How Well Does Chlorophyll Explain the Seasonal Variation in Phytoplankton Activity?

Abstract

The seasonal variation in phytoplankton activity is determined by analysing 1385 primary production (PP) profiles, chlorophyll a (Chl) concentration profiles and phytoplankton carbon biomass concentrations (C) from the period 1998-2012. The data was collected at six different stations in the Baltic Sea transition zone (BSTZ) which is a location with strong seasonal production patterns with light as the key parameter controlling this productivity. We show that the use of Chl as a proxy for phytoplankton activity strongly overestimates the contribution from the spring production to annual pelagic carbon flow. Spring (February and March) Chl comprised 16-30% of the total annual Chl produced, whereas spring C was much lower (8-23%) compared to the annual C. Spring PP accounted for 10-18% of the total annual PP, while the July-August production contributed 26-33%, i.e. within the time frame when zooplankton biomass and grazing pressure are highest. That is, Chl failed in this study to reflect the importance of the high summer PP. A better proxy for biomass may be C, which correlated well with the seasonal pattern of PP (Pearson correlation, p < 0.05). Thus, this study suggests to account for the strong seasonal pattern in C/Chl ratios when considering carbon flow in coastal systems. Seasonal data for PP were fitted to a simple sinusoidal wave model describing the seasonal distribution of PP in the BSTZ and were proposed to present a better parameterizaton of PP in shallow stratified temperate regions than more commonly applied proxies.

Uncoupling of Seasonal Variations Between Phytoplankton Chlorophyll a and Production in the East China Sea

“…Our results also suggested that the increase of Chl a concentrations preceded the increase of PP rates in coastal waters, but in off‐shelf areas, the seasonal variations of Chl a were completely out of phase with the variations of PP (Figure b). A similar seasonal pattern of Chl a and PP has been observed in the temperate Western English Channel (Xie et al, ), Danish waters (Jakobsen & Markager, ; Lyngsgaard et al, ), and the Cantabrian Sea (Calvo‐Díaz et al, ). In the Western English Channel, although the Chl a concentrations are high in the spring, PP during the spring bloom is limited by the low Chl a ‐normalized production rate of Phaeocystis sp., a reflection of the low temperatures at that time of year (Barnes et al, ; Xie et al, ).…”

“…In the Western English Channel, although the Chl a concentrations are high in the spring, PP during the spring bloom is limited by the low Chl a ‐normalized production rate of Phaeocystis sp., a reflection of the low temperatures at that time of year (Barnes et al, ; Xie et al, ). Lyngsgaard et al () have reported Chl a concentrations in the Baltic Sea transition zone during the spring are higher than at other times of year, whereas C and PP are much lower in spring than in summer. In the southern Bay of Biscay, different seasonality of Chl a and C biomass resulted in a clear temporal pattern of picophytoplanktonic C:Chl a ratios, which ranged from 10 in winter to 140 in summer (Calvo‐Díaz et al, ).…”

“…Our goal was to test the null hypothesis that there are no differences in the seasonal patterns of phytoplankton biomass and PP in the ECS. Our rejection of this hypothesis may reflect a universal phenomenon that is explained mainly by seasonal variations of C:Chla ratios (Behrenfeld et al, 2016;Jakobsen & Markager, 2016) and grazing impacts (Behrenfeld & Boss, 2014;Lyngsgaard et al, 2017). Through this study, we hoped to gain insights into the factors and processes that regulate phytoplankton communities and to better understand the dynamics of continental shelf ecosystems.…”

“…On a global scale, microzooplankton grazing consumes on average 60-80% of daily PP in the ocean (Calbet & Landry, 2004). Long-term results from the Baltic Sea transition zone have clearly shown that grazing rates are maximal during the most productive season (Lyngsgaard et al, 2017). The potential grazing on phytoplankton biomass in this transition zone was~10%/day in the winter, up to >100%/day during the summer, and averaged 54-79%/day of the phytoplankton biomass over the course of a year (Lyngsgaard et al, 2017).…”

Impact of nutrients on photoacclimation of phytoplankton in an oligotrophic lake measured with long-term and high-frequency data: implications for chlorophyll as an estimate of phytoplankton biomass

“…It is difficult to compare these results to other lake systems because few studies have published basic results documenting photoacclimation impacts of low irradiance in freshwater environments (Fahnenstiel & Scavia, 1987;Felip & Catalan, 2000;Fennel & Boss, 2003;Barbiero & Tuchman, 2004;Andrews, 2010;White & Matsumoto, 2012;Kalenak et al, 2013) and even fewer have examined the impact of growth conditions on cellular pigment levels. Knowledge of the world's oceans have benefited greatly from extensive Chl:C measurements as observing and understanding photoacclimation responses in natural ocean conditions has allowed more accurate estimates of global net primary productivity, phytoplankton growth rates, and carbon cycling from readily available chlorophyll sources, including satellite-based radiometers (Behrenfeld et al, 2005, Lyngsgaard et al, 2017. The freshwater community could similarly benefit by pairing chlorophyll readings with an independent measure of biomass (POC, biovolume via microscope, flow cytometry, Cp, Bbp) and characterizing specific physical and chemical conditions that influence Chl:C ratios in a wide and replicated range of lake systems.…”