Influence of photoacclimation on the phytoplankton seasonal cycle in the Mediterranean Sea as seen by satellite

Bellacicco, Marco; Volpe, Gianluca; Colella, Simone; Pitarch, Jaime; Santoleri, Rosalia

doi:10.1016/j.rse.2016.08.004

Cited by 48 publications

(70 citation statements)

References 63 publications

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“…S3a), indicative of iron limitation within the mixed layer and a supply mechanism (seasonal, sub-seasonal, remineralized or stormdriven) that is not sufficient to meet mixed-layer phytoplankton demands. Precaution must, however, be taken when investigating Chl a concentration as a proxy for phytoplankton biomass Bellacicco et al, 2016;Mignot et al, 2014;Westberry et al, 2008Westberry et al, , 2016, as a higher average concentration over the euphotic zone (0.8 mg m −3 ) relative to the shallower mixed layer (0.4 mg m −3 ) may represent a Chl a packaging effect due to lower light levels at depth (rather than an increase in biomass). As such, particulate backscatter (b bp ) (Fig.…”

Section: Discussionmentioning

confidence: 99%

Seasonal development of iron limitation in the sub-Antarctic zone

Ryan‐Keogh

Thomalla

Mtshali³

et al. 2018

Biogeosciences

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Abstract. The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ; ∼ 40-45 • S) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron availability is due to an interplay between winter entrainment, diapycnal diffusion, storm-driven entrainment, atmospheric deposition, iron scavenging and iron recycling processes. Biological observations utilizing grow-out iron addition incubation experiments were performed at different stages of the seasonal cycle within the SAZ to determine whether iron availability at the time of sampling was sufficient to meet biological demands at different times of the growing season. Here we demonstrate that at the beginning of the growing season, there is sufficient iron to meet the demands of the phytoplankton community, but that as the growing season develops the mean iron concentrations in the mixed layer decrease and are insufficient to meet biological demand. Phytoplankton increase their photosynthetic efficiency and net growth rates following iron addition from midsummer to late summer, with no differences determined during early summer, suggestive of seasonal iron depletion and an insufficient resupply of iron to meet biological demand. The result of this is residual macronutrients at the end of the growing season and the prevalence of the high-nutrient low-chlorophyll (HNLC) condition. We conclude that despite the prolonged growing season characteristic of the SAZ, which can extend into late summer/early autumn, results nonetheless suggest that iron supply mechanisms are insufficient to maintain potential maximal growth and productivity throughout the season.

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Section: Discussionmentioning

confidence: 99%

Seasonal development of iron limitation in the sub-Antarctic zone

Ryan‐Keogh

Thomalla

Mtshali³

et al. 2018

Biogeosciences

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“…As with Behrenfeld et al (2005), our b bp470 was corrected for contributions from non-algal organisms other than phytoplankton (which also contribute to the optical backscattering signal) by subtracting a background value of 3.5 10 −4 m −1 , with the assumption that this value represents the portion of non-algal particulate matter that does not co-vary with phytoplankton (Behrenfeld et al, 2005). Worth noting however is that the proportion of non-algal particulate matter is not constant as was shown by a study in the Mediterranean where the non-algal contribution to particulate backscattering varied both seasonally and regionally by more than one order of magnitude (Bellacicco et al, 2016). Only 0.02% of the glider backscattering data fell below this threshold and they were discarded.…”

Section: Behrenfeld Et Al (2005) Methods (B05)mentioning

confidence: 99%

“…Phytoplankton chl-a:C phyto ratios tend to decrease with increasing light conditions and decreasing temperature and nutrient concentrations (and vice versa) Socal et al, 1997;Taylor et al, 1997;Behrenfeld et al, 2005;Lü et al, 2009;Halsey and Jones, 2015;Westberry et al, 2016). Increasing chl-a:C phyto ratios as a physiological response of phytoplankton to low light conditions enables them to increase their light harvesting ability by increasing the volume of chlorophyll packed into their cells Halsey and Jones, 2015;Bellacicco et al, 2016). Indeed, photoacclimation to changes in the underwater light field as a bloom develops have been known to account for the entire range of seasonal variability observed in bulk chlorophyll (e.g., Winn et al, 1995;Westberry et al, 2008).…”

Section: Seasonal and Sub-seasonal Variations In The Chlorophyll-to-cmentioning

confidence: 99%

“…In addition, different pigment content is expressed by the phylogenetic evolution of phytoplankton species with changes in accessory pigments leading to differences in light absorption per unit chlorophyll (MacIntyre et al, 2002). As such, temporal changes in chlorophyll over large ocean regions can result form physiologically or community driven modifications in cellular chlorophyll-to-carbon ratios, rather than to changes in biomass (Behrenfeld et al, 2005Westberry et al, 2008Westberry et al, , 2016Mignot et al, 2014;Bellacicco et al, 2016). Such instances will have strong implications on assessments of long term trends in primary production, ecosystem trophic dynamics, and carbon export .…”

