Late Cretaceous to recent ocean-bottom currents in the SW Pacific Gateway, southeastern Chatham Rise, New Zealand

Lara Steinbrink,Karsten Gohl,Florian Riefstahl,Bryan Davy,Lionel Carter

doi:10.1016/j.palaeo.2020.109633

Abstract

Sedimentary drifts archive the history of the ocean-bottom current dynamics. Bottom currents associated with the Pacific Deep Western Boundary Current (DWBC) along the submarine continental margin off southern and eastern New Zealand are of particular interest because of their potential to contain records of changes in the SW Pacific circulation. Analysis of multi-channel seismic reflection data from the RV Sonne expedition SO246 together with earlier seismic data enabled us to reconstruct bottom currents and map sediment deposits along the southeastern Chatham Rise margin for the past 80 million years. The seismic records are supplemented by sub-bottom profiler and bathymetric data, which provide detailed information on the youngest stratigraphy, sedimentary structures and bathymetry. This approach allows time-dependent mapping of sedimentary deposits and reconstruction of current regimes. The opening of the Tasmanian Gateway in the early Oligocene led to the development of the DWBC, which influenced regional sedimentary processes. However, the occurrence of bottom current activity prior to opening the Tasmanian Gateway suggests the existence of a proto-DWBC. Increased bottom current activity in the Miocene indicates a change to a more dynamic circulation regime in the SW Pacific, consistent with intensification of Antarctic glaciation and increased Antarctic Bottom Water formation. Plio/Pleistocene records indicate a weakening of the bottom-water energy along the Chatham Rise margin. Overall, sediment deposition was widespread before gateway opening, almost non-existent in the Oligocene and sparse in the Neogene.

Highlights

The heat transport by the global ocean circulation influences much of the Earth's climate
Seismic data analysis allows the reconstruction of ocean current conditions along the southeastern Chatham Rise margin for the past 80 Myr
From ~80 Ma to 33.7 Ma, post-Gondwana break-up sedimentation of the southeastern Chatham Rise margin resulted in mostly regular drape-like deposition indicating generally quiescent benthic current conditions

Summary

Introduction

The heat transport by the global ocean circulation influences much of the Earth's climate. Large volumes of reworked sediments are incorporated in deepsea contourite drifts formed by deposition from DWBC and represent the impact of the Tasmanian Gateway opening, changes in the thermohaline system of the Pacific Ocean, development of Antarctic ice sheets and the tectonic evolution of the New Zealand plate boundary (Carter and McCave, 1994; Carter et al, 2004) These events are overprinted with effects of orbital forcing on sediment supply, abyssal sedimentation and current flow, which increase the complexity of the ENZOSS (Carter et al, 2004).

Data acquisition

Seismic observations and interpretation

Sediment drift formation and paleo-circulation

Conclusions