Cooling Following the Magnetic Field Weakening During the Matuyama–Brunhes Transition Recorded by Paks Loess, Hungary
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is an interesting and well written contribution discussing the long standing hypothesis on the feedbacks between the geomagnetic field intensity and climate. The authors discuss well the obtained experimental data in the light of this hypothesis and give inspirations for future works in this direction. I have several moderate remarks on the manuscript, which should be addressed by the authors during the revision.
Introduction lines 41 – 49 – the content is not directly related to the topic and may be shortened or removed.
Line 126 “The PD2 paleosol is connected to the overlaying loess layer ….” I think “is connected” is not a proper expression here.
Lines 132 – 142 Please, mention also the total number of cubic oriented samples utilized in the paleomagnetic study.
Caption of Fig. 3 “The box-and-whisker plot of the basic anisotropy parameters ….”” – Please, correct, these are not anisotropy parameters.
Caption of Fig. 4 – pleas, specify to which value is made the normalization – to RT on cooling? Are there any peculiarities on the cooling curves from ~ 400oC to RT? You may plot heating and cooling curves on separate y-axes in order to show the complete cooling curves. The presence of Hopkinson peak at ~ 650 – 700oC suggests that hematite is in SD domain state. Do you see larger temperature interval for ChRM determination for these samples?
Line 168 – please, include short description of the methodology for RPI determination.
Figures 7 and 8 – Please, check the units of NRM/Xlf ratio
Lines 322 – 327 You speak about cooling event but on Fig. 8 change in precipitation is shown, not temperature. Do you consider that temperature and precipitation change simultaneously in the same direction for MIS19 interglacial?
Author Response
Comment 1: Introduction lines 41 – 49 – the content is not directly related to the topic and may be shortened or removed.
Answer 1: Shortened significantly.
Comment 2: Line 126 “The PD2 paleosol is connected to the overlaying loess layer ….” I think “is connected” is not a proper expression here.
Answer 2: The sentence is removed from the text.
Comment 3: Lines 132 – 142 Please, mention also the total number of cubic oriented samples utilized in the paleomagnetic study.
Answer 3: The information is included in the text.
Comment 3: Caption of Fig. 3 “The box-and-whisker plot of the basic anisotropy parameters ….”” – Please, correct, these are not anisotropy parameters.
Answer 3: Thank you, corrected
Comment 4a: Caption of Fig. 4 – pleas, specify to which value is made the normalization – to RT on cooling?
Answer 4a: The figures are completed.
Comment 4b: Are there any peculiarities on the cooling curves from ~ 400oC to RT?
Answer 4b: no particularities can be found on the curves from 400 oC.
Comment 4c: You may plot heating and cooling curves on separate y-axes in order to show the complete cooling curves.
Answer 4c: The figure is modified to be able to present the whole cooling curve.
Comment 4d: The presence of Hopkinson peak at ~ 650 – 700oC suggests that hematite is in SD domain state.
Answer 4d: The caption is completed.
Comment 4e: Do you see larger temperature interval for ChRM determination for these samples?
Answer 4e: Yes, and many loess samples did not show stable ChRM orientations from the loess horizon from which the sample originated. Most likely due to the magnetic mineralogy.
Comment 5: Line 168 – please, include short description of the methodology for RPI determination.
Answer 5: The text is completed and reorganized.
Comment 6: Figures 7 and 8 – Please, check the units of NRM/Xlf ratio
Answer 6: I am not sure that in any research, the units of the NRM/Xlf components are shown, e.g., Oe/m³ × km ¹. In general, the parameters used during normalization are indicated without units (please see Tauxe 1993). If the reviewer feels it necessary, I can include it in the study.
Comment 7: Lines 322 – 327 You speak about cooling event but on Fig. 8 change in precipitation is shown, not temperature. Do you consider that temperature and precipitation change simultaneously in the same direction for MIS19 interglacial?
Answer 7: Cooling and decreasing in precipitation happened quasi-simultaneously, indicating the intensification of the coming glacial period.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper presents the results of paleomagnetic and rock-magnetic research conducted on the section where the MBT boundary is recorded. This article may be useful for expanding our knowledge of inversion studies. However, there are a number of significant comments and questions about the paper.
- The number of samples selected and studied using different methods should be specified. It is unclear how many samples were selected, how many were studied, and how many did not yield data.
- Lines 147–154: The equipment used to measure magnetic susceptibility should be specified.
