the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Jan 2024
Reviews and syntheses: Review of proxies for low-oxygen paleoceanographic reconstructions
Abstract. A growing body of observations reveals rapid changes in both the total inventory and distribution of marine oxygen over the later half of the 21st century, leading to increased interest in extending oxygenation records into the past. Use of paleo-oxygen proxies have the potential to extend the spatial and temporal range of current records, bound pre-anthropogenic baselines, provide datasets necessary to test climate models under different boundary conditions, and ultimately understand how ocean oxygenation responds beyond decadal scale changes. This review seeks to summarize the current state-of-knowledge about proxies for reconstructing Cenozoic marine oxygen: sedimentary features, sedimentary redox-sensitive trace elements and isotopes, biomarkers, nitrogen isotopes, foraminiferal trace elements, foraminifera assemblages, foraminifera morphometrics, and benthic foraminifera carbon isotope gradients. Taking stock of each proxy reveals some common limitations in that the majority of proxies function best at low-oxygen concentrations and many reflect multiple environmental drivers. We also highlight recent breakthroughs in geochemistry and proxy approaches for constraining pelagic (in addition to benthic) oxygenation that are rapidly advancing the field. In light of both the emergence of new proxies and the persistent multiple driver problem, the need for multi-proxy approaches and FAIR data storage and sharing is emphasized. Continued refinement of proxy approaches and both proxy-proxy and proxy-model comparisons are likely to support the growing needs of both oceanographer and paleoceanographers interested in paleo-oxygenation records.
- Preprint
(4680 KB) - Metadata XML
-
Supplement
(685 KB) - BibTeX
- EndNote
Status: open (until 29 Apr 2024)
-
CC1: 'Comment on egusphere-2023-2981', Ellen Thomas, 28 Jan 2024
reply
Please see attached
-
RC1: 'Comment on egusphere-2023-2981', Thomas J. Algeo, 20 Feb 2024
reply
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2981/egusphere-2023-2981-RC1-supplement.pdf
-
RC2: 'Comment on egusphere-2023-2981', Anonymous Referee #2, 11 Apr 2024
reply
Review of “Reviews and syntheses: Review of proxies for low-oxygen
paleoceanographic reconstructions”
by
Babette A. A. Hoogakker et al.
Summary:
Hoogakker and colleagues provide a very extensive review of various proxy approaches (ranging from trace elements & their isotopes, over biomarkers, nitrogen isotopes, and foraminifera-based proxies) that can be used to reconstruct marine oxygen changes over the Cenozoic. The amount of information included in the paper is immense and has almost textbook dimensions (100 pages of text, including 16 figures, and >53 pages of references). In my opinion, this can be seen as a strength and a weakness of the paper – and I suppose it is an editorial decision if Biogeosciences wants to publish such an extended review study or if it would be better to split the review paper into multiple review studies to make it more manageable for readers and also reviewers (a lot of different subsections have a separate introduction already).
Given the paper's extensive nature, I will concentrate my (more detailed) comments on the initial sections, up to and including Section 6.2.6.3. I will provide more general comments, particularly on what I perceive as the manuscript's primary limitation - its structure.
Overall, I am convinced that the information provided by the manuscript will be of great value to the community, but, in my opinion, the text should be shortened significantly. I initially thought the manuscript would be a fantastic way to learn about different proxy approaches used to quantify paleo-oxygenation changes, but I got discouraged by the very long text and vast amount of subsections of the manuscript. This might be fine for general readers who can pick and choose the sections they are interested in (in contrast to a job of a reviewer). However, I still think that a more focused text and a better organization of subsections would improve the usefulness and approachability of the manuscript.
General comments:
Comment #1.1: Shortening the manuscript and combining duplicate information
Considering the long list of authors and diverse topics covered, I suppose that different groups of authors were responsible for different sections – which is absolutely fine and necessary – however, the manuscript would benefit from a few core authors reviewing the entire manuscript and combining/deleting overlapping information (as also suggested in the review by Ellen Thomas; with nitrogen-dynamics being discussed in multiple sections only being one example).
Comment #1.2:
At times, the manuscript is quite wordy and/or provides a lot of detail on topics that are not directly related to the understanding of the specific redox proxies. A few example parts (mainly of the first half of the manuscript that I looked at in more detail) that could (in my opinion) be shortened are: Sections 3; 6.1.1. (especially in 2nd and 3rd paragraph); 6.1.2.
