scholarly journals Carbon processing by the benthic ecosystem and benthic C fixation in methane-rich sediments on the South Georgia margin

2019 ◽  
Vol 31 (2) ◽  
pp. 59-68
Author(s):  
Clare Woulds ◽  
James B. Bell ◽  
Adrian G. Glover ◽  
Steven Bouillon ◽  
Louise S. Brown
Keyword(s):  
Low Temperature ◽  
Organic Carbon ◽  
Sediment Cores ◽  
Active Role ◽  
Community Respiration ◽  
Organic C ◽  
South Georgia ◽  
Deep Site ◽  
Macrofaunal Community ◽  
Carbon Processing

AbstractAs bottom water warms, destabilisation of gas hydrates may increase the extent of methane-rich sediments. The authors present an assessment of organic carbon processing by the benthic community in methane-rich sediments, including one of the first investigations of inorganic C fixation in a non-hydrothermal vent setting. This topic was previously poorly studied, and there is much need to fill the gaps in knowledge of such ecosystems. The authors hypothesized that benthic C fixation would occur, and that a high biomass macrofaunal community would play a substantial role in organic C cycling. Experiments were conducted at a 257 m deep site off South Georgia. Sediment cores were amended with13C and15N labelled algal detritus, or13C labelled bicarbonate solution. In the bicarbonate experiment, labelling of bacteria-specific phospholipid fatty acids provided direct evidence of benthic C fixation, with transfer of fixed C to macrofauna and dissolved organic carbon (DOC). In the algae experiment, macrofauna played an active role in organic carbon cycling. Compared to similar experiments, low temperature supressed the rates of community respiration and macrofaunal C uptake. While benthic C fixation occurred, the biological processing of organic carbon was dominantly controlled by low temperature and high photic zone productivity.

scholarly journals CO<sub>2</sub> and CH<sub>4</sub> fluxes are decoupled from organic carbon loss in drying reservoir sediments

2019 ◽  
Author(s):  
Tricia Light ◽  
Núria Catalán ◽  
Santiago Giralt ◽  
Rafael Marcé
Keyword(s):  
Organic Carbon ◽  
Sediment Cores ◽  
Carbon Mineralization ◽  
Organic Carbon Content ◽  
Co2 Efflux ◽  
Carbon Loss ◽  
Organic C ◽  
Reservoir Sediments ◽  
Organic Carbon Burial ◽  
Organic Carbon Mineralization

Abstract. Reservoirs are a prominent feature of the current global hydrological landscape, and their sediments are the site of extensive organic carbon burial. Meanwhile, reservoirs frequently go dry due to drought and/or water management decisions. Nonetheless, the fate of organic carbon buried in reservoir sediments upon drying is largely unknown. Here, we conducted a 45-day-long laboratory incubation of sediment cores collected from a western Mediterranean reservoir to investigate carbon dynamics in drying sediment. Drying sediment cores emitted more CO2 over the course of the incubation than sediment cores incubated with overlaying water (206.7 ± 47.9 vs. 69.2 ± 18.1 mmol CO2 m−2 day−1, mean ± SE). Organic carbon content at the end of the incubation was lower in drying cores, which suggests that this higher CO2 efflux was due to organic carbon mineralization. However, the apparent rate of organic C reduction in the drying sediments (568.6 ± 247.2 mmol CO2 m−2 day−1, mean ± SE) was higher than C emission. Meanwhile, sediment cores collected from a reservoir area that had already been exposed for 2+ years displayed net CO2 influx from the atmosphere to the sediment (−136.0 ± 27.5 mmol CO2 m−2 day−1, mean ± SE) during the incubation period. Sediment mineralogy suggests that this CO2 influx was caused by a relative increase in calcium carbonate chemical weathering. Thus, we found that while organic carbon decomposition in newly dry reservoir sediment causes measurable organic carbon loss and carbon gas emissions to the atmosphere, other processes can offset these emissions on short time frames and compromise the use of carbon emissions as a proxy for organic carbon mineralization in drying sediments.

