Coastal and Regional Oceanography Lab

Towards an Integrated Dynamical Understanding of Coastal Marine Systems

New South Wales - IMOS

See below for an outline of NSW-IMOS research grounding and key scientific questions.

To learn more about our Integrated Marine Observing System or IMOS you can visit imos.org.au or watch this video.

1. Summary

 The marine environment on the narrow continental shelf along the coast of NSW is dominated by the poleward flowing East Australian Current (EAC) and the eddy field it produces.  The EAC and its eddies are strongly linked to fisheries recruitment, local biodiversity, marine park location and there is a strong connection between the EAC and other regional seas and currents.  The poleward extension of the EAC is strengthening, shown by an increase of over 2ºC per century at the Maria Island reference station off eastern Tasmania.  The water temperature regime has therefore been shifted ~350 km southwards.  The EAC, and its changing nature, will impact the climate and weather of NSW, as well as the state’s ecological and socio-economic values.

The natural variability of the EAC makes it difficult to forecast.  Our focus is on processes north and south of the separation zone off Coffs Harbour (30ºS) and Sydney (34ºS).  The NSW-IMOS Node aims to investigate the key feature of the EAC, including physical, bio-physical and biological properties, while building on historical observations. 

 

2. Socio-Economic Context

Most of Australia’s urban population is located on the narrow eastern and southern seaboards making the associated coastal waters among the nation's most exploited and often stressed environments. 

More than 80% of Australians are located within 50 km of the coast and more than half the nation lives within the coastal fringe from Brisbane to Melbourne.  The socio-economic issues of relevance to the NSW-IMOS Node are:

 

Australia and its continental shelf in light brown (200 m isobath), illustrating the particularly narrow shelf and proximity of the EAC off New South Wales (Figure modified from GeoScience Australia).

2.1 Climate Change

Future climate change will have wide ranging effects on the coastal and marine environment of NSW.  The East Australian Current (EAC) is predicted to both strengthen and warm significantly which will have many diverse effects from changing weather patterns to shifts in marine species distribution.  Species range shifting as a response to these and other climate change effects will have impacts for biodiversity, invasive species and fisheries.

2.2 Storm Events and Erosion

In recent years severe storm events generated by East Coast Lows (ECLs), have caused fatalities, severe flooding and erosion and caused hazards for shipping.  A recent example is the five ECL events in June 2007, which caused nearly $1000M in damage and were the cause of 10 deaths.  Predicted changes in wave climate such as an increase in wave height, change in the angle of incidence or increased frequency of high magnitude waves will affect the energy at the beach zone and alter sediment transport.  Given that the NSW coast has many substantial shoreline erosion hotspots more monitoring data is essential to give insight into the role of offshore processes in nearshore beach form, sand volumes and configuration.

2.3 Marine Park planning

The NSW Marine Parks Authority (MPA) aims to establish and manage a system of multiple-use marine parks designed to conserve marine biodiversity, maintain ecological processes and provide for ecologically-sustainable use, public appreciation and education of the marine environment.  An important factor requiring consideration during marine park zoning is the extent of connectivity among populations of key species.  There are still considerable gaps in our understanding of how the key habitats along the NSW coast are connected by larval dispersal, whether existing marine park sanctuary zones act as larval sources, sinks or neither, and how these locations vary seasonally and inter -annually.  However, it is clear that the EAC is a major driver of the spatial and temporal patterns of connectivity.  Knowledge of how economic and ecologically important benthic habitats are influenced by the EAC and climate will aid in determining marine park success in achieving biodiversity conservation.

