Characterising Atlantic deep waters during the extreme warmth of the early Eocene ‘greenhouse’.

Abstract:

The meridional overturning circulation (MOC) is a planetary-scale oceanic flow that is of direct importance to the climate system because it transports heat, salt and nutrients to high latitudes and regulates the exchange of CO₂ with the atmosphere. The Atlantic Ocean plays a strong role in the modern day MOC however, it is unclear what role it may have played during extreme climate conditions such as those found in the early Eocene ‘greenhouse’.

In order to resolve the Atlantic’s role in the MOC during the early/middle Eocene, we present a multi-proxy approach to investigate changes in ocean circulation, water mass geometry, sediment supply to the deep oceans and the physical strength of deep waters from four different IODP drill sites. Neodymium isotopes (εNd), REE profiles and cerium anomalies measured in fossilised fish teeth help to characterise geochemical changes to water masses throughout the Atlantic whilst bulk sediment εNd and XRF-core scan data documents changes in sediment supply to the region. Sortable silt data provides a physical constraint on the strength of deep-water movements during the extreme climatic conditions of the early Eocene. We utilise expanded and continuous sequences from two sites in the North west Atlantic spanning the early to middle Eocene recently recovered on IODP Exp. 342 (1403, 1409) that are located on the Newfoundland Ridge, directly in the flow path of today’s Deep Western Boundary Current. We also present data from equatorial Demerara Rise (IODP site 1258) and from further north at the mouth of the Labrador Sea (ODP Site 647).