scholarly journals Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: <i>p</i>CO<sub>2</sub> and paleoproductivity

2011 ◽  
Vol 8 (3) ◽  
pp. 6191-6226 ◽  
Author(s):  
E. C. van Bentum ◽  
G.-J. Reichart ◽  
A. Forster ◽  
J. S. Sinninghe Damsté
Keyword(s):  
North Atlantic ◽  
Co2 Sequestration ◽  
North Atlantic Ocean ◽  
Carbon Isotopic Composition ◽  
Black Shales ◽  
High Productivity ◽  
Oceanic Anoxic Event ◽  
Carbon Isotopic ◽  
Anoxic Event ◽  
Global Carbon

Abstract. A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane, a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7 ‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6 ‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle.

scholarly journals Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: <i>p</i>CO<sub>2</sub> and paleo productivity

2012 ◽  
Vol 9 (2) ◽  
pp. 717-731 ◽  
Author(s):  
E. C. van Bentum ◽  
G.-J. Reichart ◽  
A. Forster ◽  
J. S. Sinninghe Damsté
Keyword(s):  
North Atlantic ◽  
Co2 Sequestration ◽  
North Atlantic Ocean ◽  
Carbon Isotopic Composition ◽  
Black Shales ◽  
High Productivity ◽  
Oceanic Anoxic Event ◽  
Carbon Isotopic ◽  
Anoxic Event ◽  
Global Carbon

Abstract. A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane), a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle.

The rhythmic expression of mid-Cretaceous Oceanic Anoxic Event 2 at IODP Sites U1513 and U1516 (southwest of Australia) 

2021 ◽  
Author(s):  
Sietske Batenburg ◽  
Kara Bogus ◽  
Matthew Jones ◽  
Kenneth Macleod ◽  
Mathieu Martinez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Indian Ocean ◽  
Water Column ◽  
North Atlantic ◽  
Black Shales ◽  
Carbonate Content ◽  
Intergovernmental Panel ◽  
Oceanic Anoxic Event ◽  
Oceanic Anoxic Event 2 ◽  
Anoxic Event

&lt;p&gt;The widespread deposition of organic-rich black shales during the mid-Cretaceous hothouse at ~94 Ma marked a climatic extreme that is particularly well studied in the Northern Hemisphere. The expression of Oceanic Anoxic Event 2 (OAE 2) in the NH was characterised by low oceanic oxygen concentrations, likely caused by the input of nutrients through volcanism and/or weathering in combination with a peculiar geography in which the proto-North Atlantic was semi-restricted (Jenkyns, 2010; Trabucho Alexandre et al., 2010). The extent of water column anoxia outside the North Atlantic and Tethyan domains remains poorly resolved, as few Southern Hemisphere records have been recovered that span OAE 2, and only a portion of those Indian and Pacific Ocean localities experienced anoxia and organic matter deposition (Dickson et al., 2017; Hasegawa et al., 2013).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Here we present new results from IODP Expedition 369 offshore southwestern Australia. Sedimentary records across the Cenomanian-Turonian transition from Sites U1513 and U1516 in the Mentelle Basin (Indian Ocean) display rhythmic lithologic banding patterns. The OAE 2 interval is marked by a dramatic drop in carbonate content and the occurrence of several thin organic-rich black bands. The spacing of dark bands within a rhythmic sequence suggests a potential orbital control on organic matter deposition at our study sites. Time series analyses of high-resolution (cm-scale) elemental data from XRF-core scanning reveal the imprint of periodicities that can be confidently linked to Earth&amp;#8217;s orbital parameters. The new OAE 2 records from Sites U1516 and U1513 allow us to i) evaluate existing time scales over the Cenomanian-Turonian transition, and ii) investigate the mechanisms leading to a recurrent lack of oxygen in the Indian Ocean.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Climatic mechanisms translating changes in insolation to variations in organic matter deposition may have included variations in nutrient input from nearby continents and shifts in water column structure affecting local to regional stratification versus deep water formation and advection. Investigating ventilation of the deep sea during the OAE2 interval is of heightened relevance as current global warming is leading to a worldwide expansion of oxygen minimum zones&amp;#160;(P&amp;#246;rtner et al., 2019).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Dickson, A.J., et al., 2017. Sedimentology 64, 186&amp;#8211;203.&lt;/p&gt;&lt;p&gt;Hasegawa, et al., 2013. Cretaceous Research 40, 61&amp;#8211;80.&lt;/p&gt;&lt;p&gt;Jenkyns, H.C., 2010. Geochemistry, Geophysics, Geosystems 11, Q03004.&lt;/p&gt;&lt;p&gt;P&amp;#246;rtner, H.O., et al., 2019. IPCC Intergovernmental Panel on Climate Change: Geneva, Switzerland.&lt;/p&gt;&lt;p&gt;Trabucho Alexandre, J., et al., 2010. Paleoceanography 25, PA&lt;/p&gt;

