Abrupt Late Holocene Closure of San Elijo Lagoon, Northern San Diego County, California

Round 1

Reviewer 1 Report

This is a work about the recent evolution of a highly anthropized lagoon, which is an interesting subject. The data and method seem to be enough to give good results, but in my opinion, there is a lack of clarity in the methods, compromising the interpretation and results, especially the rates of accretion. Although the interpretation of the lagoon's evolution is coherent, it must be supported by the data, what does not happen in its current form.

Some speficic questions and comments are in the attached PDF file

 

Comments for author File: Comments.pdf

Author Response

Made corrections as suggested; see PDF file with answers to your questions and comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper titled "Abrupt Late Holocene Closure of San Elijo Lagoon, Northern San Diego County, California" explores the sedimentation history of the lagoon, focusing on a significant shift observed around 1,000 AD. The authors utilize 14C dating to identify this shift, characterized by a distinct boundary between a lower layer of medium to fine sand and an upper layer of dark, silty clay, indicative of lagoon closure. The sediment dating provides valuable insights into the marine conditions of the lagoon basin over time. The results indicate that approximately 7,400 ± 140 years before the present (ybp), when the sea level was -12.2 meters (m), the shoreline was situated 400 meters away from its current location. Subsequently, the sea level gradually rose at a rate of 2.84 meters per 1,000 years until approximately 4,170 ± 100 ybp. Following this period, the rate of sea-level rise decreased, ultimately reaching the present level around 3,100 years ago.

Interestingly, the lagoon remained closed for a significant duration between approximately 730 to 1,180 ybp. During this period, only fine organic sediment accumulated in the basin. This closure coincided with a severe drought in the southwest around 1,150 AD, which likely contributed to the lack of water flow necessary for lagoon reopening.

The paper also notes a higher sedimentation rate observed from bluff erosion after approximately 520 ± 40 ybp. However, despite this increased sedimentation, there was insufficient stream flow to trigger the reopening of the lagoon.

Overall, the paper presents a detailed examination of the Late Holocene closure of San Elijo Lagoon in Northern San Diego County, California. The use of 14C dating and sediment analysis provides a solid foundation for understanding the lagoon's sedimentation history and its relationship with sea-level fluctuations and climatic events, such as droughts. The findings contribute to our knowledge of coastal dynamics and highlight the complexity of lagoon ecosystems in response to changing environmental conditions.

It is an excellent job, the only thing that would improve Figure 1, and would make an evolutionary scheme, of the area, or the realization of the columns resulting from the witnesses (samples extracted) and their correlation. On the other hand, it would be good to include a bit of weather, how it has changed, to explain the abrupt change, etc. Have you thought about using what is left of the sample to carry out OSL dating, pollen dating, etc?

In the pdf they have some suggestions and corrections.

Comments for author File: Comments.pdf

Author Response

See comments on PDF document.  Changes were made as requested and all figures have been updated to reflect those changes.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,                                                            

The manuscript presents the results of an investigation of “Abrupt Late Holocene Closure of San Elijo Lagoon, Northern San Diego County, California”. The theme is of great interest for coastal evolution, and would like to see it published; major changes are necessary as suggested below.

 

·         A broad conceptual review should be carried out in introduction chapter;

·         Improve the quality of Figure 1: Metric scale and location of area in context of California / USA;

·         Remove the background (1.1) of manuscript introduction;

·         The figure 2 should be transferred to the materials and method chapter, improve your quality. By the way, all figures presented must be redone;

·         In table 1 of materials and method chapter, inform only the geographic coordinates (lat. and long.), the number of sample cores and the type of material (sediments) that was collected for radiocarbon dating. Remove from the text the measured radiocarbon, ratio, YBP and calebrad calender age. These information are part of the results obtained (table 2); 

·         The results obtained need to be better explored;

·         As this is a coastal environment, issues related to fluctuations about relative sea level - RSL in study area need to be better explored in the chapter discussing the results.

 

Therefore for the manuscript to be published in Coasts, we recommend a thorough review as suggested above.

 

 

Sincerelly,

 

 

 

 

Author Response

Redid introduction as suggested.

improved all figures as suggested

moved 1.1 as suggested by other reviewers

Figure 2 serves 2 purposes - a general overview of the lagoon and showing locations of all borings.

Table 1 - we have decided to keep all the data as was suggested by both the other reviewers

results were corrected as suggested

Please see updated paper.

Round 2

Reviewer 1 Report

The main issues have been corrected, and the paper are now improved

Reviewer 3 Report

Dear Authors,

I recommend the publication of manuscript. However, a small revision is necessary in all the maps presented.

Sincerely,

 

The English language fine. No issues detected.