the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Jan 2025
The Historical Representation and Near Future (2050) Projections of the Coral Sea Current System in CMIP6 HighResMIP
Abstract. The Coral Sea houses expansive coral reefs. Reef health is inextricably linked to water temperatures, which are regulated by the hydrodynamic environment. The current system in the Coral Sea is dominated by jets of the South Equatorial Current (SEC): the North Vanuatu Jet (NVJ), the North Caledonian Jet (NCJ) and the South Caledonian Jet (SCJ). We investigated the projected near-future (2050) changes in the temperature and transport structure of the Coral Sea. We utilized the three highest resolution climate models from the CMIP6 HighResMIP experiment as these models broadly captured the historical temperature and transport structure of the SEC jets, and their El Niño Southern Oscillation (ENSO) related variability. Surface warming of 0.78 °C and 1.12 °C was projected in the Coral Sea under 1.5 °C and 2 °C global warming, respectively. The warming signal deepened by 30 m per decade, penetrating to 400 m by 2050. This indicates the additional thermal stress that could be experienced by Coral Sea ecosystems with future global warming. Decreases in the transports of the NVJ and NCJ, and an intensification of the SCJ were projected in the HighResMIP models. While the magnitudes of the changes were relatively small (2 % to 7 % of historical means), they were similar to the variability in NVJ and NCJ transport associated with ENSO. Our analysis further shows that the transport projections of the NVJ and NCJ varied with depth, where surface intensifications coincided with the areas of greatest warming. These changes could modify upwelling dynamics on the Great Barrier Reef shelf.
Status: open (until 25 Mar 2025)
-
RC1: 'Comment on egusphere-2025-171', David Webb, 13 Feb 2025
reply
Review of:
The Historical Representation and Near Future (2050) Projections of the Coral Sea Current System in CMIP6 HighResMIP
By:
J.A. Schlaefer, C. Langlais, S. Choukroun, M. Mongin, M.E. BairdOverview
The paper uses data from some high resolution climate model runs to estimate the changes to expect in ocean currents and temperatures between now and 2025. The results may be useful for groups planning climate change mitigation studies.
Overall the writing was filled up with too much detail, much of it poorly expressed. What is lacking, or discussed much too briefly, is insight, especially what is learnt that was not known before. There is also little comparison with the results from lower-resolution models which would help in understanding the utility of the high-resolution model results.
Unfortunately I found the paper poorly written and often skipping important information. Also unfortunately I was unable to see any of the figures in the supplement as the files were in the close Microsoft *.docx format instead of an open format like *.pdf.
Detailed comments are given below. I recommend a major revision.
L 82. Are there jets north of 10S?L 91. Figure 1
The quality of the all figures is poor. They looks like jpeg copies, maybe screen copies, taken from a standard plotting package but really need to be a good quality vector graphics images.
In figure 1, the outline of the area used for the integrals later needs to be shown at large scale in figure (a). The caption should not redefine NCJ etc. Why are the differences in the heat content of the models and observations much larger than any of the variability?
L 107. The southeast trades push the ocean westwards, they are not going to shift anything eastwards. Winds cool the ocean, so reduced winds will not cool it.
The west Pacific warm pool is normally defined as lying north of the Equator. Is this what you mean?
L 152. The properties of BRAN2020 need to be described. Why was it used? Are there other datasets which could be used? If so how do they compared?
L 164. It would be better if the model details were placed in a table. This should also use information on the near surface ocean layer thicknesses, the horizontal and vertical mixing scheme used, and the boundary conditions (slip/noslip) at horizontal boundaries.
L 178. Instead of writing out the long names of everything in full, it would be best if these were defined in a table with the text used for a short explanation of the difference between SSP-5-8.5 and SSP2-4.5 as everything else seems constant.
L 183. (37 models; figure 2). This seems to be some shorthand for "(27 models) and you must now concentrate on figure 2 because the next few lines are going to be about this figure.". This really needs a new paragraph or even a new section starting "Figure 2 ...".
L 188. So far the paper has been about SST. Does this line refer to SST?
This paragraph does not explain what 1850-1879 data was used, it does not need to tell the reader that is 30 years. It should mention that it is using the average over this period.How were the averages calculated? What model fields were used.