scholarly journals An open marine record of the Toarcian oceanic anoxic event

2011 ◽  
Vol 3 (1) ◽  
pp. 385-410 ◽  
Author(s):  
D. R. Gröcke ◽  
R. S. Hori ◽  
J. Trabucho-Alexandre ◽  
D. B. Kemp ◽  
L. Schwark
Keyword(s):  
Organic Matter ◽  
Carbon Cycle ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
Global Carbon Cycle ◽  
Open Ocean ◽  
Black Shales ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Global Carbon

Abstract. Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic-rich sediments (black shales) and significant perturbations in the global carbon cycle. The expression of these perturbations is globally recorded in sediments as excursions in the carbon isotope record irrespective of lithology or depositional environment. During the Early Toarcian, black shales were deposited on the epi- and peri-continental shelves of Pangaea and these sedimentary rocks are associated with a pronounced (ca. 7‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the Early Toarcian is thought to represent an oceanic anoxic event (the T-OAE). Associated with this event, there were pronounced perturbations in global weathering rates and seawater temperatures. Although it is commonly asserted that the T-OAE is a global event and that the distribution of black shales is likewise global, an isotopic and/or organic-rich expression of this event has as yet only been recognized on epi- and peri-continental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg) of Early Toarcian cherts from Japan that were deposited in the open Panthalassa Ocean was analysed. The results show the presence of a major (>6‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the Early Toarcian negative CIE known from European epicontinental strata. Furthermore, a secondary ca. −2‰ excursion in δ13Corg is also recognized lower in the studied succession that, within the current biostratigraphical resolution, is likely to represent the excursion that occurs close to the Pliensbachian/Toarcian boundary and which is also recorded in European epicontinental successions. These results from the open ocean realm suggest that, in conjunction with other previously published datasets, these major Early Jurassic carbon cycle perturbations affected all active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric). An extremely negative δ13Corg value (−57‰) during the peak of the T-OAE is also reported, which suggests that the inferred open ocean mid-water oxygen minimum layer within which these sediments are thought to have been deposited was highly enriched in methanotrophic bacteria, since these organisms are the only plausible producers of such 12C-enriched organic matter.

scholarly journals An open ocean record of the Toarcian oceanic anoxic event

Solid Earth ◽  
2011 ◽  
Vol 2 (2) ◽  
pp. 245-257 ◽  
Author(s):  
D. R. Gröcke ◽  
R. S. Hori ◽  
J. Trabucho-Alexandre ◽  
D. B. Kemp ◽  
L. Schwark
Keyword(s):  
Organic Matter ◽  
Carbon Cycle ◽  
Carbon Isotope ◽  
Isotope Composition ◽  
Global Carbon Cycle ◽  
Open Ocean ◽  
Black Shales ◽  
Oceanic Anoxic Event ◽  
Anoxic Event ◽  
Global Carbon

Abstract. Oceanic anoxic events were time intervals in the Mesozoic characterized by widespread distribution of marine organic matter-rich sediments (black shales) and significant perturbations in the global carbon cycle. These perturbations are globally recorded in sediments as carbon isotope excursions irrespective of lithology and depositional environment. During the early Toarcian, black shales were deposited on the epi- and pericontinental shelves of Pangaea, and these sedimentary rocks are associated with a pronounced (ca. 7 ‰) negative (organic) carbon isotope excursion (CIE) which is thought to be the result of a major perturbation in the global carbon cycle. For this reason, the lower Toarcian is thought to represent an oceanic anoxic event (the T-OAE). If the T-OAE was indeed a global event, an isotopic expression of this event should be found beyond the epi- and pericontinental Pangaean localities. To address this issue, the carbon isotope composition of organic matter (δ13Corg of lower Toarcian organic matter-rich cherts from Japan, deposited in the open Panthalassa Ocean, was analysed. The results show the presence of a major (>6 ‰) negative excursion in δ13Corg that, based on radiolarian biostratigraphy, is a correlative of the lower Toarcian negative CIE known from Pangaean epi- and pericontinental strata. A smaller negative excursion in δ13Corg (ca. 2 ‰) is recognized lower in the studied succession. This excursion may, within the current biostratigraphic resolution, represent the excursion recorded in European epicontinental successions close to the Pliensbachian/Toarcian boundary. These results from the open ocean realm suggest, in conjunction with other previously published datasets, that these Early Jurassic carbon cycle perturbations affected the active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).

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