the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
North Atlantic patterns of primary production and phenology in two Earth System Models
Jenny Hieronymus
Magnus Hieronymus
Matthias Gröger
Jörg Schwinger
Raffaele Bernadello
Etienne Tourigny
Valentina Sicardi
Itzel Ruvalcaba Baroni
Klaus Wyser
Abstract. Uniquely long datasets, spanning 1750–2100, of daily output from two fully coupled CMIP6 Earth System Models, EC-Earth3-CC and NorESM2-LM, have been used to investigate the historical and future (under SSP5-8.5 scenario) evolution of marine net primary production and its phenology in a North Atlantic region (30–60° N). We compared the data to estimates of net primary production (NPP) derived from the CAFE satellite data and found significant differences between the Earth System Model simulations and the CAFE model. The low spatial resolution of the earth system models can explain much of such difference. However, the two models well represent both the magnitude of NPP and the seasonal cycles. The daily output made it possible to detect change points in peak NPP. Two major change points in peak NPP, of an amplitude not present in the PI-Control or the historical simulation, were detected in both Earth System Models in the first decade of the 21st century. The results clearly indicate a shift towards an earlier peak NPP with a clear inflection point in the beginning of the 21st century, at the end of the historical simulation. The early timing of the detected shifts in both models suggests that similar shifts could already have been initiated or start in the near future. This highlights the need for long term monitoring campaigns in the North Atlantic.
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Jenny Hieronymus et al.
Status: final response (author comments only)
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RC1: 'Comment on bg-2023-54', Anonymous Referee #1, 17 Apr 2023
General comments:
The addressed question of this paper is very interesting and the applied statistical package to detect shifts in phenology seems to be adequate. However, I am not convinced that the strategy of using an area-based average gives meaningful results. As mentioned by the authors, the North Atlantic shows a very heterogenous regional pattern between 30°-60°N. Longhurst classified at least 4-5 distinct oceanic biogeographical provinces. One might expect each biogeographic province to exhibit different temporal behaviour; e.g. Figure 5 clearly shows this for NorESM (a dipole structure for 2070-1850 and only an 1 day change of the mean peak NPP day over the entire domain, as stated in line 219). From my perspective, the analysis of peak NPP day averaged over the entire domain is therefore of little informational value.
I recommend to repeat the analysis with the kernel based model for smaller domains (Longhurst provinces or regions aligned with common characteristics of the ESMs?). Then it might also be possible to identify local drivers of the change of peak NPP day. I assume that the intention of the investigation on the "Day of MLD <= 40m" was to identify one of these potential drivers. This MLD analysis came as quite a surprise and its findings should be mentioned in the abstract. Again, I’m not convinced that the approach of using an average value of MLD day for the entire domain is reasonable. The relatively high cross correlation values with negative lag (in Fig. 9) might be related to this averaging.
However, I appreciate this data analysis and therefore recommend publication of this manuscript with major revisions. Please see also my specific comments.
Specific comments:
L75: Please motivate the analysis of the change in MLD day already in the introduction.
L96: There is a difference between “primary production” and “net primary production”. The latter is the daily growth of phytoplankton minus respiratory demand. Please use net primary production throughout the manuscript.
L101: Skyalls et al (2019) analysis did only cover a north-south transect east of 20°W from two cruises. Thus, the good agreement with observations is only shown for a very small part of the domain. Please add this information here.
L119: Please add that phytoplankton growth is also a function of light and temperature in iHAMOCC.
L 124: Please replace the subtitle “Observations”. CAFE is a model based on satellite data, which strictly speaking are also only results of an algorithm (i.e. a model) and not observations. Same for the subtitle 3.1
L163 : typo, capitalize Gulf
L171: typo, delete “the” in “For the the latter…”
L195: Statements about the multidecadal variability of an 18-year time series should be avoided. They are meaningless.
L214ff: It is difficult to reconcile the results of Fig. 4, which shows a shift towards an earlier peak NPP day in NorESM at the end of the simulation and Fig. 5, which presents an extended area with a later peak NPP day in the Gulf stream region. In L219, you give a shift of only 1 day for NorESM between 2070 and 1850. From my point of view, the weakness of area-based averaging is clearly evident here. Could you also please provide the significance of the results of Fig. 5? Is ±10 days significant, especially for EC-Earth? It might be useful to also show the peak NPP day for the CAFE data set as a longitude-latitude plot. (see also comment L259)
L252: Please find different symbols for “l1” and “l2” for a better readability (e.g. capitalize L1 ?)
L255: Could you please give an explanation why L1 and L2 do not identify the 2070 change point in NorESM? Would the results be more consistent if you decrease the penalty for L1 and L2 ?