Is the information of the “Materials/Methods” type sections really important for the review paper (e.g., 6.2.2, 6.3.7, 6.5.3, 6.6.4, 6.7.3)? I found these sections rather technical and not very informative/crucial for understanding the specific proxy (but that might, of course, be personal preference).
Some of the future directions sections are rather long (especially 6.2.6 & 6.6.8 & 6.7.8).
The introduction to “6.5 Foraminifera trace elements” (6.5.1+6.5.2) consists of more than 7 pages (just text) plus 4 Figures. It should be possible to shorten this text (or combine figures) without losing too much relevant content.
Comment #2: Structure
The manuscript includes too many subsections (sometimes up to 5 levels—see, e.g., Subsection in 6.2.3), which is confusing and makes it challenging to pinpoint where the current information ‘lives’ in relation to the overall structure of the manuscript. I think a depth of 3 or 4 subsections should be enough; otherwise, the reader loses orientation.
Section 6 consists of many, many subsections and forms the majority of the text. In contrast, the previous Sections 1 – 5 are very short and do not have any subsections. This should be better balanced. For instance, why are Sections 4 and 5 separate Sections at all – this information could be part of the general introduction. Section 6 could maybe be organized into multiple Sections of similar size (potentially just the current subsections of Sec. 6).
Comment #3: Introduction
The introduction does not introduce the topic of the review article. The second paragraph explains the causes for ocean deoxygenation and the second half of the introduction exclusively deals with problems in Earth system models to simulate ocean oxygen correctly. This is very surprising as Earth system models are not part of the review paper at all.
More relevant would be a general introduction to oxygenation changes over the Cenozoic and redox-proxies, and how they can help quantify the oxygenation changes. Information given in the different intros throughout the document could here be combined(e.g. such as the information given in 6.1, 6.2.1 and similar sections throughout the manuscript).
Comment #4:
6.2. “Sedimentary redox trace elements and isotopes”
An overview table would be very useful that summarizes/compares the key characteristics, residence times and applications of the different proxies.
Also, for Subsections 6.2.3: Why not combine the elements & their isotopes in one section?
Comment #5:
The large amount of references for some sentences (sometimes 6-12) makes it difficult to read the text (just a few examples: lines 261, 521, 561, 575, Sections 6.2.3.1.4, 6.2.5.2 in general, 628, … ). It would be helpful to shorten the references given, e.g., only provide the most important references are given or a few examples. Also, it is not necessary to cite the same paper multiple times in consecutive sentences (for instance, see 6.2.3.1.2; 6.2.3.1.4; 6.2.3.3.1)
More Technical Comments:
First two sentences of Section 2: Please rephrase. It sounds like seawater temperature, pH, and dissolved oxygen are environmental properties that can generally not be measured directly.
Fig 1: the caption says: “Proxy types shown in olive
can be used to reconstruct oxygen from benthic settings, those in green can be used for pelagic settings.” But I do not see olive and green proxies in the figure.
Ln 389: “Fully digested” what does this mean – not clear for a non-data person.
ln. 547: decomposition of organic matter is probably meant here. Organic carbon describes only the C itself contained in organic material. Please check the use of organic carbon throughout the document.
Some of the subsection titles are rather long and should be shortened, see e.g. Subsections 6.3.3; 6.3.6
Title 6.6.3 = 6.6.2 -- I suppose, 6.6.3 is Planktic foraminifera
Line 398: “This is especially true ...” please rephrase, it is unclear what 2 to 3 cm kyr-1 referes to.
Fig. 4: It could be made more obvious what boundary condition is changed between a and b.
the relatively low-oxygen concentration at a certain depth below the seafloor (blue line) leads to aU precipitation (green line).
Line 709: … the occurrences of (singular)
Figure 8: Please include the figure in higher resolution. In particular, the text looks pixelated.
Citation: https://doi.org/10.5194/egusphere-2023-2981-RC2
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 845 | 319 | 22 | 1,186 | 35 | 9 | 17 |
- HTML: 845
- PDF: 319
- XML: 22
- Total: 1,186
- Supplement: 35
- BibTeX: 9
- EndNote: 17
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1