the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Paleo±Dust: Quantifying uncertainty in paleo-dust deposition across archive types
Nicolás Juan Cosentino
Gabriela Torre
Fabrice Lambert
Samuel Albani
François De Vleeschouwer
Aloys Bory
Abstract. Mineral dust aerosol concentrations in the atmosphere varied greatly on glacial-interglacial timescales. The greatest changes in global dust activity occurred in response to changes in orbital parameters that affect dust emission intensity through glacial activity, and dust lifetime in the atmosphere through changes in the global hydrological cycle. Long-term changes in surface dust deposition rate are registered in geological archives such as loess, peats, lakes, marine sediments, and ice. Data provided by these archives is crucial for guiding simulations of dust, and for better understanding the natural global dust cycle. However, the methods employed to derive paleo-dust deposition rates differ markedly between archives and are subject to different sources of uncertainty. Here, we present Paleo±Dust, an updated compilation of bulk and <10-µm paleo-dust deposition rate with quantitative 1-σ uncertainties that are inter-comparable among archive types. Paleo±Dust incorporates a total of 284 pre-industrial Holocene (pi-HOL) and 208 Last Glacial Maximum (LGM) dust flux constraints from studies published until December 2022, including for the first time peat records. We also recalculate previously published dust fluxes to exclude data from the last deglaciation and thus obtain more representative constraints for the last pre-industrial interglacial and glacial end-member climate states. Based on Paleo±Dust, the global LGM:pi-HOL ratio of <10-µm dust deposition rate is 3.1 ± 0.8 (1σ). We expect Paleo±Dust to be of use for future paleoclimate dust studies and simulations using Earth system models of high to intermediate complexity.
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Nicolás Juan Cosentino et al.
Status: open (until 18 Oct 2023)
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RC1: 'Comment on essd-2023-241', Gabor Ujvari, 14 Sep 2023
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Review of „Paleo±Dust: Quantifying uncertainty in paleo-dust deposition across archive types” Cosentino et al.
Manuscript number: ESSD-2023-241
In recent years, there has been a renaissance in the field of spatio-temporal reconstruction of sediment mass accumulation rates (MAR), probably due to the fact that atmospheric dust does indeed play a significant role in shaping Earth's climate, in both direct and indirect ways. Yet there are considerable uncertainties about the actual role of dust that need to be clarified in order to better understand how the Earth system works under present-day or past (e.g. glacial) climate conditions. Research on MAR reconstructions is taking several directions: 1) synthesis of new data from one or more type(s) of paleo-dust archives, 2) methodological innovations in the calculation of MAR, 3) database construction, and/or 4) focusing on periods that have not been included in reconstructions so far (e.g. Marine Isotope Stage 4-5-6). As such, a new database called ChronoLoess (Bosq et al.) is currently appearing in the ESSD pages, which can be extended in a standardised format. In contrast to ChronoLoess, which focuses on only one archive, the authors of this manuscript have compiled data from a large number of paleodust archives of different types (marine/terrestrial) in the Paleo±Dust database, following a common methodology. I consider the most important advance of the present paper to be that they have discussed the uncertainties associated with the dust mass accumulation rate (DMAR) calculations of each archive type and attempted to estimate them quantitatively, which in many cases is not a simple task. In addition, paleo-dust flux estimates from peat bog cores are included in the paleodust compilation for the first time.
Having read the manuscript, I find it to be neatly written, logical and easy to follow, and I consider it to be a significant step forward in the reconstruction and comparison of LGM and Holocene dust fluxes. The authors have tried to organise the database in a way that it can be used for future Earth system modelling, which is also a positive aspect. I have, of course, some critical comments on the manuscript, which I write about below (and in the annotated pdf file attached), but these do not affect the conclusions to any significant extent and are rather just a further refinement of the methodology. On the whole, the manuscript, with some modifications, can be published in ESSD.
Line-by-line comments
Line 97, εDMAR: This is just a pedantic point, but the error of a quantity is usually denoted by the Greek sigma in statistics, I have never seen the use of epsilon for that purpose. What is the reason for using epsilon here? There is another reason of why I discourage the authors using epsilon: in dust provenance studies the Nd and Hf isotope compositions are often expressed in the epsilon notation (εNd, εHf), so this may potentially cause some misunderstandings.
Lines 98-100: The authors presented uncertainty estimations for MAR and MAR10, which disregard potential correlations between the variables in the MAR equations, so these are not full statistical treatments. I suggest the error propagations below: PLEASE SEE THE EQUATIONS IN THE ATTACHED REVIEW PDF FILE AS THEY COULD NOT BE INSERTED IN THE TEXT HERE!!!
Line 131: It is worthwile adding that this relation is true if the bottom/top ages of a segment is given as negative ages in the past calculating from e.g 1950 BP, or b2k. If the ages are positive as usually used (e. g. tbottom=23500 years, ttop=21000), then this does not hold. This can be easily fixed by changing the direction of the inequality signs.
Lines 236-246: The authors use a dry bulk density (DBD) value of 1.48 g/cm3 for CLP loess, while 1.45 for others. For European loess, DBD is relatively well-defined (at least for East Central Europe, ECE): Újvári et al. (2010) [Quat.Sci.Rev. 29, 3157-3166] published a DRD value of 1.497+-0.079 g/cm3 derived from 6 test sample measurements (2 methods), which was later confirmed by e.g. Peric et al. (2020) [Boreas 49, 841-857]. So, this value should be used for the ECE loess sites, and perhaps for others as well considering how close this is to the CLP loess DBD value. I suggest mentioning these studies here, just to provide a less CLP-biased overview of the topic.
Line 381, SBMAR equation: Why is this Eq (1)? We have seen several equations before in this manuscript. Those must be numbered and indicated as well, in my view.
14/09/2023
Gabor Ujvari
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RC2: 'Comment on essd-2023-241', Gabor Ujvari, 14 Sep 2023
reply
Please find my further comments in the annotated pdf file.
Nicolás Juan Cosentino et al.
Nicolás Juan Cosentino et al.
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