High-resolution records of Oceanic Anoxic Event 2: Insights into the timing, duration and extent of environmental perturbations from the palaeo-South Pacific Ocean

Gangl, S.K., Moy, C.M., Stirling, C.H., Jenkyns, H.C., Crampton, J.S., Clarkson, M.O., Ohneiser, C. and Porcelli, D. 2019. High-resolution records of Oceanic Anoxic Event 2: Insights into the timing, duration and extent of environmental perturbations from the palaeo-South Pacific Ocean. Earth and Planetary Science Letters 518 , pp. 172-182. 10.1016/j.epsl.2019.04.028

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Abstract

Oceanic Anoxic Event 2 (OAE 2), which took place around the Cenomanian–Turonian boundary (∼94 Ma), is associated with extreme perturbations to the global carbon cycle, affected ocean basins worldwide and was associated with significant biological turnover. Although this event has been well studied in the northern hemisphere, the evolution and character of OAE 2, particularly in terms of the vertical and lateral extent of anoxia, is poorly constrained in the palaeo-Pacific Ocean. Furthermore, the precise timing, duration and character of this event, and the exact mechanisms driving OAE 2 environmental changes, are still being debated. Here, we present the first high-resolution records of carbon isotopes, total organic carbon and magnetic susceptibility from the southern palaeo-Pacific Ocean during OAE 2, sampled at two sections in New Zealand. The carbon isotope records from both localities reveal a ∼2‰ positive excursion that represents the global change in the carbon cycle associated with OAE 2. When combined with a cyclostratigraphic age model, these new records constrain the duration of the OAE 2 carbon isotope excursion to at least 930 ± 25 ky and indicate a minimum duration of 200 ± 25 ky for the ‘Plenus Cold Event’ that took place during OAE 2. The lithologies and low organic-carbon contents of the New Zealand sections imply that oxic conditions prevailed along, at least parts of, the margins of the palaeo-Pacific Ocean at mid- to high southern latitudes during OAE 2 while, contemporaneously, conditions were locally anoxic in the mid-water column of the equatorial Pacific Ocean. Despite these apparently oxic conditions in the New Zealand region, there was a partial collapse of benthic ecosystems leading up to, and during, OAE 2, suggesting environmental deterioration caused by intermittent oxygen deprivation, or other chemical or biological disturbances in the South Pacific region that remain to be elucidated.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0012-821X
Date of Acceptance:	17 April 2019
Last Modified:	06 Nov 2023 16:00
URI:	https://orca.cardiff.ac.uk/id/eprint/163529

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