12 research outputs found
Abrupt episode of mid-Cretaceous ocean acidification triggered by massive volcanism
Large igneous province volcanic activity during the mid-Cretaceous approximately 94.5 million years ago triggered a global-scale episode of reduced marine oxygen levels known as Oceanic Anoxic Event 2. It has been hypothesized that this geologically rapid degassing of volcanic carbon dioxide altered seawater carbonate chemistry, affecting marine ecosystems, geochemical cycles, and sedimentation. Here, we report on two sites drilled by the International Ocean Discovery Program offshore of southwest Australia that exhibit clear evidence for suppressed pelagic carbonate sedimentation in the form of a stratigraphic interval barren of carbonate, recording ocean acidification during the event. We then use the osmium isotopic composition of bulk sediments to directly link this protracted ~600- kiloyear shoaling of the marine calcite compensation depth to the onset of volcanic activity. This decrease in marine pH was prolonged by biogeochemical feedbacks in highly productive regions that elevated heterotrophic respiration of carbon dioxide to the water column. A compilation of mid- Cretaceous marine stratigraphic records reveals a contemporaneous decrease of sedimentary carbonate content at continental slope sites globally. Thus, we contend that changes in marine carbonate chemistry are a primary ecological stress and important consequence of rapid emission of carbon dioxide during many large igneous province eruptions in the geologic past
Expedition 369 methods
This chapter documents the procedures and methods used in the shipboard laboratories during International Ocean Discovery Program (IODP) Expedition 369. This introductory section in particular provides a rationale for the site locations and an overview of IODP depth conventions, curatorial procedures, and general core handling/analyses during Expedition 369. Subsequent sections describe specific laboratory procedures and instruments in more detail. This information only applies to shipboard work described in the Proceedings volume; methods used in shore-based analyses of Expedition 369 samples and/or data will be described in various scientific contributions in the open peer-reviewed literature and the Expedition Research Results chapters of this Proceedingsvolume
Late Cretaceous orbitally-paced carbon isotope stratigraphy from the Bottaccione Gorge (Italy)
A refined astronomical tuning of the upper Albian-lower Campanian is proposed from the Bottaccione reference section (Gubbio, central Italy). Long-term eccentricity cycles filtered from a high-resolution delta C-13 record were tuned to the highly stable 405 kyr cycles of the new La2010 astronomical solution for the Earth's orbital elements. The achieved orbital tuning provides a new precise, and accurate age model for dating biostratigraphic, magnetostratigraphic and carbon isotope events through a similar to 23 Myr long record. Cycles of similar to 8.0, 4.7, 3.4 and similar to 2.4 Myr modulate the entire delta C-13 record, thus extending their detection from the Cenozoic to similar to 100 Ma and represent primary and stable long-term oscillation modes of Earth's climate-ocean system. Although an ultimate driver of these long-term periodicities is lacking, we speculate that specifically the periodicity at 4.7 Myr, represents a homologue of the present eccentricity grand-cycles, evolved by the chaotic behaviour of solar system planets during the Mesozoic. The long-term periodicities potentially reflect an unexplored expression of the low-frequency response of the carbon cycle to global biogeochemical dynamics of major nutrients, particularly phosphorus, associated with modulation of inputs to the ocean in turn triggered by high-order marine transgressions and formation of highly productive shelf seas. This very long-term eccentricity control, modulated by periodic low-energy cycles, is suggested to play a crucial role in carbon cycling, controlling a chain of climate sensitive global biogeochemical processes on the Earth. Finally, these grand-cycles provide a potential tool for geological correlation and provide a robust constraint for accurate calculation of the orbital evolution of the Solar System. (C) 2013 Elsevier B.V. All rights reserved
Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events
This is the author accepted manuscript. The final version is available via the DOI in this recordMercury (Hg) is increasingly being used as a sedimentary tracer of Large
Igneous Province (LIP) volcanism, and supports hypotheses of a coincidence between the
formation of several LIPs and episodes of mass extinction and major environmental
perturbation. However, numerous important questions remain to be answered before Hg
can be claimed as an unequivocal fingerprint of LIP volcanism, as well as an
understanding of why some sedimentary records document clear Hg enrichment signals
whilst others do not. Of particular importance is evaluating the impact of different
volcanic styles on the global mercury cycle, as well as the role played by depositional
processes in recording global Hg-cycle perturbations. Here, new mercury records of
Cretaceous Oceanic Anoxic Event 2 (OAE 2: ~94 Ma) and the latest Cretaceous (~67 to
66.0 Ma) are presented. OAE 2 is associated with the emplacement of multiple,
predominantly submarine, LIPs; the latest Cretaceous with subaerial volcanism of the
Deccan Traps. Both of these connections are strongly supported by previously published
trends towards unradiogenic osmium- (Os) isotope values in globally distributed
