the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Feb 2025
Quantifying Dust Deposition over the Atlantic Ocean
Abstract. Quantification of atmospheric dust deposition into the Atlantic Ocean is provided. The estimates rely on the four-dimensional structure of atmospheric dust provided by the European Space Agency (ESA) – “LIdar climatology of Vertical Aerosol Structure” (LIVAS) climate data record (CDR) established on the basis of Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) – Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) routine observations. The data record of atmospheric dust deposition rate is provided for the broader Atlantic Ocean region, the Caribbean Sea, and the Gulf of Mexico, confined between latitudes 60° S to 40° N, and is characterized by 5° (zonal) x 2° (meridional) spatial resolution, seasonal-mean temporal resolution, and for the period extending between 12/2006 and 11/2022. The estimates of dust deposition are evaluated on the basis of sediment-trap measurements of deposited lithogenic material implemented as reference dataset with good agreement between the two datasets, revealing the capacity of the satellite-based product to quantitatively provide the amount of dust deposited into the Atlantic Ocean region, as shown by the evaluation intercomparison, evaluation intercomparison characterized by correlation coefficient ~0.79 and mean bias of 5.42 mg/m2d. Moreover, integration of the satellite-based dust deposition rate dataset into AeroVal allows assessment comparison of the variability amongst the dust deposition CDR and dust deposition field estimates provided by the Multiscale Online Nonhydrostatic AtmospheRe CHemistry (MONARCH), EMEP MSC-W, and EC-Earth3-Iron Earth System Models (ESM), with the comparison revealing the capacity of the satellite-based product to follow the seasonal activation of dust source regions and the four-dimensional migration of dust transport pathways. Overall, the annual-mean amount of dust deposition into the Atlantic Ocean is estimated at 274.79 ± 31.64 Tg yr-1, of which 243.98 ± 23.89 Tg yr-1 of dust is deposited into the North Atlantic Ocean and 30.81 ± 10.49 Tg yr-1 of dust is deposited into the South Atlantic Ocean. Moreover, a negative statistically significant trend in Atlantic Ocean dust deposition is also revealed. The satellite-based dust deposition CDR is considered unique with respect to a wide range of potential applications, including compensating for geographical and temporal gaps of sediment-trap measurements, supporting evaluation assessments of model simulations, shedding light into physical processes related to the cycle of dust from emission to transport and eventually deposition, and providing a solid basis to better understand dust biogeochemical impacts on oceanic ecosystems, as well as impacts on weather and climate.
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RC1: 'Comment on essd-2025-43', Anonymous Referee #1, 10 Mar 2025
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The manuscript will become a strong contribution to the literature which deals with desert dust in the Earth atmospheric system (from the source region to the deposition region). The use of modern active spaceborne remote sensing and state of the art atmospheric modelling to investigate the flux of desert dust into the Atlantic is a very important topic in Earth science.
The paper is well written, however, to my opinion, it is much too long and tries to cover two main topics that can easily be separated. The length of the manuscript and the attempt to cover many different aspects in ONE paper leaves behind a confusing impression of the entire work.
I strongly recommend to separate this manuscript into two parts, i.e., in two articles!
Part 1: Sections 1, 2.1.1, 2.2, 3, 4, 6 plus respective summary
Part 2: Sections 1, 2.1.2, 2.1.3, 2.1.4, 2.1.5., 5 and respective summary
If the authors do not want to follow my recommendation then one should at least move section 5 to the end, before the summary. It is confusing when one switches from measurements and observational facts to comparisons with model products and then, again back to the observations and comparison with published (literature) values. For me it is very clear, the presentation in two papers will attract more readers to study BOTH articles carefully. Many readers will give up to study the contents carefully if it remains an overloaded paper.
I have a number of comments.
line 23: According to the new rules of ACP/AMT/ESSA the abstract should contain 250-300 words, only.
line 33: … evaluation intercomparison … is given 2x.
line 88: To my opinion, the paper of Kaufmann et al. (JGR, 2005) belongs to the first publications that systematically investigated dust deposition over the North Atlantic. For me, it was the first trustworthy attempt to quantify dust deposition into the ocean. Therefore, I would mention Kaufmann et al. (2005) already in the introduction.
line 147: Do you want to say: …has been extensively … used to analyze ... CALIOP and CATS optical products .… ? Some words are missing.
line 192: It is not clear what you explicitly did with the aerosol height profiles! This should be better explained. You calculated daily mean dust profiles in the first setp? In the next step, you formed monthly means for given lat-long grid cells?
line 202: Hobbs (2006) is not in the references
line 209 Doescher et al. (2022) is not in the references. There many cited papers not in the references. Please check carefully all references.
line 212: The references are in a bad shape, the year 2021 is 2020, the year 2022 is 2023,.
line 252: Perez et al., Haustein et al., Klose et al. (2021), all these papers are not in the references! I will stop here complaining about missing literature. There are many cited papers that are not in the references list.
line 272: Table 1 contains basic information about the models. But, what is the exact data analysis procedure? Is it: (1) Identification of dust in the model outputs, (2) selection of all dust events per month and (3) computation of monthly means of respective dust products? Is that the procedure applied to all model data? Is the data analysis procedure similar to the way LIVAS data are computed? All this needs to be well described so that the reader can better follow the discussion later on, on the partly huge differences ….
line 316, Figure 2: Please mention the aerosol types in Fig.2c? Also, what are the feature types in Fig.2b? Please explain in the figure caption, or in the panels.
Note the following general remark to the UNITS! To my knowledge, ESSA/ACP/AMT only accept, e.g., ‘m s^-1’ and not ‘m/s’ …. , ‘µg cm^-3’ and not ‘µg/cm^+3’ …, ‘mg m^-2 d^-1’ and not ‘mg/(m^+2 d)’.
