Reply on RC1

Thank you for your kindly comments concerning the manuscript entitled “Geophysical and biogeochemical observations using BGC Argo floats in the western North Pacific during late winter and early spring, Part 2: Biological processes during restratification periods in the euphotic and twilight layer” which we submitted for publication in Biogeosciences. We are studying all your comments carefully and reply to your comments as follows.

Author Comment (AC): As you pointed out, we focused on four evens (Case 1 to 4) and discussed their biogeochemical changes. Of those, Case 4 was the only one which we could trace the same water mass. We should have discussed the physical processes of the water mass before we discuss the biogeochemical processes. In the revised manuscript, we will revise it to include an enough physical discussion. Also, we calculated the net flux of O2 and NO3. Therefore, we cannot calculate diffusive fluxes of O2 and NO3, but we did not ignore them.
(2) POC production is not equivalent to net community production (NCP), as a fraction of the fixed carbon is released as DOC (22 to 40% in the North Atlantic, Alkire et al. 2012). NCP is also different from NPP (NCP=NPP-heterotrophic respiration), so it makes no sense to compare your POC production to NPP. Also, you argue that deviation from the Redfield ratio in the mesopelagic is due to remineralization of DOC (and not only POC). But the same argument stands for the C/N ratio in the surface layer. Production of POC alone is not supposed to reflect the total N consumption. See also comments on the Redfield ratio in the section below.
AC: Thank you for your comment. I understood that we were estimating POC production and not NPP or NCP. In the revised manuscript, we will discuss the estimate of POC production. And we will compare it to the CN ratios reported in the past, considering DOC production.
(3) The authors refer throughout the manuscript to temperature, salinity, wind, net heat flux and SSH, but none of these variables are shown. I understand that some of these variables are probably shown in the companion paper, but it is a bit frustrating not seeing them. You could at least show temperature and salinity sections.
AC: Thank you for your comment. I the revised manuscript, we will add figures of temporal variation of water temperature, salinity, and heat flux and explain them as well.
(4) Regarding the form, I think the results section contains only 'basic' observations/results, while most important results are drowned in the discussion. The most interesting figure (figure 7), from my point of view, is only introduced and discussed in the conclusion. Also, I think a statement of the objectives of this study is missing in the abstract. I found the quality of the writing to considerably decrease over the course of the paper. I had difficulties to understand some of the discussion/conclusion sentences. The writing clearly needs to be improved.
AC: I appreciate your comments. For figure 7, we will explain the temporal variations about materials (O2, POC, NO3) and discuss the degradation process in the twilight layer in the discussion section. We will add the objective of this study in the abstract. We will rewrite the manuscript and make it more readable.

Further detailed comments are listed below:
line 26: How do you calculate the euphotic depth? From what data? AC: Since our CTD was equipped with a PAR sensor, we used the data to determine the depth of the euphotic layer. We will describe this in the revised manuscript.
lines 27-29: I am not sure to understand this sentence. Do you validate the quality of the sensor by comparing your C/N ratio to the Redfield ratio? If your ratio was significantly different from the Redfield one, would you conclude that the difference is due to the sensor quality or accuracy? Several studies actually demonstrated that organic matter exhibits widely varying proportions of carbon and nutrients, partly reflecting seasonal and spatial changes of the phytoplankton community structure (Green & Sambrotto 2006, Weber and Deutsch 2010, Martiny et al 2013. So, I think comparing your local ratio with the global average Redfield one is not very conclusive. AC: We considered the sensor corrections to be approximately current because the ratio of the decrease in nitrate to the increase in POC obtained by the two independent sensors was on the same order of magnitude as the Redfield ratio when the sensors observed in the same water mass. However, we also understand that CN ratio can vary with region and season. In the revised manuscript, we will compare the CN ratios with those reported in the past.
lines 129-130: the presence or absence of optical spikes depends, among other things, on the vertical resolution of acquisition. It is pretty obvious that POC profiles from discrete water samples will have no spikes. Your sentence makes no sense.
AC: We will delete this sentence. AC: I am sorry. We will rewrite the name.
AC: We will rewrite to "32.4N". line 167: "there was no exposure of", exposure to what?, not clear. AC: The word "exposure" meant that the 25.3 sigma-theta water mass did not come to the surface of the ocean. We will rewrite this sentence.
lines 170-171: is it temporal or spatial variation? as the floats moved ~300 km northward.
AC: We described this sentence in terms of temporal variation. However, we will add a description of spatial variation as well.
line 171: what is the middle layer? AC: We wrote "the middle layer" to mean "below the euphotic layer". We will rewrite it as ""below the euphotic layer".
line 177: respiration also occurs in the euphotic layer.
AC: It was an inaccurate sentence. we would rewrite "beneath the euphotic zone" as "throughout the water column". AC: We will add some marks in figures to indicate where we focus.
lines 208-209: phytoplankton stock can also increase during winter mixing, not only once mixing ceases. This is not visible from Chla concentration records due to dilution when the MLD deepens, but it is from depth-integrated biomass records.
AC: We will integrate Chla to the deepest mixed layer depth during the observation period, and discuss that as well.
lines 218-221: You are comparing local POC to Chla ratios with worldwide Cphyto to Chla ratios. That makes no sense (average phyto contribution to POC is ~30%). It is a weak demonstration that Cphyto is correlated to POC. I recommend the authors to refer to publications that investigated the Cphyto-POC(bbp) relationship (Behrenfeld et al 2005, Martinez-Vincente 2012,2013. AC: Thank you for the literature review. We will discuss the relationship between Cphyto-POC(bbp) in our results and literatures.
line 242: The link to the Japan Meteorological Agency homepage is useless. It is more appropriate to show direct wind or net heat flux records.