 kyr B.P. (marine isotope stages MIS 23–18). This study combines analyses of organic biomarkers; organic matter content; carbon and oxygen stable isotopes on bulk sediment, surface-dwelling, deep-dwelling planktonic and benthic foraminifera, ostracods and fish otoliths; as well as foraminiferal, ostracod and sponge abundance estimates, with a statistical assessment of paleoenvironmental regime shifts and estimation of fish distribution depths in the past. Our results show that temperature and productivity played the most important role in driving ecosystem changes in the study area at different times: temperature was the primary driver during MIS 21 interglacial, whereas productivity became a dominant factor in MIS 19 interglacial. In addition, the responses of organisms throughout the water column varied. Both interglacials yielded relatively higher plankton and benthos biomasses. However, for fishes, the responses differed. The abrupt global warming that occurred in early MIS 21, which was also captured by our record, probably led to a reduction in diel vertical migration by mesopelagic fishes and consequently to the efficiency of the biological carbon pump. In contrast, increased productivity across trophic levels is attested for MIS 19 that subsequently dropped in MIS 18, affecting foraminifera, ostracod and sponge biomasses, but not inhibiting fish diel vertical migration. Therefore, we conclude that carbon sequestration during MIS 19 was likely enhanced.
Status: open (until 06 Apr 2025)
-
RC1: 'Comment on egusphere-2025-96', Anonymous Referee #1, 26 Feb 2025
reply
The submitted manuscript by Agiadi et al. is a valuable contribution to study the paleo-environmental evolution of the Island of Rhodes during the Pleistocene as it uses a multi-proxy approach to identify changes in productivity and temperature. In addition, the authors estimated the fish distribution depths at Lardos to assess the response of fish to the environmental changes. The study provides unique SST and SSS data of the Island of Rhodes that contribute to the understanding of climate change in the eastern Mediterranean Sea. Therefore, I believe the manuscript is a valuable contribution to the field and worth being published.
However, there are some aspects that should be clarified and adapted before publication, which is why I suggest a major revision.
For once I believe the many proxies used in this study are rather confusing and not all contribute to the understanding of the paleo-environmental conditions. Much of the discussion focuses on the d13C of benthic and planktic foraminifera, while ostracods and sponge spicules for example seem not to contribute to the understanding. In that regard, a summarizing figure would additionally be needed, where the reader better can follow the discussion.
The authors suggest capturing the MPT and use the age model provided by Titschack et al., 2013. However, in 2024 the age model for Lardos has been refined by Eichner et al. towards a younger age. I suggest that the authors also check and discuss whether they are really in the time frame of the MPT by also considering the refined age model from 2024. In this regard, I would suggest changing the title because in the discussion the MPT is not mentioned at all. From the discussion it is not clear if the MPT did influence the study area or not.
In the discussion I am missing a critical view on the data provided by the study. It is not really clear what these regime shifts are and some of the suggested changes are not as clear to me as suggested in the text. Further the authors should discuss the data to a much greater extend, especially chapters 4.1.1-4.1.4. I also suggest changing the structure of the discussion and instead of describing the regime shifts individually, discuss them as a whole. What are the changes and what is responsible for it?
Please be more precise when talking about depth. You should specify in the whole manuscript if you are talking about water depth/section depth/ fish depths etc. It is not entirely clear.
The authors should make clear that Agiadi et al., 2024b is a database with the data generated for this study and not an earlier publication where the data was already described in. Why not refer to it in the journals section “data availability” where you can add the doi. At the moment it is just confusing.
The reference list was not checked for completeness. My specific comments and suggestions can be found in the following attached pdf:
-
RC2: 'Comment on egusphere-2025-96', Anonymous Referee #2, 17 Mar 2025
reply
Dear
EGUsphere
I hereby you receive my report on the submitted manuscript " Pelagic ecosystem responses to changes in seawater conditions during the Middle Pleistocene Transition in the Eastern Mediterranean” by Agiadi et al.
The submitted manuscript provided information about the paleoenvironmental changes in marine records in the Eastern Mediterranean basin over the Middle Pleistocene Transition, and in particular between Marine Isotope Stages MIS 23–18. The multiproxy approach used to analyzed the marine record from Rhodes Island allowed the authors to produce SST data as well as changes in productivity signal. Analyses on change in biomass have been used to reconstruct the fish distribution depths during the MPT time interval.
It is clear evident the huge amount of data produced by the authors and it is not easy to combine all the information derived from these proxy records, but I think that the present version of the manuscript is really confused and most of the manuscript is really a description of results and it is completely missing a deep discussion as well as a global view of the MPT problem and the impact on marine ecosystem. In fact, in my opinion, the Middle Pleistocene Transition is not the target on this manuscript. The study record falls well within the changes occurring during the MPT. In the study record is missing the onset of the MPT as well as the end. So that I would like to suggest changing the title of the manuscript.
