[Paper Review] Intrinsically episodic Antarctic shelf intrusions of circumpolar deep water via canyons

Ellie Q. Y. Ong, Edward Doddridge+3 more|arXiv (Cornell University)|Apr 26, 2023

Cryospheric studies and observationsEarth and Planetary Sciences3 citations

TL;DR

This study uses an eddy-resolving isopycnal model to demonstrate that warm circumpolar deep water intrusions onto the East Antarctic shelf via submarine canyons occur intrinsically in episodic bursts, driven by internal feedbacks between wind energy and eddy generation in the Antarctic Slope Current—even without external temporal forcing. Narrower canyons exhibit more irregular cross-shelf transport than wider ones, highlighting the role of canyon geometry in modulating episodic intrusions.

ABSTRACT

The structure of the Antarctic Slope Current at the continental shelf is crucial in governing the poleward transport of warm water. Canyons on the continental slope may provide a pathway for warm water to cross the slope current and intrude onto the continental shelf underneath ice shelves, which can increase rates of ice shelf melting, leading to reduced buttressing of ice shelves, accelerating glacial flow and hence increased sea level rise. Observations and modelling studies of the Antarctic Slope Current and cross-shelf warm water intrusions are limited, particularly in the East Antarctica region. To explore this topic, an idealised configuration of the Antarctic Slope Current is developed, using an eddy-resolving isopycnal model that emulates the dynamics and topography of the East Antarctic sector. Warm water intrusions via canyons are found to occur in discrete episodes of large onshore flow induced by eddies, even in the absence of any temporal variability in external forcings, demonstrating the intrinsic nature of these intrusions to the slope current system. Canyon width is found to play a key role in modulating cross-shelf exchanges; warm water transport through narrower canyons is more irregular than transport through wider canyons. The intrinsically episodic cross-shelf transport is found to be driven by feedbacks between wind energy input and eddy generation in the Antarctic Slope Current. Improved understanding of the intrinsic variability of warm water intrusions can help guide future observational and modelling studies in the analysis of eddy impacts on Antarctic shelf circulation.

Motivation & Objective

• To investigate the mechanisms behind episodic intrusions of warm circumpolar deep water onto the East Antarctic continental shelf.
• To determine whether such intrusions can occur intrinsically due to internal dynamics, even without external temporal forcing.
• To assess the influence of canyon width on the variability and magnitude of cross-shelf warm water transport.
• To clarify the role of eddy generation and wind energy feedbacks in driving episodic cross-shelf exchange.
• To improve understanding of shelf circulation dynamics for guiding future observational and modeling studies in East Antarctica.

Proposed method

• An idealized, eddy-resolving isopycnal ocean model is configured to simulate the dynamics and topography of the East Antarctic sector.
• The model emulates the Antarctic Slope Current and its interaction with submarine canyons on the continental slope.
• Simulations are conducted under constant external forcing to isolate intrinsic variability in the system.
• Eddy activity and energy feedbacks between wind input and eddy generation are analyzed to identify drivers of episodic intrusions.
• Cross-shelf transport is quantified through canyons of varying widths to assess geometric control on intrusion patterns.
• The model tracks warm water fluxes and identifies episodic onshore flow events linked to eddy activity.

Experimental results

Research questions

• RQ1 Can warm water intrusions onto the Antarctic shelf occur episodically without any external temporal forcing?
• RQ2 What is the role of eddy generation and wind energy feedbacks in driving episodic cross-shelf transport?
• RQ3 How does canyon width modulate the irregularity and magnitude of warm water intrusion events?
• RQ4 To what extent is the observed episodicity intrinsic to the slope current system rather than externally forced?
• RQ5 How do internal dynamics in the Antarctic Slope Current lead to intermittent onshore flow through submarine canyons?

Key findings

• Warm water intrusions through submarine canyons occur in discrete, episodic bursts even under constant external forcing, demonstrating intrinsic variability in the system.
• Eddies generated within the Antarctic Slope Current are the primary driver of episodic onshore flow, with feedbacks between wind energy input and eddy activity sustaining the episodes.
• Narrower canyons exhibit more irregular and less predictable cross-shelf transport compared to wider canyons, indicating a strong geometric control on intrusion dynamics.
• The episodic nature of intrusions is not due to external forcing but arises from internal instabilities and feedback mechanisms within the slope current system.
• The findings suggest that eddy-driven cross-shelf exchange is a fundamental feature of Antarctic shelf circulation, particularly in regions with submarine canyons.
• This intrinsic episodicity must be accounted for in future modeling and observational studies to accurately assess ice shelf melting rates and sea level rise contributions.