Spatial extent and degree of oxygen depletion in the deep proto‐<scp>N</scp>orth <scp>A</scp>tlantic basin during <scp>O</scp>ceanic <scp>A</scp>noxic <scp>E</scp>vent 2

Helmond, Niels A. G. M. van; Baroni, Itzel Ruvalcaba; Sluijs, Appy; Damsté, Jaap S. Sinninghe; Slomp, Caroline P.

doi:10.1002/2014gc005528

Cited by 43 publications

(49 citation statements)

References 76 publications

(136 reference statements)

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“…Abbreviations as in Figure . Supporting information are from van Helmond et al [] and Sinninghe Damsté et al [].…”

Section: Resultsmentioning

confidence: 99%

“…Site 386 is the most centrally located North Atlantic site yielding upper Cenomanian to lower Turonian sediments. The Late Cretaceous sediments predominantly consist of green, grey and black clay, and mudstones, with a maximum TOC content up to 13% [ van Helmond et al , ], that were deposited at a water depth >2000 m. The OAE 2 interval was clearly identified by a ∼2.5‰ positive shift in δ 13 C org [ van Helmond et al , ].…”

Section: Study Sitesmentioning

confidence: 99%

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The nitrogen isotope composition of sediments from the proto‐North Atlantic during Oceanic Anoxic Event 2

et al. 2015

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Sediment records of the stable isotopic composition of N ( 15 N) show light 15 N values at several sites in the proto-North Atlantic during Oceanic Anoxic Event 2 (OAE 2) at the Cenomanian-Turonian transition (∼94 Ma). The low 15 N during the event is generally attributed to an increase in N 2 fixation and incomplete uptake of NH + 4 for phytoplankton growth. A compilation of all reliable data for the proto-North Atlantic during OAE 2 demonstrates that the most pronounced negative shift in 15 N from pre-OAE 2 to OAE 2 occurs in the open ocean but with 15 N never lower than −3‰. Using a box model of N cycling for the proto-North Atlantic during OAE 2, we show that N 2 fixation is a major contributor to the 15 N signal, especially in the open ocean. Incomplete uptake of NH + 4 for phytoplankton growth is important in regions dominated by downwelling, with lateral transport of NH + 4 acting as a major source. In the southern proto-North Atlantic, where bottom waters were euxinic, the light 15 N signature is largely explained by upwelling of NH + 4 . Our study provides an overview of regional differences in 15 N in the proto-North Atlantic and highlights the role of lateral exchange of water and nutrients, in addition to local biogeochemical processes, in determining 15 N values of OAE 2 sediments.

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“…Abbreviations as in Figure . Supporting information are from van Helmond et al [] and Sinninghe Damsté et al [].…”

Section: Resultsmentioning

confidence: 99%

Section: Study Sitesmentioning

confidence: 99%

The nitrogen isotope composition of sediments from the proto‐North Atlantic during Oceanic Anoxic Event 2

et al. 2015

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“…To assess the degree of restriction of the water column at our three sites during the T‐OAE, crossplots of sediment TOC and Mo content were compared with TOC and Mo crossplots for modern sediments from the well‐ventilated Saanich Inlet and the restricted Black Sea (Algeo & Lyons, ) and Cretaceous OAE2 sediments (van Helmond et al, ; Figure ). We find that the regression lines for the T‐OAE of our three sites plot below the regression lines for the Black Sea and OAE2 (Figure a), in accordance with results reported previously for Yorkshire (McArthur et al, ; Pearce et al, ; Them et al, ; Thibault et al, ), indicating extremely restricted conditions.…”

Section: Discussionmentioning

confidence: 99%

“…Corresponding regression slopes are indicated with the same color as the symbol. Dashed lines show regression slopes for Mo and TOC data of the well mixed Saanich Inlet, the restricted modern Black Sea (Algeo & Lyons, ), and the restricted deep proto‐North Atlantic during OAE2 (van Helmond et al, ). Specific regression lines for the (c) lower and upper falciferum Subzones in Yorkshire are plotted to show differences within the falciferum Subzone.…”

Section: Discussionmentioning

confidence: 99%

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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“…Trace metals precipitate as sulfides under anoxic and euxinic conditions, some with valence changes (e.g., Mo and V) and some without, such as Zn [ Hetzel et al , ]. During OAE 2, some trace metals, such as As, Bi, Cd, Co, Cr, Cu, Mo, Ni, Sb, Tl, V, and U, were concentrated in organic matter or precipitated with sulfide, suggesting euxinia in the sediments and/or in the water column [ Arthur et al , ; Kuypers et al , ; Jenkyns , ], as documented for the proto‐Atlantic [ Kuypers et al , ; Kolonic et al , ; Brumsack , ; Forster et al , ; Hetzel et al , ; Tribovillard et al , ; van Helmond et al , ; Little et al , ] and for southern Europe [ Scopelliti et al , , ; Turgeon and Brumsack , ]. Molybdenum isotope data [ Westermann et al , ] and uranium isotope data [ Montoya‐Pino et al , ] also indicate expanded bottom water euxinia during the OAE 2.…”

Section: Introductionmentioning

confidence: 99%

Upper ocean oxygenation dynamics from I/Ca ratios during the Cenomanian‐Turonian OAE 2

et al. 2015

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Global warming lowers the solubility of gases in the ocean and drives an enhanced hydrological cycle with increased nutrient loads delivered to the oceans, leading to increases in organic production, the degradation of which causes a further decrease in dissolved oxygen. In extreme cases in the geological past, this trajectory has led to catastrophic marine oxygen depletion during the so-called oceanic anoxic events (OAEs). How the water column oscillated between generally oxic conditions and local/global anoxia remains a challenging question, exacerbated by a lack of sensitive redox proxies, especially for the suboxic window. To address this problem, we use bulk carbonate I/Ca to reconstruct subtle redox changes in the upper ocean water column at seven sites recording the Cretaceous OAE 2. In general, I/Ca ratios were relatively low preceding and during the OAE interval, indicating deep suboxic or anoxic waters exchanging directly with near-surface waters. However, individual sites display a wide range of initial values and excursions in I/Ca through the OAE interval, reflecting the importance of local controls and suggesting a high spatial variability in redox state. Both I/Ca and an Earth System Model suggest that the northeast proto-Atlantic had notably higher oxygen levels in the upper water column than the rest of the North Atlantic, indicating that anoxia was not global during OAE 2 and that important regional differences in redox conditions existed. A lack of correlation with calcium, lithium, and carbon isotope records suggests that neither enhanced global weathering nor carbon burial was a dominant control on the I/Ca proxy during OAE 2.

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Spatial extent and degree of oxygen depletion in the deep proto‐North Atlantic basin during Oceanic Anoxic Event 2

Cited by 43 publications

References 76 publications

The nitrogen isotope composition of sediments from the proto‐North Atlantic during Oceanic Anoxic Event 2

The nitrogen isotope composition of sediments from the proto‐North Atlantic during Oceanic Anoxic Event 2

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

Upper ocean oxygenation dynamics from I/Ca ratios during the Cenomanian‐Turonian OAE 2

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