Braking the Antarctic Circumpolar Current

How does a standing meander southeast of Tasmania brake the Antarctic Circumpolar Current?
Voyage No

IN2018_V05

16 Oct, 2018

to

16 Nov, 2018

Hobart

to

Hobart

Chief Scientist

Prof Nathan Bindoff

Institution

University of Tasmania

Voyage summary

Research voyage to the Southern Ocean to study the Antarctic Circumpolar Current (ACC), the world's largest and strongest current.

The ACC plays a large role in our climate: it distributes heat, fresh water and carbon-dioxide among the major oceans. It also keeps Antarctica cool and frozen. Although westerly winds in the Southern Ocean have been strengthening over the last forty years (by approximately 40%), the strength of the east-flowing ACC has remained constant.

Researchers will study the ACC and the Southern Ocean's capacity to absorb heat and carbon dioxide, as well as and how it may respond to climate variability and change. The research aims to obtain a unique three dimensional survey of a standing meander in the ACC, and deliver simulations to quantify the processes that slow the ACC.

Understanding how the ACC responds to additional wind energy is a major puzzle which will help researchers piece together climate variability.

There is one piggyback project on this voyage:

  • Upper ocean biogeochemistry in the Macquarie Meander of the Antarctic Circumpolar Current (Dr Peter Strutton, IMAS): Project to assess the biogeochemical impact of the physical braking of the ACC.

Voyage blog: Explainer - how the Antarctic Circumpolar Current helps keep Antarctica frozen

The Antarctic Circumpolar Current, or ACC, is the strongest ocean current on our planet. It extends from the sea surface to the bottom of the ocean, and encircles Antarctica. It is vital for Earth’s health because it keeps Antarctica cool and frozen. It is also changing as the world’s climate warms. Scientists like us are studying the current to find out how it might affect the future of Antarctica’s ice sheets, and the world’s sea levels.
Read more on CSIROscope
Scientists deploying a piece of equipment off Investigator
Scientists deploying a vertical microstructure profiler (VMP-2000), which measures temperature, salinity, pressure and turbulence, from RV Investigator in the Antarctic Circumpolar Current,

Voyage outcomes

Researchers successfully deployed a tall mooring at a permanent 'meander' in the Polar Front (a branch of the ACC) south of Tasmania. This mooring will collect data on temperature, salinity and ocean currents from the surface to the sea floor over a two year period. These data will help researchers address fundamental questions about the role of the Southern Ocean in the global climate system and will assist in improving understanding of how ocean dynamics are affected by increasing winds.

The meander, which is a loop or bend in the ACC, is likely to exist because of the sharp change in water depth as the ACC passes over the southeast Indian Ridge. The meander flexes and steepens in response to changes in the winds and currents, and this leads to the formation of energetic eddies. The eddies are a central element of the transfer of heat toward Antarctica and to slowing or braking the ACC flow. The research conducted during this voyage will help inform Australia’s strategy for ocean modelling and provide potential new methods for monitoring the poleward heat fluxes using satellite observations.

A host of additional physical and biochemical measurements gained on this voyage allowed researchers to obtain a unique 3-dimensional survey of the meander and deliver companion high-resolution simulations to quantify the processes that slow the ACC.