the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jan 2026
Including the triple isotopic composition of dissolved oxygen in the ocean into the iLOVECLIM model (version 1.1.7): development and evaluation
Abstract. Contributing around half of the oxygen produced on Earth, marine photosynthetic production is one of the main mechanisms for carbon fixation, with a central role in the oxygen cycle. The triple isotopic composition of atmospheric oxygen (17Δ), measured in ice cores, provides a global integrator of past biospheric oxygen fluxes, and by extension carbon fluxes. However, deconvolving the signal of 17Δ requires to isolate the oceanic biosphere productivity (17Δocean). Here, we present the first implementation of 17Δocean in the intermediate-complexity climate model iLOVECLIM. The three main processes controlling 17Δocean, i.e. photosynthesis, respiration, and air-sea gas exchange, are explicitly represented and evaluated under preindustrial conditions. Model results show overall good agreement with available measurements, particularly in the Pacific Ocean. In contrast, systematic overestimation is found in the Southern Ocean. At fixed stations, seasonality is reproduced but with underestimated amplitude. These discrepancies mainly reflect challenges in representing remineralization and oxygen minimum zones, and highlight opportunities to refine the representation of primary productivity and vertical mixing. Overall, this new implementation provides the first coupled model framework for simulating 17Δocean, both as a diagnostic of biogeochemical processes and as a tool for reconstructing past changes in marine productivity. Extending the implementation to the terrestrial biosphere will further allow reconstruction of the past global biosphere and direct comparison with 17Δ records from ice cores.
Competing interests: At least one of the (co-)authors (DMR) serves as topic editor for the special issue to which this paper belongs.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
(5290 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2025-5230', Anonymous Referee #1, 09 Jun 2026
- AC1: 'Reply on RC1', Emeline Clermont, 07 Jul 2026
-
RC2: 'Comment on egusphere-2025-5230', Anonymous Referee #2, 04 Aug 2026
Overall, I think this is a useful advance to be published, and brings together understanding implemented in models of different parts of the Earth System into a coupled ocean-atmosphere framework.
General points to address:
More justification is needed for the simplification 'GPPO2 = 2 × PP'. You state from Juranek and Quay that the range in the ocean is 18-4.5 and that the ratio is close to 2.7, then chose a value of 2. If going for a single number, why not 2.7? Then whet is the implication of not considering the spatial variability? For example, if you were to consider spatial correlation between the GPPO2/PP ratio and e.g. spatial variability in O2 fluxes, does that lead to a bias in from the mean impact of this assumption that might suggest that you should be using a higher or lower value? As I say, simplification is quite understandable, it just needs more justification and explanation.
I'm not 100% clear as to whether oxygen is prognostic or not in the model. You state that you are inferring O2 fluxes from CO2 fluxes, which in my view may be acceptable in steady state system, but O2 and CO2 have vastly different equilibration timescales due to the slow hydration reaction of aqueous CO2. But you also describe the O2 flux calculation in the paragraph starting on line 176. I would suggest having a very clearly written summary at the start of the implementation section so the reader is clear when they go into this section what assumptions you are making, then you can fill them in on the detail subsequently. Please then explore with clear justification, how if these assumptions were not made the results would change, and in the context of this, explain why the choices made here are (or are not) acceptable.
The observational comparison is hard to take a lot from in this stud, as the model physics and background O2 concertation are not very good (for understandable reasons given the nature of the model). I wonder if it would be more useful to go the observational comparison in water-mass space rather than geographical coordinates, so the reader can assess the d17O more meaningfully?
Specific points to address:
'…provides a global integrator of past biospheric oxygen fluxes, and by extension carbon fluxes'. Not all processes change C and O together, particularly on longer timescale - moderate this statement.Wording flow: 'However, deconvolving the signal of 17Δ requires to isolate the oceanic biosphere productivity (17Δocean).' -> ‘However, deconvolving the signal of 17Δ requires one to isolate the oceanic biosphere productivity (17Δocean) from …..[state what it is deconvolved from]’
Line 39, "have employ isotope-enabled." -> "have employed isotope-enabled."
Line 49, missing a space in ").T"
Citation: https://doi.org/10.5194/egusphere-2025-5230-RC2
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 978 | 672 | 82 | 1,732 | 101 | 145 |
- HTML: 978
- PDF: 672
- XML: 82
- Total: 1,732
- BibTeX: 101
- EndNote: 145
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The 17ΔO2 preserved in ice cores is a key proxy for reconstructing past global biosphere productivity, yet interpreting this signal requires a robust understanding of both the oceanic and terrestrial end-members. Previous studies have incorporated oxygen isotopes into the ocean biogeochemical component of CESM, but a fully coupled Earth system modeling framework has remained unavailable. This study addresses this gap for the oceanic component by implementing the triple oxygen isotope composition of dissolved oxygen (17Δocean) into the intermediate-complexity Earth System Model iLOVECLIM.
The authors incorporate the three principal processes controlling the isotopic composition of dissolved O2—photosynthesis, respiration, and air–sea gas exchange—and evaluate model performance against a compilation of 2482 observational measurements under pre-industrial boundary conditions. The manuscript is generally well structured, the methods are described in sufficient detail, and the model–data comparison is comprehensive. I believe this work represents a valuable contribution and is suitable for publication in Geoscientific Model Development after the authors address the comments below.
Major comments
Minor comments
1, In Eq. (7), should the asterisks on Osurf and Oeq be removed? Please verify the notation.
2, Line 184: “the the model” contains a duplicated word.
3, Table 1 uses inconsistent formats for reporting parameter uncertainty. Some entries are presented as ranges (e.g., [0.982–0.990]), whereas others are reported as mean ± uncertainty (e.g., 0.980 ± 0.003). Consider adopting a consistent format throughout the table.
4, In Table 2, the simulated global GPPO2 value (9.68 × 1015 mol O2 yr−1) is compared with estimates from Huang et al. (2021). However, the Huang et al. estimates represent the modern ocean, whereas the model is run under pre-industrial boundary conditions. Although the difference in global productivity between these two states may be modest, this mismatch should be acknowledged. The same caveat applies to the comparison of isotope tracers with modern observational datasets.
References
1, Yeung, L. Y., Young, E. D., & Schauble, E. A. (2012). Measurements of 18O18O and 17O18O in the atmosphere and the role of isotope-exchange reactions. Journal of Geophysical Research, 117(D18).
2, Li, B., Yeung, L. Y., Hu, H., & Ash, J. L. (2019). Kinetic and equilibrium fractionation of O2 isotopologues during air–water gas transfer and implications for tracing oxygen cycling in the ocean. Marine Chemistry, 210, 61–71.