- Lines 167–168: The method used to calculate RPI should be specified. Although a reference to another article can be used, it is better to describe the method for the convenience of readers, especially since it would only take two or three lines of text.
- Lines 218-219: It would be interesting to know how magnetite forms from clay minerals?
- Fig. 4: Error? Is it PD instead of BD?
- Fig. 5: Lines indicating the components should be provided.
- Fig. 6: There is no MBT boundary designation. Is this an error? There are two PD2.1 designations.
The AFD and ThD results in Fig. 6 differ significantly in declination and VGP longitude in the 150–350 cm range, as well as in VGP latitude in the 150–200 cm range, which is precisely around the MBT. This discrepancy needs to be explained, as well as which results (AFD or ThD) are preferred. If we rely on VGP latitude to find the MBT, the boundary will be higher when taking ThD into account. If the study examines behavior at the boundary of magnetic zones, then this discrepancy is of fundamental importance.
It is unclear why the MS study was conducted on a much larger set of samples than the AFD or ThD experiments. Was no component analysis performed on these samples, or were no data obtained for them?
- The authors point out the presence of different minerals with low and high coercivity in the paper. If their ratio changes along the section, it can have a decisive effect on the behavior of RPI. Ultimately, this may make the RPI value uninformative. Additional experiments must be conducted to assess the ratio of high- and low-coercivity components along the section.
Author Response
Comment 1: The number of samples selected and studied using different methods should be specified. It is unclear how many samples were selected, how many were studied, and how many did not yield data.
Answer 1: Additional information is added to the Methods and Results sections.
Comment 2: Lines 147–154: The equipment used to measure magnetic susceptibility should be specified.
Answer 2: It has been specified at the first sentence of the suggested paragraph: SM-100 ZH-Instrument portable magnetic susceptibility meter
Comment 3: Lines 167–168: The method used to calculate RPI should be specified. Although a reference to another article can be used, it is better to describe the method for the convenience of readers, especially since it would only take two or three lines of text.
Answer 3: The text is completed with the requested information.
Comment 4: Lines 218-219: It would be interesting to know how magnetite forms from clay minerals?
Answer 4: The text is corrected.
Comment 5: Fig. 4: Error? Is it PD instead of BD?
Answer 5: Yes, corrected.
Comment 6: Fig. 5: Lines indicating the components should be provided.
Answer 6: The line (anchored to the origin), related to the ChRM components, is included in the figure.
Comment 7: Fig. 6: There is no MBT boundary designation. Is this an error? There are two PD2.1 designations.
Answer 7: There is a difference between the depth/allocation of the reversal defined by the AF and ThD demagnetization methods. Such differences may appear due to the differences in the frequency of sampling and due to the differences in the successfully separated ChRM from the samples in the MBT zone of the profile. There have been more samples representing higher resolution sampling used during the AFD method, however, a larger number of samples failed regarding the separation of ChRM components. The sampling resolution of the samples used during ThD was lower, with a bigger success of separating ChRM. All the possible MBT sections are marked on Fig. 6, 7 and 8
+PD2.1 corrected.
Comment 8: The AFD and ThD results in Fig. 6 differ significantly in declination and VGP longitude in the 150–350 cm range, as well as in VGP latitude in the 150–200 cm range, which is precisely around the MBT. This discrepancy needs to be explained, as well as which results (AFD or ThD) are preferred. If we rely on VGP latitude to find the MBT, the boundary will be higher when taking ThD into account. If the study examines behavior at the boundary of magnetic zones, then this discrepancy is of fundamental importance.
Answer 8: Considering such differences, all the MBT based on VGP latitude and inclination data from both AFD and ThD were marked in Figures 6, 7, and 8. Please find additional explanation in Answer 7 and is included it in the text.
Comment 9: It is unclear why the MS study was conducted on a much larger set of samples than the AFD or ThD experiments. Was no component analysis performed on these samples, or were no data obtained for them?
Answer 9: During the high-resolution sampling, the samples were taken in overlapping sections. It produced a higher number of samples at various depths, which were used during the susceptibility measurements. Still, not all were used during the demagnetization experiments, due to different (technical) issues, such as there was not enough time to analyze all samples and execute a series of additional paleomagnetic measurements due to the limitations of a postdoctoral fellowship. In addition, around 50% of the measured samples failed to separate ChRM.
