In:
Biogeosciences, Copernicus GmbH, Vol. 18, No. 18 ( 2021-09-23), p. 5203-5222
Abstract:
Abstract. Marine sedimentation rate and bottom-water O2 concentration control
organic carbon remineralization and sequestration across continental margins,
but whether and how they shape microbiome architecture (the ultimate effector
of all biogeochemical phenomena) across shelf and slope sediments is still
unclear. Here we reveal distinct microbiome structures and functions, amidst
comparable pore fluid chemistries, along 300 cm sediment horizons underlying
the seasonal (shallow coastal; water depth: 31 m) and perennial (deep sea; water depths: 530 and 580 m) oxygen minimum zones
(OMZs) of the Arabian Sea, situated across the western Indian margin. The sedimentary
geomicrobiology was elucidated by analyzing metagenomes, metatranscriptomes,
enrichment cultures, and depositional rates measured via radiocarbon and
lead excess dating; the findings were then evaluated in light of the
other geochemical data available for the cores. Along the perennial-OMZ sediment cores, microbial communities were dominated by
Gammaproteobacteria and Alphaproteobacteria, but in the seasonal-OMZ core communities were dominated by Euryarchaeota and Firmicutes. As a perennial-OMZ signature, a cryptic
methane production–consumption cycle was found to operate near the
sediment surface, within the sulfate reduction zone; overall diversity, as
well as the relative abundances of anaerobes requiring simple fatty acids
(methanogens, anaerobic methane oxidizers, sulfate reducers, and acetogens),
peaked in the topmost sediment layer and then declined via synchronized
fluctuations until the sulfate–methane transition zone was reached. The
microbiome profile was completely reversed in the seasonal-OMZ sediment
horizon. In the perennial-OMZ sediments, deposited organic carbon was higher
in concentration and rich in marine components that degrade readily to
simple fatty acids; simultaneously, lower sedimentation rate afforded higher
O2 exposure time for organic matter degradation despite perennial
hypoxia in the bottom water. The resultant abundance of reduced carbon
substrates eventually sustained multiple inter-competing microbial processes
in the upper sediment layers. The entire geomicrobial scenario was opposite
in the sediments of the seasonal OMZ. These findings create a
microbiological baseline for understanding carbon–sulfur cycling in distinct
depositional settings and water column oxygenation regimes across the
continental margins.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-18-5203-2021
DOI:
10.5194/bg-18-5203-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2158181-2
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