Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes

Blättler, Clara L.; Jenkyns, Hugh C.; Reynard, Linda M.; Henderson, Gideon M.

doi:10.1016/j.epsl.2011.06.029

Cited by 181 publications

(153 citation statements)

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“…Calcium and strontium isotopes, both measured in Resolution Guyot, are taken from Blättler et al (2011) and , respectively. Osmiumisotope data, measured on the Cismon section in northern Italy, are taken from Bottini et al (2012).…”

Section: Methods and Experimental Set-upmentioning

confidence: 99%

“…Li isotopes can be used as a proxy for silicate-weathering congruency, although weathering of basaltic (oceanic) or granitic (continental) crust cannot be differentiated due to their similar isotopic values (Teng et al, 2004). Ca isotopes may hold information about weathering of both continental crust and carbonates (Blättler et al, 2011). Strontium isotopes and, similarly, osmium isotopes are mainly influenced by the competing effects of continental silicate weathering, driving the isotopic ratios to more radiogenic values, and oceanic hydrothermal activity, basalt and/or carbonate weathering, which drive the Sr-and Os-isotope ratios to more unradiogenic values (Allègre et al, 2010;Palmer & Edmond, 1989 for Sr; Peucker-Ehrenbrink & Ravizza, 2000 for Os).…”

Section: Constraints From Multi-isotope Excursionsmentioning

confidence: 99%

“…Enhanced weathering rates have been also proposed on the basis of a negative shift in  44/42 Ca (Blättler et al, 2011), although calcium isotopes can potentially be affected by ocean acidification, temperature changes and/or calcification rate (Fantle & Tipper, 2014). This continental weathering pulse is not unequivocally captured by the marine strontium-isotope curve, although some relatively radiogenic values do overlap with the OAE 1a record (Jones & Jenkyns, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…The early Aptian OAE 1a or Selli event (~120 Ma) has been much studied in terms of carbon-, calcium-, osmiumand strontium-isotope stratigraphy: Blättler et al (2011); Bottini et al (2012); Erba et al (2010); ; ; Jones & Jenkyns (2001); Keller et al (2011); Méhay et al (2009) ;Menegatti et al (1998); Tejada et al (2009);van Breugel et al (2007); Wissler et al (2004). This event is conventionally interpreted as triggered by the massive outgassing of the Ontong Java, Manihiki and Hikurangi submarine large igneous province (LIP; Larson & Erba, 1999;Méhay et al, 2009;Tarduno et al, 1991Tejada et al, 2009, which introduced large quantities of isotopically light carbon into the atmosphere-ocean system, producing a stepwise decline in  13 C and lowering the pH of the oceans.…”

Section: Introductionmentioning

confidence: 99%

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Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lechler

Strandmann

Jenkyns

et al. 2015

Earth and Planetary Science Letters

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An abrupt rise in temperature, forced by a massive input of CO 2 into the atmosphere, is commonly invoked as the main trigger for Oceanic Anoxic Events (OAEs). Global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas, stimulating biological productivity.The end-result was widespread anoxia and deposition of black shales: the hallmarks of OAEs. In order to assess the role of weathering as both an OAE initiator and terminator (via CO 2 sequestration) during the Early Aptian OAE 1a (Selli Event, ~120 Ma) the isotopic ratio of lithium isotopes was analysed in three sections of shallowmarine carbonates from the Pacific and Tethyan realm and one basinal pelagic section from the Tethyan domain. Because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high-and lowtemperature alteration of basaltic material, a shift to lighter  7 Li values is expected to characterize OAEs. The studied sections illustrate this phenomenon:  7 Li values decrease to a minimum coincident with the negative carbon-isotope excursion that effectively records the onset of OAE 1a. A second negative  7 Li excursion occurs coeval with the minimum in strontium isotopes after the event. The striking similarity to the strontium-isotope record argues for a common driver. The formation and destruction (weathering) of an oceanic LIP could account for the parallel trend in both isotope systems. The double-spike in lithium isotopes is probably related to a change in weathering congruencies. Such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering, in conjunction with organic-carbon burial, led to drawdown of atmospheric CO 2 during the early Aptian OAE 1a.

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Section: Methods and Experimental Set-upmentioning

confidence: 99%

Section: Constraints From Multi-isotope Excursionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lechler

Strandmann

Jenkyns

et al. 2015

Earth and Planetary Science Letters

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105

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“…This distribution could reflect an expansion of the OMZ, reaching shallower areas on the margins, coincident with a major transgres sion, which could favor increased continental runoff and an increase in nutrient inputs (i.e. Burla et al, 2008;Castro et al, 2008;Blattler et al, 2011;Najarro et al, 2011a). Similar models of expansion of the OMZ have been proposed for the OAE2 (i.e.…”

Section: Om Sources and Environmental Conditionsmentioning

confidence: 99%

Organic geochemistry, stable isotopes, and facies analysis of the Early Aptian OAE—New records from Spain (Western Tethys)

