the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Apr 2026
Exploring the Cenozoic Earth system with extraterrestrial 3He
Abstract. A key method for contextualizing climate today and into the future is to draw upon the past. Marine sediments accumulating at the bottom of the ocean serve as the only continuous archive of Earth's climate history spanning tens of millions of years. From the earliest studies of marine sediments, reconstructed changes in the inputs of sedimentary constituents such as volcanic glass, ice-rafted debris, particulates carried by rivers, desert dust, organic and inorganic remnants of organisms and biological process, and even extraterrestrial material, have been used to discern past environmental conditions. Specifically, it is the rate at which these different components of sediments from the bottom of the ocean accrue over time that can provide unique and important insight into how Earth system dynamics operated in the near and distant past. Traditional techniques for quantifying sediment mass accumulation rates (MARs) contain numerous complexities that can lead to erroneous MAR determinations. Constant flux proxies (CFPs), particularly extraterrestrial 3He (3HeET) delivered in interplanetary dust particles from space, are underutilized geochemical tools that alleviate these issues as long as key assumptions can be constrained. In this perspective, we review CFP 3HeET as a CFP and outline its benefit for understanding Cenozoic climate beyond the Quaternary. Ultimately, we suggest that the application of 3HeET is valuable for providing the broader paleoclimate and paleoceanography communities with accurate records of Cenozoic Earth system change from a MAR perspective.
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Status: open (until 08 Jun 2026)
- CC1: 'Comment on egusphere-2026-1583', Giacomo Medici, 16 Apr 2026 reply
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RC1: 'Comment on egusphere-2026-1583', David McGee, 13 May 2026
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This manuscript presents a helpful and clear review of the use of extraterrestrial helium-3 (3HeET) to calculate vertical rain rates of marine sediments, and it argues that applications of this tool have been limited relative to its potential for providing insight into past climate and marine productivity changes.
The writing is thoughtful and well-organized, and the manuscript presents two helpful case studies documenting how mass accumulation rates (MARs) estimated from 3HeET lead to very different results than previous work relying on age model-based MARs. The authors make a good argument that 3HeET should be more widely used in the field, and the manuscript is worthy of publication with a few revisions.
Much of the manuscript is essentially an updated version of section 4.2 of McGee and Mukhopadhyay (2013); that work also noted the advantages of 3HeET-based MARs over age model-based MARs and highlighted examples where use of 3HeET substantially changes conclusions, and it ended with a similar argument: “the use of 3HeET as a constant flux proxy has been relatively limited compared to its potential applications.” That is not to say that this overlap makes the current manuscript unnecessary: reviews need updating every decade or so, and it is worthwhile to have such a review appear in a journal rather than a (rather obscure) book. Moreover, this manuscript is much more specifically addressed to the paleoceanography community.
I have a few suggestions for improvements:
Line Comment
67-69 This sentence is confusing.
76 “loss”->”lost”
78 I suggest changing “at least from a MAR perspective” to “at least those based upon MARs”
93 “Ee”->”We”
104 I suggest changing “from an age model perspective” to “based on age models”
Fig 1 I was unclear about the meaning of this figure. The text doesn’t explain how the higher-resolution age model was determined, beyond mentioning a “statistical tuning approach” in the caption. I guess the point is that there can be substantial MAR changes between low-resolution age model tie points, but a) this could be said more clearly, and b) the high-resolution MAR doesn’t appear to average to the same value as the low-resolution MAR over the same intervals (e.g. see the interval from the coretop to ~15 ka), which is confusing.
134 Equations 3 and 4 seem unnecessary and misleading – Equation 3 states an assumption, and Equation 4 states something that is usually but not always true. I think equations should be saved for definitions or relationships that are always true.
185 Change “thought of as the ‘excess’ or ‘missing’ sediment” to “thought of as the ratio of the total sediment”
225 “works”->”work”
226 “heavy particle scavenging” is confusing to me. Are you talking about scavenging by heavy particles, or about the extent to which vertical fluxes are impacted by scavenging?
226 I don’t find the age model-dependence argument to be a reason for favoring 3HeET over 230Th. My sense is that in most sediment core records of the last ~400-500 ka (i.e. where 230Th is an option), the age model-based uncertainty is only a small fraction of the total uncertainty in 230Th-based MARs; and if the age model is so uncertain that it is a dominant part of the 230Th uncertainty, then your flux time series is not going to be very useful for paleoceanographic purposes anyway.
Fig 4 Why is Fig 4A the same as Fig 3C?
