| 27 Jun 2025
Assessment of the Cape Blanc (Northwest Africa) upwelling ecosystem response to recent climate change, reflected by using wavelet analysis on dinoflagellate cyst export
Abstract. The constant changing of the recent climate has urged comprehensive investigations of its impact on marine ecosystems, notably those with high bio-, socio-, and economic importance, such as the upwelling ecosystem off Cape Blanc, Northwest Africa. This paper discusses the relationship between changes in this ecosystem and climate-induced changes of major environmental steering factors between 2003 and 2020. The study area is characterised by annual permanent upwelling, indicating a cyclic character, with a strong interannual variability. Thus, we employed Morlet wavelet analysis to detect periodicities and interannual variations on an 18-year high-resolution sediment trap record of dinoflagellate cyst (dinocyst) export flux and the local environmental steering factors (e.g., wind direction, wind speed, Saharan dust input and sea surface temperature). Dinocyst is a fossilisable structure produced by dinoflagellates, which is a major plankton group that contains both primary and secondary producers. Significant half-year and annual cycles in the time series of dinocyst, the upwelling winds, and the dust input time series were detected. Those cycles demonstrated variations that were divided into three distinct phases: Phase I (2003–2008), Phase II (2009–2012), and Phase III (2013–2020). We also observed changes in the taxonomic composition of the dinocyst assemblages in every phase, demonstrating dinocysts as a bioindicator for environmental changes. The significant variations within each phase were mostly explained by changes in upwelling intensity and dust input into the area. Our results suggested that there is a strong interaction between these two factors (which depend on the surface wind dynamics) and the export flux of dinocysts off Cape Blanc, representing the ecosystem's sensitivity to local climate variability.
Review of Roza et al., egusphere-2025-2271. Assessment of the Cape Blanc (Northwest Africa) upwelling ecosystem response to recent climate change, reflected by using wavelet analysis on dinoflagellate cyst export, by Manuel Bringué, Natural Resources Canada, Geological Survey of Canada - Calgary
General comments
The manuscript by Roza and coauthors presents an interesting assessment of the utility of plankton records to investigate climate forcings, through the lens of periodicities in dinoflagellate cyst production off Cape Blanc, Mauritania. The authors leverage an impressive, high resolution, 18-year sediment trap record recently published by Roza et al. (2024) from an ecologically-relevant site nested in one of the four major eastern boundary upwelling systems, and consider it closely together with environmental parameters driving the local ecosystem. While wavelet analyses of dinoflagellate cyst time series have been published before, it is quite novel to use them as primary evidence to infer connections between the first trophic levels of the planktonic web and the environmental factors that drive them.
I think the manuscript deserves publication, but only after addressing several points that I will detail below.
Scientifically speaking, the study is relevant and advances the state of knowledge of the field. On the form, the text is well written but needs fine-tuning (I’ve made several suggestions). The figures are clear and well designed, illustrating well the data and facilitating interpretations.
The authors’ decision to divide the time series into 3 phases is rather subjective. Personally, I would have probably divided it in only two main phases (pre- and post-2011), but this would not change the interpretations, only the break-down of descriptions.
Specific comments
Points that need to be addressed, in order of appearance in the text, with more important points highlighted:
Introduction
Materials and methods
I am not saying this parameter is not useful, rather that its definition and labeling need justification. Was it used anywhere else (please provide reference and rationale)? If not, why call it anomaly, as opposed to "200 km longitudinal SST gradient" or some locally-defined upwelling index?
Results
Discussion
However, this highlights a missed opportunity that I think the authors should address. Your figure 4 nicely dissected the overall signal of total dinocyst production of Fig. 3b into ecologically meaningful groups. What Fig. 4 shows well is which groups have driven the cyclicities (in total dinocyst production) over the time series: groups A and D were more influential in the first half of the time series, and groups B and C became prevalent in the second half (Phase 2 can be seen as transitional)... as you describe elsewhere. To me, it suggests phyto- and microzooplankton is driven less by dust input over time, with more important contributions from "upwelling" and "cosmopolitan" groups. I think it agrees with the data from Roza et al. 2024 fig. 6F. While ecological implication were probably more the focus of Roza et al. 2024, your wavelet analyses at least confirm these "ecological" findings in the cyclicities.
Figures
Captions of figures 4, 5 and 6: consider replacing the repetitive parts with a shorter statement like “Wavelet color spectra, lines and cone of influence as in Fig. 4”.
Figure 7: For better readability, I suggest moving the legend for Dust-storm (N. Airport) to the right, so SST legends are displayed by the left panel and dust legends by the right panel.
Table 1: Please spell out genus names (Protoperidinium, Lingulodinium) as they are not mentioned anywhere else in the text.
Technical corrections
There are too many to copy here but I will attach my annotated PDF to the review. A few recurring themes are (1) using plural “analyses” instead of “analysis”, (2) I suggest deleting quite a few “the” to lighten the text, (3) simplifying the wording in sometimes convoluted sentences