L259: The finding of the kernel based model for EC-Earth is consistent with the findings of Fig. 5 (12 days change in peak NPP day compared to 11 ). However, the result for NorESM is quite different (10 days instead of 1). In addition, Fig.6 seems to give a much larger change for the end of the simulation than 1 or 10 days. Could you please elaborate this issue for NorESM? Furthermore, why didn’t you already show the period 2010-2029 in Fig. 5? It seems to contain a strong change pattern. Why do you use 30-year averages for Fig. 5 and here you use a 50-year average?
L273: Please give this motivation to look at the MLD already in the introduction
I have to admit that I’m not familiar with the used kernel based model. However, results shown for day of peak NPP in Fig.6 seem plausible: the decreasing penalty increases the numbers of change points that are found, but the change point with highest penalty is identical with one of the two changes points (there is an overlap of the pink line with one red lines in both models). I became confused when I looked at the results of “Day of MLD <= 40 m”. There is no alignment between pink/red lines. Why does the kernel based model miss the largest change point with a decreasing penalty?
L292: Could you explain why both models have relatively high cross correlations for negative lag ( -3 to -1) years?
L313: Here just to summarize that the change in peak NPP day is 1 day for NorESM is not convincing. For a different time period (1960-2010) versus (2010-2060) it was 10. It would be helpful to provide a little more discussion.
L316 Please share your view on the results of the cross correlation analysis. Does it support the theory of Behrenfeld and Boss?
Figure captions:
Fig. 1 Give period for the data averaging; is it 2003-2021 as in Fig 2 or 2002-2021 as stated in L135? Did you also masked the model data as in Fig 2? Please indicate in the text if you always use masked ESM data for comparison with CAFE. How large is the difference between masked and unmasked ESM data ?
Fig. 3 The overlapping colour coding is difficult. Please find a better solution (e.g. instead of full time series show only mean/min/max for each ESM model.)
Fig. 5 Please add significance level
Fig. 6 I assume that the centre of the symbols (circle and triangle) corresponds to the year of the change point. Please add this information. Please use the same names for I1 and l2 through the manuscript and in the figures. E.g. L1 and L2, not “model l1” or “model=l1”
Fig. 7 I assume you used the highest penalty level (corresponding to the pink line). Please note. Please also change order of figures – usually EC-Earth is the top figure.
Fig. 8 The figure caption is incomplete ; add …in the median (model l1). Or just write : same as Figure 6, but for first day of ….
Citation: https://doi.org/10.5194/bg-2023-54-RC1 -
AC1: 'Reply on RC1', Jenny Hieronymus, 15 Jun 2023
The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2023-54/bg-2023-54-AC1-supplement.pdf
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AC1: 'Reply on RC1', Jenny Hieronymus, 15 Jun 2023
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RC2: 'Comment on bg-2023-54', Anonymous Referee #2, 28 Apr 2023
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AC2: 'Reply on RC2', Jenny Hieronymus, 15 Jun 2023
The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2023-54/bg-2023-54-AC2-supplement.pdf
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AC2: 'Reply on RC2', Jenny Hieronymus, 15 Jun 2023
Jenny Hieronymus et al.
Data sets
North Atlantic patterns of primary production and phenology in two Earth System Models - Data Jenny Hieronymus, Magnus Hieronymus, Matthias Gröger, Jörg Schwinger, Raffaele Bernadello, Etienne Tourigny, Valentina Sicardi, Itzel Ruvalcaba Baroni, and Klaus Wyser https://doi.org/10.5281/zenodo.7716480
Model code and software
NorESM2 source code as used for CMIP6 simulations (includes additional experimental setups, extended model documentation, automated inputdata download, restructuring of BLOM/iHAMOCC input data) Øyvind Seland, Mats Bentsen, Dirk Olivié, Thomas Toniazzo, Ada Gjermundsen, Lise Seland Graff, Jens Boldingh Debernard, Alok Kumar Gupta, Yanchun He, Alf Kirkevåg, Jörg Schwinger, Jerry Tjiputra, Kjetil Schanke Aas, Ingo Bethke, Yuanchao Fan, Shuang Gao, Jan Griesfeller, Alf Grini, Chuncheng Guo, Mehmet Ilicak, Inger Helene Hafsahl Karset, Oskar Landgren, Johan Liakka, Anne Moree, Kine Onsum Moseid, Aleksi Nummelin, Clemens Spensberger, Hui Tang, Zhongshi Zhang, Christophe Heinze, Trond Iversen, and Michael Schulz https://doi.org/10.5281/zenodo.3905091
Jenny Hieronymus et al.
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