scholarly journals Holocene polynya dynamics and their interaction with oceanic heat transport in northernmost Baffin Bay

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rebecca Jackson ◽  
Anna Bang Kvorning ◽  
Audrey Limoges ◽  
Eleanor Georgiadis ◽  
Steffen M. Olsen ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Active Role ◽  
Atlantic Water ◽  
The Arctic ◽  
Negative Consequences ◽  
Baffin Bay ◽  
The North ◽  
North Water ◽  
History Of ◽  
Ocean Conditions

AbstractBaffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.

scholarly journals Late Quaternary paleoenvironment of the Ross Sea continental shelf, Antarctica

1998 ◽  
Vol 27 ◽  
pp. 275-280 ◽  
Author(s):  
Akira Nishimura ◽  
Toru Nakasone ◽  
Chikara Hiramatsu ◽  
Manabu Tanahashi
Keyword(s):  
Organic Carbon ◽  
Marine Environment ◽  
Environmental Changes ◽  
Ross Sea ◽  
Late Quaternary ◽  
Sedimentary Environment ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Accelerator Mass Spectrometer

Based on sedimenlological and micropaleontological work on three sediment cores collected at about 167° Ε in the western Ross Sea, Antarctica, and accelerator mass spectrometer l4C ages of organic carbon, we have reconstructed environmental changes in the area during the late Quaternary. Since 38 ka BP at latest, this area was a marine environment with low productivity. A grounded ice sheet advanced and loaded the sediments before about 30-25 ka BP. After 25 ka BP, the southernmost site (76°46'S) was covered by floating ice (shelf ice), preventing deposition of coarse terrigenous materials and maintaining a supply of diatom tests and organic carbon until 20 ka BP. The northernmost site (74°33'S) was in a marine environment with a moderate productivity influenced by shelf ice/ice sheet after about 20 ka BP. Since about 10 ka BP, a sedimentary environment similar to the present-day one has prevailed over this area.

Long-term effects of fertilisers and organic sources on soil organic carbon fractions under a rice–wheat system in the Indo-Gangetic Plains of north-west India

Soil Research ◽  
2017 ◽  
Vol 55 (3) ◽  
pp. 296 ◽  
Author(s):  
D. Das ◽  
B. S. Dwivedi ◽  
V. K. Singh ◽  
S. P. Datta ◽  
M. C. Meena ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Crop Yields ◽  
Soil Depth ◽  
Farmyard Manure ◽  
Microbial Biomass C ◽  
Gangetic Plain ◽  
Organic C ◽  
Labile C ◽  
Labile C Fractions

Decline in soil organic carbon (SOC) content is considered a key constraint for sustenance of rice–wheat system (RWS) productivity in the Indo-Gangetic Plain region. We, therefore, studied the effects of fertilisers and manures on SOC pools, and their relationships with crop yields after 18 years of continuous RWS. Total organic C increased significantly with the integrated use of fertilisers and organic sources (from 13 to 16.03gkg–1) compared with unfertilised control (11.5gkg–1) or sole fertiliser (NPKZn; 12.17gkg–1) treatment at 0–7.5cm soil depth. Averaged across soil depths, labile fractions like microbial biomass C (MBC) and permanganate-oxidisable C (PmOC) were generally higher in treatments that received farmyard manure (FYM), sulfitation pressmud (SPM) or green gram residue (GR) along with NPK fertiliser, ranging from 192 to 276mgkg–1 and from 0.60 to 0.75gkg–1 respectively compared with NPKZn and NPK+cereal residue (CR) treatments, in which MBC and PmOC ranged from 118 to 170mgkg–1 and from 0.43 to 0.57gkg–1 respectively. Oxidisable organic C fractions revealed that very labile C and labile C fractions were much larger in the NPK+FYM or NPK+GR+FYM treatments, whereas the less-labile C and non-labile C fractions were larger under control and NPK+CR treatments. On average, Walkley–Black C, PmOC and MBC contributed 29–46%, 4.7–6.6% and 1.16–2.40% towards TOC respectively. Integrated plant nutrient supply options, except NPK+CR, also produced sustainable high yields of RWS.

