Neodymium Evidence for Increased Circumpolar Deep Water Flow to the North Pacific During the Middle Miocene Climate Transition

Sev Kender,Ty D. Cobb,Deborah J. Thomas,Kara A. Bogus

doi:10.1029/2017pa003309

Abstract

AbstractLow salinity surface water inhibits local deepwater formation in the modern North Pacific. Instead, southern‐sourced Circumpolar Deep Water (CDW) fills the basin, which is the product of water masses formed from cold sinking centers in the Southern Ocean and North Atlantic. This CDW is responsible for transporting a significant amount of global heat and dissolved carbon in the deep Pacific Ocean. The history of its flow and the broader overturning circulation are widely assumed to be sensitive to climate perturbations. However, insufficient records exist of CDW presence in the deep North Pacific with which to evaluate its evolution and role in major climate transitions of the past 23 Ma. Here we report sedimentary coatings and fish teeth neodymium isotope values—tracers for water‐mass mixing—from deepwater International Ocean Discovery Program Site U1438 (4.7 km water depth) in the Philippine Sea, northwest Pacific Ocean. Our results indicate the water mass shifted from a North Pacific source in the early Miocene to a southern source by ~14 Ma. Within the age model and temporal constraints, this major reorganization of North Pacific water mass structure may have coincided with ice sheet build up on Antarctica and is most consistent with an increased northward flux of CDW due to enhanced sinking of cold water forced by Antarctic cooling. The northward extent of this flux may have remained relatively constant during much of the past 14 Ma.

Highlights

Overturning circulation in the modern Pacific Ocean is driven by Circumpolar Deep Water (CDW), which is sourced from cold sinking centers around Antarctica and the North Atlantic (Ferrari et al, 2014; Talley, 2013; Talley et al, 2011)
Our results indicate that the water source for the deep Philippine Sea remained relatively stable for the majority of the last 23 Ma, as εNd values follow the gradual trends that are present in both intermediate and deepwater sites in the Pacific Ocean attesting to its long term stratification
The gradual increase toward more radiogenic values in all Pacific intermediate and deep sites from ~15 to ~5 Ma may be due to a gradual decline in Atlantic Ocean inflow through a closing Isthmus of Panama (Martin & Haley, 2000)

Summary

Introduction

Overturning circulation in the modern Pacific Ocean is driven by Circumpolar Deep Water (CDW), which is sourced from cold sinking centers around Antarctica and the North Atlantic (Ferrari et al, 2014; Talley, 2013; Talley et al, 2011). Changes in PMOC have the potential to impact global temperature, moisture supply, and the carbon cycle, and there have been several attempts to reconstruct PMOC over the Cenozoic to understand its past roles in climate change and tectonic evolution (e.g., Butzin et al, 2011). It is not yet known how PMOC responded to major climate transitions such as the middle Miocene climate transition (MMCT, ~14 Ma)

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Conclusion