[PAOCQ] Sophie Hines (WHOI)

“Revisiting the paradigm: New insights on ocean circulation using eNd from the MPT to today”

Neodymium isotopes are a powerful tracer of ocean circulation, despite having a complex marine cycle. Within the deep Atlantic Ocean, they appear to predominantly reflect water mass mixing, facilitating their use as a circulation proxy. Neodymium isotope reconstructions can therefore be used to investigate the role of ocean circulation in glacial-interglacial climate variability over a range of timescales. We use high-resolution paired neodymium, carbon, and oxygen isotope data from a sediment core in the South Atlantic to re-examine the role of deep ocean circulation in driving the Mid-Pleistocene Transition (MPT; ~1.25-0.85 Ma). This interval marks a fundamental shift in the character of glacial-interglacial climate. Before the MPT, glacial-interglacial cycles occurred at a period of ~41 kyr, responding linearly to solar forcing. During the MPT, these cycles strengthened, lengthened to a period of ~100 kyr, and became more sawtooth in shape. Many drivers have been suggested for this change in glacial-interglacial variability, but one prevailing hypothesis for the origin of the MPT involves a dramatic change in glacial ocean circulation, marked by a circulation “crisis” at 900 ka. Our combined neodymium, carbon, and oxygen isotope records instead suggest that glacial deep ocean variability before and during the early MPT closely resembled that of the most recent glacial cycle, and only modest circulation adjustments were required to facilitate increased carbon storage in the deep ocean during this major climate transition. Through our analysis, we highlight the importance of high-resolution circulation reconstructions for accurately characterizing glacial-interglacial variability.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

Contact: paoc-colloquium-comm@mit.edu