scholarly journals Shelf erosion and submarine river canyons: implications for deep-sea oxygenation and ocean productivity during glaciation

2010 ◽  
Vol 7 (6) ◽  
pp. 1973-1982 ◽  
Author(s):  
I. Tsandev ◽  
C. Rabouille ◽  
C. P. Slomp ◽  
P. Van Cappellen
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Sea Level ◽  
Deep Sea ◽  
Oxygen Demand ◽  
Coupled Model ◽  
Submarine Canyon ◽  
Open Ocean ◽  
Oxygen Levels ◽  
Organic Carbon Burial

Abstract. The areal exposure of continental shelves during glacial sea level lowering enhanced the transfer of erodible reactive organic matter to the open ocean. Sea level fall also activated submarine canyons thereby allowing large rivers to deposit their particulate load, via gravity flows, directly in the deep-sea. Here, we analyze the effects of shelf erosion and particulate matter re-routing to the open ocean during interglacial to glacial transitions, using a coupled model of the marine phosphorus, organic carbon and oxygen cycles. The results indicate that shelf erosion and submarine canyon formation may significantly lower deep-sea oxygen levels, by up to 25%, during sea level low stands, mainly due to the supply of new material from the shelves, and to a lesser extent due to particulate organic matter bypassing the coastal zone. Our simulations imply that deep-sea oxygen levels can drop significantly if eroded shelf material is deposited to the seafloor. Thus the glacial ocean's oxygen content could have been significantly lower than during interglacial stages. Primary production, organic carbon burial and dissolved phosphorus inventories are all affected by the erosion and rerouting mechanisms. However, re-routing of the continental and eroded shelf material to the deep-sea has the effect of decoupling deep-sea oxygen demand from primary productivity in the open ocean. P burial is also not affected showing a disconnection between the biogeochemical cycles in the water column and the P burial record.

scholarly journals Shelf erosion and submarine river canyons: implications for deep-sea oxygenation and ocean productivity during glaciation

2010 ◽  
Vol 7 (1) ◽  
pp. 879-903 ◽  
Author(s):  
I. Tsandev ◽  
C. Rabouille ◽  
C. P. Slomp ◽  
P. Van Cappellen
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Sea Level ◽  
Deep Sea ◽  
Oxygen Demand ◽  
Coupled Model ◽  
Submarine Canyon ◽  
Open Ocean ◽  
Oxygen Levels ◽  
Organic Carbon Burial

Abstract. The areal exposure of continental shelves during glacial sea level lowering enhanced the transfer of erodible reactive organic matter to the open ocean. Sea level fall also activated submarine canyons thereby allowing large rivers to deposit their particulate load, via gravity flows, directly in the deep-sea. Here, we analyze the effects of shelf erosion and particulate matter re-routing to the open ocean during interglacial to glacial transitions, using a coupled model of the marine phosphorus, organic carbon and oxygen cycles. The results indicate that shelf erosion and submarine canyon formation may significantly lower deep sea oxygen levels, by up to 25%, during sea level low stands, mainly due to the supply of new material from the shelves, and to a lesser extent due to particulate organic matter bypassing the coastal zone. Our simulations imply that deep-sea oxygen levels can drop significantly if eroded shelf material is deposited to the seafloor. Thus the glacial ocean's oxygen content could have been significantly lower than during interglacial stages. Primary production, organic carbon burial and dissolved phosphorus inventories are all affected by the erosion and rerouting mechanisms. However, re-routing of the continental and eroded shelf material to the deep sea-sea has the effect of decoupling deep-sea oxygen demand from primary productivity in the open ocean. P burial is also not affected showing a disconnection between the biogeochemical cycles in the water column and the P burial record.

scholarly journals Secular variation in Late Cretaceous carbon isotopes: a new δ13C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)

2006 ◽  
Vol 143 (5) ◽  
pp. 561-608 ◽  
Author(s):  
IAN JARVIS ◽  
ANDREW S. GALE ◽  
HUGH C. JENKYNS ◽  
MARTIN A. PEARCE
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Sea Level Rise ◽  
Sea Level ◽  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Reference Curve ◽  
Organic Carbon Burial ◽  
Isotope Stratigraphy ◽  
Using Data

Carbon stable-isotope variation through the Cenomanian–Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and δ13C values that provide a basis for high-resolution correlation. Positive and negative δ13C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive δ13C excursions of up to +2‰: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite δ13C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian–Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian–Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-iso-tope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian–Santonian strata than biostratigraphy. With the addition of Campanian δ13C data from one of the English sections, a composite Cenomanian–Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies.The Cenomanian–Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing δ13C values accompanying sea-level rise associated with transgression, and falling δ13C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of 12C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling δ13C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing δ13C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios.

Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand, SE Asia

2020 ◽  
Author(s):  
Bin Wu ◽  
Xiaodan Wu ◽  
Xuefa Shi ◽  
Shuqing Qiao ◽  
Shengfa Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
National Laboratory ◽  
Coastal Current ◽  
Gulf Of Thailand ◽  
Se Asia ◽  
Organic Carbon Burial ◽  
Water Stratification ◽  
Tropical Monsoon ◽  
Upper Gulf Of Thailand

<p>The seasonal reversal of monsoon climatology modulates precipitation, currents, river influx and a variety of biogeochemical processes. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT), SE Asia. This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during the tropical cyclones impacted November 2013. POC in the estuarine sections is influenced more by the seasonal shift than the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the CHAO and MK impacted estuarine sections. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is obviously influenced more by marine-derived factors. TOC in surface sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input as evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr<sup>-1</sup>) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.</p><p><strong>Acknowledgements</strong></p><p>This study was supported by National Programme on Global Change and Air-Sea Interaction (GASI-02-IND-CJ05, GASI-GEOGE-03), the Natural Science Foundation of China (U1606401), the Qingdao National Laboratory for Marine Science and Technology (2016ASKJ13), the China-Thailand cooperation project “Research on Vulnerability of Coastal Zones”, and the Taishan Scholar Program of Shandong.</p>

A record of seafloor methane seepage across the last 150 million years

2020 ◽  
Author(s):  
Davide Oppo ◽  
Luca De Siena ◽  
David Kemp
Keyword(s):  
Organic Carbon ◽  
Sea Level ◽  
Methane Emission ◽  
Temporal Correlation ◽  
Biogenic Methane ◽  
Methane Seepage ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Rapid Generation ◽  
Extinction Events

<p>Methane seepage at the seafloor is a source of carbon in the marine environment and has long been recognized as an important window into the deep geo-, hydro-, and bio-spheres. However, the processes and temporal patterns of natural methane emission over multi-million-year time scales are still poorly understood. The microbially-mediated methane oxidation leads to the precipitation of authigenic carbonate minerals within subseafloor sediments, thus providing a potentially extensive record of past methane emission. In this study, we used data on methane-derived authigenic carbonates to build a proxy time series of seafloor methane emission over the last 150 My. We quantitatively demonstrate that variations in sea level and organic carbon burial are the dominant controls on methane leakage since the Early Cretaceous. Sea level controls variations of methane seepage by imposing smooth trends with cyclicities in the order of tens of My. Organic carbon burial shows the same cyclicities and instantaneously controls the volumes of methane released thanks to the rapid generation of biogenic methane. The identified fundamental (26-27 My) cyclicity matches those observed in the carbon cycle associated with plate tectonic processes, the atmospheric CO<sub>2</sub>, the oceanic anoxic events, and mass extinction events. A higher (12 My) cyclicity relates to modulations of Milankovitch eccentricity cycles and to variations in global tectonics. These analogies demonstrate that the seafloor methane seepage across the last 150 My relates to a large spectrum of global phenomena and thus has key implications for a better understanding of methane cycling at the present day. Temporal correlation analysis supports the evidence that the modern expansion of hypoxic areas and its effect on organic carbon burial may lead to higher seawater methane concentrations over the coming centuries.</p>

Terrestrial organic carbon accumulation on the Amazon deep sea fan during the last glacial sea level low stand

1999 ◽  
Vol 159 (1-4) ◽  
pp. 263-281 ◽  
Author(s):  
B Schlünz ◽  
R.R Schneider ◽  
P.J Müller ◽  
W.J Showers ◽  
G Wefer
Keyword(s):  
Organic Carbon ◽  
Sea Level ◽  
Deep Sea ◽  
Carbon Accumulation ◽  
Last Glacial ◽  
Sea Fan ◽  
The Last Glacial

scholarly journals Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. Recent oxygen minimum zones

2015 ◽  
Vol 12 (4) ◽  
pp. 1169-1189 ◽  
Author(s):  
J. Schönfeld ◽  
W. Kuhnt ◽  
Z. Erdem ◽  
S. Flögel ◽  
N. Glock ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Bottom Water ◽  
Carbon Accumulation ◽  
Marine Biota ◽  
Accumulation Rates ◽  
Oxygen Minimum Zones ◽  
Oxygen Levels ◽  
Water Oxygen ◽  
Oxygen Minimum

Abstract. Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of < 7 μmol kg−1 under the Peruvian upwelling and < 5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at > 10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.