The manuscript is well written but it is missing a real discussion and in the manuscript the authors consider only part of the data (i.e. they focused on d13C signal and d18O is strongly underestimated).
- Concerning the age model: I have several doubts on the chronology of the study record. The authors referees to the Titschack et al. (2013) and they improve the chronology according to the new stable isotope data. But the proposed chronology is based only on visual correlations of the news stable isotope data with LR04 global (Lisiecki and Raymo, 2005) and Mediterranean (Konijnendijk et al., 2015) benthic δ18O stacks, and with that occurring in the planktonic foraminifera Mediterranean δ18O Medstack (Wang et al., 2010). There are no data on calcareous nannofossils and planktonic foraminifera to support the proposed chronology. In addition, for the Mediterranean planktonic record I would like to suggest to use Grant et al. (2022) recently published for ODP site 967 (eastern Mediterranean). In my opinion it is necessary to improve the chronology of the study record. At present this issue is really weak.
- Chapter introduction: the authors report as follows: Such warmer and saltier conditions were last observed in the area in the Late Miocene (Besiou et al., 2024; Kontakiotis et al., 2022; Vasiliev et al., 2019) and it becomes intuitive that seawater conditions during the MPT may have also been very different from those in the Western Mediterranean. This issue is questionable. The Late Miocene is forced by a different climate regime and a possible connection with the MPT is very difficult.
- Subchapter 1 Study area, sampling and chronostratigraphic background: the chronology has to be improved and supported by data. When the authors reported as follows: The total section comprises 30 meters of marine marls and silts. In this work, we focus on the 2.4 m lowest marls of the section already studied by Titschack et al. (2013), it is necessary a new figure where it is reported clearly the stratigraphic interval analyzed in this manuscript respect to the published ones.
- Subchapter 2.3 Oxygen and carbon isotope analyses: the stable isotopes on bulk can be removed from this paper. They are not useful. The authors produced stable isotopes on different matrixes
- I do not understand if all the data plotted in the figures of this manuscript have been acquired for this work or derived by a compilation from different sources. Please clarify this issue
- Figure 1: The authors proposed in Fig 1 two different figures. Please it is necessary to separate these informations. In figure 1 is missing the location of Montalbano Jonico section.
- Fig 2: in the observing d18O G. ruber, G. inflata as well as in U. peregrina patterns is not clear the position of warm and cold MIS in time domain. I think that there is a problem with chronology. MIS 21 (warm) shows in G. ruber signal a strong cold event, at the base of this MIS, followed by a warm pick event, followed by a cold phase along the MIS21. This pattern is strongly different to the signal reported in the reference curves. Also, the signal in MIS 22 (cold) is the same reported in MIS 23 (warm). How can you separate these MIS? Again, in U. peregrina it is not clear the signature and the signal is flat. Are you sure of the chronology? Please try to control the age model.
- Chapter discussion: Basically, the authors have to write this chapter. I think that it is necessary to specify how the authors define the boundaries of the identified regimes, and it is necessary to discuss seriously what are the climate/oceanographic changes those impact on the different time interval and secondly the impact of these changes on the marine ecosystem. In my opinion without the quantitative distribution of marine proxy records (i.e., calcareous plankton, ostracods and others) it is very difficult to use the term ecosystem in this manuscript.
- SubChapter 2 Thermohaline gradient: this subchapter is a descript of results
My overall conclusion is that the manuscript is suitable for the journal but the present version is not acceptable for publication. In my opinion the manuscript needs major revision before publication
Citation: https://doi.org/10.5194/egusphere-2025-96-RC2
Data sets
Dataset K. Agiadi, I. Vasiliev, A. Vite, S. D. Zarkogiannis, and F. Quillévéré https://doi.org/10.5281/zenodo.14623783
Model code and software
Code for estimating the fish lifetime-average depth A. Fuster-Alonso, J. Mestre Tomás, and K. Agiadi https://doi.org/10.5281/zenodo.14565733
Viewed
Since the preprint corresponding to this journal article was posted outside of Copernicus Publications, the preprint-related metrics are limited to HTML views.
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
82 | 0 | 0 | 82 | 0 | 0 |
- HTML: 82
- PDF: 0
- XML: 0
- Total: 82
- BibTeX: 0
- EndNote: 0
Viewed (geographical distribution)
Since the preprint corresponding to this journal article was posted outside of Copernicus Publications, the preprint-related metrics are limited to HTML views.
Country | # | Views | % |
---|---|---|---|
United States of America | 1 | 23 | 25 |
Germany | 2 | 18 | 19 |
France | 3 | 8 | 8 |
Greece | 4 | 8 | 8 |
China | 5 | 6 | 6 |
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1
- 23