Bacteria are important dimethylsulfoniopropionate producers in marine aphotic and high-pressure environments

Dimethylsulfoniopropionate (DMSP) is an important marine osmolyte. Aphotic environments are only recently being considered as potential contributors to global DMSP production. Here, our Mariana Trench study reveals a typical seawater DMSP/dimethylsulfide (DMS) profile, with highest concentrations in the euphotic zone and decreased but consistent levels below. The genetic potential for bacterial DMSP synthesis via the dsyB gene and its transcription is greater in the deep ocean, and is highest in the sediment.s DMSP catabolic potential is present throughout the trench waters, but is less prominent below 8000 m, perhaps indicating a preference to store DMSP in the deep for stress protection. Deep ocean bacterial isolates show enhanced DMSP production under increased hydrostatic pressure. Furthermore, bacterial dsyB mutants are less tolerant of deep ocean pressures than wild-type strains. Thus, we propose a physiological function for DMSP in hydrostatic pressure protection, and that bacteria are key DMSP producers in deep seawater and sediment

Regulation of algal blooms in Antarctic shelf waters by the release of iron from melting sea ice

During summer 1995-96, we measured iron in the water column and conducted iron-enrichment bottle-incubation experiments at a station in the central Ross Sea (76°30′S, 170°40′W), first, in the presence of melting sea ice, and 17 days later, in ice-free conditions. We observed a striking temporal change in mixed-layer dissolved iron concentrations at this station, from 0.72-2.3 nM with sea ice present, to 0.16-0.17 nM in ice-free conditions. These changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal (diatom) biomass. Our incubation experiments suggest that conditions were ironreplete in the presence of sea ice, and iron-deficient in the absence of sea ice. We surmise that bioavailable iron was released into seawater from the melting sea ice, stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer, until iron-limited conditions developed. These observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production, particularly ice-edge blooms, in seasonally ice-covered Antarctic waters. Copyright 1997 by the American Geophysical Union

Evidence for the regulation of algal blooms in the Southern Ross Sea by the release of iron from melting sea ice

No description availabl

Iron and manganese in the Ross Sea, Antarctica: Seasonal iron limitation in Antarctic shelf waters

© 2000 by the American Geophysical Union.Dissolved iron and manganese and total dissolvable iron were measured in water column samples collected from the polynya region of the southern Ross Sea during cruises in November-December 1994 (spring 1994) and December 1995 to January 1996 (summer 1995). Iron and manganese addition bottle incubation experiments were also performed during these cruises in order to assess the nutritional sufficiency of ambient iron and manganese concentrations for growth of the phytoplankton community. Generally high dissolved iron concentrations (> 0.5 n\f) and relatively complex iron and manganese vertical profiles were obtained during the spring cruise, compared with the summer 1995 data. Dissolved iron concentrations in the upper water column averaged 1.0 nM during spring 1994 and 0.23 nM in summer 1995. excluding two stations where concentrations exceeding 1 nM arc attributed to inputs from melting sea ice. The observed differences in the distribution of iron and manganese between spring 1994 and summer are attributed to seasonal decreases in the upwelling of bottom waters and melting of sea ice, which supply these metals into the upper water column, combined with the cumulative removal of iron and manganese from the water column throughout the spring and summer, due to biological uptake, vertical export and scavenging by suspended and sinking particles. Results of the metal addition bottle incubation experiments indicate that ambient dissolved iron concentrations are adequate for phytoplankton growth requirements during the spring and early summer, when algal production is highest and Phaeocystis antarctica dominates the algal community, whereas low dissolved iron concentrations limit algal community growth later in the summer, except in the stratified, iron-enriched waters near melting sea ice, where diatoms arc able to bloom. Our observations and the inferred seasonal distributions of P. antarctica and diatoms in these waters suggest that iron availability and vertical mixing (i.e., irradiance) exert the primary controls on phytoplankton growth and community structure in the southern Ross Sea during the spring and summer