Comment 10: The authors point out the presence of different minerals with low and high coercivity in the paper. If their ratio changes along the section, it can have a decisive effect on the behavior of RPI. Ultimately, this may make the RPI value uninformative. Additional experiments must be conducted to assess the ratio of high- and low-coercivity components along the section.
Answer 10: I agree with the reviewer, and a description about the possible bias, additional information is included in the text. In the future, as a further stapes I will try to execute such measurements e.g. IRM→decomposition of IRM→using the various coercivity population data to normalize during the calculation of the RPI and compare the multiple curves. Despite missing such experiments, I believe that the results are still worth publishing.
Reviewer 3 Report
Comments and Suggestions for Authorsreview of "An attempt to identify the signs of cooling following the magnetic field weakening during the Matuyama-Brunhes Transition (Paks Loess Profile, Hungary)" by Bradák et al.
This paper study the loess magnetic properties at the B/M transition at Paks section and discuss the possibility that a peculiar characteristic, namely incompletely developed part of MIS 19 soil, which corresponds to the geomagnetic intensity low related to the B/M transition is an effect of increased cosmic rays according to the hypothesis of the so-called "Umbrella effect".
To answer this question one should consider the following points:
1. Among the possible causes of non-periodic climate changes the most common are the dynamics of oceanic and atmospheric circulation and related feedbaks, which is an internal cause and does not require external forcing.
2. The geomagnetic field is not the only factor controlling the intensity of cosmic rays reaching Earth. Even assuming the geomagnetic field is the dominant factor, it varies independently of polarity reversals. The magnetic field's control on the climate via the umbrella effect should apply to all cases where the magnetic field has low intensity, which are frequent during the Brunhes epoch, not only during the B/M.
3. Considering a single event, as in this case, exposes the analysis to the risk of statistical fluctuation, which cannot be quantified. One reasonable way to verify the effectiveness of this mechanism (umbrella effect) in the geological record would be to compare the correlation or spectral coherence of the paleointensity record with the paleoclimatic record (e.g., δ¹⁸O isotopes). Incidentally, this has been done for the Oligocene and did not yield positive results https://doi.org/10.1016/j.gloplacha.2019.103095.
Considering the specific environment of this study (Loes/paleosoil deposits), and given for granted that all possible "technical" problems (e.g. M/B position, RPI record, pedogenesis, etc. ) are properly solved, -and I think the authors did a reasonably goog job- there are still a few important questions that a study like this should answer to be meaningful:
are the magnetic (or non magnetic) characteristics of MIS 19 significantly different (in a statistical sense) from the other interglacials in the Loess sequence? This would suggests that the topic of this study is indeed peculiar.
If so, are these features also observed in Loess/paleosoil deposited during other geomagnetic intensity lows (e.g. Lashamp, but more generally the global paleointensity record)? This would suggests that the peculiarity is likely correlated to geomagnetic cause.
Unfortunately, I think that the study is inconclusive probably because it was not designed to properly answer its main question, hence does not adds a significant contribution to what is already known.
A few random comments:
Lines 42-45: "Beyond the well-known Schwabe, or sunspot cycles [3], a slightly longer, so-called Gleissberg cycle, consisting of a low frequency (50-80 years) and high frequency (90-140 years)"
Actually, cycles of 50-80 yr have a _higher_ frequency than cycles od 90-140 yr (frequency=1/period, i.e. 1/50 vs. 1/90)
Line 344: "Approximately 515 mm/year precipitation was calculated during the formation of the lower, PD2.2, which decreased to 410 mm/year during PD2.1"
Why could this not be due to glacial/interglacial circulation dynamics? Is this value (410 mm/year) uncommon compared to other interglacial?
Line 351: "Recently, a similar phenomenon was observed at a Late Pleistocene paleosol, in the Dunaszekcső loess succession, where the trigger of the aggradation and the forming of a cumulative/compound paleosol complex was the increasing sediment input during the cooler period of the MIS5 interglacial [53]"
This actually advocate against the umbrella effect since this occurred without the need of the umbrella effect.
Line 385: "Although the marks of cooling event presumably linked to the weakening geomagnetic field and the Umbrella effect were identified in various successions [21], the results are still not convincing enough from loess profiles, due to e.g., the lack of signs of cooling in the majority of sections consisting the MBT (Table 2)".
Again this suggests that rather than a global ombrella effect this is due to regional variability of precipitation due to circulation dynamics...
