The manuscript presents an interesting study of the water balance of the Baltic Sea. The authors are continuing their previous work defining the dynamic topography of the Baltic Sea and using the gathered information to draw some conclusions on the dynamics of the basin. The study seems to be done rigorously and there are no evident problems with it. The biggest drawback is the logic of the text, as it is organized in somewhat confusing manner, some more explanation below (and in the attachement).

The introduction is somewhat hard to follow. The general explanation of Baltic Sea characteristics, previous studies and authors’ own previous results are not explained in a very logical order. The “traditional” logic to an introduction is “general description – what has been done before – what has been missed – what are our solutions to the problem”.

Also in the following chapters the text jumps between what will be done in the current study and what has been done before, sometimes not really explaining the previous results (e.g. RefBias). There are hints to coming results, general explanations and even discussion on the results in the methods part. Chapter 3 should be renamed to results and discussion, as there is not separate discussion chapter in the manuscript. Some of the figures are a bit too busy, e.g. Figure 2 (see attachment) as well as time series plots showing different basins and happenings (e.g. Figures 5, 8, 9).

The methods used in the manuscript as well as the results and conclusions drawn from them seem to be rigorous and show no problems. With reorganizing the text and clarifying some details the manuscript should be publishable, although with my expertise I am not comfortable to assess the importance of the results from oceanographical aspect.

Like the other reviewer, I found this manuscript difficult to follow, mainly because of how it was structured. For example, there are many instances in Sections 2 and 3 where background information on the Baltic Sea sea level and known mass/volume transports are presented for the first time. This background should all go in Section 1 as motivation for the exact problem the authors are investigating. Then Section 2 should be on specific methods used, and Section 3 on an analysis of the results and comparing them to previous studies. Section 3 is not the time to introduce background/motivation information, as it distracts from the actual results.

The authors make a big deal (multiple time throughout the paper) that'll theirs is the first to do this with a model and observations related to a geoid. Okay. But please, this only needs to be stated once in the introduction and you don't have to keep repeating it. It is distracting!

I really do not see the point of section 2.1, comparing geostrophic currents. First of all, this is mixing methods and results. Second, as far as I can tell, this has nothing to do with the motivation of the paper (looking for overall mass transports into/out of the Baltic). It seems this is mainly to further motivate that their geoid-referenced model DT is good, but this has been demonstrated in other papers. While there is nothing wrong with the analysis, it is distracting from the main goals of this manuscript. I would cut this completely. 

I also do not see the point of Section 3.1 -- yes, the DT varies differently in different sub-basins. But how is this relevant to the overall goals of the paper, to assess transport between the Baltic and North Sea, and to estimate river inflow from the DT variations? It feels like it is tacked onto the study, but is not really motivated in Section 1.

Finally, I have one methodology concern. It is not at all clear to me (although it may be buried in the introductory material in Section 3) that the authors have considered annual and low frequency steric (density) variations that contribute to the volume changes. The volume balance equation being used is based on a mass balance (barotropic) approach, where the density is unchanging (e.g., basically freshwater density). The authors emphasize the north-south mean density gradients in the Baltic, but do these change in time? Have the authors quantified if this is small enough to ignore, or is it even included in their model. My concern is that some of the volume changes are not actually related to the water fluxes into and out of the Baltic, but changes in the density structure.