Deep Water Moorings

Summary

Deep water mooring at Totten Glacier. Image credit: Steve Rintoul, CSIRO and ACE CRC.

The Deep water moorings facility provides the coordination of national efforts in the sustained observation of open ocean properties with particular emphasis on observations important to climate and carbon cycle studies.  The major areas of research driving the facility include; tracking multi-decadal ocean change and predicting regional and marine impacts; understanding the modes and drivers of climate variability in the Australian region; improved understanding and prediction of ocean currents; and discovering the links between ocean and climate variability, marine chemical cycling and ecosystem structure and function at various time scales.  The Deep water moorings facility is comprised of a number of moorings located in Antarctic, sub-Antarctic, sub-Tropical and Tropical open-ocean waters around Australia.  Depending on location, each of these deep water moorings is equipped with particular instrumentation to measure desired variables and to cope with local conditions. 

The Southern Ocean Time Series Observatory provides high temporal resolution observations in sub-Antarctic waters. Observations are broad and include measurements of physical, chemical and biogeochemical parameters from multiple deep-water moorings. The emphasis is on seasonal and inter-annual variations of the lower atmosphere and upper ocean properties and their influence on exchange with the deep ocean. The continuous time-series information permit investigation into issues of ocean and atmospheric physics and chemistry, climate change, carbon cycling and biogeochemical controls on marine productivity. These moorings provide cost-effective observations and overcome the infrequent availability of ships in the region.

The Deep water arrays sub-facility targets 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. They will contribute to improved estimates of the regional and global sea level budget, improvements to the climate model simulations via direct comparison with observations, assimilation and development of improved model physics and parameterisations.

Indonesian Throughflow mooring array
Southern Ocean Time Series mooring array
East Australian Current mooring array

Instrumentation and Data

There are four deep water mooring sites located around Australia. The longest records are from the Southern Ocean Time Series site southwest of Tasmania. This site includes three separate moorings – a deep ocean sediment trap, a Pulse biogeochemical mooring and an air-sea flux mooring. Located in the sub-Antarctic Zone near 140oE, 47oS, the site is particularly vulnerable to the extreme weather events that typify the area including very large waves, strong currents and severe storms, presenting significant technical and engineering challenges. The Pulse biogeochemistry mooring is used to measure upper ocean carbon cycle and phytoplankton productivity processes. The sediment trap mooring is used to collect sinking particles to quantify carbon transports, and provides current meter measurements and a deep ocean CTD to measure heat contents below the depth of Argo profiling float measurements. The flux station mooring provides the measurements necessary for computing air-sea fluxes of heat, momentum and mass.

Between 2011 and 2013 three mooring arrays were deployed in a polynya off the coast of East Antarctica, in the Indonesian Throughflow and in the East Australian Current. 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. The data deliverable from the moorings arrays are mass, temperature and salt time series and are used to measure mean transport. 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.  

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.
  • Among the key tasks for the maiden voyage in March 2015 of the RV Investigator into the Southern Ocean was the redeployment of three high-precision deep-water moorings as part of IMOS. These moorings are capable of measuring a large array of ocean properties including temperature, salinity, currents, waves, and biological activity, as well as atmospheric conditions. To read the blog updates for Eric Schulz's travels on the maiden voyage 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.

  • Pteropod shell weights in the high-CO2 Southern Ocean: This study present observations of pteropod shell-weight and flux from 1997–2006 in sediment traps deployed at 47S, 142 E at 2000 meters below sea surface in the Southern Ocean. A decadal trend of –1.17±0.47 µg yr−1 (P =0.02) in mean shell weight in the pteropod Limacina helicina antarctica forma antarctica suggests a small but detectable reduction in calcification. Gaps in the data make it difficult to state with certainty the significance of the trend. However, this data set represents the first attempt to estimate interannual variations in pteropod calcification and establish a benchmark against which future impacts of ocean acidification may be detected. Reference: D. Roberts, W. R. Howard, A. D. Moy, J. L. Roberts, T. W. Trull, S. G. Bray, and R. R. Hopcroft. 2008. Interannual variability of pteropod shell weights in the high-CO2 Southern Ocean. Biogeosciences Discuss., 5: 4453–4480  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.

Contacts:

Dr Tom Trull, Dr Eric Schulz, and Dr. Bernadette Sloyan

Partners:

CSIRO Oceans and Atmosphere, BoM, ACE CRC

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.