L 189. Why could you not calculate the offset from the 1850-1879 average? What was it about the initial conditions that meant this could not be done?
L 192 Figure 2. Quality problem as before.
Better colours are needed. The dotted yellow colour is not clear.
The caption does not need "Shared Socioeconomic ..." etc.
A description of how the 'observations' was calculated would should be in the text.L 201-225 This section needs rewriting.
The main point appears to be that, on the basis of the low resolution models, the 5-8.5 forcing is too strong but the reduced response of FGOALS is probably most realistic of the tree high resolution models. However the way you get there is very confusing.
As this paper is about the ocean, why do you not also compare SST from the different models?
On the question of acronyms, you might like to find something shorter for FGOALS and HighResMIP.L 235 "energy and mass budgets". I suspect "heat and salt budgets" would be less misleading.
L 248 Write down the equation in mathematical form and define the various terms after the equation.
L 252 Shouldn't the integral be over latitude and longitude?
OHC is clumsy. Why not just 'H' or 'H' with some subscript.L 254 Why is this figure placed in the supplement - which I could not see.
Previously you have used scenario runs, presumably to distinguish them from the control runs. Here it is the control scenario and SSP5-8.5 scenario. Why not use 'run' - and as you only use one scenario, why give the extended name?L 255 What does cell-wise mean?
Briefly summarise Iving et al (2021).
How did you calculate the coefficients to use in the CMCC correction? Did these vary with position and depth? Presumably the drift changed with time. Why use a linear approximation and not just subtract the corresponding drift each month?L 269 Why two figures, one in the supplement?
L 270 What is a focal current?
L 271 'u', 't', 's' not needed.
L 272 I expect the jets to be eddying, It would be nice to see a typical distribution of SST in at least one of the models, which can be compared with the corresponding control SSH field.
In calculating heat transport, the best estimate is the integral over time of velocity time temperature. If you are working with monthly average values this misses a lot of the signal but the archive datasets often include a heat flux field. Do any of the models have such a field?
Assuming you do not have access to such fields, why use a mask so that only westward flows are used. What is gained over just using a latitude mask for each current jet?
L 274 "u t s slices" -> "data"
L 277 A mathematical equation properly written out would be better.
L 282 "Specifically ..." -> "The data was decomposed into seasonal and interannual components and a long term trend"
L 282 Equation for seasonal decomposition - here or in an appendix.
Only 1% of readers will know what the STL function is. Again give the equation .
Similarly with LOWESS.L 289 The logic of the text indicates that epsilon should be zero.
L 290 "The same ...". Unneeded.
L 293 "was not explored" - why include this.
L 294 Here you say the Nino 3.4 index was calculated for BRAND ...
L 299 Here you say it was not necessary. Why is it not necessary if it is a reanalysis product?
L 306 Again I would like to see some equations, either here or in an Appendix.
L 309 In the main body of the text the use of mathematical symbols, except when they are being defined, is bad. What does it sound like when you try to read this section aloud?
L 314 What does 'isolated trend profiles' mean.
L 315 J/s. Not the place to say that you are using SI units.
L 316 If you have defined variables correctly earlier in the manuscript you do not need to repeat here.
L 319 If you need to define a variable, do it properly, not in this way.
L 323 Within the main text expand variables such as U_trend in words.
L 328 Ditto. In the following I will not repeat the comment.
L 329 Only 1% of readers will know what the gsw toolbox is.
L 337-338 Paragraph need rewriting. "Therefore" is out of place.
L 241 What is meant by 'scale'
L 342 What is it about Fig 1b which supports this statement? For a start the differences seem to be much bigger than any drift or the size of an short term fluctuations.
L 344 Why is this statement about the jump here? Why is it relevant?
L 346 'well represented'. Justify the use of 'well'. All I see is the normal exponential decay with depth plus some kinks. Are there similar plots from low resolution runs of similar models?
L 354 The models are now not so good.
L 355 'shared the characteristics with'. What characteristics are shared? How can the statement be checked?
L 357 Is this profile in Ganachaud.
"derived from ... in", not neededL 358 "Overall ... " - not proven.
L 366 What does 'historical' mean here.
L 368 How do the crosses within a circle indicate direction?
L 379 This way of representing the change due to El Nino/La Nina does not really work. Something better is needed.
