Bacterial response to contrasting sediment geochemistry in the Central Indian Basin

Abstract

In order to investigate whether geochemical, physiographic and lithological differences in two end-member sedimentary settings could evoke varied microbe-sediment interactions, two 25 cm long sediment cores from contrasting regions in the Central Indian Basin have been examined. Site TVBC 26 in the northern siliceous realm (10°S, 75AE5°E) is organic-C rich with 0AE3 ± 0AE09% total organic carbon. Site TVBC 08 in the southern pelagic red clay realm (16°S, 75AE5°E), located on the flank of a seamount in a mid-plate volcanic area with hydrothermal alterations of recent origin, is organic-C poor (0AE1 ± 0AE07%). Significantly higher bacterial viability under anaerobic conditions, generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones, characterize core TVBC 26. In the carbon-poor environment of core TVBC 08, a doubling of the 14 C uptake, a 250 times increase in the number of autotrophic nitrifiers, a four-fold lowering in the number of aerobic sulphur oxidizers and a higher order of denitrifiers exists when compared with core TVBC 26; this suggests the prevalence of a potentially autotrophic microbial community in core TVBC 08 in response to hydrothermal activity. Microbial activity at the northern TVBC 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tan-green mottled zones. The southern TVBC 08 is autotrophic with increased heterotrophic activity in the deepest layers. Notably, the bacterial activity is generally dependent on the surface productivity in TVBC 26, the carbon-rich core, and mostly independent in TVBC 08, the carbon-poor, hydrothermally influenced core. The northern sediment is more organic sink-controlled and the southern sediment is more hydrothermal source-controlled. Hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep-sea sediments. Thus, this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial responses in the Central Indian Basin sediments.

Distribution and Diagenesis of Phosphorus in the Deep‐Sea Sediments of the Central Indian Basin

“…High biological productivity leads to enhanced fish production and enrichment of biogenic apatite in this area. Relatively low values of P bio associated with pelagic red clays are due to lower productivity in the overlying waters (30 to 50 mg·C·m −2 ·day −1 corresponding to 10.95 to 18 g·C·m −2 ·year −1 ; Prabhu Matondkar et al, ; A. Das, Fernandes, et al, ). The ammonium chloride leach used to determine P bio can also extract loosely adsorbed fraction (Schenau & De Lange, ).…”

“…Among them, organic matter degradation and reduction of iron oxyhydroxides are major processes that affect the porewater DIP concentration (e.g., Ingall & Jahnke, ; Slomp et al, ). However, the deep sea environments are characterized by a low input of photosynthetically produced organic matter (e.g., A. Das, Fernandes, et al, ; Nath et al, ; Suess et al, ). Most of the organic matter degradation occurs during its transport through the water column and deep‐sea sediments receive only ~1–5% of the organic matter exported from surface waters (e.g., Broecker & Peng, ).…”

Immobilisation of manganese, cobalt and nickel by deep-sea-sediment microbial communities

“…Modified from Mascarenhas-Pereira et al [19]. environment is more oxidising [20] and is known for the slower rate of sediment deposition [21]. The formation and dissolution of authigenic (oxyhydr)oxides of Fe and Mn influence the cycling of trace metals in oxic/sub-oxic surface sediments [23].…”

“…The region for box core (BC) 26 is located at 10 • S latitude and 75.5 • E longitude in the northern region of the ocean. The sampling site has a water depth of 5339 m, the environment is relatively less oxidising [20] and receives more clay from rivers [21,22]. BC36 is located at the southern region of the basin at 16 • S latitude and 75.5 • E longitude.…”

Dynamics of formation of ferromanganese nodules in the Indian Ocean

“…As nodule formation requires undisturbed bottom conditions, a low sedimentation regime (Piper and Williamson, 1977), low bottom water currents (Glasby et al, 1982), the formation of nodules is supported by the abundance of aerobic/anaerobic bacteria (Das et al, 2005). It is important to note that the equatorial part of the CIOB is practically devoid of nodules, which may well be due to higher rate of terrigenous sedimentation thereby inhibiting nodule growth.…”