| 28 Apr 2026
Comparison of Modified Bligh-Dyer and Ultrasonic Organic Solvent Methods for GDGT Extraction from Surface Sediments of Lakes with Different Salinities
Abstract. Accurately quantifying core lipid (CL) and intact polar lipid (IPL) GDGTs is essential for investigating the sources of GDGTs and their responses to climatic and environmental changes in lacustrine systems. However, systematic comparisons of the performance of different methods for extracting GDGTs (both abundance and distribution) from lake sediments remain limited. In this study, we compared two ultrasonic organic solvent extraction methods, including a stepwise gradient extraction with dichloromethane/methanol (DCM/MeOH) solvent mixtures of different polarities and a single solvent extraction with DCM : MeOH (9 : 1, v : v), and two modified Bligh-Dyer (BD) methods (phosphate buffer; trichloroacetic acid) for extracting CL-GDGTs and IPL-GDGTs from saline and freshwater lake sediments. The results showed that, for CL-GDGTs, stepwise gradient extraction yielded the highest recovery, whereas no significant differences were observed in the CL-derived GDGTs proxies among the different extraction methods. For IPL-GDGTs, the BD (phosphate buffer) method achieved the highest recovery for isoprenoid GDGTs (isoGDGTs), while stepwise gradient extraction was most effective for extracting branched GDGTs (brGDGTs) and archaeol from saline lake sediments. Moreover, the consistently lower relative abundance of crenarchaeol to other isoGDGTs in CLs than in IPLs for all methods suggests that crenarchaeol is primarily produced in the lake water column, whereas other isoGDGTs have a relatively greater autochthonous production within the sediments or at the water-sediment interface. In saline lake sediments, we also observed higher relatively abundance of ≥ 7-methyl brGDGTs and tetramethylated brGDGTs in IPLs than in CLs, indicating that their source bacteria are active at the water-sediment interface or in the sediments of saline lakes. These findings will provide insights for the quantitative analysis of GDGTs in lake sediments and for the study of their sources in lacustrine environments.
Review of « Comparison of modified Bligh-Dyer and ultrasonic solvent methods for GDGT extraction from surface sediments of lakes with different salinities » by R. Miao et al. (2026).
The authors of this paper tested different protocols based on ultrasonication and Bligh-Dyer to extract GDGTs in both intact polar (IPLS) and core lipid (CL) forms from lake sediments. They showed that the extraction procedure did not have an obvious influence on the distribution of CL GDGTs, while the both the yield and distribution of IPL GDGTs was impacted by the choice of the extraction methodology.
The manuscript is generally well-written and structured. Nevertheless, I have several concerns which should be addressed :
Other comments are given below.
Line 14. This is very abrupt to start an abstract with the quantification of GDGTs without explaining what are GDGTs (and why studying them).
Lines 24-26. Are the conclusions valid for all the sediments ?
Lines 26-30. Please clarify this sentence.
Lines 26-34. The paper is focused on the comparison of extraction methods of GDGTs from lake sediments. Why talking here about the sources of the GDGTs in the lakes ? This is not relevant when considering the main objective ofthe manuscript.
Line 55. « An increasing number of studies » : please cite these studies.
Lines 88-89. I would specify here that this indirect method leads to loss of information on the nature of the polar head groups of the IPLs.
Lines 112-119. What about the influence of the extraction method on the IPL distribution ?
Lines 120-121. « emerging extraction methods » : which methods ? Please specify them.
Lines 127-128. « Evaluation of GDGT extraction from lake sedments remain limited » : this is also the case for soils and marine sediments.
Lines 130-132. Why choosing the 4 specific lakes (see my main comment) ? This should be justified.
Lines 132-136. Same comment as above : please also justify the choice of these 4 extraction techniques.
Lines 138-139. The evaluation of the GDGT sources is not in the main scope of this paper.
Lines 167-168. Please specify how the sediment samples were preserved (and how long) before freeze-drying as it could have an impact on the IPL amount and distribution.
Line 191. Why 9 extractions (this is much more than usual) ?
Line 241. Please specify which HPLC columns were used to separate GDGTs.
Line 256. What do the authors mean by « high recoveries » ? Please specify.
Line 260. Please specify how is determined the 100% recovery (after direct hydrolysis ?).
Lines 262-264. Please explain in the caption why error bars are only presented for one sample (SG) (this should not be the case, cf. may main comment).
Line 265. What do the authors mean by « abundant CL-GDGTs and IPL-GDGTs » ?
Lines 266-267. This result is not obvious for all samples.
Lines 281-283. This is not obvious for brGDGTs.
Line 288. « Under the optimal extraction method » : which one ?
Line 293. Same comment as above.
Lines 307-308. Fig. 4 appears as redundant with Fig. 3.
Lines 315-317. Such a comparison is difficult as the samples were extracted only once in each condition (and error bars are missing).
Lines 335-340. Please explain how the standard erros are calculated.
Lines 340-343. Such a conclusion cannot be made from one specific sediment sample from saline lake.
Line 348. Statistical tests are needed to talk about « significant » differences.
Line 368-372. What about the residues of the 4 samples after extraction ?
Line 384. What could be the effect of the biological sources on the extraction efficiencies ? Please explain this.
Line 391. Same comment as above regarding the biological sources.
Lines 400-403. Why would 7-methyl brGDGTs extracted more easily than 6-methyl and 5-methyl brGDGTs ? « Specific polar head groups » : which head groups ?
Line 410. Please do not use « significant » without statistical test.
Lines 410-411. Please clarify this sentence.
Lines 424-427. I don’t understand the link between the two parts of the sentence.
Line 435. You could also refer to Huguet et al. (2010a) here.
Line 466. What do the authors mean by « low IPL concentrations » ?