scholarly journals Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. III. Distribution and kinetics of soil organic carbon in particle size fractions

Soil Research ◽  
1986 ◽  
Vol 24 (2) ◽  
pp. 293 ◽  
Author(s):  
RC Dalal ◽  
RJ Mayer
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Size Fraction ◽  
Organic C ◽  
Size Fractions ◽  
Particle Size Fractions ◽  
Clay Size Fraction ◽  
Sand Size

Distribution of soil organic carbon in sand-, silt- and clay-size fractions during cultivation for periods ranging from 20 to 70 years was studied in six major soils used for cereal cropping in southern Queensland. Particle-size fractions were obtained by dispersion in water using cation exchange resin, sieving and sedimentation. In the soils' virgin state no single particle-size fraction was found to be consistently enriched as compared to the whole soil in organic C in all six soils, although the largest proportion (48%) of organic C was in the clay-size fraction; silt and sand-size fractions contained remaining organic C in equal amounts. Upon cultivation, the amounts of organic C declined from all particle-size fractions in most soils, although the loss rates differed considerably among different fractions and from the whole soil. The proportion of the sand-size fraction declined rapidly (from 26% to 12% overall), whereas that of the clay-size fraction increased from 48% to 61% overall. The proportion of silt-size organic C was least affected by cultivation in most soils. It was inferred, therefore, that the sand-size organic matter is rapidly lost from soil, through mineralization as well as disintegration into silt-size and clay-size fractions, and that the clay fraction provides protection for the soil organic matter against microbial and enzymic degradation.

Soil organic carbon and nitrogen sequestration and turnover in aggregates under subtropical leucaena–grass pastures

Soil Research ◽  
2018 ◽  
Vol 56 (6) ◽  
pp. 632 ◽  
Author(s):  
Kathryn Conrad ◽  
Ram C. Dalal ◽  
Ryosuke Fujinuma ◽  
Neal W. Menzies
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Aggregates ◽  
Soil Mass ◽  
Δ13c And Δ15n ◽  
Organic C ◽  
Carbon And Nitrogen ◽  
Nitrogen Sequestration ◽  
C And N

Stabilisation and protection of soil organic carbon (SOC) in macroaggregates and microaggregates represents an important mechanism for the sequestration of SOC. Legume-based grass pastures have the potential to contribute to aggregate formation and stabilisation, thereby leading to SOC sequestration. However, there is limited research on the C and N dynamics of soil organic matter (SOM) fractions in deep-rooted legume leucaena (Leucaena leucocephala)–grass pastures. We assessed the potential of leucaena to sequester carbon (C) and nitrogen (N) in soil aggregates by estimating the origin, quantity and distribution in the soil profile. We utilised a chronosequence (0–40 years) of seasonally grazed leucaena stands (3–6 m rows), which were sampled to a depth of 0.3 m at 0.1-m intervals. The soil was wet-sieved for different aggregate sizes (large macroaggregates, >2000 µm; small macroaggregates, 250–2000 µm; microaggregates, 53–250 µm; and <53 µm), including occluded particulate organic matter (oPOM) within macroaggregates (>250 µm), and then analysed for organic C, N and δ13C and δ15N. Leucaena promoted aggregation, which increased with the age of the leucaena stands, and in particular the formation of large macroaggregates compared with grass in the upper 0.2 m. Macroaggregates contained a greater SOC stock than microaggregates, principally as a function of the soil mass distribution. The oPOM-C and -N concentrations were highest in macroaggregates at all depths. The acid nonhydrolysable C and N distribution (recalcitrant SOM) provided no clear distinction in stabilisation of SOM between pastures. Leucaena- and possibly other legume-based grass pastures have potential to sequester SOC through stabilisation and protection of oPOM within macroaggregates in soil.

