Deep water arrays

Summary

Deployment of the Polynya Deepwater Array off the Adelie Land Coast in January 2011.

The three Deep water array sites target observations of deep ocean currents and properties needed to monitor and understand the role of the ocean on climate and climate variability.  The arrays monitor ocean circulation and property variability in the ocean surrounding Australia and provide estimates of the ocean contribution to the regional and global circulation, heat and freshwater content and change.  These observations contribute to improved understanding of ocean dynamics, estimates of the regional and global sea level budget and result  in more reliable climate and ocean models  via direct comparison with observations and the assimilation and development of improved model physics and parameterisations. 

Deepwater Arrays have been deployed at three sites:

  • The three mooring in the Polynya Array, off the Adelie Land Coast in Antarctica, are designed to monitor the transport and properties of Antarctic Bottom Water that outflow to the deep Southern Ocean from the Antarctic continental shelf. Initially the moorings were deployed in the Mertz Polynya but following the calving of the Mertz Glacier in 2010 changes in the regional icescape have made this region logistically infeasible. A one-year pilot deployment was undertaken in 2014 in the polynya near the Totten Glacier to assess this site for sustained observations. The mooring were not deployed in 2015 as we are reassessing the best way to monitor bottom water production in this region.
  • The Indonesian Throughflow mooring array aims to sustainably and directly measure the leakage of Pacific thermocline and intermediate waters from the western equatorial Pacific into the South Indian Ocean in the two major passages – Timor Passage and Ombai Strait. The Indonesian Passages represent an important ‘choke point’ of the global ocean overturning circulation and the climate system. The mooring array monitors ~80% of the interbasin exchange of mass, temperature and salt between the Pacific and Indian Ocean.
  • The East Australian Current (EAC) deep water array is designed to monitor the mean and time-varying flow of the East Australian Current transport. The East Australian Current (EAC) is the complex and highly energetic poleward western boundary current system of the South Pacific subtropical gyre. It is the dominant mechanism for the redistribution of heat between the ocean and atmosphere in the Australian region by transporting heat from the tropical Pacific Ocean to the mid-latitude ocean and atmosphere. The EAC Array is deployed from the continental slope to the abyssal waters off Brisbane (27oS).

Instrumentation and Data

The Deep water arrays current deployed are the Polynya, Indonesian Throughflow (ITF) and East Australian Current (EAC). Each of these array consist of 3 to 6 moorings positioned across the continental shelf and slope and abyssal waters.  The data deliverable from the moorings arrays are velocity, temperature and salt time series. The mooring data are delivered in delayed-mode, because the subsurface instruments store data which is only retrieved during the 18 month or 2 year servicing of the arrays. The arrays provide high temporal resolution observations in topical, sub-tropical and Antarctic waters.  Each of the mooring sites provide the ability to track multi-decadal climate change, and to improve our understanding and prediction of both climate variability in the Australian region and global climate.  

The two Polynya arrays, located near the Mertz and Totten Glaciers off the Adelie Land Coast in Antarctica, were deployed for four and one year respectively in regions that have been dominated by heavy pack ice. The sensors on each mooring are located at four depths between the sea floor and 300m.  Sensors are not positioned higher in the water column on these moorings to avoid any potentially damaging contact with icebergs.  The sensors collect a time-series of full-depth profiles of water velocity and discrete temperature and salinity measurements. 

The Indonesian Throughflow array in the Timor Sea north of Australia uses temperature and salinity sensors to collect data for the entire water column.  Current meters fixed to the moorings profile velocity data above 500m and point source velocity between 500m and 1200m depth. The ITF Array (2011-present) is an extension of the INSTANT (2003-2006) time series data of the Indonesian Throughflow mass, heat and salt fluxes between the Pacific and Indian Ocean.

The East Australian Current mooring array captures the mean and time-varying flow of the East Australian Current. The mooring sensors collect temperature, conductivity and depth measurements and include an array of full-depth current meters.

Deployment of the ITF Deep water array

Application of Data

  • The IMOS Deep water moorings will provide significant new insights into the variable nature of the East Australian Current (EAC). The EAC has important implications for Australia’s weather and climate, and is the dominant mechanism for the redistribution of tropical Pacific Ocean heat between the ocean and atmosphere in the Australian region. The waters in the Tasman Sea have warmed by more than 2oC, faster than other parts of the world’s oceans. Western boundary current regions, such as the EAC system, are highly variable and linked to large-scale ocean changes. Monitoring the EAC therefore, provides information of the large-scale drivers of regional ocean change. These changes may result in subtropical marine species moving into temperate waters, altering the habitat of many species. To read more click here.
  • The Totten Glacier contains an amount of ice equivalent to 6 metres of global sea level rise. Glaciers grounded on bedrock below sea level, like the Totten, are particularly vulnerable to changes in ocean temperature and currents, because the ocean can penetrate deep under the glacier. IMOS deep water moorings that had been deployed for up to two years at six different locations adjacent to the Totten glacier were recovered by the Australian icebreaker Aurora Australis in early 2015. The mooring records will provide the first ocean measurements spanning the full year in this area, giving us an idea of what happens during the long cold winter months when access to the region is impossible. The measurements we've collected here are crucial for setting a benchmark that can be used to assess future change. To read more click here.

Useful Links

The Deep water moorings Facility Publication Report - If you have any questions regarding the data, or corrections, or would like to add a publication or presentation that uses IMOS data please contact the IMOS office via email: publication(at)emii.org.au.

Contact:

Dr. Bernadette Sloyan

Partners:

CSIRO Oceans and Atmosphere

International programs:

OceanSITES

NOAA Ocean Climate Observation Program

Tropical Pacific Observing System (TPOS2020)

Research Moored Array for African-Asian-Australia Monsoon Analysis and Prediction

GODEA OceanView

 

Your access to IMOS Deep Water Mooring data discovery and exploration is through the Australian Ocean Data Network (AODN) Portal.