the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Oct 2023
North Atlantic Oscillation polarity during the past 3 ka derived from lacustrine sediments of large lowland lake Schweriner See, NE-Germany
Abstract. Based on a multi-dating and multi-proxy approach, we reconstruct Late Holocene environmental changes from sediments of Schweriner See, a large lowland lake in NE-Germany spanning the past 3070+170/-210 cal BP. We infer large-scale atmospheric variations using a combination of in-lake productivity indicators using traditional and high-resolution techniques (e.g. LOI550, TOC, inc/coh), diatom assemblages, which are sensitive to ice-cover duration, as well as compound-specific hydrogen isotopes (δ2HC25) reflecting variability in the moisture source region distinguishing the southern and northern North Atlantic and/or Arctic region and/or the degree of evaporative lake water enrichment. Our study shows that before 1850 CE, in-lake productivity at Schweriner See was mainly influenced by winter temperature variability, which modulates ice-cover duration and growing-season length. Low productivity co-occurs with the occurrence of the diatom species Stephanocostis chantaicus, which blooms below the ice cover, indicating temporal prolonged ice cover duration. Simultaneously, changes to a moisture source region in the northern North Atlantic and/or Arctic regions and/or low evaporative lake water enrichment are inferred from δ2HC25. In contrast, high productivity is linked to the disappearance of S. chantaicus and moisture originating from the southern North Atlantic and/or high evaporative lake water enrichment. These distinct changes are driven by variations between positive and negative NAO polarity during the past 3070+170/-210 cal BP. Besides these long-term shifts in atmospheric conditions, short-term variations can be inferred from titanium concentrations, which mainly reflect paleo-shoreline distance likely linked to precipitation variability and, after the 12th century, to anthropogenic impacts. Since 1850 CE, productivity has been driven by nutrient availability.
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Status: final response (author comments only)
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RC1: 'Comment on cp-2023-73', Anonymous Referee #1, 09 Nov 2023
General comments:
The manuscript by Adolph et al. provides a reconstruction of North Atlantic Oscillation (NAO) polarity during the past 3,000 years, derived from lake sediment profiles from Schweriner See, located in NE Germany. The authors employ a multi-proxy approach to interpret past climatic signals. The manuscript presents data of good quality, with clear and organized figures. The supplementary data is well-structured and easy to navigate. In general, the manuscript aligns with the scope of the journal.
However, I have several concerns that should be addressed before publication. Firstly, the authors employ an impressive number of methods (over 10), but many of them lack proper descriptions in the results section, and some are not even mentioned (e.g., grain size analysis). The discussion requires revision since, in its current form, it covers various aspects, such as NAO, climatic events, lake level fluctuations, and minerogenic delivery. However, most of these aspects remain speculative at this point, as the discussion rarely relates to the results. I strongly recommend focusing on the obtained results first, and then comparing them with findings from other sites. The lack of a comprehensive discussion of the results creates the impression that many of the analyses conducted were unnecessary, as their usefulness in the current form of the manuscript is unclear.
Specific comments:
The introduction should clearly state the knowledge gap, specific study goals, and hypotheses.
The term "dominating mode of the NAO" needs a better explanation for clarity.
Explain the uneven uncertainty of the age-depth model.
Rewrite the results section. Currently, it combines results with their interpretation and references to the literature. In this section, only the authors' results should be described. Additionally, the authors have provided over 10 analyses in the methods, some of which are poorly described or not mentioned, such as grain size analysis.
Extending the profile to 1000 cm without time control may not provide a broader perspective. If the extension is relevant, it should be mentioned in the methods section and discussed.
Address the discrepancy in the age designation (with changed uncertainty sign) in the introduction part of the discussion.
Clarify the resolution of distinct analyses and the number of years covered by each sample. Discuss whether the diatom signal related to long-lasting ice covers could have been captured for a single, extreme winter event.
Explain the link between inc/coh and milder winter temperatures, as this ratio was previously associated with lake productivity.
Technical corrections:
Add "years" to the title: "...during the past 3 ka years..."
Use a consistent age unit (CE, cal BP, centuries) for clarity.
Correct the syntax error in lines 34-37.
Provide the lengths of cores SAS21-11 and SAS21-12 (line 121).
Color is also is one of the sedimentological properties (line 126).
Correct the sentence in line 237: “…variations in organic matter variations…”.
Ensure that depth ranges are consistently provided, with the shallower depth mentioned first.
Line 250 is an interpretation, not a result.
Use consistent language (British English vs. American English) throughout the manuscript.
Add a period at the end of the sentence in line 359.
Include information on the location of Dosenmoore (line 402).
