Obliquity forcing of organic matter accumulation during Oceanic Anoxic Event 2

An analysis of orbitally influenced climate-sensitive sedimentation is conducted across a meridional transect of the proto-North Atlantic, to reconstruct the behavior of the carbon cycle and climate during Oceanic Anoxic Event 2 (OAE 2; similar to 94 Ma). Midlatitude to near equatorial sites spanning deep-ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata. The results yield consistent independent astrochronologies at each location-compatible with the recently published radioisotopic/astrochronologic time scale at the Cenomanian-Turonian GSSP-and thus provide a unified high-resolution temporal context for evaluation of the event. The proto-North Atlantic astrochronologies document an amplification of obliquity power during OAE 2, indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event. The strong obliquity signal suggests an influence of high-latitude climate processes across midlatitude deep-ocean to tropical shelf environments. Changes in oceanic circulation during OAE 2 represent a likely mechanism for the propagation of a high latitude signal, and proxy data from Demerara Rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification. We hypothesize that a dense high-latitude water mass displaced a pre-existing nutrient-rich anoxic deep-water layer in the proto-North Atlantic (augmented by enhanced volcanism), driving an episode of high productivity that lasted 700-800 ka. The development and intensification of the new intermediate/deep water source was potentially driven by eustatic sea level rise, which created expansive seaways in mid to high latitudes.