Section: Introductionmentioning

confidence: 99%

“…In addition, they can be measured both in situ and with satellite remote sensing. Unlike chlorophyll, these measures are more likely to be insensitive to changes in the intracellular concentration of pigments (Behrenfeld and Boss, 2006;Behrenfeld et al, 2016;Bellacicco et al, 2016;Westberry et al, 2016). However, the use of optical proxies for total organic carbon is complicated by the highly variable relationships reported in the literature for POC vs. backscattering which can vary by a factor of five (Cetinić et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Using Optical Sensors on Gliders to Estimate Phytoplankton Carbon Concentrations and Chlorophyll-to-Carbon Ratios in the Southern Ocean

et al. 2017

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One approach to deriving phytoplankton carbon biomass estimates (C phyto ) at appropriate scales is through optical products. This study uses a high-resolution glider data set in the Sub-Antarctic Zone (SAZ) of the Southern Ocean to compare four different methods of deriving C phyto from particulate backscattering and fluorescence-derived chlorophyll (chl-a). A comparison of the methods showed that at low (<0.5 mg m −3 ) chlorophyll concentrations (e.g., early spring and at depth), all four methods produced similar estimates of C phyto , whereas when chlorophyll concentrations were elevated one method derived higher concentrations of C phyto than the others. The use of methods derived from particulate backscattering rather than fluorescence can account for cellular adjustments in chl-a:C phyto that are not driven by biomass alone. A comparison of the glider chl-a:C phyto ratios from the different optical methods with ratios from laboratory cultures and cruise data found that some optical methods of deriving C phyto performed better in the SAZ than others and that regionally derived methods may be unsuitable for application to the Southern Ocean. A comparison of the glider chl-a:C phyto ratios with output from a complex biogeochemical model shows that although a ratio of 0.02 mg chl-a mg C −1 is an acceptable mean for SAZ phytoplankton (in spring-summer), the model misrepresents the seasonal cycle (with decreasing ratios from spring to summer and low sub-seasonal variability). As such, it is recommended that models expand their allowance for variable chl-a:C phyto ratios that not only account for phytoplankton acclimation to low light conditions in spring but also to higher optimal chl-a:C phyto ratios with increasing growth rates in summer.

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Assessing the Variability in the Relationship Between the Particulate Backscattering Coefficient and the Chlorophyll a Concentration From a Global Biogeochemical‐Argo Database

et al. 2018

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Characterizing phytoplankton distribution and dynamics in the world's open oceans requires in situ observations over a broad range of space and time scales. In addition to temperature/salinity measurements, Biogeochemical‐Argo (BGC‐Argo) profiling floats are capable of autonomously observing at high‐frequency bio‐optical properties such as the chlorophyll fluorescence, a proxy of the chlorophyll a concentration (Chla), the particulate backscattering coefficient (bbp), a proxy of the stock of particulate organic carbon, and the light available for photosynthesis. We analyzed an unprecedented BGC‐Argo database of more than 8,500 multivariable profiles collected in various oceanic conditions, from subpolar waters to subtropical gyres. Our objective is to refine previously established Chla versus bbp relationships and gain insights into the sources of vertical, seasonal, and regional variability in this relationship. Despite some regional, seasonal and vertical variations, a general covariation occurs at a global scale. We distinguish two main contrasted situations: (1) concomitant changes in Chla and bbp that correspond to actual variations in phytoplankton biomass, e.g., in subpolar regimes; (2) a decoupling between the two variables attributed to photoacclimation or changes in the relative abundance of nonalgal particles, e.g., in subtropical regimes. The variability in the bbp:Chla ratio in the surface layer appears to be essentially influenced by the type of particles and by photoacclimation processes. The large BGC‐Argo database helps identifying the spatial and temporal scales at which this ratio is predominantly driven by one or the other of these two factors.

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Influence of photoacclimation on the phytoplankton seasonal cycle in the Mediterranean Sea as seen by satellite

Cited by 48 publications

References 63 publications

Seasonal development of iron limitation in the sub-Antarctic zone

Seasonal development of iron limitation in the sub-Antarctic zone

Using Optical Sensors on Gliders to Estimate Phytoplankton Carbon Concentrations and Chlorophyll-to-Carbon Ratios in the Southern Ocean

Assessing the Variability in the Relationship Between the Particulate Backscattering Coefficient and the Chlorophyll a Concentration From a Global Biogeochemical‐Argo Database

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