Line 446: "Any features that differ from such a smooth, gradual transition from the local maxima of the MIS19 paleosol to the overlying loess, represented by low susceptibility, are considered as a result of some unusual event, e.g., the step-like feature and its interpretation as a colder period during MIS19, related to the weakening geomagnetic field". I disagree, consider -for instance- the Younger Dryas during the last deglaciation, it is an abrupt (not smooth) event due to changes in oceanic circulation (well, some says meteoritic impact, not geomagnetic, anyway).
Line 477: "Despite the effort put into the identification of the MIS19 cooling episode, triggered by the weakening geomagnetic field and the related Umbrella effect, loess and paleosol suc- cessions seem not to be the ideal candidates to verify the theory. Cooling episodes of the paleoclimate, regardless of their origin, result in very similar marks in paleosols and similar patterns of a magnetic susceptibility curve." I agree as the authors realize that the evidences are not conclusive, but then what is the purpose of the paper?
Author Response
Comment 1: 1. Among the possible causes of non-periodic climate changes the most common are the dynamics of oceanic and atmospheric circulation and related feedbaks, which is an internal cause and does not require external forcing.
Response 1: We did not exclude any other possibilities, as suggested in Section 5.3 (Concerns), some of which are related to non-extraterrestrial factors.
In addition, we believe that despite discussing causes related to hydrosphere-atmosphere interaction (or all the geospheres), which would provide a common topic, this is not the goal of the study and falls outside its scope. Involving other factors in detail would lead to a different direction, e.g., a review-style paper.
Our study aims to test a hypothesis or theory related to the connection between climate change and changes in the geomagnetic field, but it never states that the change in the geomagnetic field is the sole cause of the observed features in the profile or in the magnetic parameters.
In summary, the study focuses on one theory (out of many that may explain climate fluctuations) and its potential implications in loess paleosol sequences, considering other factors as suggested in Section 5.3.
Comment 2: 2. The geomagnetic field is not the only factor controlling the intensity of cosmic rays reaching Earth. Even assuming the geomagnetic field is the dominant factor, it varies independently of polarity reversals. The magnetic field's control on the climate via the umbrella effect should apply to all cases where the magnetic field has low intensity, which are frequent during the Brunhes epoch, not only during the B/M.
Response 2: We partly agree with the reviewer. Yes, in certain periods, the variation of the geomagnetic field varies independently of the reversals. Still, as shown by some of the cited studies in the manuscript, it also correlates with the period of geomagnetic field changes. Among those geomeagnetic field changes, B/M was chosen due to the following reasons:
- i) a technical issue: the location of B/M was expected and reachable in the Paks profile, providing a good opportunity to a high resolution sampling and analysis
- ii) pedogenic issue: although pedogenic processes makes the RPI analysis difficult, pedogenic processes are sensitive to climate changes and identifying those changes may provide certain evidence combined with RPI and other proxies.
iii) loess issue: loess as well maybe not the best candidate to identify such an event due to the high variation of magnetic contributors. The quasi-pioneering and unique nature of the challenge (testing the theory - RPI and umbrella effect- marks in loess from the ELB) make the profile as a target.
Comment 3: Considering a single event, as in this case, exposes the analysis to the risk of statistical fluctuation, which cannot be quantified. One reasonable way to verify the effectiveness of this mechanism (umbrella effect) in the geological record would be to compare the correlation or spectral coherence of the paleointensity record with the paleoclimatic record (e.g., δ¹⁸O isotopes). Incidentally, this has been done for the Oligocene and did not yield positive results https://doi.org/10.1016/j.gloplacha.2019.103095.
Answer 3: We agree with the reviewer that the method or methods may be subject to bias. In addition, beyond some magnetic methods and micromorphology or paleopedological analysis, it is challenging to quantify pedogenic changes.
On the other hand, the correlation of certain stable isotopes, the ones known as a good proxy to indicate changes in the cosmic ray intake (e.g. Be) may provide different results. https://doi.org/10.1016/j.epsl.2019.05.004 Unfortunately, we do not have access to extensive stable isotope measurements.
In general, as the study also stated, there is no clear answer to support or deny the theory, not only from our study, but also from research from all around the world involved in the Umbrella effect (Introduction, Discussion, and Conclusion sections).
Comment 4: are the magnetic (or non magnetic) characteristics of MIS 19 significantly different (in a statistical sense) from the other interglacials in the Loess sequence? This would suggests that the topic of this study is indeed peculiar.
