CO Editor

Suggestions for revision or reasons for rejection

General comments
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The authors did a good job in editing the original manuscript. Most of the ambiguities in the first version have been corrected, so that this new version reads much better. Furthermore, the content has been tuned and now better highlight the originality of the proposed Lagrangian approach and the associated results. Although the presented analysis remains to a certain degree too much qualitative/descriptive, the authors did a better job at discussing the consistencies and inconsistencies of their results with respect to existing in-situ observations.
Rephrasing and reorganising some of the paragraphs greatly improved the readability and clarity of the manuscript, however in few instances there are still some sentences that can be corrected and/or modified to improve the flow of the read. I recommend some minor (mostly stylistic) modifications before publication.
Here some examples:

Abstract:
“A Lagrangian methodology is developed to simulate...”
“By computing trajectories for a large...”
“...in situ measurements, showing a good qualitative correspondance”

Page1:
L45: “It is known as the Kuroshio-Oyashio...”
L53: “...zone is populated with several mesoscale eddies...”

Page2:
L9 : “Moreover, as real trajectories...in initial conditions, they are practically...”
(This to avoid confusion with the simulated ones discussed previously)
L13: “A specific Lagrangian approach...”
L29: “The present authors have developed a set of Lagrangian tools...”
LL38 to 47: “…each water parcel can be attributed to other types of diagnostics which are exclusively function of its trajectory. (…) They are, for example: distance travelled by (…) positions; number of cyclonic and anticyclonic rotations of a particle; time of residence of fluid particles inside a given area; exit time out of that area; ...”
LL51 to 57: “...allow the identification of water masses that move coherently, either by propagating together or by rotating together. (…) say, by temperature (e.g. the satellite SST images indicate no thermal front) the corresponding water masses could still be distinguishable...”

Page 3:
LL26 to 32: “...day. The velocity field is from altimetry data, which provide the geostrophical component of the real (…) valid at the mesoscale(…) information, we plot maps of a specific Lagrangian indicator versus...”
L41: “...informative to also identify….”
LL70 to 77: “...one can track the origin and fate of water masses within a given eddy if it is sufficiently large and long lived (more than a week). For this purpose Lagrangian diagnostics are more appropriate than commonly used Eulerian techniques, because Lagrangian maps are imprints of the history of water masses involved in the vortex motion, whereas vorticity, Okubo-Weiss parameter and similar indicators are only “instantaneous” snapshots...”
LL89 to 91: “...AVISO grid cell with two or more corners touching the land in order to avoid artifacts due to the inaccuracy of the altimeter-based velocity field near the coast.
In what follows, we define the “yellow” waters on the maps...”
L102: “The blue waters are fresher and colder waters...”

Page 4:
In first paragraph of result section replace “centers at” with “centers marked by”
LL29 and 40: replace “to have concentrations of” with “showing concentrations of”
L45: “….could have gained water masses from the Fukushima area or from other origin...”
L55: “...with other eddies...”
L66: “More precisely, the red tracers were advected for two years from the red line segment to their current place in the map”.
L74: “...due to a system of currents wrapping around the eddies present in the area”

Pag 8
LL57 to 67: replace “consists” with “is consistent”

Other minor comments:
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Pag 3: I do not see why the reference Nencioli et al. 2011 should be left out of that list: it is the same type of analysis as Olascoaga et al., 2013, but from two years earlier!!! Please add it in the text.

Regarding the origin of the “yellow” waters (Pag 3 L95):
My apologies to the authors for having misinterpreted the text. However, the sentece they cit in their response has been now removed from the text.
I suggest to keep it: “...the yellow straight lines in Fig 1a, AND for the period from from the day of the accident, March 11, 2011, to May 18, 2011, when direct releases of radioactive isotopes to the ocean and the atmosphere stopped.”
(by adding AND , the two distinct conditions required to mark an advected particle as yellow water are further remarked).

Regarding the use of the adjective “special”:
To avoid any sort of confusion, I think that the adjective “specific” could be used, instead, in the following sentences:
Pag 3 L81: “...in the area, in this paper, we develop a specific Lagrangian diagnostic oriented to...”
Pag 10 L1: “We developed a specific Lagrangian methodology...”

Figure 2:
It would make more sense if reference to figure 2 and 1 were swapped in the text:
L77 to 83: ...Fig 2a on March 26,2011 (…) lines in Fig.1a restricting…
Moreover, the figure would be clearer if the boundary showed in fig 1 would be repeated again in Fig.2a.

Interactive discussion

Peer-review completion