Unlocking the Deep Ocean Circulation Mysteries of the Subantarctic South Pacific Ocean and its Influence on Climate Over the Last 2 Million Years

University Of Delaware, Newark DE

Investigators

Abstract

Both the amplitude and recurrence frequency of Earth’s glacial-interglacial cycles have evolved over the past two million years. Prior to 1.2 Myr, glaciers were small and appeared every 41 thousand years. Larger glaciers that appeared every 100 thousand years became dominant after 0.7 million years ago. The period between 1.2-0.7 million years ago is known as the Mid-Pleistocene Transition (MPT). During the MPT, Earth did not experience any significant changes in its orbit to support the observed changes in ice age patterns. Why the Earth’s glacial rhythm changed during the MPT has been a topic of debate for the last several decades. Changes in deep ocean circulation during the MPT have been proposed to have a major role in perturbing the Earth’s carbon cycle and ushering the 100 thousand-year world. The overarching goal of this project is to reconstruct the changes in deep ocean circulation and how the water mass geometry evolved over time, with a special emphasis on the MPT. It will also investigate the link between deep Southern Ocean stratification, associated changes in the carbon cycle, and subsequent changes in glacial rhythm. This project will use Nd isotopes preserved in fossil fish teeth and Fe-Mn coatings on foraminifera as a water mass proxy to reconstruct past changes in deep ocean circulation. These analyses will be performed at two sites drilled in the central South Pacific during the International Ocean Discovery Program Expedition 383. This project will support a graduate student and create research opportunities for undergraduate students from a Minority-Serving Institution. The deep ocean is a critical component of the climate system because it can act as a carbon reservoir and, consequently, influence glacial cycle behavior. Very recently, a few Neodymium (Nd) isotope studies from the Atlantic Ocean have reported that changes in deep ocean circulation during the MPT could have ushered/supported the late Pleistocene 100 kyr glacial periodicity. Currently, there is limited knowledge about the state of deep ocean circulation in the deep South Pacific and its relationship to concurrent climate changes. This project will use Nd isotopes preserved in fossil fish teeth and Fe-Mn coatings on foraminifera as a water mass proxy to reconstruct past changes in deep ocean circulation at two sites drilled in the central South Pacific during the International Ocean Discovery Program Expedition 383. The South Pacific represents the largest volume fraction of the deep Southern Ocean and could have acted as a carbon reservoir storing and releasing carbon on a glacial-interglacial time scale. By integrating the results from the South Pacific with findings from the Atlantic Ocean, this project will generate a more comprehensive understanding of the role of deep ocean circulation in driving climate changes during the MPT. Mechanisms that changed oceanic carbon cycling in the past are of particular importance to understanding present and future climate change. This project will also support a graduate student and create research opportunities for undergraduate students from a Minority-Serving Institution. The researchers will participate in local community outreach activities to communicate the importance of scientific ocean drilling, and this work in general will serve the US scientific ocean drilling community during the transition period post-JOIDES Resolution. This project is jointly funded by the Marine Geology and Geophysics Program in the Division of Ocean Sciences and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.