sedimentary records. Hg data from both events show considerable variation between
different locations, attributed to the effectiveness of different sediment types in
registering the Hg signal, with lithologically homogeneous records documenting more
clear Hg enrichments than sections with major changes in lithology such as limestones to
claystones or organic-rich shales. Crucially, there is no geographically consistent signal
of sedimentary Hg enrichment in stratigraphic records of either OAE 2 or the latest
Cretaceous that matches Os-isotope evidence for LIP emplacement, indicating that
volcanism did not cause a global Hg perturbation throughout the entire eruptive history
of the LIPs formed at those times. It is suggested that the discrepancy between Os-isotope
and Hg trends in records of OAE 2 is caused by the limited dispersal range of Hg emitted
from submarine volcanoes compared to the global-scale distribution of Os. A similar lack
of correlation between these two proxies in uppermost Cretaceous strata indicates that,
although subaerial volcanism can perturb the global Hg cycle, not all subaerial eruptions
will do so. These results highlight the variable impact of different volcanogenic processes
on the efficiency of Hg dispersal across the globe. Factors that could influence the impact
of LIP eruptions on the global mercury cycle include submarine versus subaerial
volcanism, volcanic intensity or explosivity, and the potential contribution of thermogenic
mercury from reactions between ascending magma and surrounding organic-rich
sediments.We acknowledge the UK Natural Environment Research Council Grant NE/G01700X/1 (to Tamsin
Mather), PhD studentship NE/L501530/1 (to Lawrence Percival), Grant NE/H020756/1 (to Ian Jarvis), the
European Commission (FP7/2007â2013 grant number 215458), National Science Foundation Grant
EAR0643290 (to Bradley Sageman and Jennifer McElwain), Shell International Exploration and Production
Inc., and the Leverhulme Trust for funding
Specific coronary drug-eluting stents interfere with distal microvascular function after single stent implantation in pigs.
Objectives The aim of this study was to compare the effects of single drug-eluting stents (DES) on porcine coronary function distal to the stent in vivo and in vitro. Background The mechanism of endothelial dysfunction occurring in human coronary conduit arteries up to 9 months after DES implantation is unknown. Methods A sirolimus-eluting stent (SES), paclitaxel-eluting stent (PES), and a bare-metal stent (BMS) were implanted in the 3 coronary arteries of 11 pigs. After 5 weeks, in vivo responses in distal coronary flow to different doses of bradykinin (BK) and nitrates were measured. In vitro, vasodilation to BK and nitrates, as well as vasoconstriction to endothelin (ET)-1 were assessed in both distal coronary conduit and small arteries. In addition, contributions of nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHFs) and cyclic guanosine monophosphate (cGMP) responses to BK-stimulation were determined in vitro. Results Both DES did not alter in vivo distal vasomotion. In vitro distal conduit and small arterial responses to BK were also unaltered; DES did not alter the BK-induced increase in cGMP. However, after NO synthase blockade, PES showed a reduced BK-response in distal small arteries as compared with BMS and SES (p <0.05). The ET-1âinduced vasoconstriction and vascular smooth muscle cell function were unaltered. Conclusions In this study of single stenting in healthy porcine coronaries for 5 weeks, SES did not affect distal coronary vascular function, whereas PES altered distal endothelial function of small arteries under conditions of reduced NO bioavailability. Therefore, specifically the EDH-component of microvascular function seems affected by PES
Specific coronary drug-eluting stents interfere with distal microvascular function after single stent implantation in pigs.
Objectives The aim of this study was to compare the effects of single drug-eluting stents (DES) on porcine coronary function distal to the stent in vivo and in vitro. Background The mechanism of endothelial dysfunction occurring in human coronary conduit arteries up to 9 months after DES implantation is unknown. Methods A sirolimus-eluting stent (SES), paclitaxel-eluting stent (PES), and a bare-metal stent (BMS) were implanted in the 3 coronary arteries of 11 pigs. After 5 weeks, in vivo responses in distal coronary flow to different doses of bradykinin (BK) and nitrates were measured. In vitro, vasodilation to BK and nitrates, as well as vasoconstriction to endothelin (ET)-1 were assessed in both distal coronary conduit and small arteries. In addition, contributions of nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHFs) and cyclic guanosine monophosphate (cGMP) responses to BK-stimulation were determined in vitro. Results Both DES did not alter in vivo distal vasomotion. In vitro distal conduit and small arterial responses to BK were also unaltered; DES did not alter the BK-induced increase in cGMP. However, after NO synthase blockade, PES showed a reduced BK-response in distal small arteries as compared with BMS and SES (p <0.05). The ET-1âinduced vasoconstriction and vascular smooth muscle cell function were unaltered. Conclusions In this study of single stenting in healthy porcine coronaries for 5 weeks, SES did not affect distal coronary vascular function, whereas PES altered distal endothelial function of small arteries under conditions of reduced NO bioavailability. Therefore, specifically the EDH-component of microvascular function seems affected by PES