Abstract
The early Pliocene shoaling of the Central American Seaway (CAS), ~4.7–4.2 million years ago (mega annum-Ma), is thought to have strengthened Atlantic Meridional Overturning Circulation (AMOC). The associated increase in northward flux of heat and moisture may have significantly influenced the evolution of Pliocene climate. While some evidence for the predicted increase in North Atlantic Deep Water (NADW) formation exists in the Caribbean and Western Atlantic, similar evidence is missing in the wider Atlantic. Here, we present stable carbon (δ13C) and oxygen (δ18O) isotope records from the Southeast Atlantic-a key region for monitoring the southern extent of NADW. Using these data, together with other δ13C and δ18O records from the Atlantic, we assess the impact of the early Pliocene CAS shoaling phase on deep-water circulation. We find that NADW formation was vigorous prior to 4.7 Ma and showed limited subsequent change. Hence, the overall structure of the deep Atlantic was largely unaffected by the early Pliocene CAS shoaling, corroborating other evidence that indicates larger changes in NADW resulted from earlier and deeper shoaling phases. This finding implies that the early Pliocene shoaling of the CAS had no profound impact on the evolution of climate.
Highlights
The early Pliocene shoaling of the Central American Seaway (CAS), ~4.7–4.2 million years ago, is thought to have strengthened Atlantic Meridional Overturning Circulation (AMOC)
It has been proposed that the progressive closure of the CAS, which occurred during the Pliocene[1], was a necessary precondition for establishing enhanced Atlantic Meridional Overturning Circulation (AMOC) conditions[2,3]
Prior to the early Pliocene CAS shoaling phase (Fig. 7a), we find strong evidence for a well-ventilated deep Atlantic as far a ~28oS, suggesting that North Atlantic Deep Water (NADW) formation was active despite the open gateway
Summary
The early Pliocene shoaling of the Central American Seaway (CAS), ~4.7–4.2 million years ago (mega annum-Ma), is thought to have strengthened Atlantic Meridional Overturning Circulation (AMOC). The additional salt carried northward would have increased density in the surface waters of deep-water formation regions, such as the Nordic and Labrador Seas This is expected to have led to stronger NADW formation, driving enhanced AMOC along with a marked reorganization of the deep-water flow in the Atlantic Ocean[3,4]. Such closure induced changes have been implicated in enhancing ice sheet growth and promoting the onset of Northern Hemisphere Glaciation through an increase in the North Atlantic moisture budget[5,6,7], as well as in triggering an overall shoaling of the tropical thermocline and promoting the development of the Eastern Equatorial Pacific cold tongue[8]. In this study, the early Pliocene shoaling of the CAS refers to these well-documented changes in Caribbean surface-water oceanography
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