Basin-scale controls on the molybdenum-isotope composition of seawater during Oceanic Anoxic Event 2 (Late Cretaceous)

Dickson, Alexander J.; Jenkyns, Hugh C.; Porcelli, D.; Boorn, Sander van den; Idiz, Erdem

doi:10.1016/j.gca.2015.12.036

Cited by 79 publications

(101 citation statements)

References 83 publications

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“…Interestingly, the area of anoxic waters estimated for the Cretaceous OAE2 is an order of magnitude larger than that calculated here for the EES and was mainly confined to the proto‐North Atlantic (Dickson et al, ; Owens et al, ). The burial of organic carbon, which was most pronounced on the continental shelves (e.g., Nederbragt et al, ; van Bentum et al, ), has been suggested to have played a key role in removing carbon from the atmosphere during OAE2 (Barclay et al, ; Graly et al, ).…”

Section: Discussioncontrasting

confidence: 51%

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

Baroni

Pohl

Helmond

et al. 2018

Paleoceanog and Paleoclimatol

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The Toarcian Oceanic Anoxic Event (T‐OAE, ∼183 Myr) was a long‐lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarcian and its influence on marine biogeochemical cycles are still not fully understood. Here we assess the spatial extent of anoxia in the NW Tethys Ocean during the T‐OAE, the relationship with ocean circulation and the impact on organic carbon burial, using new and existing sedimentary records from the European Epicontinental Shelf in combination with general circulation model results. We demonstrate that bottom waters on the southwestern part of the shelf were mainly oxic during the T‐OAE, while those in the northeastern basins were mostly anoxic or even sulfidic. Results for two ocean‐atmosphere models (Fast Ocean‐Atmosphere Model and Massachusetts Institute of Technology general circulation model) suggest the presence of a strong clockwise gyre over the European Epicontinental Shelf, which brought oxygenated equatorial waters from the Tethys Ocean to the southern shelf. The northward limb of the gyre was significantly weakened due to the rough bathymetry of the northern shelf, making this relative small region highly sensitive to local ocean stratification. These sluggish ocean dynamics promoted bottom water anoxia and enhanced burial of organic carbon in the northeastern basins, which accounted for 3–5% of the total carbon extracted from the ocean‐atmosphere system as recorded by the positive carbon isotope shift.

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Section: Discussioncontrasting

confidence: 51%

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

Baroni

Pohl

Helmond

et al. 2018

Paleoceanog and Paleoclimatol

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“…Molybdenum isotopes were measured by adding a precise mass of a 100 Mo‐enriched and 97 Mo‐enriched double‐isotope spike to sample aliquots containing ca 400 ng of natural Mo. The samples were digested in inverse aqua regia at 150°C for 48 h to ensure spike–sample equilibration, before purification of Mo using anion‐exchange chromatography (Dickson et al ., ). Isotope ratios were measured using a Nu Plasma MC‐ICP‐MS (Nu Instruments Limited, Wrexham, UK) and are expressed as δ 98/95 Mo = ((( 98/95 Mo sample − 98/95 Mo standard )/ 98/95 Mo standard )*1000) relative to NIST 3134 (Nägler et al ., ).…”

Section: Methodsmentioning

confidence: 97%

A Southern Hemisphere record of global trace‐metal drawdown and orbital modulation of organic‐matter burial across the Cenomanian–Turonian boundary (Ocean Drilling Program Site 1138, Kerguelen Plateau)

