Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific

Mackinson, B. L.; Moran, S. B.; Lomas, M. W.; Stewart, G. M.; Kelly, R. P.

doi:https://doi.org/10.5194/bg-12-3429-2015

Articles | Volume 12, issue 11

https://doi.org/10.5194/bg-12-3429-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-12-3429-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 11

Research article

|

05 Jun 2015

Research article |

| 05 Jun 2015

Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific

B. L. Mackinson, S. B. Moran, M. W. Lomas, G. M. Stewart, and R. P. Kelly

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Final revised paper (published on 05 Jun 2015)
Supplement to the final revised paper
Preprint (discussion started on 27 Aug 2014)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C5484: 'Review of Mackinson et al.', Anonymous Referee #1, 26 Sep 2014
- AC C8364: 'Response to Referee #1 Comment', Brendan Mackinson, 30 Jan 2015
RC C7103: 'Comments on Mackinson et. al', Anonymous Referee #2, 04 Dec 2014
- AC C8376: 'Response to Referee #2 Comment', Brendan Mackinson, 30 Jan 2015

Peer-review completion

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

AR by Brendan Mackinson on behalf of the Authors (20 Feb 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Feb 2015) by Koji Suzuki

RR by Anonymous Referee #1 (14 Mar 2015)

Suggestions for revision or reasons for rejection

I think that the manuscript is for the most part ready for publication. I would still, however, recommend that the authors add in a table that summarizes all of their abbreviations. While the abbreviations are spelled out in the manuscript, the authors should consider that some readers still read manuscripts on paper, and on paper it is not always easy to find the first time that an abbreviation is explained.

I also still disagree with the authors’ assertion that the fecal pellet pathway is likely to transport a higher proportion of picoplankton carbon than microplankton carbon (lines 455-457). In their response to reviewers, the authors cite Gifford (1993) – note that of the papers they cite, this is the only one that pertains to the relative contribution of protozoans and phytoplankton in North Pacific mesozooplankton. Gifford found (in a very nice study) that protozoans were cleared by copepods at the same rate that microphytoplankton were cleared. In their experiments, however, protozoans were much more numerous than microphytoplankton, and hence they concluded that (during their study) protozoans were the dominant prey source for copepods. For the authors’ current study, microphytoplankton make up 31% of the phytoplankton standing stock (their results). If we start by assuming constant specific growth rates for all phytoplankton taxa (a naïve assumption, granted – diatoms often grow with higher specific growth rates than other taxa, though that might not be the case if Fe limitation is significant), then production of pico- and nanoplankton combined would be equal to 69% of total production. If we assume a protozoan gross growth efficiency of 30% (Straile et al. 1997), protozoan production will be ~21% of phytoplankton production (compared to 31% for microphytoplankton). It should be noted that this is an UPPER estimate of protozoan production, because picoplankton are primarily grazed by ~5-um flagellates, which in turn are grazed by ciliates and heterotrophic flagellates before being passed to mesozooplankton and hence the efficiency of the protozoan shunt as a whole is likely less than 30%. Thus it seems likely that mesozooplankton (which according to Gifford prey upon microzooplankton and microphytoplankton in proportion to their relative biomasses) have diets that contain >50% microphytoplankton. I thus think that it is misleading for the authors to suggest that potential fecal pellet export would invalidate their core findings. In reality, it is likely that sinking fecal pellets would support their results that microphytoplankton were preferentially exported.
Regardless, I would like to congratulate the authors on what I consider a fine study.

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RR by Anonymous Referee #3 (14 Mar 2015)

Suggestions for revision or reasons for rejection

Comments to manuscript by Mackinson et al..

Message of this paper is that small (nano- and pico-) phytoplankton also contributes to the biological pump although it has been thought that only large (micro-) phytoplankton play a crucial role in the biological pump. Authors reported that minor fraction of small phytoplankton in settling particle collected by sediment trap might be attributed to that small phytoplankton are grazed by zooplankton and involved into fecal pellet (FP) and thus small phytoplankton also play a role in biological pump. This hypothesis is very unique. In addition, authors responded to almost every comment correctly. Thus this article is publishable.

However I have one question.
Major premise of this paper is that small phytoplankton is incorporated into FP and FP is not collected by sediment trap. However I think that settling particle collected by sediment trap should include FP. How do author answer this question?

In addition, followings need minor revisions or considerations before acceptance.

L178 Why was preservative such as formalin and HgCl2 not used although three days drifting? How do authors thing quality of sample?

Numbers in text are not coincident with those in Table 2.
L198 Where does NPP of 91.8 come from? Average of 105.14 and 78.75?
L199 12.4 -> 23.41 (?)
L202 2.2 -> 3.58 (?)

L235, L240, L244, L247, L251 Fig.4 -> Fig.4a
L235 POC/234Th ratios can be easily understand with not only Fig. 4, but also Fig.9.

Table 2 What are P26-D and P26R? Please explain these in caption.

Table S1, S2, S3 Season for observation period is unreadable. How about inserting the boundary line between different cruises?

Table S1 How about showing integrated Chl-a for each fraction? Because integrated Chl-a are discussed in text (section 3.4). It is difficult to know fraction of chl-a (e.g. >5um is >30% and maximum is 50%) with current Table S1.

Do author think which is close to true value, Th-based POC or sediment trap-based POC?

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ED: Publish subject to minor revisions (Editor review) (28 Mar 2015) by Koji Suzuki

AR by Brendan Mackinson on behalf of the Authors (08 Apr 2015) Author's response Manuscript

ED: Publish as is (18 Apr 2015) by Koji Suzuki

AR by Brendan Mackinson on behalf of the Authors (27 Apr 2015)

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