Humus transformation at the bank filtration water plant

1994 ◽  
Vol 30 (10) ◽  
pp. 179-187 ◽  
Author(s):  
I. T. Miettinen ◽  
P. J. Martikainen ◽  
T. Vartiainen
Keyword(s):  
Organic Matter ◽  
Surface Water ◽  
Organic Carbon ◽  
Chemical Oxygen Demand ◽  
Total Organic Carbon ◽  
Lake Water ◽  
Oxygen Demand ◽  
Bank Filtration ◽  
Water Plant

Transformations in the amount and quality of organic matter (humus) during bank filtration of surface water were studied by analyzing the changes in total organic carbon (TOC), non-purgeable organic carbon (NPOC), chemical oxygen demand (COD), color of water, and UV absorbing humus fractions. The amount of organic matter expressed as TOC, NPOC, and COD depended on temperature and filtration distance from lake water. The color of water and the UV absorbing humus peaks presenting different humus molecule fractions decreased more effectively than other parameters measuring the amount of organic matter in water. The ratio of COD to TOC decreased when the filtration distance of water increased. Our observations indicated that bank filtration of humus-rich lake water changed more the quality of organic matter than its total amount.

Organic matter transport by cyclonic eddies formed in eastern boundary upwelling system supports heterotrophy in the open oligotrophic ocean

2021 ◽  
Author(s):  
Quentin Devresse ◽  
Kevin W Becker ◽  
Anja Engel
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Microbial Activity ◽  
Mesoscale Eddies ◽  
Open Ocean ◽  
Cyclonic Eddy ◽  
Positive Anomaly ◽  
Eastern Boundary ◽  
Biogeochemical Parameters ◽  
Epipelagic Layer

&lt;p&gt;Mesoscale eddies formed in Eastern boundary upwelling systems are elementary components of ocean circulation and play important roles in the offshore transport of organic carbon and nutrients. Yet, most of our knowledge about this lateral transport and its influence on biogeochemical cycles relies on modelling studies and satellite observations, while in situ measurements of biogeochemical parameters are scarce. For example, little is known about the effects of mesoscale eddies on organic carbon distribution, microbial activity, and organic matter (OM) turnover in the open oligotrophic ocean. To address this gap, we investigated the horizontal and vertical variability of phytoplankton and bacterial activity as well as dissolved organic carbon along a zonal corridor of the westward propagation of eddies between the Cape Verde Islands and Mauretania in the Eastern Tropical North Atlantic (ETNA). We additionally collected samples from a cyclonic eddy along this transect at high spatial resolution. Our results indicate a strong impact of cyclonic eddies on both microbial abundance and metabolic activity in the epipelagic layer (0&amp;#8211;200 m). Generally, all determined parameters (bacterial abundance, heterotrophic respiration rates, bacterial biomass production, bacterial growth efficiency, bacterial carbon demand and net primary production) were higher in the eddy than in the stations along the meridional transect. Along the transect, microbial biomass and activity rates were gradually decreasing from the coast to the open ocean. We further observed high variability of biogeochemical parameters within the eddy with elevates microbial abundances as well as process rates in the south-western periphery. This can be explained by the rotational flow of the cyclonic eddy, which perturbs local OM and nutrient distribution via azimuthal advection. The local positive anomaly of microbial activity in the cyclonic eddy compared to all other stations including the near coast ones results from eddy pumping of nutrient into the epipelagic layer that promotes growth of phytoplankton. Overall, our study supports that cyclonic eddies are important vehicles for the transport of fresh OM that fuel heterotrophic activity the open ocean, highlighting the coupling between productive EBUS and the adjacent oligotrophic ETNA.&lt;/p&gt;

What Controls Atmospheric Oxygen Concentrations?

2017 ◽  
Author(s):  
Donald Eugene Canfield
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Black Sea ◽  
Atmospheric Oxygen ◽  
Fundamental Question ◽  
The Black Sea ◽  
Microbial Process ◽  
The Past ◽  
Carbon Burial ◽  
Organic Carbon Burial

This chapter deals with the fundamental question of why there is oxygen in the atmosphere at all. It seeks to identify the main processes controlling the oxygen concentration. Plants and cyanobacteria produce the oxygen, but it accumulates only because some of the original photosynthetically produced organic matter is buried and preserved in sediments. Another oxygen source is an anaerobic microbial process called sulfate reduction that respires organic matter using sulfate and produces sulfide. This process is quite common in nature but are most prominent in relatively isolated basins like the Black Sea, and in most marine sediments at depths where oxygen has been consumed by respiration. If there is iron around, the sulfide reacts with the iron, forming a mineral called pyrite. While organic carbon burial has been the main oxygen source to the atmosphere over the past several hundred million years, for some intervals further back in time, pyrite burial may well have dominated as an oxygen source.

Sign in / Sign up

Export Citation Format

Share Document