A 5000-Year Sedimentary Record of East Asian Winter Monsoon from the Northern Muddy Area of the East China Sea
Round 1
Reviewer 1 Report
I liked the article very much, it is short and very specific. The described well is unique and is the key to deciphering the paleoclimate of the region. The conclusion made about the contribution of winter monsoons to the distribution of particle size fractions is very important. We ask the authors to explain in more detail why the revealed patterns of sedimentation in the southern region are correlated with events in the Arctic region. What is the reason for this correlation? The rest of the article can be accepted in the author's edition.
Author Response
Response to the comments
Reviewer 1#
I liked the article very much, it is short and very specific. The described well is unique and is the key to deciphering the paleoclimate of the region. The conclusion made about the contribution of winter monsoons to the distribution of particle size fractions is very important. We ask the authors to explain in more detail why the revealed patterns of sedimentation in the southern region are correlated with events in the Arctic region. What is the reason for this correlation? The rest of the article can be accepted in the author's edition.
Reply: We thank you for reviewing our draft and the kind advice.
Agree and revised.
In studying change in Asian monsoon, Arctic climate is one of key factors dominates the variabilities of monsoon system, such as in studies of cave deposits, lake records, loess sequences, and marine sediments. The mechanism behind this linkage is supposed to be an effective teleconnection between the Arctic region and the East Asia. We added this case in the revision.
Page 9, Lines 218-222:
The Bond IRD events represent a major climate state of high-latitude areas of the Northern Hemisphere on a millennial timescale [41,44], and play a critical role in winter climates across the East Asia [e.g., 12,40,45], thus inferring a tightened and rapid atmospheric teleconnection between the North Atlantic and the Asian monsoon [43,46,47].
Reviewer 2 Report
The study addresses the relationship between the sediment characteristics of a muddy area of the East China Sea and the intensity of the East Asian winter monsoon. A new proxy is proposed to relate the size of the sediment to the significance of the winter monsoon to understand the sedimentary dynamics in the northern part of the East China Sea.
The manuscript has a correct structure and clearly presents the most representative aspects of the research carried out. However, there are some aspects that must be reviewed:
In figure 1, the latitude of the map on the right is incorrect, as north latitude should be indicated instead of east.
Line 91-93. “Accordingly, the upper 2.8 m mainly contains fluid mud with a high-water content, and the 11.8 m in depth is a sedimentary boundary with ~4 kyr hiatus [19]. Thus, we sampled 2.8-11.8 m depth with an interval of 0.1 m to study sedimentary dynamics over the past 5,000 years.” This observation should perhaps move to the results section.
Line 159-160. “we analyzed sediment grain-size spectra through varimax-rotated, principal component analysis 159 (VPCA)” The explanation of the method would be in the Methods section , and probably extended.
Section 3.1. Age-depth model
I’m not expert on radiocarbon and OSL dating, but this section results a bit confusing and brings some doubts about the model. As this age model is the basis of the correlation with the winter monsoon, some questions arise. First, it is unclear what type of material has been dated by 14C. Authors said that it was “organic carbon” (lines 96 and 111), but are they refering to organic carbon from organic matter in the sediment?, or to charcoal?. This may be important, as the marine reservoir must be applied to shells, and because the calculated reservoir of 2.5 kyr seems really high, compared with the values obtained in the Marine20 database using the data of Yoneda et al, 2007.
Author Response
Response to the comments
Reviewer 2#
The study addresses the relationship between the sediment characteristics of a muddy area of the East China Sea and the intensity of the East Asian winter monsoon. A new proxy is proposed to relate the size of the sediment to the significance of the winter monsoon to understand the sedimentary dynamics in the northern part of the East China Sea. The manuscript has a correct structure and clearly presents the most representative aspects of the research carried out. However, there are some aspects that must be reviewed:
Reply: We thank you for reviewing our draft and the kind advice. Our response to the comments is listed below.
