National Reference Stations vessel-based sampling


Sensor-based observations at the National Reference Stations are supplemented by vessel-based biogeochemical sampling. This water sampling program is an expansion of the long-term water sampling program established at the historical sampling sites Port Hacking, Maria and Rottnest Islands. The expanded program generally replicates the monthly time scale of the historical sampling frequencies as this has proved to be sufficient to detect multi-decadal change.

Detailed documentation of the vessel-based sampling methods are provided in an NRS Biogeochemical Operations handbook and NRS standardized profiling CTD cast procedures found in the National mooring network documentation page.

Sampling time varies with location, with reduced sampling at some sites due to logistical constraints and local conditions. For example at the Darwin reference station the extreme nature of the tides reduces the sampling to four times a year but spread across the tidal cycle. This quarterly sampling was designed to capture the variability in sediment and nutrient loads across dry and wet seasons and spring and neap tides. Samples at Kangaroo Island are collected eight times a year due to limited availability of research vessels.

Instrumentation and Data

The National Reference Stations collect observations of both physical and biogeochemical variables to characterise the ocean environment and to understand fundamental biological processes within the environment. Core variables observed include temperature, salinity, dissolved oxygen, nutrients, turbidity, carbon, phytoplankton, and zooplankton. The vessel-based sampling comprises:

  • Vertical profiling sensor measurements of conductivity (salinity), temperature and depth, oxygen, fluorometry and turbidity;
  • Niskin bottle samples at discrete 10 m intervals for measurements of total dissolved inorganic carbon, alkalinity and nutrients;
  • A combined water column sample from all Niskin bottles for phytoplankton and pigments;
  • Zooplankton samples from a plankton drop net;
  • Additional Niskin bottle water samples taken adjacent to moored instruments to allow for cross validation and characterization of data collected by the moored sensors; and
  • Measurement of turbidity with a Secchi disk.

Laboratory analysis

Samples of similar suites of parameters are freighted to centralized laboratories for analysis by specialized teams of technicians and scientists. Three different laboratories at CSIRO’s Oceans and Atmosphere (OA) Business Unit in Tasmania conduct analysis on hydrochemistry, plankton pigments and carbon respectively. Tropical and temperate phytoplankton and zooplankton samples are processed at the OA laboratories in Queensland, while cool temperate phytoplankton samples are processed at the Australian Antarctic Division in Tasmania. Pico-plankton analysis is undertaken by the Australian Microscopy and Microanalysis Research Facility at the University of Western Australia (Lynch et al 2014).

There are other sampling programs that have started from this vessel-based monthly sampling, namely the Australian Marine Microbial Biodiversity Initiative (AMMBI) program. This program started in 2012 with a one year pilot to test the feasibility of including microbial sampling in the routine, monthly biogeochemical and oceanographic observation of the IMOS National Reference Stations. The pilot study was undertaken at three NRS along the EAC and was expanded to all NRS in the 2014-2015 period. This program is now part of a new project, led by Bioplatforms Australia, that will use AMMBI observations and apply its genomics network to perform DNA sequencing to generate the large-scale datasets scientists require to understand fundamental marine processes.