Aggregation and Sedimentation of Thalassiosira weissflogii (diatom) in a Warmer and More Acidified Future Ocean

Abstract

Increasing Transparent Exopolymer Particle (TEP) formation during diatom blooms as a result of elevated temperature and pCO2 have been suggested to result in enhanced aggregation and carbon flux, therewith potentially increasing the sequestration of carbon by the ocean. We present experimental results on TEP and aggregate formation by Thalassiosira weissflogii (diatom) in the presence or absence of bacteria under two temperature and three pCO2 scenarios. During the aggregation phase of the experiment TEP formation was elevated at the higher temperature (20°C vs. 15°C), as predicted. However, in contrast to expectations based on the established relationship between TEP and aggregation, aggregation rates and sinking velocity of aggregates were depressed in warmer treatments, especially under ocean acidification conditions. If our experimental findings can be extrapolated to natural conditions, they would imply a reduction in carbon flux and potentially reduced carbon sequestration after diatom blooms in the future ocean.

Ocean acidification as one of multiple stressors: growth response of Thalassiosira weissflogii (diatom) under temperature and light stress

“…In 109 of our samples, we measured 3 carbonate parameters, pH, TA, and DIC, effectively over-determining the carbonate system; the inconsistencies between pCO 2 concentrations calculated from the over-determined dataset (data not shown) were consistent with those described previously (Hoppe et al 2012, Passow 2012, Seebah et al 2014). The pCO 2 as calculated from TA and DIC was 20−30% lower than that calculated from pH and either TA or DIC (Hoppe et al 2012).…”

“…Briefly, the carbonate system of the collected seawater (TA media = 2370 µmol kg −1 , pH Tmedia = 7.99) was altered chemically by adding appropriate amounts of HCl, NaHCO 3 , and Na 2 CO 3 . This type of perturbation leads to a carbonate chemistry identical to the chemistry produced by bubbling with pCO 2 -enriched gas, but avoids artifacts like TEP formation that are caused by bubbling (Passow 2012, Seebah et al 2014, Taucher et al 2015. At the beginning of each experiment, one batch of medium was prepared and divided between the 4 replicates.…”

“…Cell quotas and stoichiometry may vary widely as a function of light, temperature, and nutrient availabilities; for example, cellular POC content, even within the same strain of Thalassiosira weissflogii (CCP 1336), may differ by a factor of 3 or more (between 80−228 pg C cell −1 ) depending on growth conditions (Ho et al 2003, Price 2005, Finkel et al 2006, Liu et al 2011. The abiotic production of transparent exopolymer particles (TEP) from dissolved precursors released by diatoms (Passow 2000) likewise varies as a function of nutrients, light, or temperature (Corzo et al 2000, Engel et al 2004, Piontek et al 2009, Fukao et al 2012, Seebah et al 2014, Taucher et al 2015.…”

Introduction to the project VAHINE: VAriability of vertical and tropHIc transfer of diazotroph derived N in the south wEst Pacific

“…It was highest for NO − 3 concentrations (42 %), which is consistent with the fact that NO − 3 concentrations were close to quantification limits of conventional methods (∼ 0.05 µmol L −1 ) during the 23-day experiment: when the mean value is close to 0, the CV approaches infinity and is therefore sensitive to small changes in the mean. For flux measurements of primary production (PP), bacterial production (BP) and N 2 fixation, the CVs were 29, 26 and 34 %, respectively, which is also satisfactory given the natural spatial heterogeneity of plankton in the environment due to aggregation (Seebah et al, 2014) or to the buoyancy of some diazotrophs, such as Trichodesmium (Capone et al, 1997), which introduces spatial variability, well known in the natural environment for N 2 fixation (Bombar et al, 2015).…”

Identification of Bacterial Genes Expressed During Diatom-Bacteria Interactions Using an in Vivo Expression Technology Approach

“…The corresponding mutants showed a reduced attachment to live diatoms suggesting that chemotaxis is a substantial initial step for the interaction. The co-culture model system was further used to assess the impact of temperature and acidification on aggregate formation demonstrating that aggregation rates and sinking velocities decrease in warmer and more acidified seawater (Seebah et al, 2014). In order to get first hints on gene products potentially important for the interaction, a proteomics analysis of HP15 in response to the diatom was conducted (Stahl and Ullrich, 2016) suggesting a distinct nutrient supply for M. adhaerens during co-cultivation.…”