L 389 Use no space or non-breaking space between dimensions.
L 392 'aligned with' - too vague for a scientific paper.
transport/speed - choose one.L 392 ' diverged' - usually 'diverged from' something.
Sentence need tidying up.L 402 It sounds as if these figures should be part of the main text.
L 416 - 452. I cannot comment on details as the I do not have access to the figures. However I am do not understand the point of these detailed descriptions: What is learnt that is important? What will be important when the paper considers changes over the next 25 years?
L 455 As written this sentence may not be referring to BRAN. Again what will be important later?
L 482 Having previously indicated that for global surface temperatures FGOALS is best - why average the three models here?
L 489 What does 'simulated to be carried' mean here. Why is the first sentence needed?
L 490 "over the 100-year period from mid 20th century to mid 21st century" !!
l 491 Figure 1 does not show significant changes in heat content.
L 493 This is one of the main sections of the paper but it concentrates too much on details. Given the model results and the climatology, what do the authors think are the key changes?
L 514 "There are marked changes ... under 1.5 and 2 C ...". Looking at figure 5b there looks as if there is an almost linear relationship between the global temperature anomaly and the change in near surface ocean temperatures. Would the agreement be even better if a comparison was made with the global SST anomaly or the tropical SST anomaly?
L 559 What does 'projected' mean here and in line 661. Is the first sentence needed?
L 562 How does "projected near future decreases" differ from "predicted drop"
L 566 Why are the words 'ensemble mean' needed here.
L 570 Intensification of what? What am I supposed to see in Fig 7 which is not in Fig 6?
L 571 The manuscript needs a better description of Figure 7. What prompted the split into an upper and lower layer and how are these layers connected with 'a minor shallowing'.
L 592 Where are the major conclusions from section 5?
L 599 After finding the previous sections of the paper hard work, I found this final section much better. I would have liked to see some comparison with the results from lower resolution versions of the same models to see how much the results are dependent on improved resolution.
The biological section contains a few too many motherhood statements but one result of the present work which I find unexpected is the increase in cold water at depth. I would welcome more on why it occurs. Globally we expect surface heating to penetrate more with time, as is found in the results - so more cold water close to the surface in the Coral Sea is an anomaly which is worth is bit more understanding.
Citation: https://doi.org/10.5194/egusphere-2025-171-RC1 -
RC2: 'Comment on egusphere-2025-171', Alexandre Ganachaud, 25 Feb 2025
reply
This work analyses the future of the South Equatorial Current and temperatures based on CMIP6 2050 projections. The authors select three climate model with a high resolution ocean and compare them with the BRAN reanalysis and published estimates of transports and temperatures, and their variations, before documenting their projections. I found the paper well-structured, and easy to follow. I recommend publication with minor revision.
Minor comments:
- L83: SPG only 3 times used, would not introduce this acronym
- L105-110. not necessary – just provide a ref to ENSO.
- L111: specify what is “after” (3 months ? 3 weeks…?)
- L196: a transparent line… is not visible! Please correct, eg “grey”.
- L207-208: I am not sure I understand: does it make sense to compare HR models forced with SPP5-8.5 with the SPP2-4.5 models ? I would only compare HR models forced with SPP2-4.5, if needed.
- L285: “leaving the interannual variability around the trend” what does «around the trend» mean? would «and the trend» be suitable?
- L289bis (equation): I would recommend tu use capital letters for T and S, as t is generally time, and s various, pdf, frequency…
- L306: how well do these models simulate El Nino et La Nina ? (Reference?)
- L319: I cannot follow - please specify, or provide explanation, eg we first replaced t_trend with the observed climatological trend in equation X, to evaluate…
- L323-326: It is confusing to me. It seems that you identify the max with depth, but as you then use «peak», it is not clear wether it is a peak in depth or time; please uniformize, I would suggest using maximum instead of peak then.
