Pollen Geochronology from the Atlantic Coast of the United States during the Last 500 Years

Round 1

Reviewer 1 Report

Please see the attached document.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 1,

Thank you for your time and comments on our paper. I greatly appreciate the time you spent reviewing it and the revisions you suggested. Below, I have described how I have addressed each of the points that you brought up in your review.

Sincerely,

Margaret Christie

Point 1: Salt marsh and mangrove are delicate ecosystems which provide valuable ecosystem services to coastal population, currently threaten by mean sea level rise and increasing anthropogenic pressure. The heath of salt marshes has relevant implications on the protection of coastal environments. Indeed, these areas are becoming intensely exposed to the impact of

hydro-meteorological events, such as coastal floods induced by storm surges and sea level rise or human induced impact s.  I suggest the authors to mention this topic in the introduction of the manuscript, providing a brief description of the multiple services provided by these environments and the major treats related to their survival (e.g. ref. 1,2 and 3).

Response 1: I have updated the last paragraph of the introduction (lines 89 – 106) to read:

Here, we have collected published and unpublished pollen and chronology data (e.g., radiocarbon, ¹³⁷Cs and pollution horizons) from sediment cores collected from eight coastal wetlands (salt marshes and mangroves) along the U.S. Atlantic Coast. Coastal wetlands are ecologically and economically important environments [Barbier et al 2011], which are under threat from sea-level rise, storm surges, and eutrophication [Gedan et al 2009; Craft et al, 2009; Deegan et al 2012; Horton et al., 2018]. We investigated the applicability of pollen chronohorizons from salt marsh and mangrove environments that have been studied using a consistent methodology for dating, sediment sampling, and analysis [27,42,53]. We documented eight unique pollen chronohorizons with up to three chronohorizons per study site (17 chronohorizons in total). We compared pollen chronohorizons to other age markers (radiocarbon, 137Cs, and pollution markers) to examine their consistency with other markers and their influence on the precision of age-depth models. We applied a Bayesian age-depth framework (Bchron) [54], which illustrated that 13 out of 17 ages assigned to individual pollen chronohorizons were consistent when compared with dates derived using other age markers. Inconsistencies are likely due to hyperlocality, sediment mixing, misinterpretation of pollen signals, and/or incorrect pollution and radiocarbon dates. We show that the greatest influence on the precision of age models occurred at coastal wetland sites with limited chronological data, highlighting the importance of pollen chronohorizons and providing a better understanding of age-depth modeling in these critical coastal environments.

I have left the references written out here for convenience but have updated them with numbers in the revised manuscript.

Point 2: I suggest the authors (e.g. in the conclusions Section) to provide more information concerning applications and benefits related to the improvement of the precision of age depth models.

Response 2: I added the following to the conclusions, (lines 598-602):

Sedimentary environments which contain abundant pollen with a known vegetation history are excellent candidates for this approach, particularly if other dates are lacking, unavailable, or uncertain. Including one or more pollen chronohorizons in such cases improves the robustness of the age-depth model.

Point 3: - The paper would finally benefit from a final proofreading.

Response 3: I made various corrections throughout as needed (additions are marked in red in the revised copy, deletions are marked in red with a strikethrough).

Reviewer 2 Report

This is an excellent paper. The only concern I have is that Water might not be the most suitable journal for its publication. The scope of Water is very much water-focused, and this paper does not fit that scope at all. Journals such as Quaternary Science Review, Quaternary Geochronology, or Journal of Quaternary Science might be a better place for this paper. 

My suggestion is to reject the paper, not because of any issues with the paper, but because it is outside of the scope of the journal.

Author Response

Dear Reviewer,

Thank you for your time and positive review of our paper. I appreciate your comments and suggestions regarding it. 

Thank you again.

Cheers,

Margaret Christie