Zooplankton diel vertical migration and downward C flux into the oxygen minimum zone in the highly productive upwelling region off northern Chile

Tutasi, Pritha; Escribano, Ruben

doi:https://doi.org/10.5194/bg-17-455-2020

Articles | Volume 17, issue 2

Biogeosciences, 17, 455–473, 2020

https://doi.org/10.5194/bg-17-455-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Ocean deoxygenation: drivers and consequences – past, present...

Biogeosciences, 17, 455–473, 2020

https://doi.org/10.5194/bg-17-455-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 2

Research article 30 Jan 2020

Research article | 30 Jan 2020

Zooplankton diel vertical migration and downward C flux into the oxygen minimum zone in the highly productive upwelling region off northern Chile

Pritha Tutasi and Ruben Escribano

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Final revised paper (published on 30 Jan 2020)
Supplement to the final revised paper
Preprint (discussion started on 23 Apr 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Tutasi & Escribano Zoopankton-mediatex C-flux', Anonymous Referee #1, 29 Apr 2019
- AC1: 'Response to reviewer 1', Pritha Tutasi, 26 Jun 2019
RC2: 'Tutasi and Escribano', Anonymous Referee #2, 15 May 2019
- AC2: 'Response to reviewer 2', Pritha Tutasi, 26 Jun 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (26 Jun 2019) by Hermann Bange

AR by Anna Wenzel on behalf of the Authors (30 Jul 2019) Author's response

ED: Referee Nomination & Report Request started (30 Jul 2019) by Hermann Bange

RR by Anonymous Referee #2 (15 Aug 2019)

Suggestions for revision or reasons for rejection

The manuscript by Tutasi and Escribano is a quite interesting and valuable report about the vertical distribution of different groups and species of zooplankton in relation to the oxygen minimum zone (OMZ) in the upwelling zone off Chile. They also showed the diel movements of the different zooplankton groups and species and their range of migration in relation to the OMZ. This is a rather important data set of general interest and the results deserve publication. In relation to the requirements made in my previous report, now the authors provide a better explanation about their estimation of migrant biomass and active flux by zooplankton.

However, this reviewer consider their assessment of active flux not properly done. The authors use a value of 0.12 d-1 for respiration at the residence depth of migrants. This is a rather high value of respiration for mesopelagic zooplankton. These rates should be half of the value used by the authors, or even less. As stated in the previous report, I recommended the authors to use the equation given by Ikeda (1985) or even better the equation by Ikeda (2014) considering depth to estimate respiration. The authors assessed the individual biomass of zooplankton which jointly with temperature could provide a rather useful estimate of respiration at depth using these equations. Mortality and egestion should also be much lower than the given values as these parameters are normally lower than respiration rates. Therefore, values of active flux are too high, something that is observed in their comparison to other assessments in Table 4 (excepting Escribano et al., 2009). Although this estimation is carried out in a eutrophic system such as the quite productive upwelling off Chile, these values of active flux are still too large due to the considerations given above. Thus, I consider this a major revision before definitive publication.

Finally, the authors stated in the material and methods section that migrant biomass was calculated as the difference between day and night biomass in the upper 90 m depth layer. Thus, biomass during night should be larger than during day in this layer, something which is not visually observed in Figure 6. Please, provide some explanation to this.

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RR by Anonymous Referee #1 (21 Aug 2019)

ED: Reconsider after major revisions (21 Aug 2019) by Hermann Bange

AR by Ruben Escribano on behalf of the Authors (01 Oct 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Oct 2019) by Hermann Bange

RR by Anonymous Referee #2 (22 Oct 2019)

RR by Anonymous Referee #1 (08 Nov 2019)

ED: Publish subject to minor revisions (review by editor) (08 Nov 2019) by Hermann Bange

AR by Ruben Escribano on behalf of the Authors (13 Nov 2019) Author's response Manuscript

ED: Publish as is (19 Nov 2019) by Hermann Bange

Short summary

Vertical migration of zooplankton has rarely been studied under the effect of a variable community structure, which depending on the behavior and size of its groups can strongly alter the magnitude of C being actively taken to depth by migrants. Here, we address this issue in a highly productive upwelling system, where a high amount of zooplankton can daily move below the mixed layer despite presence of an extremely low–oxygen water and so contribute to a significant export of C to depth.