Biotic induction and microbial ecological dynamics of Oceanic Anoxic Event 2

Abstract

Understanding the causal mechanisms of past marine deoxygenation is critical to predicting the long-term Earth systems response to climate change. However, the processes and events preceding widespread carbon burial coincident with oceanic anoxic events remain poorly constrained. Here, we report a comprehensive biomarker inventory enveloping Oceanic Anoxic Event 2 that captures microbial communities spanning epipelagic to benthic environments in the southern proto-North Atlantic Ocean. We identify an abrupt, sustained increase in primary productivity that predates Oceanic Anoxic Event 2 by ∼220 ± 4 thousand years, well before other geochemical proxies register biogeochemical perturbations. During the event, recurrent photic zone euxinia triggered a major marine microbial reorganization accompanied by a decrease in primary production. These findings highlight how organic carbon burial drivers operated along a continuum in concert with microbial ecological changes, with antecedent, localized increases in primary production destabilizing carbon cycling and promoting the progressive marine deoxygenation leading to Oceanic Anoxic Event 2.

Production of diverse brGDGTs by Acidobacterium Solibacter usitatus in response to temperature, pH, and O2 provides a culturing perspective on brGDGT proxies and biosynthesis

“…BrGDGTs were identified using their corresponding retention times in an in‐house environmental reference sample (0–1 cm surface sediment from lake 3LN, northern Quebec, Raberg et al, 2021 ), their molecular masses, and the MS/MS spectra generated by data‐dependent acquisition mode (ddMS/MS). A subset of TLE samples was also analyzed by reverse phase (RP) LC (Connock et al, 2022) to confirm relative elution order of brGDGT isomers and further constrain their identity (data not shown). Cellular tetraether abundances were calculated relative to fatty acids (FA) and mono/diethers using the C24 and C46 internal standards.…”

Biosynthesis of H-GDGTs linked to ocean oxygen deficiency

“…(B) Relative amount of H-GDGTs was accumulated in sediments during the OAE-2 interval (ODP Site 1258, 422-426 mcd). The δ 13 Corg (%) and Calculated SST data are from Connock et al ( 45 ).…”

“…Furthermore, the H-GDGTs (‰) are slightly higher in the post-OAE-2 interval (420-422 mcd) compared to the pre-OAE-2 interval (426-430 mcd), a trend consistent with δ 13 Corg (%) records. More specifically, the H-GDGTs proxy provides a more detailed and explicit depiction of the ocean oxygen deficiency in the interval that bound the OAE-2, as the enrichment of H-GDGTs was sustained until the onset of OAE-2 (426.40-426.30 mcd) and is approximately contemporaneous with a thallium isotope excursion ( 44, 45 ), indicating the regional deoxygenation occurred before the globally recognized carbon cycle perturbation. Additionally, the variations of H-GDGTs (‰) were not correlated with the calculated sea surface temperature (SST) (Fig.…”

Aridification of Northwest Australia and Nutrient Decline in the Timor Sea During the 40 Kyr World

“…Sample preparation and instrument setup followed method published in Connock et al. (2022). The Prahl and Wakeham (1987) calibration was applied to the $${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$$—based SST, which exhibits same features and trend as using Müller et al.…”

“…This new analytical approach exhibits greater sensitivity in detecting the low-concentration tri-unsaturated alkenones compared to conventional gas chromatography-flame ionization detector (GC-FID) analyses, therefore the tri-unsaturated C 37 alkenones were distinctly detected in all analyzed samples of this study. Sample preparation and instrument setup followed method published in Connock et al (2022). The Prahl and Wakeham (1987) calibration was applied to the 𝐴𝐴 U K ′ 37 -based SST, which exhibits same features and trend as using Müller et al (1998) calibration (Zhang et al, 2023).…”