We would like to thank Piotr Kowalczuk for reviewing our paper and for his helpful and constructive comments and remarks. In the revised version of the paper, we will address the mentioned criticisms. We will add to the revised version a more detailed discussion of the changes in the composition of the DOM/CDOM locked in the ice. Since the fast ice in the southeastern Laptev Sea forms in the tDOM-rich Lena River plume, not only the formation of the brines is important, but also the chemical changes in the structure and degradation of the DOM in the ice are important processes that should be discussed in more detail. We are also perhaps too brief on the description of the DOM in the only ice core of signs sympagic algae. This ice core is from thinner fast ice (see paper) from the northern edge of the fast ice and was taken only a few 100 m from the polynya adjacent to the north. We will describe this ice core, which is fundamentally different from the other ice cores in its DOM properties, in more detail. However, this description is not essential for the core thesis of our paper. We would like to reiterate that in this study we sampled the mostly 2 m thick and snow-covered (~10 - 20 cm) fast ice and not the drifting pack ice. Due to the range of MI-8 helicopters, which is about 500 km when loaded (one way), the pack ice cannot be reached from land. Landing on the young ice north of the flaw lead in the Laptev Sea is impossible. At the same time, the entire marine area is closed to navigation in spring. Therefore, direct sampling of the drifting sea ice in the Laptev Sea in spring was not possible and could therefore only be discussed based on previous studies. However, our study suggests that the possibly DOM-rich meltwater of the young drifting pack ice probably plays no role in the processes we describe. At least not in the Laptev Sea.

In the revised version of our paper we will also add to the abstract and give more precise figures for the flux input.

We thank the referee for the constructive comments and questions. We also thank the anonymous reviewer for the positive comment on the publication of the entire data set. To "fully" analyze this dataset, which spans a 9-year period and multiple summer and winter expeditions, and present the results in this study is beyond the scope of this paper. However, we believe that the results presented in this paper give a key to any further interpretations. The main objective is to show, using measurements and calculation of budgets, that the distribution of DOM concentrations in the Laptev and East Siberian Sea is determined primarily by the mixing of three freshwater "parent water masses" (river water during the freshet, river water after the freshet, and meltwater from the fast ice) with different DOM concentrations and compositions. As far as we understand, this central hypothesis is not challenged by the reviewer. Although this paper addresses only one aspect of the topic of DOM transport and degradation in the Arctic Ocean, we believe it makes an important contribution to the scientific debate. In order to give other scientists the opportunity for further analysis regarding other aspects, we have decided to publish the entire data set in full spectral resolution. In trying to write the paper as concisely as possible, we seem to have inadequately presented important results of our analysis (such as the presentation of the ratio of the river water fraction - O18 data - to CDOM absorption). We hope that the reviewer will nevertheless believe us when we emphasize that we have thoroughly analyzed the data set.

A detailed determination of the degradation rates of tDOM on the Siberian shelves is not the central topic of this study. Our data set also indicates that some tDOM is mineralized in the area of the Siberian shelves. However, it also indicates that degradation of tDOM cannot adequately explain the observed concentration distribution on the shelves. However, we agree with the reviewer that we should better elaborate on the key messages by including figures of river water fraction (O18 data) and CDOM absorption and discussing these data in more detail. We will do this in the revised version of the manuscript and hope to address the reviewer's main criticisms. We will also discuss the slope values (S275-295) and their significance in more detail. However, the inclusion of these results, which is certainly necessary, does not disprove the central conclusions of this paper but is further evidence of the plausibility of our hypotheses. We have summarized the response to all of the referee’s comments and questions in a separate document (see Appendix).

The formation of the Arctic halocline is an important and interesting research topic that our group has also been working on for more than 20 years. However, the description of this physical-oceanographic process is not - and cannot be - the subject of this paper. In this context, we refer to the published studies of some of the coauthors: Bauch et al. (2009, JGR), Bauch et al. (2011, Prog in Oceanogr.), Bauch et al. (2014), Janout et al. (2017), and Janout et al. (2020). These papers, which are cited in our paper, provided an important basis for the hypotheses presented in this study.