The influence of true polar wander on glacial inception in North America

A Daradich,P Huybers,J.X Mitrovica,N.-H Chan,J Austermann

doi:10.1016/j.epsl.2016.12.036

Abstract

The impact that long-term changes in Earth's rotation axis relative to the surface geography, or true polar wander (TPW), and continental drift have had in driving cooling of high-latitude North America since the Eocene is explored. Recent reanalyses of paleomagnetic pole positions suggest a secular drift in Earth's rotation axis of ∼8° over the last 40 Myr, in a direction that has brought North America to increasingly higher latitudes. Using modern temperature data in tandem with a simple model, a reduction in the annual sum of positive degree days (PDDs) driven by this polar and plate motion over the last 20 Myr is quantified. At sites in Baffin Island, the TPW- and continental drift-driven decrease in insolation forcing over the last 20 Myr rivals changes in insolation forcing caused by variations in Earth's obliquity and precession. Using conservative PDD scaling factors and an annual snowfall equal to modern station observations, the snowiest location in Baffin Island 20 Myr ago had a mass balance deficit of ∼0.75–2 m yr−1 (water equivalent thickness) relative to its projected mass balance at 2.7 Ma. This mass balance deficit would have continued to increase as one goes back in time until ∼40 Myr ago based on adopted paleopole locations. TPW and continental drift that moved Arctic North America poleward would have strongly promoted glacial inception in Baffin Island at ∼3 Ma, a location where the proto-Laurentide Ice Sheet is thought to have originated.

Highlights

The fossil record in North America shows evidence of a longterm secular cooling over the past 65 Myr
Given that such changes in obliquity were sufficient to transition between glacial and interglacial states during the Early Pleistocene (e.g., Imbrie et al, 1992), when glacial cycles occurred at the obliquity period, this range provides a measure of the threshold in positive degree days (PDDs) that needs to be surpassed in order for glaciation of the Canadian Arctic to occur, and we return to it when we explore the possible impact of true polar wander (TPW) on glacial inception in North America
Our simple models find that even a modest rate of TPW (∼0.2 deg/Myr) in tandem with plate tectonic motion would have resulted in cooling that contributed significantly to glacial inception in North America at ∼3 Ma

Summary

Introduction

The fossil record in North America shows evidence of a longterm secular cooling over the past 65 Myr. TPW refers to a motion of the rotation axis relative to the Earth’s surface and it has a direct impact on climate by changing the latitude (and insolation history) of all points on the surface This process has previously been proposed as a mechanism for secular cooling of North America during the Cenozoic (Donn and Shaw, 1977), paleomagnetic inferences of TPW from the 1970s (Jurdy and Van der Voo, 1975) suggested that polar motion, and its effect on climate, would have been minor since the beginning of the Cenozoic. In this paper we revisit this possible connection using a recently updated estimate of TPW since the Late Cretaceous and simple models of North American climate

True polar wander and climate

Modern climatological gradients

Insolation and summer energy

Glacial inception and mass balance

Conclusions