Pathways of ocean heat towards Pine Island and Thwaites grounding lines

Yoshihiro Nakayama,Patrice Klein,Helene Seroussi,Pierre Dutrieux,Dimitris Menemenlis,Georgy Manucharyan,Hector S Torres,Michael Schodlok,Hong Zhang,Eric Rignot

doi:10.1038/s41598-019-53190-6

Abstract

In the Amundsen Sea, modified Circumpolar Deep Water (mCDW) intrudes into ice shelf cavities, causing high ice shelf melting near the ice sheet grounding lines, accelerating ice flow, and controlling the pace of future Antarctic contributions to global sea level. The pathways of mCDW towards grounding lines are crucial as they directly control the heat reaching the ice. A realistic representation of mCDW circulation, however, remains challenging due to the sparsity of in-situ observations and the difficulty of ocean models to reproduce the available observations. In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments in qualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104°W and 74.3°S. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates.

Highlights

In the Amundsen Sea, the Pine Island and Thwaites Glaciers are the two fastest-flowing outlet glaciers[1,2], contributing to an ice loss equivalent of about 0.3 mm yr−1 of recent global sea level rise[3,4,5,6]
Existing observations are sparse in time and space and the importance of cavity circulation has only been inferred for Pine Island Glacier in previous studies[9,12]
For austral summer conditions, (1) pathways of warm modified Circumpolar Deep Water (mCDW) from the continental shelf region into the Pine Island Ice Shelf (PIIS) and Thwaites Ice Shelf (TIS) ice shelf cavities and towards their grounding lines and (2) processes that determine the magnitude of ice shelf melt near the PIIS and TIS grounding lines

Summary

Introduction

In the Amundsen Sea, the Pine Island and Thwaites Glaciers are the two fastest-flowing outlet glaciers[1,2], contributing to an ice loss equivalent of about 0.3 mm yr−1 of recent global sea level rise[3,4,5,6]. The bed topography of these glaciers slopes downward inland, to as deep as 2500 m below sea level, making the glaciers prone to marine ice sheet instability[7,8] and further acceleration of grounded ice loss These glaciers have been accelerating over the past two decades, hypothetically triggered by variable and relatively recent high basal melting of their ice shelves[9,10]. The main cause for high basal melting of Pine Island Ice Shelf (PIIS) and Thwaites Ice Shelf (TIS) is the relatively warm modified Circumpolar Deep Water (mCDW, about 0.5–1.5 oC, located below ~300–500 m depth)[11]. Ice shelf melt rates near grounding lines (1) are generally a few orders of magnitude higher than at other locations of the same ice shelves The model-data disagreement at high frequencies may be caused by the model’s inability to represent fast processes, such as higher-baroclinic-mode internal gravity waves, the variability of meltwater plumes, or the lack of remote internal gravity wave energy input at the northern model www.nature.com/scientificreports/ (a)

Objectives

Methods