Estimates of Eddy Heat Flux Crossing the Antarctic Circumpolar Current from Observations in Drake Passage

D Randolph Watts,Teresa K Chereskin,Karen L Tracey,Kathleen A Donohue

doi:10.1175/jpo-d-16-0029.1

Abstract

AbstractThe 4-yr measurements by current- and pressure-recording inverted echo sounders in Drake Passage produced statistically stable eddy heat flux estimates. Horizontal currents in the Antarctic Circumpolar Current (ACC) turn with depth when a depth-independent geostrophic current crosses the upper baroclinic zone. The dynamically important divergent component of eddy heat flux is calculated. Whereas full eddy heat fluxes differ greatly in magnitude and direction at neighboring locations within the local dynamics array (LDA), the divergent eddy heat fluxes are poleward almost everywhere. Case studies illustrate baroclinic instability events that cause meanders to grow rapidly. In the southern passage, where eddy variability is weak, heat fluxes are weak and not statistically significant. Vertical profiles of heat flux are surface intensified with ~50% above 1000 m and uniformly distributed with depth below. Summing poleward transient eddy heat transport across the LDA of −0.010 ± 0.005 PW with the stationary meander contribution of −0.004 ± 0.001 PW yields −0.013 ± 0.005 PW. A comparison metric, −0.4 PW, represents the total oceanic heat loss to the atmosphere south of 60°S. Summed along the circumpolar ACC path, if the LDA heat flux occurred at six “hot spots” spanning similar or longer path segments, this could account for 20%–70% of the metric, that is, up to −0.28 PW. The balance of ocean poleward heat transport along the remaining ACC path should come from weak eddy heat fluxes plus mean cross-front temperature transports. Alternatively, the metric −0.4 PW, having large uncertainty, may be high.

Highlights

The Southern Ocean heat balance affects Antarctic climate and glacial melting directly and 34 global climate in general through its effect upon down- and upwelling across the Antarctic Cir35 cumpolar Current (ACC)
78 It included a transect spanning the channel plus a local dynamics array sited in a region of elevated eddy kinetic energy (Lenn et al 2007; Firing et al 2011) in the Polar Frontal Zone between the 80 Subantarctic Front and the Polar Front
The Local Dynamics Ar17 ray (LDA) was centered on the inter602 frontal zone between the Polar Front and Subantarctic Front, where satellite altimetry and repeat 603 shipboard ADCP measurements (Lenn et al 2007; Firing et al 2011) indicate high eddy kinetic energy (EKE)

Summary

Introduction

The Southern Ocean heat balance affects Antarctic climate and glacial melting directly and 34 global climate in general through its effect upon down- and upwelling across the Antarctic Cir cumpolar Current (ACC). Our study, called cDrake, deployed an extensive array of current- and pressure-recording inverted echo sounders (CPIES) to measure the current and temperature structure through the full water column for four years in Drake Passage It included a transect spanning the channel plus a local dynamics array sited in a region of elevated eddy kinetic energy (Lenn et al 2007; Firing et al 2011) in the Polar Frontal Zone between the Subantarctic Front and the Polar Front.

Objectives

Methods

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Discussion

Conclusion