Scratching Beneath the Surface: A Model to Predict the Vertical Distribution of Prochlorococcus Using Remote Sensing

Abstract

Abstract:The unicellular cyanobacterium Prochlorococcus is the most dominant resident of the subtropical gyres, which are considered to be the largest biomes on earth. In this study, the spatial and temporal variability in the global distribution of Prochlorococcus was estimated in the Atlantic Ocean using an empirical model based on data from 13 Atlantic Meridional Transect cruises. Our model uses satellite-derived sea surface temperature (SST), remote-sensing reflectance at 443 and 488 nm, and the water temperature at a depth of 200 m from Argo data. The model divides the population of Prochlorococcus into two groups: ProI, which dominates under high-light conditions associated with the surface, and ProII, which favors low light found near the deep chlorophyll maximum. ProI and ProII are then summed to provide vertical profiles of the concentration of Prochlorococcus cells. This model predicts that Prochlorococcus cells contribute 32 Mt of carbon biomass (7.4 × 10 26 cells) to the Atlantic Ocean, concentrated mainly within the subtropical gyres (35%) and areas near the Equatorial Convergence Zone (30%). When projected globally, 3.4 × 10 27 Prochlorococcus cells represent 171 Mt of carbon biomass, with 43% of this global biomass allocated to the upper ocean (0-45 m depth). Annual cell standing stocks were relatively stable between the years 2003 and 2014, and the contribution of the gyres varies seasonally as gyres expand and contract, tracking changes in light and temperature, with lowest cell abundances during the boreal and austral winter (1.4 × 10 13 cells m −2 ), when surface cell concentrations were highest (9.8 × 10 4 cells mL −1 ), whereas the opposite scenario was observed in spring-summer (2 × 10 13 cells m −2 ). This model provides a three-dimensional view of the abundance of Prochlorococcus cells, revealing that Prochlorococcus contributes significantly to total phytoplankton biomass in the Atlantic Ocean, and can be applied using either in situ measurements at the sea surface (r 2 = 0.83) or remote-sensing observables (r 2 = 0.58).

Dynamics of Prochlorococcus Diversity and Photoacclimation During Short-Term Shifts in Water Column Stratification at Station ALOHA

“…HL ecotypes were able to express chlorophyll at similar levels as LL ecotypes in order to photoacclimate to low light intensities, demonstrating a physiological plasticity that was unexpected based on previously published laboratory experiments. These results emphasize the importance of incorporating the process of photoacclimation into prediction of phytoplankton biomass from chlorophyll concentrations (Behrenfeld et al, 2016;Lange et al, 2018;Morozov and Tang, 2018), as we show that chlorophyll properties of the subtropical ocean's dominant phototroph are highly dynamic in space and time.…”

“…The dim and bright populations are reminiscent of the HL/LL ecotype dichotomy but their genetic identity has not been directly linked to their in situ chlorophyll physiology, despite the many studies of Prochlorococcus ecotype distribution mentioned above. The relationships between Prochlorococcus chlorophyll concentration in situ, ecotype community structure, and productivity remain unknown but is critical for measuring and modeling Prochlorococcus contributions to global cycles under different oceanic scenarios (Follows et al, 2007;Lange et al, 2018;Morozov and Tang, 2018).…”

Widespread methane formation byCyanobacteriain aquatic and terrestrial ecosystems

“…This study does not account for the increase in blooms of toxic and non-toxic cyanobacteria in freshwater systems (Bowling, Blais, & Sinotte, 2015; Glibert, Maranger, Sobota, & Bouwman, 2014; Huisman et al, 2018; Paerl & Huisman, 2008; Visser et al, 2016), nor for less monitored cyanobacterial environments such under the ice-cover of frozen lakes (Bižić-Ionescu, Amann, & Grossart, 2014). Recent evaluations of Prochlorococcus (Lange et al, 2018) suggest a global biomass larger by 33 % than estimated in 2003 by Garcia-Pichel et al . Second, while our experiments demonstrate inarguably the ability of Cyanobacteria to produce CH 4 independent of external substrates, as well as to transfer fixed CO 2 to CH 4 under laboratory conditions, we cannot account for the effect of nutrients concentrations and light quality in the natural environment.…”

“…Due to their small size, conversion of CH 4 production rates of picophytoplankton to µmol g −1 h −1 results in values exceeding those of methanogenic Archaea . Nevertheless, to obtain 1 g of Prochlorococcus cells one would need to integrate 0.1-10 m 2 over a depth of 200 m (Lange et al, 2018) as compared to ca. 20 Kg of soil for methanogenic Archaea (assuming 10 9 cells per g sediment of which 50 % are methanogens).…”

“…MIT9312, MIT0604 and MED4 averaging at 0.4 µmol CH 4 h −1 10 −6 cells. Based on recent estimates of Prochlorococcus abundances (Lange et al, 2018) the standing stock global surface communities were estimated to consist of 2.48×10 19 cells (out of a total of 3.4×10 27 ). When taken together, these numbers result in a potential production by global surface Prochlorococcus communities of 1.39 Tg CH 4 y −1 .…”