Eric Schulz (E.Schulz AT bom.gov.au)
Marian Wiltshire (Marian.Wiltshire AT utas.edu.au)
Tom Trull (Tom.Trull AT csiro.au)
Australia has maintained a real-time ocean observatory in the Southern Ocean Sub-Antarctic Zone, 580km southwest of Tasmania since 2010.
The Southern Ocean Flux Station (SOFS) – a moored weather buoy, has been relaying hourly observations of the wind, air and sea temperature, humidity, air pressure, sunlight and rain back to shore, providing us with the first air-sea flux mooring measurements for the Southern Ocean. This not only gives insight into the present conditions, but also helps to build a long-term record in this climatically important region of the global ocean.
Figure 1: Map of the Australian sector of the Southern Ocean indicating the location of the Southern Ocean Flux Station (red star). Observations collected at this site are representative of the Sub-Antarctic Zone, indicated by the region north of the red line. The light grey shading indicates winter ice.
As well as aiding weather forecasting, meteorological observations are used to compute the total heat, mass and momentum fluxes between the surface ocean and lower atmosphere on timescales from diurnal to annual. While the Southern Ocean plays a significant role in the global climate system, there is a paucity of sustained in situ air-sea flux observations in this harsh and remote region. This lack of “ground truth” has led to significant differences in global flux products in the mid- to high-latitudes. The high quality observations recorded by the SOFS are a valuable contribution to building the climate record and understanding climate variability.
The Southern Ocean Flux Station produced the first ever annual air-sea flux time series in the Southern Ocean, published in 2012 (Schulz, E, Josey, SA, Verein, R 2012, First air-sea flux mooring measurements in the Southern Ocean, Geophysical Research Letters, vol. 39, doi:10.1029/2012GL052290). The data has revealed an air-sea flux regime that is rich in extreme heat loss events and has a small, annual net heat loss from the ocean to the atmosphere. Further analysis of data from the ongoing series of deployments of the SOFS mooring will enable a more detailed determination of the ocean-atmosphere interaction in the largely under sampled Southern Ocean. Australia’s new Marine National Facility, the RV Investigator, will redeploy the SOFS mooring in March 2015.
Air-sea flux observations from the Southern Ocean have been identified by the Southern Ocean Observing System (SOOS) as a priority observation gap. Development of a long-term strategy to address this gap is underway with an Air-Sea Fluxes task group formed and a workshop planned for April/May 2015. Australia’s SOFS is well positioned to be a key data contributor to this burgeoning international effort.
SOFS is part of a multidisciplinary ocean observatory—the Southern Ocean Time Series, which forms part of the Australian Integrated Marine Observing System (IMOS). In addition to SOFS, the Southern Ocean Time Series includes the Sub-Antarctic Zone Sediment Trap and the Pulse bio-geo-chemical moorings. The Southern Ocean Time Series is tasked with collecting sustained observations of the atmospheric surface layer, as well as the upper and deep ocean to understand the transfer of heat, moisture, energy and carbon dioxide between the atmosphere and ocean. This will improve our knowledge of climate, carbon cycling and the role of the oceanic ecosystem. The Southern Ocean Time Series is one of a few high temporal resolution time-series sites identified in the global OceanSITES project, and the only one presently located in the Southern Ocean (although two additional observatories are in development).
Figure 2: SOTS data holdings for SAZ (red), Pulse (blue) and SOFS (green) since 1997. Solid is data in archive, outline is currently being collected, dashed outline is planned next deployment.
All data collected by these moorings are available from the IMOS Ocean Portal.
SOFS is operated by the Bureau of Meteorology; the SAZ and Pulse moorings are operated by the CSIRO and the Antarctic Climate and Ecosystems Cooperative Research Centre (which also incorporates collaborations with NOAA).