Bacterial profiles in Amazon Fan sediments, Sites 934 and 940

Abstract

Bacterial populations were quantified at two Ocean Drilling Program (ODP) Leg 155 sites in the Amazon Fan system to depths of 108 and 245 meters below seafloor (mbsf) in water depths of ~3400 and 3200 m, respectively. Bacteria were present in all samples, and populations decreased gradually with depth. However, divided/dividing cells were absent in some samples below 70 mbsf. Sediment accumulation rates in the Amazon Fan periodically have been very rapid (to 25 m/k.y.), and the structure of the sediment at both sites was dominated by turbidites, debris flows, and levee slumps. Bacterial profiles at both sites indicated that bacterial populations could be related to changes in the lithostratigraphy. Zones of frequent, small turbidites coupled with bioturbation and zones of massive mud flows or slumps were generally associated with unusually constant bacterial profiles. Conversely, outside these zones where sedimentary input was more dominated by material from the water column, the expected gradual decrease in bacterial populations with depth was observed. A particularly striking change was a strongly positive increase (× 3.7) of bacterial numbers (P << 0.001) coincident with sediment layers rich in plant remains and wood fragments between 17 and 26 mbsf at Site 934. Despite this, the overall profiles conformed to a bacterial depth distribution derived from other ODP sites (exclusively from the Pacific Ocean) indicating that deep bacterial populations are characteristic of all marine sediment. A few tens of centimeters of sediment have accumulated since the fan has been inactive, and near-surface bacterial populations (5.6 − 6.0 × 10 8 cells/cm 3 ) are consistent with a trend in near-surface populations with varying water depth observed at Pacific Ocean sites.

The response of bacterial populations to sapropels in deep sediments of the Eastern Mediterranean (Site 969)

“…The total bacterial population profile agrees with a general profile, almost exclusively derived from Pacific Ocean sites, previously calculated by Parkes et al (1994;Fig. 3), and since augmented by Cragg et al (1997), given by the expression:…”

“…Depth distribution of total bacteria (large solid circles) from Eastern Mediterranean Hole 969B, compared to the distributions of bacterial populations (n = 550) with depth at 15 other sites from seven ODP legs (small solid circles). Heavy slanting dashed lines represent the 95% prediction limits for the regression line given by the equation: Log 10 bacterial numbers = 7.94 − 0.64 × Log 10 depth (m), from Cragg et al (1997).…”

“…The presence of a deep bacterial biosphere in marine sediments has now been confirmed by a large amount of work, primarily on Ocean Drilling Program (ODP) sediments (Whelan et al, 1986;Tarafa et al, 1987;Parkes et al, 1990Parkes et al, , 1993Parkes et al, , 1994Parkes et al, , 1995Cragg et al, 1990Cragg et al, , 1992Cragg et al, , 1995aCragg et al, , 1995bCragg et al, , 1996Cragg et al, , 1997Cragg and Parkes 1994;Cragg and Kemp, 1995), and recent work indicates a bacterial presence in basaltic basement rocks (Furnes et al, 1996;Giovannoni et al, 1996). The depth profile of sediment bacteria is remarkably consistent across different oceans and shows population sizes of ~9 × 10 8 cells/cm 3 at the near surface decreasing exponentially to ~1.5 × 10 6 cells/cm 3 at 500 mbsf.…”

PEaCH4 v.2.0: A modelling platform to predict early diagenetic processes in marine sediments with a focus on biogenic methane – Case study: Offshore Namibia

“…In contrast to PeaCH 4 v.2.0, it lacks the option to calculate the early diagenetic formation of biogenic methane in the upper few hundred metres of marine sediments. Hence, this approach neglects that organic matter conversion predominates over the upper few hundred metres of marine sediments (e.g., Westrich and Berne (1984), Middelburg (1989), Parkes et al (1994), Cragg et al (1996), Cragg et al (1997) and Lipp et al (2008)). Further, biogeochemical reactions, interactions between minerals and fluids, and the corresponding changing chemical equilibriums are not integral parts of Biogenix.…”

Integration of Biodegradation and Migration of Hydrocarbons in a 2d Petroleum Systems Model: Application to the Potiguar Basin, Ne Brazil

“…(ii) Density of the microbial population Cragg et al (1999) derived a law describing the density of microbial populations from ODP data (e.g. Cragg et al, 1997;Parkes et al, 2000): Log 10 (bacterial number) = 7.95-0.64 Log 10 (depth in m) (2) In order to determine the evolution of the microbial population, it was assumed that micro-organisms are confined to the oil-water interface. A simple model of the rock micro-structure was used in which pores are represented by spheres, and where the number of pores per unit of solid volume depends on the lithology and remains constant during burial.…”