Preliminary remark. This reviewer is not competent for the review of the statistical analysis in the manuscript.

In general: this is an excellent manuscript. The authors are to be congratulated for their extensive and important work on the non-marine ostracods of Greenland. The text has been carefully written. The figures are of excellent quality. The references are up to date. I agree with the identifications of the species recorded.

I have only a few comments and suggestions for improvement. I recommend publishing the ms after a minor revision.

Here are my comments:

1. I propose to add ‘Greenland’ to the title. The title will be more informative.
2. Line 51: 022 > 2022.
3. Throughout the manuscript, I suggest adding the ‘inferred salinity’ to the EC values. This has not been done in all occurrences.
4. Line 424, Patagonia: a reference is needed.
5. Line 475: variable > variables
6. References.
   
   a. References. The DOIs are given for 2 of them. I suggest adding them for all the references where available.
7. Meisch, C. 2000. Gustav Fischer > Spektrum Akademischer Verlag. Gustav Fischer.
8. Supplementary Table S2 is a bit uneasy to read. I suggest moving the species names in the title row to the right to match the columns below. 
   
   Claude Meisch

This manuscript by Roberts et al. provides important and new information about the distribution of freshwater ostracods in Greenland and the ecological preferences of the recorded species. Such information is very relevant and needed in regions where lakes are affected most intensively by current climate warming.

The manuscript is generally well-structured, well-written and well-illustrated. The inferences are supported by the presented data.

I have only a single major concern:

The authors describe that ostracod specimens were collected alive and as those represented by empty carapaces and disarticulated valves. These different specimens were apparently carefully differentiated. Such dataset is very valuable because those specimens collected alive are directly linked to the measured environmental parameters. In addition, the timing of the occurrence of the specific species during the year’s seasons can be assessed based on such data. However, the authors did not make use or full use of this differentiation. In the discussion section, the different recorded species are discussed with respect to measured environmental parameters such as nutrients, apparently regardless whether actually specimens collected alive or as empty carapaces and disarticulated valves were recorded. I suggest to differentiate more clearly between those specimens collected alive on the one hand side, and those collected as empty carapaces and disarticulated valves.

Minor comments follow below. I added also some suggestions for improvements in an annotated pdf file.

The abstract

The abstract could provide some more detailed information. The authors state that ostracods from lakes in a specific region in Greenland were systematically investigated. How many lakes were sampled? What are the depth ranges for all these samples? Which ranges of conductivities or pH or alkalinities (or other important factors) were sampled?

Two species are mentioned in the abstract. How many species were recorded in general? Which are the three or five most abundant taxa?

Introduction

line (l) 57: The mentioned relationship between light penetration and changes in mixing depth is not very obvious and a short hint to explain this link here would be helpful.

2.1 Study area

The mean annual temperature is provided here but the seasonality is very important in such Arctic environment, and mean January and July temperatures should be added.

Anderson et al. (2012) is provided as reference for the climate data but this is apparently not the source of the original climate data. Is it possible to refer to the original source which is possibly some weather monitoring authority?

I suggest to add some information about the local geology in the catchments of the lakes. The authors mention the many lakes in the region and the potential to use lake-sediment records as climate archives. However, preservation of ostracod valves in cold-water lake deposits can be poor in regions with igneous crustal or volcanic rocks. Also, “geological weathering of the glacial bed” is mentioned in the discussion section but not very helpful without information of the local geology.

2.2 Field methods

The authors describe (l 140) that the top ~1 cm of sediment was sampled where submerged macrophytes were present. So, was the top sediment not generally sampled, and were therefore, empty carapaces and disarticulated valves mostly not included in the survey? Sampling with a net is surely very appropriate to collect specimens alive, but endobenthic taxa and those not present as larger instar or adult stages during the sampling period might not be included.

How were sediment samples collected at positions where macrophytes were present? Which type of grab or corer or dredge was used and how much sediment or which area was sampled?

Results

l 230

The authors describe that the electrical conductivity in these lakes ranged from 0.9 to 4.1 mS/cm but Table 3 includes lake 15 with a conductivity of 0.01 mS/cm and some more lakes with conductivities <0.9 mS/cm.

l 231

Water temperature data are provided here with two decimal positions. Is this precision justified? Are temperatures in the lakes laterally very stable, is the used device very accurate and are temporal changes insignificant to support this precision?

Figures

Fig. 1

A study-area map such as those shown in Fig. 1 should include coordinates.

Fig. 2

The caption should explain the abbreviations “LV” and “RV”.

Fig. 4

Abundances of ostracods are shown in Fig. 4 and the unit is “values per gram”. Are these values specimens collected alive, carapaces, disarticulated valves, or all together? It is important because some of the measured lake parameters may change seasonally and it can be useful to differentiate here specimens collected alive from empty carapaces and valves.

Tables

Table 2

Genera names should be written in italics.

Format, style

• The authors write about ostracod valves and shells in the text and figures. A consistent term should be used.
• Numerals and numbers are not used in a consistent way. A consistent format should be used to write about records from three lakes (or 3 lakes). In general, numerals are used for such items and numbers smaller than 11 or 13. Consistent use of numerals is important here to avoid confusion of “3 sites and lake 3”, for example.
• Italics are sometimes not used in tables and the text.
• The author refer to figures in two ways, for example “Fig 4” and “Fig. 4”.
• Two salinity classification terminologies were used, for example “oligosaline” and “oliogohaline”. The latter is part of the more commonly used Venice system for the salinity-related characterisation of waters.
• Literature references in the text are a bit inconsistent regarding the use of commas. Which format is needed: “Smith et al. 2000” or “Smith et al., 2000”? Same for papers authored by two persons.
• Units are inconsistently formatted such as “mS cm^-1” and “μgL^-1” (with and without space).

I tried to spot and mark issues 2 and 3.