Fig 4 “Gubbio” is misspelled in two places.
285 Perhaps clearer to replace “LSRs” with “age models”?
288 can you be more specific about what is meant by “certain sedimentation patterns”? In general, this section could be more convincing in making the case that the 3HeET-based MARs at 885/886 are more accurate than age model-based MARs, not just that they’re different.
303 It’s unclear whether “contemporaneous” refers to the fact that the studies came out at around the same time, or whether they covered the same time interval.
318 Can you be clearer about what is meant by “core-specific characteristics”? I think it would be helpful to state specifically that the difference between the two MARs suggests that the sites are affected by substantial winnowing prior to 3.6 Ma, and that the large inferred increase in dust flux after 3.6 Ma instead reflects a decrease in winnowing/increase in focusing.
Fig 6A I’m not sure where it would go in the manuscript, but I would encourage the authors to emphasize more than they currently do that the age model-based MARs for specific sedimentary constituents are in reality limited to the resolution of the age model; age model-based dust and opal flux records that appear to be high resolution (like those shown in Fig 6A and 6C) reflect an assumption that all changes in dust and opal concentration are from changes in flux rather than changes in dilution.
340 The use of the word “driver” here makes it sound like you are talking about a driver of the PETM, not a driver of the recovery from the PETM.
368 “be”->”can be”
371 “less-than-optimal”->”low”
381 It would be helpful to point out that this sensitivity of the 3HeET concentration leads to large uncertainties in the 3HeET-based fluxes. In general, I think the authors can be clearer in pointing out that use of 3HeET might not be possible in quickly accumulating sediments with high detrital content.
422 Somewhere, the authors should point out that the inferred 3HeET fluxes for older time intervals may reflect site-specific differences in 3HeET loss (e.g. due to burial heating). For example, the data from Gubbio are from lithified, uplifted sediments that may have been heated.
438 I’m not clear that the Elderfield proxy curve applies to 3HeET…did 3HeET go through a “Pessimism” phase? If so, the authors should provide evidence of this phase – maybe it was during the time when people were suggesting cyclic 100-kyr changes in 3HeET flux to Earth? I feel like (as the authors later state), the real issues are lack of analytical facilities, the slow pace of data gathering (due to analytical procedures and the need for replicates), and the continued need for community education about the importance of CFPs (which this manuscript aims to address).
449 I am conflicted about writing this, but for #2 I guess feel that the McGee and Mukhopadhyay chapter also tried to “describ[e] 3HeET’s utility to the broader Earth science community”? Again, it’s clear this manuscript has an important role to play, but I think the authors could be a bit more specific in stating how this manuscript is different from previous work.
460 to me, “heavily stymied” is a bit of an awkward phrase.
Nice work, and I look forward to seeing this published.
-David McGee
Citation: https://doi.org/10.5194/egusphere-2026-1583-RC1
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General comments
Good research on paleoclimate. Please, follow my specific comments to improve your manuscript.
Specific comments
Lines 34-36. “High resolution archives that are also temporally expansive are integral for understanding the modern Earth system”. Insert further and recent literature on Cenozoic climate changes registered in the sedimentary record:
- Medici, G., Marianelli, D., Gori, F., Cornacchia, I., Brandano, M. 2026. Multi-disciplinary approach to paleokarst occurrence in the Eocene–Oligocene succession of the Apulia Carbonate Platform (Salento, Italy). Facies, doi: 10.1007/s10347-026-00729-5
- Jaramillo-Vogel D, Strasser A, Frijia G, Spezzaferri S (2013) Neritic isotope and sedimentary records of the Eocene-Oligocene greenhouse–icehouse transition: the Calcare di Nago Formation (northern Italy) in a global context. Palaeogeogr Palaeoclimatol Palaeoecol 369:361–376
Line 94. “Goals”. I would stick with “objectives” as you have done a few lines below.
Line 134. You have many equations and this one is obvious. Can you avoid at least Equation 3?
Line 212. Eleven equations are too many for me in a non-engineering manuscript. Some equations are very basic in this manuscript.
Line 464. A clear conclusion that re-calls your good four objectives would be useful.
Figures and tables
Figure 2. The figure can be divided in two separate figures, one with the maps and one with the graphs.
Figure 3. This figure works also in smaller size.
Figure 3. The caption is too long. Some detail can be moved to the main body of the manuscript.
Figure 4. Increase the graphic resolution in terms of dpi.
Figure 6. The caption is too long also for this figure. Some detail can be moved to the main body of the manuscript.
Figure 7. The timescale is missing and unclear.