In figure 1, the latitude of the map on the right is incorrect, as north latitude should be indicated instead of east.
Reply: Agree and revised. Thanks!
Line 91-93. “Accordingly, the upper 2.8 m mainly contains fluid mud with a high-water content, and the 11.8 m in depth is a sedimentary boundary with ~4 kyr hiatus [19]. Thus, we sampled 2.8-11.8 m depth with an interval of 0.1 m to study sedimentary dynamics over the past 5,000 years.” This observation should perhaps move to the results section.
Reply: Revised.
This part was proposed to clarify the reason that we chose the interval of 2.8-11.8 m depth for this study. Thus, we changed the title of this section to “Core ECS-DZ1 and experiments” in this reivsion.
Line 159-160. “we analyzed sediment grain-size spectra through varimax-rotated, principal component analysis 159 (VPCA)” The explanation of the method would be in the Methods section, and probably extended.
Reply: Agree and revised.
This part was moved to the Methods section, and expanded as follows.
Page 3, Lines 107-116
Grain-size analysis of the sediments is a useful and effective tool for various sedimentary and paleoenvironmental inferences [e.g., 20,21-23]. To identify the processes controlling sediment grain size changes and extract potential paleoenvironmental signals, we analyzed sediment grain-size spectra through varimax-rotated, principal component analysis (VPCA), which can partition various sediment inputs or dynamics components [24,25]. This method assumes that each sedimentary process is related with a specific grain-size spectral shape. Similarly, polymodal grain-size spectra can be mathematically partitioned [26], following a particular theoretical distribution [27-29]. These two methods allow us to separate out orthogonal modes (independent grain-size spectral components/factors) and thus to identify potential changes of input functions [24,25,30]. The exported one hundred grain-size classes between 0.3 and 700 μm were used for the two analyses.
Section 3.1. Age-depth model
I’m not expert on radiocarbon and OSL dating, but this section results a bit confusing and brings some doubts about the model. As this age model is the basis of the correlation with the winter monsoon, some questions arise. First, it is unclear what type of material has been dated by 14C. Authors said that it was “organic carbon” (lines 96 and 111), but are they refering to organic carbon from organic matter in the sediment? or to charcoal?. This may be important, as the marine reservoir must be applied to shells, and because the calculated reservoir of 2.5 kyr seems really high, compared with the values obtained in the Marine20 database using the data of Yoneda et al, 2007.
Reply: Agree and revised.
This part was revised to clarify the reliability of the age-depth model.
1) The dated materials are organic carbons in the sediments.
Page 3, Lines 97-101:
Four samples were collected for radiocarbon dating. Organic carbon from organic matters in the sediments was extracted and measured at Beta Analytic Inc. USA using the Accelerator Mass Spectrometry method (AMS). To identify reservoir effects of dating organic carbons in the sediments, a comparison was conducted with a luminescence age [19], and all radiocarbon dates were calibrated using the age difference between these two methods.
2) We explained the calibration of radiocarbon dates more in the revision.
Pages 3-4, Lines 124-130:
Unlike radiocarbon dating on foraminifera, dating organic carbons in the sediments is usually influenced by the input of old organic carbon by rivers and currents [e.g., 31,32,33]. To remove this old-carbon influence in previous studies, the age difference between two dating methods on the same sample should be determined; and in this study, the value is ~ 2,500 year. Thus, subtracting the reservoir effect of organic carbons (~2,500 years) from the original radiocarbon dates, an age-depth model was established using a regression model by fitting the all five ages.
3) As reported in other studies, the reservoir effect ranges from hundreds of years to thousands of years, which is dependent on the input of regional old carbons to the deposits. For example, in the Antarctic region, the average value was about 1,300 years and the upper estimate can be over 4,000 years; and the Asian lakes and the East China Sea, this value has a greater range, 600-3,000 years. We added some references to support our inference in this revision. Thus, we believe that the reservoir effect, 2,500 years, in the sediments of the ECS is reasonable, and chose this value for the calibration.
