the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Jul 2026
A high-resolution coupled atmosphere-ocean model of the Great Barrier Reef: ACCESS-EMS-GBR v1.0
Abstract. We present a new regional coupled atmosphere and ocean model of the Great Barrier Reef (GBR), Australia, called ACCESS-EMS-GBR. The model comprises a regional configuration of the Australian Community Climate and Earth System Simulator (ACCESS) atmospheric model (the United Kingdom Met Office Unified Model), coupled to the Commonwealth Scientific and Industrial Research Organisation Environmental Modelling Suite (EMS) hydrodynamic and biogeochemical model of the GBR. The model includes detailed aerosol and cloud microphysics in the atmosphere, as well as hydrodynamics, biogeochemistry, ecology and coral reef processes in the ocean. When coupled, the models form a valuable tool for simulating interactions between the atmosphere and ocean. The ACCESS-EMS-GBR model was developed to assess the plausibility and implications of marine cloud brightening (MCB) in the GBR, as part of the Reef Restoration and Adaptation Program (RRAP) Cooling and Shading Sub-program (RRAP-CS) but can also be utilised to study various processes including sources of marine aerosol and the impact of aerosol deposition on marine biogeochemistry. Here, we describe the model as configured for the GBR region, including the coupling framework, and evaluate the model skill in simulating measured aerosol and seawater temperature and irradiance. We configure the model aerosol scheme and emission sources to capture observed aerosol properties over the GBR region, with boundary layer nucleation and terrestrial biogenic emissions having a large influence on aerosol number concentration, size distribution and composition. The distribution of sea salt emissions is also expanded to include the soluble Aitken mode; a significant improvement in capability for simulating MCB and possibly for improving global climate model biases.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2761', Anonymous Referee #1, 05 Aug 2026
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RC2: 'Comment on egusphere-2026-2761', David Webb, 29 Aug 2026
egusphere-2026-2761
===================Review of: "A high-resolution coupled atmosphere-ocean model of the Great Barrier Reef: ACCESS-EMS-GBR v1.0"
Authors: Rebecca L. Jackson, Matthew T. Woodhouse, Mark Baird, Clothilde Langlais, Mathieu Mongin, Anthony Jones, Daniel Partridge, Luke Harrison, Johanna Horchler, Joel Alroe, Luke Cravigan, Zoran Ristovski and Daniel P. Harrison
Overall:
========The code describes a regional couple model developed primarily to study the impact of atmospheric aerosols on the Australian Great Barrier Reef. In its present form the paper contains too much on the development of the aerosol code and contains too little on the ocean model and the way in which data from a relatively coarse (4km) grid was used to predict ocean properties in the shallow lagoon, shallow reef front and deep reef front zones of individual reefs. The description of the model forcing and coupling also needs attention.
I have no useful experience of aerosol or biogeochemical modelling so have not commented on the details in the related sections.
Major points
============1. Line 1 Title.
The model is designed primarily for studying the impact of aerosols and the validation section is primarily about aerosols. This needs to be apparent from the title.
2. Abstract
This needs to say something about the size of of the model grid.
3. Introduction
"Coral reefs in particular require high-resolution modelling ...".
"ACCESS-EMS-GBR is a high-resolution, regional coupled atmosphere-ocean model of the GBR and provides a valuable tool to undertake these assessments, ..."By this stage I was expecting a reef resolving ocean grid, and when I later read " a curvilinear horizontal grid spacing of approximately 4 km", I imagined a high resolution curvilinear fitted grid, typical of those used in coastal locations, using a 4 km grid in the open ocean and reducing to a few hundred metres around individual reefs.
But no, I was wrong. You need to be clear with the reader earlier on.
4. Section 2.1.2A history of the development of the code is not needed here. The paper would be tighter if the main text concentrated on describing just the sub-models used in the latest version of the coupled model. Notes on the development of individual sub-models, or differences with previous versions, could then be placed in an appendix or a supplement to the m/s.