Quijano

Jiménez

Pancost

et al. 2012

Palaeogeography, Palaeoclimatology, Palaeoecology

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The Early Aptian Oceanic Anoxic Event (OAEla) is a time interval characterized by increased organic carbon accumulation in marine sediments, notable sedimentary and biotic changes, and abrupt carbon-isotope excursions indicative of significant major palaeoenvironmental changes linked to a perturbation in the global carbon cycle. Here we present the study of four sections recording the OAEl a (Early Aptian) in Spain, which are located in two broad basins respectively located in the South and the North of Iberia: the Southern Iberian Palaeomargin (Carbonero, La Frontera and Cau sections) and the Basque-Cantabrian Basin (Puentenansa section), which represent depositional settings ranging from shallow marine (distal ramp -Cau-and drowned platform -Puentenansa-) to pelagic environments (Carbonero, La Frontera). Biomarker compositions, C-isotope profiles, biostratigraphic data and fades analysis from the four sections are correlated and integrat ed. The C-isotope curves all present a clear negative excursion followed by a positive shift. The integration of the C-isotope curves with the biostratigraphic data has been used to correlate the studied sections and to ten tatively identify the eight segments formerly proposed from the Alpine domain, and subsequently identified in sections worldwide. Four main groups of compounds are present in all sections: n-alkanes, isoprenoids, hopanes and steranes. n-Alkanes and acyclic isoprenoids (pristane and phytane) are dominant in most samples.The hopanes are represented by a range ofC27 to C35 components, with the specific isomers varying amongst the sections due to differences in thermal maturity. Steranes ocrur as a range of C27, C28 and C29 isomers, whereas diasteranes only occur in the most thermally mature section (Carbonero). Other compounds of interest include gammacerane and dinosterane. Differences in thennal maturity appear to be the first order control on different biomarker assemblages amongst the studied sections. The Carbonero section is thermally mature, whereas the nearby La Frontera and Cau sections are immature. Puentenansa has intermediate values. Organic matter is de rived from a range of terrestrial, marine and bacterial sources. The dominance of the C29 sterane isomers in all sections suggests a strong contribution from higher plants. The presence of gammacerane indicates water col umn stratification, and high C2g/C30 hopane ratios suggest anoxia at the water/sediment interface, respectively.Sedimentologic analysis also suggests anoxic conditions during sedimentation, but evidence for strong and per sistent water column anoxia is equivocaL The correlation of the sections reveals that sedimentation of organic-rich fades started earlier in pelagic and later in the shallow marine settings, which can be related to an expansion of the favorable conditions for organic matter accumulation and preservation from deep marine waters to shallower platform environments during the development ofOAEla.

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Why are the δ¹³C_org values in Phanerozoic black shales more negative than in modern marine organic matter?

Meyers

2014

Geochem Geophys Geosyst

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The d13 C org values of Phanerozoic black shales average 227&, whereas those of modern marine organic matter average 220&. The black shale isotopic values mimic those of continental organic matter, yet their organic geochemical properties mandate that they contain predominantly marine organic matter. Hypotheses that proposed to explain the low d13 C values of black shales include diagenetic losses of isotopically heavier organic matter components, releases of isotopically light carbon from methane clathrates or extensive magmatic events, greater photosynthetic discrimination against 13 C during times of higher atmospheric pCO 2 , and greenhouse climate stratification of the surface ocean that magnified photic zone recycling of isotopically light organic matter. Although the last possibility seems contrary to the vertical mixing that leads to the high productivity of modern oceanic upwelling systems, it is consistent with the strongly stratified conditions that accompanied deposition of the organic carbon-rich Pliocene-Pleistocene sapropels of the Mediterranean Sea. Because most Phanerozoic black shales contain evidence of photic zone anoxia similar to the sapropels, well-developed surface stratification of the oceans was likely involved in their formation. Existence of isotopically light land plant organic matter during several episodes of extensive magmatism that accompanied black shale deposition implies massive release of mantle CO 2 that added to the greenhouse conditions that favored oceanic stratification. The 13 C depletion common to most Phanerozoic black shales apparently resulted from a greenhouse climate associated with elevated atmospheric pCO 2 that led to a strongly stratified ocean and photic zone recycling of organic matter in, augmented by magmatic CO 2 releases.

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Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes

Cited by 181 publications

References 70 publications

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Organic geochemistry, stable isotopes, and facies analysis of the Early Aptian OAE—New records from Spain (Western Tethys)

Why are the δ¹³C_org values in Phanerozoic black shales more negative than in modern marine organic matter?

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Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes

Cited by 181 publications

References 70 publications

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

Organic geochemistry, stable isotopes, and facies analysis of the Early Aptian OAE—New records from Spain (Western Tethys)

Why are the δ13Corg values in Phanerozoic black shales more negative than in modern marine organic matter?

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Why are the δ¹³C_org values in Phanerozoic black shales more negative than in modern marine organic matter?