Answer 4: Yes, the representation of MIS19 is different from other interglacials in the profile (different pedogenic characteristics and magnetic parameters). One of the reasons for the study was the unusual appearance of the paleosol representing MIS19.
Comment 5: If so, are these features also observed in Loess/paleosoil deposited during other geomagnetic intensity lows (e.g. Lashamp, but more generally the global paleointensity record)? This would suggests that the peculiarity is likely correlated to geomagnetic cause.
Answer 5: The study of other geomagnetic changes was not the aim of the study. We agree with the reviewer about the importance of such a comparison. In the case of Paks (and in general, many loess profiles in, e.g., the ELB), it is challenging to identify geomagnetic intensity lows along with geomagnetic polarity changes/fluctuation (events, excursions, etc.), due to the nature of the material from its rock magnetic properties, depositional processes, pedogenesis and so on.
Comment 6: Unfortunately, I think that the study is inconclusive probably because it was not designed to properly answer its main question, hence does not adds a significant contribution to what is already known.
Answer 6: I believe that the study can be developed further, and yes, there are some additional measurements which (theoretically, given e.g. the financial and geological circumstances) can be made to get more accurate results. Such methods can be, e.g., stable isotope analysis, most likely Be, considering the known potential bias of pedogenesis and postpedogenic processes on O and C stable isotope composition. (which most likely influences the Be composition also). Still, I believe that the study provides essential information about B/M from the ELB, even regardless from the original goal of the study (test of Umbrella effect)
In addition, I would like to address this comment partly by referencing a previous comment from the reviewer. “Considering the specific environment of this study (Loes/paleosoil deposits), and given for granted that all possible "technical" problems (e.g. M/B position, RPI record, pedogenesis, etc. ) are properly solved, -and I think the authors did a reasonably goog job-“
Receiving the final comment, I feel that there is a contradiction between the previous comment of the reviewer (as summarized in Comment 3 before Comment 4) and the conclusion of the review (Comment 6).
Reviewer 4 Report
Comments and Suggestions for AuthorsPlease read the file attached.
Comments for author File: 
Comments.pdf
Author Response
Comment 1: Title: A bit long. It could be “Cooling following the magnetic field weakening during the Matuyama-Brunhes Transition recorded by Paks Loess, Hungary”.
Answer 1: The title is shortened, following the suggestion of the reviewer
Comment 2: Methods: More detailed descriptions for calculating “χlf” from “κlf”, measuring ARM, and calculating RPI should be given.
Answer 2: χlf and κlf were measured separately. Additional information was included in the text to avoid confusion in the future. Further information about ARM and RPI is also included.
Comment 3: Results: The section is confused! It could be some parts, including “4.1 Environmental magnetic parameters”, “4.2 Magnetic mineral features”, and “4.3 Paleomagnetism”.
Answer 3: Subsections are included in the text.
Comment 4: The RPI is a complex parameter. The RPI NRM/magnetic mineral content is inevitably influenced by magnetic minerals and may not fully reflect the actual geomagnetic field intensity. Therefore, it should be discussed that RPI is accurate and has little relation with magnetic parameters. Some plots, such as RPI vs χlf should be given.
Answer 4: The “Concerns” section is completed by the results of the correlation, and more critical words about the relevance of RPI were included in the text.
Comment 5: The viewpoint of this paper is very interesting. However, the current evidence seems to all have been obtained from the loess proles. Are there any records of marine sedimentation? If there are deep-sea sedimentary records for comparison, it will enhance the research value of the entire work and make the study a global issue.
Answer 5: We agree with the reviewer, but it seems a bit early to proceed further with correlation of various sedimentary records. The primary objective of the study was to investigate the connection between magnetic field variations, connected to geomagnetic polarity changes, and climate/environmental changes, particularly in loess. As further steps of the research, more correlation may be expected, especially if additional rock magnetic experiments strengthen the RPI record.
Comment: L48: “14” and “10” - superscript.
Answer: The section is removed from the text following the suggestion of another reviewer.
Comment: L122: “3” - subscript.
Answer: corrected
Comment: L135: “Please...” is not written language. It could be “Notably, ....”
Answer: Thank you, corrected.
Comment: L141: “3” - superscript.
Answer: corrected
Comment: L152: “nanosized superparamagnetic (SP)” is not accurate. It could be SP and SSD. More references are needed.
Answer: “nanosized” is deleted
Comment: L456: Delete “(Kraus, 1999)
Answer: deleted
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAccept in present form