- L354: “Cool with depth” mislead me, as «cooling» is usually used as an evolution with time. How about using «temperature decrease with depth» to avoid this
- L369: not clear; just state «positive eastward»
- Fig S8: legend: time-varYing , add «y»
- L406-407: If “observed” refer to the Ganachaud et al or Kessler and Cravatte ones, make it explicit, eg, “the BRAN 2020 matched the observed mean structure of the NVJ of Ganachaud et al; K&C “; specify -Fig 13g for Kessler and Cravatte: I suggest to add: something like «with the 0.1cm/s isotach close to 250m, compare Fig 4a to their their Fig13g»
- L410: delete “and HighresMIP models”
- L417: replace the period with “, in comparison with that of the NVJ”
- L420-421: I see only one maximum between 200 m and 350m in their fig 13h
- l424: replace Fig S4 with Fig 4c
- l425-426: I would word this in an opposite way, eg, «the NCJ transport of 12 Sv in CESM and FGOALS underestimated by 25% the BRAN 2020 transport of 15Sv». (since the latter is your reference.)
- l427: Notably,… replace with «In CESM, the overestimated subsurface transport balances the underestimated deep transport»
- l439-440: “What do you call «observations»? the Ganachaud/Kessler/Cravatte ? If comparing with Kessler and Cravatte 2013 Fig 13i, those are geostrophic currents, therefore, BRAN may carry Ekman components that are not in Kessler and Cravatte near the surface.
- L450: a comment on why this different finding would be welcome (different model/forcing, etc…)
- L456-459: “was cooling (warming) I recommend to ban this wording that constraints one to read the same sentence 3 times with risks of confusion. Just write anoter sentence for La Nina, eg, for La Niña, the effect is reversed. Also: «cooling «down to 1000m»
- L460: «small» is quite subjective (even smaller in °Kelvin): is it significant ? (correlation >0.4) ? is it important ? If it is neither, I suggest skip the paragraph and just state there are little, insignificant variations with ENSO.
- L461: ref to Fig S7?
- L474-476: confusing sentence: I suggest to find a better wording.
- l526: the vertical profiles Fig S13a look like a depth-integral. Is it really a velocity anomaly? All velocity anomalies are westward in the upper 200m on Fig 13a in CESM too, but not in d, g, j.
- l532-534: this belongs to the discussion
- l536: I would be intersested to know if such magnitude is important an why
- l544: I do not understand the circle cross in relation with the graphic: positive eastward ? westward ?
- l550: The profiles of S15b look really different from those of S16e (and others). Is that all due to the fact that those are 1.5° or 2° whereas, the S15b are 2050 ?
- l582: need to label dash-dot/plain lines on i and j; define «positive eastward» if so
- l596-597: not clear: please re-word
- l599: Could you discuss sensitivity to the choice of definition of the transports lines min and max latitudes, Fig S2a. Actually this definition is so fundamental it should be on Fig. 1 too
- l619-631: This all looks like a disperate justification of using SPP5-8.5 that is now considered unlikely because it would assume irrealistic political decisions and technological backing, where you could have used a more realistic scenario. I suggest to shorten the discussion, and just state that your projections are for 1.5° and 2°, regardless of the scenario.
- L650: More appropriate is Cravatte et al 2015, p. 269: «The coherent SCJ as seen in the long-term mean near-surface field (Fig. 4b) is most often masked by eddies aliasing synoptic surveys. « https://doi.org/10.1016/j.jmarsys.2015.03.004
- L656-657: Before you make this conclusion, you may want to check the meridional extent of the warm pool, as El Nino provides cooler SST near New Caledonia. I have this oldish reference, but there are certainly newer ones.: https://doi.org/10.1007/s00382-009-0526-7
- L663-664: you can’t state this without further justification. What leads you to make this assumption for one model, and not the other ones ?
- L665-666: why?
- L680: wind stress curl positive? Negative? anomaly; location ?
- L722: As you write below, this should be substanciated, ie: the circulation in lagoons can also be independent of the large-scale currents, but depend mostly on local winds and tides. I suggest to just state that the influence needs to be studied to avoid being considered as «alarmist» versus «alarming».
Citation: https://doi.org/10.5194/egusphere-2025-171-RC2
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 | |
|---|---|---|---|---|---|
| 51 | 0 | 0 | 51 | 0 | 0 |
- HTML: 51
- PDF: 0
- XML: 0
- Total: 51
- 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 | 16 | 31 |
| China | 2 | 10 | 19 |
| Australia | 3 | 9 | 17 |
| France | 4 | 5 | 9 |
| United Kingdom | 5 | 3 | 5 |
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
- 16