Size distribution of dimethylsulfoniopropionate (DMSP) in areas of the tropical northeastern Atlantic Ocean and the Mediterranean Sea

Abstract

Size fractionation of dimethylsulfoniopropionate (DMSP) was carried out in 2 areas of the Mediterranean Sea and 2 areas of the tropical northeastern Atlantic Ocean. In the Mediterranean Sea, particles in the size range 10–200 μm collected 15 m deep accounted for 16.0 ± 4.6% and 39% of total particulate DMSP off Villefranche/Mer and off Banyuls/Mer, respectively. In the Atlantic Ocean, the study of the vertical size distribution of particulate DMSP revealed that DMSP containing particles in the size range 10–200 μm tend to accumulate at the pycnocline and accounted for 26.0 ± 7.2% and 36.3 ± 11.6% of total particulate DMSP at sites 18°30′N, 21°W and 21°N, 31°W, respectively. Although particulate DMSP in mixed layer waters of the tropical northeastern Atlantic Ocean was carried mainly by particles in the size range 0.7–10 μm, no significant correlation was found between concentration of dissolved compounds (dissolved DMSP + DMS in samples filtered through GF/F filters) and this DMSP fraction. Dissolved DMSP + DMS levels were significantly correlated ( r 2 = 0.33, n = 24, P = 0.002) only with levels of particulate DMSP in the size range 10–200 μm. Since particulate DMSP in the size range 10–200 μm appeared not to be associated with microphytoplanktonic populations (diatoms and dinoflagellates), it is suggested that some heterotrophic organisms (microzooplankton) and/or detrital microscopic material (aggregates, fecal pellets) could play a key role in controlling the concentrations of dissolved DMSP and DMS in these waters. Depth profiles of DMSP levels in the size range 0.7–10 μm revealed that DMSP covaried with diadinoxanthin and zeaxanthin, two nonphotosynthetic carotenoids with photoprotective properties. This result provides the first in-situ indication of light-dependent DMSP accumulation in nannophytoplankton (most likely prymnesiophytes) and prochlorophytes.