Variability in sulfur isotope composition suggests unique dimethylsulfoniopropionate cycling and microalgae metabolism in Antarctic sea ice

Abstract

Sea ice microbial communities produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), a precursor of the climate cooling gas dimethylsulfide. Despite their importance to the polar sulfur cycle, drivers and metabolic pathways of sea ice DMSP are uncertain. Here we report the first measurements of sea ice DMSP sulfur isotopic composition (34S/32S ratio, δ34S). δ34S values in ice cores from the Ross Sea and Weddell Sea reveal considerable variability across seasons and between ice horizons (from +10.6 to +23.6‰). We discuss how the most extreme δ34S values observed could be related to unique DMSP cycling in the seasonally extreme physiochemical conditions of isolated brine inclusions in winter-spring. Using cell cultures, we show that part of the DMSP δ34S variability could be explained by distinct DMSP metabolism in sea ice microalgae. These findings advance our understanding of the sea ice sulfur cycle and metabolic adaptations of microbes in extreme environments.

Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle

“…Because the δ 34 S values of st-, vl-, and anth-SO 4 2− are mutually overlapping, we designated them as nonmarine biogenic sources and assumed δ 34 S nmb values as their sum (0 to 5‰) 35–37 . Since these δ 34 S nmb values are distinguishable from the possible range of δ 34 S mb values (16.6 to 20.3‰) 38–40 , the f mb and f nmb can be estimated by Eqs (4) and (5), with the assumption of mixing of the two endmembers. Note that it has been recently observed that biologically produced dimethylsulfoniopropionate (DMSP) in Antarctic sea ice possesses δ 34 S values largely ranging from 10.6 to 23.6‰, whose lowest values were observed in only the extreme physiochemical conditions of isolated brine pockets 40 .…”

“…Since these δ 34 S nmb values are distinguishable from the possible range of δ 34 S mb values (16.6 to 20.3‰) 38–40 , the f mb and f nmb can be estimated by Eqs (4) and (5), with the assumption of mixing of the two endmembers. Note that it has been recently observed that biologically produced dimethylsulfoniopropionate (DMSP) in Antarctic sea ice possesses δ 34 S values largely ranging from 10.6 to 23.6‰, whose lowest values were observed in only the extreme physiochemical conditions of isolated brine pockets 40 . However, given that such low δ 34 S values are spatially limited and that the mean δ 34 S value of DMSP for the corresponding sea ice core sample was 17‰ 40 , this sulfur source is unlikely to go beyond the range of general δ 34 S values of mb-SO 4 2− .…”

“…Note that it has been recently observed that biologically produced dimethylsulfoniopropionate (DMSP) in Antarctic sea ice possesses δ 34 S values largely ranging from 10.6 to 23.6‰, whose lowest values were observed in only the extreme physiochemical conditions of isolated brine pockets 40 . However, given that such low δ 34 S values are spatially limited and that the mean δ 34 S value of DMSP for the corresponding sea ice core sample was 17‰ 40 , this sulfur source is unlikely to go beyond the range of general δ 34 S values of mb-SO 4 2− . The selection of δ 34 S i values of each source and the validity of the assumption are discussed in detail in the Supplementary Information.…”

Sea Ice CO2 Dynamics Across Seasons: Impact of Processes at the Interfaces

“…Ice cores, snow and seawater samples were collected during twelve ice stations. For the sake of consistency with other reports of YROSIAE results (Carnat et al, 2014(Carnat et al, , 2018, each station number, referenced hereafter as YRS#, corresponds to a dedicated sampling date as indicated in Figure 2 and in Table 1. Each time the site was visited, a new sampling square area of 10 m 2 was delimitated next to the sampling site of the previous station in order to minimize the bias from spatial heterogeneity.…”

Response of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) cell quotas to salinity and temperature shifts in the sea-ice diatom Fragilariopsis cylindrus

“…The same studies also showed that increase of salinity and decrease of temperature induced a reduced growth but an increased EPS production suggesting the importance of EPS in the acclimation system in sea ice. As part of this acclimation system, DMSP and DMSO pathways of production could also be influenced by the combination of salinity and temperature changes (Carnat et al 2018). DMSP and/or DMSO response to temperature changes could also suggest a cryoprotectant function in the cell as mentioned by Karsten et al (1996).…”