5. Ocean Model and Hydrodynamics
This section needs revision. There should be more information about the grid being used. It is said to be curvilinear but I suspect it is similar to a regular grid but with a much greater computational cost. Neither the grid nor the hydrodynamics are described in Baird 2020.
Unfortunately Herzfeld's paper is behind a paywall, so I cannot at the moment comment on the hydrodynamics. However the m/s could include a sentence or two explaining why it was chosen, given that whereas most of the computer requirements come from the deep ocean, most of the scientific interest is in the shallow shelf seas - where I suspect the model only includes a few levels. A brief descrition of the mixing and time-stepping schemes would also be useful.
The m/s says that the model uses Topex/Poseidon tidal data to specify sea level. This could be used as a horizontal boundary condition to the hydrodynamic model, or it could be imposed in each grid box (presumably by smoothing). The paper need to be more specific. If it is the latter, how does the code deal with the normal pattern of sea level changes due to the winds in shallow water or the propagation of meso-scale eddies in the deep ocean.
6. Coupling
Diurnal effects on the reef are very important and short-term feedbacks between the ocean and atmosphere also have the potential of being important so I am surprised that coupling only occurs once a day. The reasons for this need to be explained.
I found that explanation of why the atmospheric model was run using the ocean model results from the previous day to be unclear. What in the atmosphere has a short 'circulation time' and what in the atmosphere is responding faster to what in the ocean?
The last part of this section is more a report on the development program, not a description of the model. It should be moved to the discussion section on possible future improvements.
7. Coupled fields
Again future developments are best placed in the discussion.
8 Coupled ocean fields
Should this be titled "Ocean Forcing"?
I think this is trying to explain how the couple system deals with the fact that the ocean model covers only a small part of the ocean region seen by the atmospheric model.
However the solution, as stated in the first paragraph, seems to be that in both ACCESS-GBR (the ocean model) and ACCESS-EMS-GBR (the whole coupled model or do you mean just the atmospheric component?), SST is prescribed by data from a daily mean ancillary file. So what it the point of running a coupled model with a dynamical ocean (and later validating the ocean model SST values) if the SST is prescribed?
The next paragraph does seem to treat the ocean model SST separately, as it described a merged dataset is used to force the atmospheric model. However there remains the implication that the ocean model has an imposed SST.
9. Coupled atmospheric fields
Should this be titled "Atmospheric Forcing by the Ocean"
10 Model evaluation
As stated earlier, this is really about aerosol validation. The title should reflect this.
11. Seawater temperature and PAR
With a grid size of 4 km, there is no way that the model can estimate Heron Island lagoon and reef front variables. I can only suppose that an addition 'sub-grid' scale model is also used which somehow reflects how the ocean outside the reef affects the water, biogeochemistry etc close to and within some typical reef complex. Whether I am wrong or not - please explain.
12. Discussion/Future developments
As a personal comment, not part of the review - I can believe that the coupled model does a reasonable job of modelling aerosols over the Barrier Reef region, but I am not convinced that the ocean model component helps very much. If you are not going to use much of the deep ocean region, then a dedicated coastal model with a grid that can give better resolution close to reefs would probably be better.
Also - I am not happy about the coupling system only exchanging fluxes at very long periods. You should implement an OASIS type system as soon as possible and try and couple at least once an hour. The extra computer overhead is comparatively minor.
Minor points
============1. Line 19
Is the m/s describing the "ACCESS-EMS-GBR v1.0" or the "ACCESS-EMS-GBR"?
2. Line 22
"The model includes ...". There is a confusion of models.
3. Line 230"and operate across different time-steps, meaning that they are inefficient when fully coupled". Mangled English. You are really saying something about the optimal timesteps for each models being different and the inefficiency of running both using the shortest of the two timesteps.
