Disparities between in situ and optically derived carbon biomass and growth rates of the prymnesiophyte <i>Phaeocystis globosa</i>

Peperzak, L.; van der Woerd, H. J.; Timmermans, K. R.

doi:https://doi.org/10.5194/bg-12-1659-2015

Articles | Volume 12, issue 6

https://doi.org/10.5194/bg-12-1659-2015

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

https://doi.org/10.5194/bg-12-1659-2015

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

Articles | Volume 12, issue 6

Research article

|

16 Mar 2015

Research article |

| 16 Mar 2015

Disparities between in situ and optically derived carbon biomass and growth rates of the prymnesiophyte Phaeocystis globosa

L. Peperzak, H. J. van der Woerd, and K. R. Timmermans

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Final revised paper (published on 16 Mar 2015)
Preprint (discussion started on 29 Apr 2014)

Interactive discussion

Status: closed

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

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RC C2076: 'Review of manuscript', Anonymous Referee #1, 03 Jun 2014
RC C2077: 'Review of Manuscript', Anonymous Referee #2, 03 Jun 2014
RC C3410: 'Review of Manuscript', Anonymous Referee #3, 10 Jul 2014
AC C6837: 'Author comments in response to the reviewers', L. Peperzak, 18 Nov 2014

Peer-review completion

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

AR by L. Peperzak on behalf of the Authors (16 Jan 2015) Manuscript

ED: Referee Nomination & Report Request started (21 Jan 2015) by Emmanuel Boss

RR by Anonymous Referee #1 (02 Feb 2015)

RR by Anonymous Referee #2 (02 Feb 2015)

Suggestions for revision or reasons for rejection

\noindent{\bf General comments}\\
This study utilizes controlled batch-culture mesocosms to examine the performance of optical proxies for {\it Phaeocystis} biomass, physiology, and growth rates. Because the transition from exponential to N-limited stationary growth leads to non-linear relationships between the C:Chl ratio, Chl-specific absorption, and Chl fluorescence yield, the authors conclude that optical proxies may not provide useful estimates of production and growth rate for this species under such environmental conditions.

I commend the authors for the extensive revisions in response to comments received on the original manuscript, which in my opinion have led to a significant improvement in the paper. The study's aim and description of the methodology is much clearer, and I believe the results provide some worthwhile observations to the literature on relationships between growth and the remotely-sensed chlorophyll-a fluorescence signal.

I have only two more additional comments for the authors to consider below.

\noindent{\bf Specific comments}\\
Sec. 2.4 - Despite the improvements in defining symbols and the addition of Table 1, it is still difficult to follow the steps in the calculation of fluorescence emission flux, F, and subsequently the derivation of quantum efficiency, $\varphi_F$.

In Table 1, the symbol F is defined as “Chla fluorescence” derived from eq. 2 with units of sr$^{-1}$. However, in Fig. 5 the units of F are depicted as quantum irradiance, $\mumol photons m^{-2} s^{-1}$. Later in Table 1 and the discussion (line 24 of page 13), fluorescence quantum efficiency $\varphi_F$ is defined as the ratio of F/$a_{ph}$ with units of percent, which is inconsistent with either of the above ($a_{ph}$ has units of $m^{-1}$) and cannot be correct (fluorescence needs to be normalized to the flux of absorbed photons, i.e. the product of absorption coefficient and incident light). I realize that these calculations are (better) described in the L&O Methods paper, but the description given here in sec. 2.3 needs to be written more carefully (with explict distinguishing between quantities such as fluorescence line height, fluorescence volume emission, etc.) so that a reader can understand it.

Fig. 5 – Because the incident light intensities are slightly different between the two mesocosms, I think it would be better to show fluorescence normalized to incident irradiance as the dependent variable in these plots. This would eliminate the confounding effect of different excitation intensities between the two experimental systems; for example, in Fig. 5B is the increased fluoresence from mesocosm 2 simply a result of higher excitation intensity?

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ED: Publish subject to minor revisions (Editor review) (02 Feb 2015) by Emmanuel Boss

AR by L. Peperzak on behalf of the Authors (16 Feb 2015) Author's response Manuscript

ED: Publish as is (17 Feb 2015) by Emmanuel Boss

AR by L. Peperzak on behalf of the Authors (20 Feb 2015)