Energetics of Eddy-Mean Flow Interactions in the Amery Ice Shelf Cavity

Yang Wu,Chengyan Liu,Liangjun Yan,Zhaomin Wang

doi:10.3389/fmars.2021.638741

Abstract

Previous studies demonstrated that eddy processes play an important role in ice shelf basal melting and the water mass properties of ice shelf cavities. However, the eddy energy generation and dissipation mechanisms in ice shelf cavities have not been studied systematically. The dynamic processes of the ocean circulation in the Amery Ice Shelf cavity are studied quantitatively through a Lorenz energy cycle approach for the first time by using the outputs of a high-resolution coupled regional ocean-sea ice-ice shelf model. Over the entire sub-ice-shelf cavity, mean available potential energy (MAPE) is the largest energy reservoir (112 TJ), followed by the mean kinetic energy (MKE, 70 TJ) and eddy available potential energy (EAPE, 10 TJ). The eddy kinetic energy (EKE) is the smallest pool (5.5 TJ), which is roughly 8% of the MKE, indicating significantly suppressed eddy activities by the drag stresses at ice shelf base and bottom topography. The total generation rate of available potential energy is about 1.0 GW, almost all of which is generated by basal melting and seawater refreezing, i.e., the so-called “ice pump.” The energy generated by ice pump is mainly dissipated by the ocean-ice shelf and ocean-bottom drag stresses, amounting to 0.3 GW and 0.2 GW, respectively. The EKE is generated through two pathways: the barotropic pathway MAPE→MKE→EKE (0.03 GW) and the baroclinic pathway MAPE→EAPE→EKE (0.2 GW). In addition to directly supplying the EAPE through baroclinic pathway (0.2 GW), MAPE also provides 0.5 GW of power to MKE to facilitate the barotropic pathway.

Highlights

The Amery Ice Shelf (AIS) is the third largest Antarctic ice shelf located in East Antarctica, with an area of about 62,000 km2 (Herraiz-Borreguero et al, 2016a)
As the kinetic energy mainly concentrates in the ocean circulation, the distribution of mean kinetic energy (MKE) reflects the main cyclonic circulations beneath the ice shelf, i.e., inflow of shelf water in the east and outflow of Ice Shelf Water (ISW) in the west (Williams et al, 2001, 2002; Hemer et al, 2006; Galton-Fenzi et al, 2012)
MKE is the leading energy reservoir in region AIS1 which is 1.4, 8 and 12.2 times as large as mean available potential energy (MAPE), EAPE, and eddy kinetic energy (EKE), respectively. These results indicate a strong conversion of MAPE to MKE and significant suppression of EKE over the whole AIS cavity, especially in region AIS1 (Figures 10A,B)

Summary

INTRODUCTION

The Amery Ice Shelf (AIS) is the third largest Antarctic ice shelf located in East Antarctica, with an area of about 62,000 km (Herraiz-Borreguero et al, 2016a). To better understand the important impacts of ocean-ice shelf interaction on the Antarctic climate system and ecosystem, a deeper understanding of ocean dynamics in the sub-ice-shelf cavity is essential For this purpose, we conducted a thorough examination of the eddy-mean flow interaction by analyzing the Lorenz energy cycle (LEC). In the sub-ice-shelf cavity, for example, the buoyancy power input supplies almost all the energy to drive the circulation as wind stress cannot be exerted on sea water (Foldvik and Kvinge, 1974; Lewis, 1985; Schodlok et al, 2016). We used the outputs of a recently developed eddy-resolving ocean-sea ice-ice shelf model (Liu et al, 2017) to conduct a quantitative study on the LEC in the sub-ice-shelf cavity of the AIS. This paper is summarized with a conclusion and discussion in section “Concluding Remarks and Discussion”

MATERIALS AND METHODS

Experiments

RESULTS

CONCLUDING REMARKS AND DISCUSSION

DATA AVAILABILITY STATEMENT