4. 'Line 118
"Aerosol processes are represented by the GLObal Model of Aerosol Processes modal version(GLOMAP-mode) aerosol scheme ".
a) Clumsy use of 'represented'.
b) Is "GLOMAP-mode" a version number, is it a shortened form of "GLObal Model of Aerosol Processes modal version aerosol scheme" or what?Citation: https://doi.org/10.5194/egusphere-2026-2761-RC2
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Review: Jackson et al., 2026: “A high-resolution coupled atmosphere-ocean model of the Great Barrier Reef: ACCESS-EMS-GBR v1.0”
Reviewer Summary
This manuscript describes a new, regional scale coupled ocean-atmosphere model designed to study Earth system feed backs and interactions over North-Eastern Australia and the Great Barrier Reef. The main novelty of the work is coupling atmosphere and ocean climate modelling systems (ACCESS and EMS respectively) to a hydrodynamic/biogeochemical model (GBR4). This allows key atmosphere-land-ocean-climate interactions, such as the impact of riverine runoff on ocean biogeochemistry and ocean-atmosphere fluxes, to be simulated and will facilitate detailed analysis of how the Great Barrier Reef system will respond to climate change and/or climate intervention.
The manuscript also tests several new parameterizations for the UKCA model. While the author’s findings show that these parameterizations improve the model’s skill in simulating e.g. aerosol number concentrations over the North-Eastern Australia and the Great Barrier Reef region, they also suggest that the parameterizations could be usefully deployed more widely.
The manuscript is generally clear and well written. I have a few General and Technical comments and once these are addressed, I recommend that the manuscript is published.
General Comments
1. The new model configuration presented here is, by nature, complex. I think that it would be useful if the main components (and important updates like the use of CASIM) were presented in a Table or perhaps a schematic to help the reader understand the whole system.
2. Could the authors please clarify a few points regarding the revised aerosol parameterisations and their impacts on model behaviour:
Figure 4 and L473-484:
Figure 4 shows that the revised aerosol parameterizations improve the model’s simulation of Aitken mode aerosol (which is positive) but worsen the simulation of accumulation mode aerosol. If I understand correctly, the authors suggest that too many particles grow into the accumulation mode rather than ‘growing within’ the Aitken mode. Can the authors suggest how this could be addressed in GLOMAP-mode?
Have the authors tested the impact of the BLN scheme and the Aitken mode sea salt emissions independently to understand their individual impacts on the Aitken and accumulation mode aerosol (and CCN)? From the results shown, the benefit of the BLN scheme is not immediately clear to me because it appears to (1) have little impact on sulphate and organic aerosol concentrations (Figure 6) and (2) introduce a model bias by adding aerosol at particle diameters < ~20 nm that are not observed (Figure 4). While the BLN scheme improves the model’s process realism, which is an important goal, is there a scientific benefit to using the BLN in this region?
3. The new model system, as described, is specific to the North-Eastern Australia and the Great Barrier Reef region, for example bespoke emissions data sets are used. While I think this necessary to benefit from a regional scale Earth system model, could the authors add a comment on how their approach could be deployed for other locations with appropriate modifications?
Technical Comments
“Here, the SOA yield is further scaled to a factor of 0.1 (0.013) in both…”
Could the authors please clarify what the SOA is further scaled to in their configuration? If it’s 0.013, I suggest modifying the sentence to: “Here, the SOA yield is scaled further by an additional factor of 0.1 (to 0.013) in both….”
For clarity I suggest modifying “GLOMAP-mode and the cloud schemes are …..” to “Within ACCESS-EMS-GBR GLOMAP-mode and the cloud schemes are …..”
For me, there is little contrast between the line colours used for the model results making the figure less easy to interpret. Please consider using a brighter colour for the control simulation. See also Figures 4, 6 and 7.
Could the authors please clarify if the data presented in Figure 5 is from the control model simulation?
Could the author’s please increase the font sizes, particularly for the y-axis label as these are hard to read. Please also consider the font sizes for Figure 9.
I don’t think that this reference alone is suitable.