Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling

Abstract

Seawater concentrations of the climatecooling, volatile sulphur compound dimethylsulphide (DMS) are the result of numerous production and consumption processes within the marine ecosystem. Due to this complex nature, it is difficult to predict temporal and geographical distribution patterns of DMS concentrations and the inclusion of DMS into global ocean climate models has only been attempted recently. Comparisons between individual model predictions, and ground-truthing exercises revealed that information on the functional relationships between physical and chemical ecosystem parameters, biological productivity and the production and consumption of DMS and its precursor dimethylsulphoniopropionate (DMSP) is necessary to further refine future climate models. In this review an attempt is made to quantify these functional relationships. The description of processes includes: (1) parameters controlling DMSP production such as species composition and abiotic factors; (2) the conversion of DMSP to DMS by algal and bacterial enzymes; (3) the fate of DMSPsulphur due to, e.g., grazing, microbial consumption and sedimentation and (4) factors controlling DMS removal from the water column such as microbial consumption, photo-oxidation and emission to the atmosphere. We recommend the differentiation of six phytoplankton groups for inclusion in future models: eukaryotic and prokaryotic picoplankton, diatoms, dinoflagellates, and other phytoflagellates with and without DMSP-lyase activity. These functional groups are characterised by their cell size, DMSP content, DMSP-lyase activity and interactions with herbivorous grazers. In this review, emphasis is given to ecosystems dominated by the globally relevant haptophytes Emiliania huxleyi and Phaeocystis sp., which are important DMS and DMSP producers.

Annual cycle of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) related to phytoplankton succession in the Southern North Sea

“…These results ware in accordance with measurements made on a few key-species of the studied area in batch cultures and with the data compiled by Keller et al (1989) and Stefels et al (2007) (Table 2). As a general pattern, diatoms were on average characterized by a DMSPp:Chl-a around 4 ± 6 mmolS gChl-a − 1 (Table 2; Stefels et al, 2007). However, some species such as Skeletonema costatum blooming in early spring in the area has a higher DMSP quota.…”

“…5d) followed the same pattern than DMSP with spatially averaged concentration of 180 nmol L − 1 in May (with local maximum up to 250 nmol L − 1 ). The timing of the DMS peak was closely linked to the DMSP peak suggesting that DMS was formed from the transformation (cleavage) of DMSP (mainly during the Phaeocystis bloom), a typical interpretation of seasonal DMS(P) cycles (Kwint and Kramer, 1996), in line with the general understanding of DMSP-DMS dynamics (Stefels et al, 2007), based for instance on the study of sulfur isotopes of DMSP and DMS (Kiene and Linn, 2000b). Phaeocystis is known for its high DMSP production (Keller et al, 1989) and DMSP-lyase activity (Stefels et al, 1996) than can cleave DMSP into DMS.…”

“…DMSPp:Chl-a ratio from Keller et al (1989) were re-calculated from DMSP:C ratio assuming an average C:Chl-a of 60 (g:g) for all species. Stefels et al (2007) a Indicates cultures growing in K-medium instead of F/2 North Sea-medium.…”

“…DMS emissions depend directly on surface water DMS concentration which is regulated by marine microorganisms and abiotic processes such as photo-oxidation. When released in the water through exudation, lysis of senescent cells, grazing or viral attack, DMSP and DMSO are involved in a complex chain of phytoplanktonic and bacterial processes leading, among others, to their transformation into DMS (Stefels et al, 2007). Although DMSP and DMSO are produced by phytoplankton, correlating DMS production with phytoplankton biomass (generally expressed in term of Chlorophyll a) is challenging (Kettle et al, 1999) because DMSP and DMSO production are species-specific and vary with environmental conditions (e.g.…”

“…Although DMSP and DMSO are produced by phytoplankton, correlating DMS production with phytoplankton biomass (generally expressed in term of Chlorophyll a) is challenging (Kettle et al, 1999) because DMSP and DMSO production are species-specific and vary with environmental conditions (e.g. Stefels et al, 2007). Therefore, DMS concentration in seawater is ⁎ Corresponding author.…”