Add a space between "spread" and the citation (line 438).
It would be good to include map of Europe in Figure 1 for clarity and changing the brackets in the depth scale from () to [] for consistency.
Ensure consistent terminology in Figure 2 (yellow "remains" vs. "residue").
Label the panels in Figure 3 for clarity (e.g., A and B or upper and lower).
Revise Figure 6 to have consistent numbering for regions (e.g., A, B, and C for Poland, Eastern Central Europe, and Mid Europe). Clarify the difference between "Mid" and "Central."
Citation: https://doi.org/10.5194/cp-2023-73-RC1 - AC1: 'Reply on RC1', Marie-Luise Adolph, 21 Dec 2023
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RC2: 'Comment on cp-2023-73', Anonymous Referee #2, 09 Nov 2023
General comments:
The manuscript by Adolph et al. titled 'North Atlantic Oscillation polarity during the past 3 ka derived from lacustrine sediments of large lowland lake Schweriner See, NE Germany' presents a study of a lake sediment core integrating scanning techniques, sedimentological, bulk geochemical, pollen, diatom and leaf wax records. Aim of the study is to reconstruct the environmental factors modifying sediment deposition.
The efforts undertaken are methodologically state of the art and the results provide insights into the regional climate dynamics within the last 3000 years. Therefore, the study can be of interest for a broader geoscience community and would be suitable for publication in Climate of the Past. However, before publication the results/proxy interpretations should be discussed in a more rigorous way, some generalizing statements should be specified or revised and the manuscript would benefit from reorganization.
Main points:
I would prefer to read a more focussed, results-based and mechanistic discussion of the possible factors controlling organic matter accumulation, preservation and degradation in Schweriner See and, consequently, the relevance of the area600-700, LOI550, TOC, TN and inc/coh proxies. In this version of the manuscript area600-700 is defined as productivity indicator in the methods section based on one citation (lines 156-157) and LOI550, TOC, TN and inc/coh are defined as productivity proxies based on their correlation with area600-700 in the results section (lines 256-258). Therefore, the presented proxy interpretations and lenghty paleoclimate implications remain ta degree speculative. In addition, the reconstructed NAO polarity and precipitation records from Schweriner See do not match well (e.g. around 700 or 2500 a BP). Please discuss these discrepancies between both proxies, as both should be interconnected. In general, the manuscript would benefit from a clearer distinction between the methods, results and discussion sections.
Specific comments:
- Lines 39-40: Continentality is to my knowledge controlled by a place’s distance from the ocean and not directly connected with the NAO.
- In think the introduction can be streamlined and better organized.
- Lines 327-328: This statement is not true. Small lakes do not generally suffer from anthropogenic overprinting. For example, the sediment records from small Lakes Tiefer See, Belau and Woserin located in the Schweriner See region allowed to reconstruct changes in NAO polarity, humidity and wind speed.
- Is the construction work for the Paulsdamm AD 1848 visible in the investigated sediment core? This could be a nice time marker.
- The lake sediment record investigated in Olsen et al. (2012) is located in Greenland which is not mentioned in the list.
- Since ice cover duration is interpreted to play an important role for productivity changes in Lake Schwerin, it would be interesting to read a sentence about varying ice cover durations during the instrumental period.
- Lake level reconstruction: Please discuss the role of the Stör river draining Schweriner See for the presented lake level reconstruction. Is the river too small to level out lake level changes?
- Lines 403-405. Different moisture sources do not influence the amount of precipitation.
- Lines 429-431. This sentence connects a positive NAO polarity with a coinciding period of dryness in Europe. This contradicts with the statement in lines 64-65, associating a positive NAO with more humid conditions.
- Please provide a definition on how you distinguish NAO+ and NAO- time slices based on the Schweriner See data.
Detailed comments:
Line 52: Delete ‘s’ in ‘circulations’.
Lines 244-245: Shortly mention why 897.5 cm core depth is the lower limit.
Lines 372-375: Does a distance of 120 km substantially change the degree of continentality and evaporative enrichment?
Lines 376-386: This part can be shortened, as a detailed description of the NAO is already given in the introduction.
Title: Change ‘3 ka’ to ‘3000 years’ in the title, as ka is not used within the text. Delete 'lacustrine' as lake is mentioned too.
Fig.1. Except for the coring location is Fig. 1b already included in Fig. 1a. Add the coring location to Fig 1a and delete Fig. 1b?
Fig. 6. Add ’Grand’ to ‘Solar Minima’.
Citation: https://doi.org/10.5194/cp-2023-73-RC2 - AC2: 'Reply on RC2', Marie-Luise Adolph, 21 Dec 2023
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