Carbon, nitrogen and phosphorus storage in subtropical seagrass meadows: examples from Florida Bay and Shark Bay

2012 ◽  
Vol 63 (11) ◽  
pp. 967 ◽  
Author(s):  
James W. Fourqurean ◽  
Gary A. Kendrick ◽  
Laurel S. Collins ◽  
Randolph M. Chambers ◽  
Mathew A. Vanderklift
Keyword(s):  
Organic Carbon ◽  
Carbon Content ◽  
Primary Productivity ◽  
Florida Bay ◽  
Organic Carbon Content ◽  
Nitrogen And Phosphorus ◽  
Organic C ◽  
Shark Bay ◽  
Seagrass Meadows ◽  
C Storage

Seagrass meadows in Florida Bay and Shark Bay contain substantial stores of both organic carbon and nutrients. Soils from both systems are predominantly calcium carbonate, with an average of 82.1% CaCO3 in Florida Bay compared with 71.3% in Shark Bay. Soils from Shark Bay had, on average, 21% higher organic carbon content and 35% higher phosphorus content than Florida Bay. Further, soils from Shark Bay had lower mean dry bulk density (0.78 ± 0.01 g mL–1) than those from Florida Bay (0.84 ± 0.02 mg mL–1). The most hypersaline regions of both bays had higher organic carbon content in surficial soils. Profiles of organic carbon and phosphorus from Florida Bay indicate that this system has experienced an increase in P delivery and primary productivity over the last century; in contrast, decreasing organic carbon and phosphorus with depth in the soil profiles in Shark Bay point to a decrease in phosphorus delivery and primary productivity over the last 1000 y. The total ecosystem stocks of stored organic C in Florida Bay averages 163.5 MgCorg ha–1, lower than the average of 243.0 MgCorg ha–1 for Shark Bay; but these values place Shark and Florida Bays among the global hotspots for organic C storage in coastal ecosystems.

scholarly journals Potential Production of Carbon Gases and Their Responses to Paleoclimate Conditions: An Example From Xiaolongtan Basin, Southeast Tibetan Plateau

2021 ◽  
Vol 9 ◽  
Author(s):  
Gen Wang ◽  
Yongli Wang ◽  
Zhifu Wei ◽  
Zepeng Sun ◽  
Wei He ◽  
...  
Keyword(s):  
Organic Matter ◽  
Tibetan Plateau ◽  
Low Temperature ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Higher Plants ◽  
The Tibetan Plateau ◽  
Climate Conditions ◽  
Burial Flux ◽  
Carbon Gases

Uplift of the Tibetan Plateau plays a significant and lasting role in the variations of climate conditions and global carbon cycle. However, our knowledge is limited due to the lack of long-sequence records revealing rates of CO2 and CH4 production, hampering our understanding of the relationship between paleoclimatic conditions, carbon cycling and greenhouse gas flux. Here, we present a combination of paleoclimate records and low-temperature thermal simulation results from sediments of the Xiaolongtan Basin at the southeastern margin of the Qinghai-Tibetan Plateau, spanning the late Miocene (14.1 ∼ 11.6 Ma). The n-alkane-derived proxies suggested that the sources of organic matter were obviously different: a mixed source including lower organisms and terrestrial higher plants for the Dongshengqiao Formation from 14.1 to 12.6 Ma, and a predominant contribution from terrestrial higher plants for Xiaolongtan Formation between 12.6 and 11.6 Ma. The paleoclimate was generally warm and humid as reflected by the lipid biomarkers, consistent with previous studies. In addition, the carbon gases (including CO2 and hydrocarbon gases) generated by the low-temperature thermal simulation experiments indicated a production rate of CO2 and CH4 were as high as 88,000 ml/kg rock and 4,000 ml/kg rock, respectively, implying there were certain amounts of carbon gases generated and released into the atmosphere during their shallow burial stage. Besides, the calculated production rate of carbon gases and the estimated burial flux of organic carbon varied in response to the variations of paleoclimate conditions. Based on these observations, we propose that the climate conditions predominantly controlled the formation and accumulation of organic matter, which consequently affected the production of carbon gases and burial flux of organic carbon. The results presented here may provide a significant insight into the carbon cycle in the southeast of the Tibetan Plateau.

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