Geochemical Signatures of Paleoclimate Changes in the Sediment Cores from the Gloria and Snorri Drifts (Northwest Atlantic) over the Holocene-Mid Pleistocene
Round 1
Reviewer 1 Report
The few remarks in the text are primarily editorial in nature. If the authors agree with some of these comments, this may contribute to a better perception of their work. It seems to me that the article can be published after minimal editing of the text and figures (I would like to see a lithological column in Figure 3) by the authors.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Review of manuscript:
Geochemical signatures of paleoclimate changes in the sediment cores from the Gloria and Snorri Drifts (Northwest Atlantic) over the Holocene-Mid Pleistocene By L. Demina, E. Novichkova, A. Lisitsyn, and N. Kozina
This paper presents new geochemical data (including oxygen isotopes, IRD counts, biogenic opal and carbonate contents, and terrigenous element concentrations) for a Gloria Drift sediment core spanning the past ~190 ka and compare it to existing data from the Snorri Drift. The authors discuss their records within the broader climate context of the North Atlantic and suggest possible mechanisms driving the observed downcore geochemical variability. While the new results presented in this work may eventually prove useful to increasing our knowledge of North Atlantic climate variability, the impact of this manuscript is difficult to assess in its current form (for example, I cannot tell what the primary question is that this work seeks to address). Therefore, I do not recommend this manuscript for publication at this time.
I have made several suggestions below for how to further develop this manuscript into a more widely beneficial contribution to the field.
General comments:
This work bases many of its conclusions on the downcore variability of sediment concentrations and elemental ratios (for example, Mn/Fe). However, it is difficult to tell if a ratio like Mn/Fe varies over time due to changes in Mn, or changes in Fe, or both. This work would be improved if the authors provided elemental flux data that allows for the targeted evaluation of variability in each sediment component, in addition to concentration and ratio data. Such records would be very informative in figuring out if terrigenous concentrations are changing due to variable terrigenous input, for example, or if they result from variable carbonate dilution. Although lateral sediment transport associated with the formation of the Snorri and Gloria Drift deposits may complicate interpretation of age model-derived flux records, flux records for the Snorri drift computed using the available 230Th data (line 108) could be very useful (e.g., Francois et al., 2004).
The primary conclusions of this manuscript are drawn from apparent coincident variations in North Atlantic climate and the geochemical properties of each core. However, the reader cannot independently evaluate these relationships using the current set of tables and figures. This manuscript would be significantly improved if the age model tie points described in section 2 were provided in separate data table. Further, Tables 1 and 2 would be improved if age estimates, oxygen isotope values, and IRD counts were included for each sample depth. It is worth noting that Table 1 of this manuscript is an exact replicate of Table 1 in reference #36 (Demina et al., 2019), but is not captioned as such. In addition, Figures 2 and 3 would be more compelling if the data were plotted as a function of age, rather than of depth. Finally, it would be nice to see a more quantitative comparison of the oxygen isotope, IRD, CaCO3 and terrigenous element records for each core using R2 and p-values in order to better assess the significance of the relationships suggested by the authors.
More broadly, this manuscript would be improved by providing a larger-scale comparison of the Gloria and Snorri drift data with those of other North Atlantic sediment cores. A figure comparing the Gloria and Snorri IRD records with IRD records from more southerly North Atlantic cores, for example, would be very useful in evaluating these sites in the broader North Atlantic context. The same would be true for a comparison of the Gloria and Snorri climate records to other North Atlantic proxy records for variability in deep circulation. Such comparisons could help highlight the take home messages of this manuscript.
Some specific comments:
Line 52: The authors point out that previous work on the Gloria Drift did not identify a relationship between local IRD deposition and climate. Perhaps in the discussion section, the authors could elaborate on why they think the new core exhibits a different relationship between IRD and climate than found in the previous work.
Lines 237-242: The correlation coefficients are listed here as R2, but some of the values are negative (suggesting that these are R values, not R2 values).
Line 241: The data suggest that Ca is dominantly associated with CaCO3, rather than siliceous minerals, but it does not rule out the possibility that the CaCO3 is derived from detrital carbonates (commonly found in North Atlantic IRD associated with discharge from northeastern Canada, e.g., Broecker et al., 1992).
Lines 298-304: I do not understand the argument that is being made here. Are the authors suggesting that bioturbation brought additional Fe to the drift deposits, or that bioturbation drove the migration of existing Fe within the sediments from colder periods to warm periods? Is the majority of the excess Fe observed found on the carbonate shells within the sediments?
Lines 305-309: I do not follow the logical steps here. Are the authors suggesting that, because Si/Al, Ti/Al, and Fe/Al ratios are correlated with low CaCO3 contents, then these ratios should serve as proxies for cold periods? This is a large extrapolation given the data. Such an argument would benefit from reporting of correlation coefficients between CaCO3 and Si/Al, Ti/Al, and Fe/Al in each record.
Figure 2: The caption for this figure should cite reference #36, in which most of these plots (including the lithology, IRD counts, oxygen isotopes, Corg, CaCO3, SiO2, and Si/Al) were first published.
Figure 3: The caption for this figure mentions SiO2 (%), but this plot is not available in the figure.
Table 3: The comparison of average elemental values between the drift sites and the average upper continental crust is interesting. Given that crustal values vary from one region to the next, it would be helpful to additionally include elemental information for the likely continental source-regions for the terrigenous material of the drift sites (such as Greenland, Iceland, and northern North America).
Table 4: It would be good to see correlation coefficients reported on a carbonate-free basis as well, since many of the terrigenous element concentrations may be diluted by variations in CaCO3.
Throughout: Snorri Drift is often spelled as Snorry Drift throughout the manuscript (including the Figure 2 caption and Tables 3 and 4).
Throughout: There are a variety of English grammar mistakes that make this manuscript difficult to follow. I strongly recommend that the authors find someone to proof-read the text for English before resubmitting this manuscript.
References:
Francois, R., Frank, M., Rutgers van der Loeff, M.M., Bacon, M.P., 2004. 230Th-normalization: an essential tool for interpreting sedimentary fluxes during the late Quaternary. Paleoceanography 19, PA1018.
Broecker W.S., Bond G., Klas M., Clark E., McManus J., 1992. Origin of the northern Atlantic's Heinrich events. Clim. Dyn., 6 , pp. 265-273
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have made substantial improvements to the manuscript.