et al. 2016

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Despite its assumed global nature, there are very few detailed stratigraphic records of the late Cenomanian to the early Turonian Oceanic Anoxic Event 2 from the Southern Hemisphere. A highly resolved record of environmental changes across the Cenomanian–Turonian boundary interval is presented from Ocean Drilling Program Site 1138 on the central Kerguelen Plateau (southern Indian Ocean). The new data lead to three key observations. Firstly, detailed biostratigraphy and chemostratigraphy indicate that the record of Oceanic Anoxic Event 2 is not complete, with a hiatus spanning the onset of the event. A decrease in glauconite and highly weathered clays after the onset of Oceanic Anoxic Event 2 marks the end of the hiatus interval, which can be explained by a relative sea‐level rise that increased sediment accommodation space on the Kerguelen Plateau margin. This change in depositional environment controlled the timing of the delayed peak in organic‐matter burial during Oceanic Anoxic Event 2 at Site 1138 compared with other Oceanic Anoxic Event 2 locations worldwide. A second key observation is the presence of cyclic fluctuations in the quantity and composition of organic matter being buried on the central Kerguelen Plateau throughout the latter stages of Oceanic Anoxic Event 2 and the early Turonian. A close correspondence between organic matter, sedimentary elemental compositions and sediments recording sea‐floor oxygenation suggests that the cycles were mainly productivity‐driven phenomena. Available age‐control points constrain the periodicity of the coupled changes in sedimentary parameters to ca 20 to 70 ka, suggesting a link between carbon burial and astronomically forced climatic variations (precession or obliquity) in the Southern Hemisphere mid‐latitudes both during, and after, Oceanic Anoxic Event 2: fluctuations that were superimposed on the impact of global‐scale processes. Finally, trace‐metal data from the black‐shale unit at Site 1138 provide the first evidence from outside of the proto‐North Atlantic region for a global drawdown of seawater trace‐metal (Mo) inventories during Oceanic Anoxic Event 2.

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“…2) suggests a dramatic and widespread perturbation to the marine geochemical redox system that impacted global metal inventories and isotopes (Dickson et al, 2016;Goldberg et al, 2016;Hetzel et al, 2009;van Helmond et al, 2014). Again, the persistence of local euxinia throughout the analyzed interval at Site 1258 confirms that shifting local redox is not the primary control on the observed metal enrichment pattern, and we can think of no reasonable local inventory control that would assert itself differentially over the entire interval of interest (see below).…”

Section: Drawdown Of Metals During the Oae And Biotic Responsementioning

confidence: 95%

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Owens

Reinhard

Rohrssen

et al. 2016

Earth and Planetary Science Letters

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Available online xxxx Editor: D. Vance Keywords: oceanic anoxic event (OAE2) trace metal drawdown geochemistry anoxia euxinia biomarkersUnderstanding the global redox state of the oceans and its cause-and-effect relationship with periods of widespread organic-carbon deposition is vital to interpretations of Earth's climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency. Here, we present a compilation of new and published data from an organic-rich locality within the proto-North Atlantic Ocean during the Cenomanian-Turonian boundary event that shows a dramatic drawdown of redox-sensitive trace elements. Iron geochemistry independently suggests euxinic deposition (i.e., anoxic and sulfidic bottom waters) for the entire section, thus confirming its potential as an archive of global marine metal inventories. In particular, depleted molybdenum (Mo) and vanadium (V) concentrations effectively record the global expansion of euxinic and oxygen-deficient but non-sulfidic waters, respectively. The V drawdown precedes the OAE, fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia. Molybdenum drawdown, in contrast, is delayed with respect to V and coincides with the onset of OAE2. Parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the OAE in this region of the proto-North Atlantic, with the smallest relative eukaryotic contributions to total primary production occurring during metal-depleted intervals. This relationship may be related to decreasing supplies of enzymatically important trace elements. Similarly, box modeling suggests that oceanic drawdown of Mo may have approached levels capable of affecting marine nitrogen fixation. Predictions of possible nitrogen stress on eukaryotic production, locally and globally, are consistent with the low observed levels of Mo and a rise in 2-methylhopane index values during the peak of the OAE. At the same time, the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades, calcareous nanofossils, and foraminifera, suggesting that the temporal patterns of anoxia/euxinia and associated nutrient limitation may have contributed to the fabric of OAE2-related turnover.

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Basin-scale controls on the molybdenum-isotope composition of seawater during Oceanic Anoxic Event 2 (Late Cretaceous)

Cited by 79 publications

References 83 publications

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

Ocean Circulation in the Toarcian (Early Jurassic): A Key Control on Deoxygenation and Carbon Burial on the European Shelf

A Southern Hemisphere record of global trace‐metal drawdown and orbital modulation of organic‐matter burial across the Cenomanian–Turonian boundary (Ocean Drilling Program Site 1138, Kerguelen Plateau)

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

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