You write ‘mg/m+2 d’ is mathematically bad. Correct is: ‘mg/(m+2 d)’
line 333: Haarig
line 335: Provide references for pollen depolarization ratios, maybe Sicard et al. (20??) and recent papers from the Finish lidar group (2022-2024).
line 340: I would prefer all depol numbers in %.
line 361: Haarig, Bohlmann
line 365: Here, you can introduce c_v,d. The conversion factor needs to be introduced somewhere.
line 371: I am confused, you calculate seasonal means (by using data collected in 15 years) and in Figure 3 you show annual means.
line 380 Figure 3: Only the experienced eye is able to get an idea what is shown. The readers not familiar with lidar (or CALIOP) are probably lost without further explanations! Where is Africa, where is South America? What do the color plumes show? …height-latitude cross sections of x,y,z…..! What does the longitude of -100° mean? What does 4D mean here, I only see 3D?
line 384: I miss an equation for mass flux, or a clear definition, the link between mass concentrations and wind field components. How is the zonal and meridional dust flux and transport defined in terms of dust mass concentration and wind components?
line 404: Having such definitions and equations, it is much more easy to discuss Fig.4.
Figure 4: In confused: There is almost no wind at height 4 km height and strong wind at 2 km height, and the mass concentrations at both heights are similar, and finally the mass fluxes at 2 and 4 km height are similar. Why is that?
Further questions here: Are all individual mass concentration profiles combined with respective wind profiles (in the first step)? And in the next step, the average flux profile (for JJA) is computed? Or did you combine the JJA mean dust profile in Fig. 4a with the JJA mean wind profile in Fig. 4b. All this may be explained in the text and I overlooked it! Sorry, if that is the case!
What is the meaning of the color arrows at the horizontal bars in Fig 4c? This indicates the wind speed (according to the color bar)? And the color of the bars indicate transport direction?
line 454: I miss a general section: RESULTS, …. before discussing the different products, and later on comparisons, uncertainties, etc. Section 3 is the main and most important section but presented as just one of many sections, from section 3 to section 6.
line 485: Besides HABOOBS (Knippertz et al., JGR, 2007, SAMUM campaign in Morocco) the SAMUM researchers even monitored dust devils with LIDAR in Morocco (Ansmann et al., Tellus, 61B, 2009, 10.3402/tellusb.v61i1.16833). Could be cited in this LIDAR paper on dust..
line 520: The Saharan Air Layer is also well illustrated, based on LIDAR observations, in the more recent papers by Weinzierl et al. (2016) and Rittmeister et al. (2017). These papers are already listed in the references section.
line 544: Haarig
Page 22, Fig.6: The color scale for DDR is ok! One can even see the deposition values east of southern South America. The color scale for DOD is not ok. The DOD east of southern South America is not visible, at least not in the printed version. This not satisfactory.
line 557: Here the unit for DDR is well written!
Table 3 seems to contain the key results of the paper! This could or should be better highlighted in histogram plots or in box-and-whisker plots (25%, 75% percentiles, mean, median, …).
Table 4 presents an excellent summary and review of sediment-trap climatologies!
However, this very long and detailed discussion on arguments, why we should not try to compare sedimentation trap deposition rates and EO deposition rates, is not needed to my opinion.
line 756: Even after checking the text several times, it seems that Table 5 was never mentioned in the main text body.
Section 5 (pages 30-36): The Figures 8-15 and Table 6 should be moved into another article (part 2). The manuscript is heavily overloaded.
line 763: Section title is bad, better: EO-based Dust Deposition Rate vs respective ESM results
line 770: The AERONET coarse mode AODs may underestimate the total dust AERONET (fine and coarse dust) by 20-30%.
line 789 and Figure 8: It makes obviously no sense to compare monthly mean DOD and deposition fluxes. The uncertainties are in many cases -50 to -100% or 50 to 100%. Integrated CALIOP dust extinction profiles and AERONET DOD should not deviate much (<20%), on a case by case basis.
Further remark: Gray circles on a gray continent (Africa background) are not easy to find.
line 822: What do we learn from Fig. 9?
line 841: Instead of Fig. 10, one could present a Table.
line 858: So large mean biases over large areas!!! What is the reason to show all this in a dust deposition paper? Is the conclusion: If the DOD product of the models is so uncertain, what can we expect from modeled dust deposition rates? Does it really make sense to compare observations and modeling on the AOD or DOD level? Furthermore, the differences in the results are partly so large. What is the message, what do we learn?
As mentioned, better move the entire Section 5 into another article. The comparison of DOD and deposition rates (observations vs modeling) is an independent story, a new article! The main goal of this article (part 1) should be just EO dust deposition rates in the context with other dust deposition studies performed during the last 4-5 decades.
Section 6 (should remain in part 1)
line 926: Table 7 should have 3 columns instead of three lines.
line 933: Open circles and thin dashed line in Fig. 16 is not explained in the caption or in the figure.
Figure 17: What show the colored horizontal bars, what show the colored horizontal lines, what show the open circles? Please add this information.
Section 7 must be re-written (adjusted to part 1 and part 2). Summaries should be compact, highlight the most important aspects only, and present an outlook.
My personal outlook-related question: Since CALIOP/LIVAS provides global dust profiles, one could compute dust deposition rates as a function of height, e.g., flux from the layer at 4-6 km to the layer below 4 km, etc. In this way one may learn a lot about residence times of dust at different heights and dust particle sedimentation behavior and speed.
Citation: https://doi.org/10.5194/essd-2025-43-RC1
Data sets
Atmospheric dust deposited into the Atlantic Ocean Emmanouil Proestakis https://doi.org/10.5281/zenodo.14608538
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