Effects of increased pCO2 and temperature on the North Atlantic spring bloom. III. Dimethylsulfoniopropionate

Abstract

The CLAW hypothesis argues that a negative feedback mechanism involving phytoplankton-derived dimethylsulfoniopropionate (DMSP) could mitigate increasing sea surface temperatures that result from global warming. DMSP is converted to the climatically active dimethylsulfide (DMS), which is transferred to the atmosphere and photochemically oxidized to sulfate aerosols, leading to increases in planetary albedo and cooling of the Earth's atmosphere. A shipboard incubation experiment was conducted to investigate the effects of increased temperature and pCO 2 on the algal community structure of the North Atlantic spring bloom and their subsequent impact on particulate and dissolved DMSP concentrations (DMSP p and DMSP d ). Under 'greenhouse' conditions (elevated pCO 2 ; 690 ppm) and elevated temperature (ambient + 4°C), coccolithophorid and pelagophyte abundances were significantly higher than under control conditions (390 ppm CO 2 and ambient temperature). This shift in phytoplankton community structure also resulted in an increase in DMSP p concentrations and DMSP p :chl a ratios. There were also increases in DMSP-lyase activity and biomass-normalized DMSP-lyase activity under 'greenhouse' conditions. Concentrations of DMSP d decreased in the 'greenhouse' treatment relative to the control. This decline is thought to be partly due to changes in the microzooplankton community structure and decreased grazing pressure under 'greenhouse' conditions. The increases in DMSP p in the high temperature and greenhouse treatments support the CLAW hypothesis; the declines in DMSP d do not.

Effects of increased pCO2 and temperature on the North Atlantic spring bloom. II. Microzooplankton abundance and grazing

“…A significant decrease in dissolved dimethylsulfoniopropionate (DMSP d ) was noted in the greenhouse treatment relative to controls on the final day of the experiment (Lee et al 2009). Microzooplankton grazing has been shown to contribute significantly to DMSP d ; thus, a decline in DMSP d in the greenhouse treatment would also be consistent with reduced microzooplankton grazing in this treatment (Lee et al 2009). Our data suggest that the initial increased grazing pressure observed in the greenhouse treatment may have opened the door for growth of unpalatable phytoplankton taxa, resulting in overall net gains for the phytoplankton community in this treatment.…”

“…Coccolithophores such as Emiliania huxleyi have been hypothesized to produce chemicals reducing microzooplankton grazing rates according to previous field-and laboratory-based studies (Wolfe et al 1997, Olson & Strom 2002, Strom et al 2003, which would be consistent with our results. A significant decrease in dissolved dimethylsulfoniopropionate (DMSP d ) was noted in the greenhouse treatment relative to controls on the final day of the experiment (Lee et al 2009). Microzooplankton grazing has been shown to contribute significantly to DMSP d ; thus, a decline in DMSP d in the greenhouse treatment would also be consistent with reduced microzooplankton grazing in this treatment (Lee et al 2009).…”

“…The phytoplankton group that dominated the microphytoplankton community at the end of the experiment was a coccolithophore, based on microscopic counts (Feng et al 2009). Additionally, the pigment data and DMSP p concentrations from the total phytoplankton community indicate that the phytoplankton community as a whole was also dominated by coccolithophores, suggesting that there was also a strong coccolithophore component to the nanoplankton size class (Feng et al 2009, Lee et al 2009). Coccolithophores such as Emiliania huxleyi have been hypothesized to produce chemicals reducing microzooplankton grazing rates according to previous field-and laboratory-based studies (Wolfe et al 1997, Olson & Strom 2002, Strom et al 2003, which would be consistent with our results.…”

Distribution of calcifying and silicifying phytoplankton in relation to environmental and biogeochemical parameters during the late stages of the 2005 North East Atlantic Spring Bloom

“…Further studies need to elucidate the net contribution of diatoms and coccolithophores to C export through a better quantification of the relative impact of processes such as grazing, TEP production, flocculation events and passive sinking. Finally, a challenge will be to understand how the dynamics of the North Atlantic Bloom will respond to future changes in climate forcing, a question that was addressed during our study by parallel experiments examining the response of the same NAB communities sampled here to increasing pCO 2 and temperature Lee et al, 2009;Rose et al, 2009). …”

“…The South-North transect was initially intended to track the 20 • W meridian but included several deviations in order to follow real-time satellite information locating major coccolithophore blooms and calcite patches. Ship-board CO 2 , temperature and nutrient perturbation experiments accompanied the field measurements presented here (companion papers Rose et al, 2009;Lee et al, 2009;Benner et al, 2009). …”