Chemosynthetic activity prevails in deep-sea sediments of the Central Indian Basin

Abstract

It is hypothesized that in the deep-sea, under psychrophilic, barophilic and oligotrophic conditions, microbial community of Central Indian Basin (CIB) sediments could be chemosynthetic. In the dark, at near ambient temperature, 4 ± 2°C, 500 atm pressure, pelagic red clay could fix carbon at rates ranging from 100 to 500 nmol C g(-1) dry wt day(-1). These clays accumulate in the deepest and the most remote areas of the ocean and contain <30% biogenic material. These clays with volcanic signatures fixed 230-9,401 nmol C g(-1) dry wt day(-1) while siliceous radiolarian oozes of the basin fixed only 5-45 nmol C g(-1) dry wt day(-1). These rates are comparable to those of white smoker waters and are 1-4 orders of magnitude less than those of bacterial mats and active vents recorded at other localities worldwide. The experimental ratios of carbon fixation to metal oxidation in the sediments were 0-1 order of magnitude higher than the corresponding average theoretical ratio of 0.0215 (0.0218, 0.0222, 0.0207 and 0.0211 for Fe, Mn, Co and Ni, respectively) in the siliceous ooze. In case of pelagic red clay it was 0-2 orders higher than theoretical ratio. Thus, chemosynthetic activity could be more widespread, albeit at low rates, than previously considered for abyssal basins. These environments may be dependent partially or even wholly on in situ microbial primary production for their carbon requirements rather than on photosynthetically derived detritus from surface waters.

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

“…Chemosynthetic activity was reported earlier in this site (A. Das, Sujith, et al, ). Chemosynthetic bacteria use chemical energy to produce biomass and such microbial processes were reported earlier at the hydrothermal vent of Loihi seamount (Karl et al, ), an intraplate region such as in the CIB.…”

“…The oxygenated bottom water of the CIB promotes the adsorption of P onto the surface of iron oxyhydroxides. The distribution of P Fe (Figure ) and total Fe (Figure S4) indicates that the concentration increases toward the southern part of the basin, where pelagic red clays are dominant and the sediments from this region bear the signature of hydrothermal activity (A. Das, Sujith, et al, ; Iyer et al, ; Mascarenhas‐Pereira & Nath, ; Nath et al, ). This influence of hydrothermal activity results in the enrichment of Fe in the pelagic region.…”

“…Furthermore, in this location, a doubling of 14 C uptake, a 250 times increase in the number of autotrophic nitrifiers, a fourfold lowering in the number of aerobic sulfur oxidizers and a higher order of denitrifiers were found when compared to the northern CIB. These were attributed to the prevalence of a potentially autotrophic microbial community in response to hydrothermal activity (A. Das, Sujith, et al, ). Thus, the highest P total content observed at location AA/8 may be related to hydrothermal activity.…”

State of Knowledge of Coastal and Marine Biodiversity of Indian Ocean Countries

“…What is more interesting is the likelihood that the deep ocean oligotrophic sediments have retained their chemosynthetic potential: at 1 atm (0.1013 MPa) and at 5°C, the siliceous oozes of CIOB fixed 5–45 nmol C (g dry wt) −1 d −1 and red clay with volcanic signatures fixed 230–9,401 nmol C (g dry wt) −1 d −1 [50]. The rate of carbon fixation in CIOB sediments thus is comparable to that in white smoker waters and one to four orders of magnitude less than that of bacterial mats and active vents.…”

Depositional environment of the surface sediments in Central Indian Basin (CIB), Indian Ocean, between 8°–18°S latitude and 72°–79°E longitude, based on their geochemical characteristics

“…On the other hand, Banakar, Parthiban, Pattan, and Jauhari (1998) mentioned that the lysocline and CCD in the CIB area lies within 4400-4700 m of water depth. The total organic carbon content of the CIB sediments vary from <0.05% to 1.54%, while their total inorganic carbon content vary from below detection limit up to 10% in calcareous oozes (Das, Sujith, Mourya, Biche, & LokaBharathi, 2011;Gupta & Jauhari, 1994). A major part of this total inorganic carbon comes from the dissolution of the calcareous test of marine planktons such as coccoliths and forams.…”