2.4 Fisheries

Nearly 20% of the Australian population fish at least once a year (17% in NSW), and recreational fishers harvest up to 27,000 t of finfish with an annual value of around $2 billion (Henry and Lyle 2003).  Most of the marine technology industry is related to recreational fishing, which faces significant problems of declining catch rates.  Target species that are especially relevant to recreational fishing, tourism and IMOS are bream, flathead, mulloway, prawns, Australian salmon, grey nurse shark, bullshark and white shark.  Although commercial fishing occurs off the NSW coast, it is not large in the EMP (East Marine Planning region), valued in 2002-2006 at around $320 m and 1.4% of the national value.  The combination of phytoplankton cycles and blooms with upwelling, EAC strengthening and sea-surface warming or an increase in ECL’s, have yet to be investigated against fish occurrences and stocks.  Natural algal food sources for in-situ aquaculture farming also require observation against increasing sea-surface temperatures and associated shifts in plankton stocks, cycles and dispersion.

2.5 Shark Attacks

In February-March 2009, 3 separate shark attacks occurred in Sydney waters and the first for nearly 50 years, despite observations of sharks in earlier summers. The presence of sharks in the harbour surprised the public and resulted in a decline in beach attendance. This period was distinguished by strong, wind induced upwelling which reduced local water temperatures at the warmest time of the year from 25ºC to as low as 15ºC. The actual bio-physical relationships and a risk model for management remain a challenge for the NSW-IMOS Node.

2.6 Marine Tourism

Marine tourism is the largest marine industry in NSW.  The value of the marine industry (i.e. all recreational and light commercial vessels) in NSW is valued at over $2 billion pa and employs over 11,000 – both figures are almost equivalent to all other states combined (http://www.bia.org.au/data.html).  Over a third of the national marine industry employment (36%) is in NSW – and mostly in marine tourism.

 

3. Science Background

3.1 Multi-decadal Ocean Change

One of the key research areas of the NSW-IMOS Node is to contribute to national observations of decadal changes and climate variability of the East Australian Current (EAC), Leeuwin Current and Flinders Current using common platforms and metrics.

The East Australian Current (EAC) is the major western boundary current of the South Pacific Gyre, flowing from the southern Coral Sea and along the northern NSW coast (Ridgway & Dunn 2003). The EAC is Australia’s largest current and is typically 30 km wide, 200 m deep and travelling up to 4 knots. 

The core of the EAC is centred over the continental slope, although its coastal presence is felt by eddy encroachment.  Southeast Australian waters have experienced a multi-decadal warming over recent decades at a rate of between three and four times the global average (Holbrook and Bindoff 1997; Ridgway 2007).  The strengthening of the EAC is predicted to further warm Australian waters by 1-2ºC by 2030 and 2-3 ºC by 2070s, particularly off Tasmania (Poloczanska et al. 2008).  Consequently, the southeast Australian region is a global hot-spot for ocean temperature change.

Key Science Questions

  • To determine the variability in EAC strength from its source in the Coral Sea, the seasonal and spatial variability in the separation of the EAC from central NSW, and the EAC’s southward extension.
  • Contribute to monitoring the Bass Strait outflow and the northward coastally trapped wave propagation.
  • Contribute to the national backbone through the National Reference Station network and the supplementation of Satellite Remote Sensing products with local data.

3.2 Major Boundary Currents and Inter-basin Flows

A key research focus for the NSW-IMOS Node is to investigate the East Australian Current (EAC), its separation from the coast, and the resultant eddy field along the coast of South East Australia.

The East Australian Current (EAC) is the major western boundary current of the South Pacific Gyre, flowing from the southern Coral Sea and along the northern NSW coast (Ridgway & Dunn 2003). The EAC is Australia’s largest current and is typically 30 km wide, 200 m deep and travelling up to 4 knots. 

The core of the EAC is centred over the continental slope, although its coastal presence is felt by eddy encroachment.  Our knowledge of processes at the shelf break is very limited.  By comparison to the knowledge of the behaviour and variability of other western boundary currents there has been a significant lack of investigation into the EAC and its eddy field, for a current renowned for its mesoscale variability.

Key Science Questions

  • To determine the frequency, form and function (horizontal and vertical) of EAC eddies.
  • To understand air sea interactions, particularly to determine the development of East Coast Lows and severe winter storms in relation to warm core eddies.
  • Quantify the impact of key physical processes such as onshore encroachment of the EAC, slope water intrusions, upwelling, downwelling and internal waves.

3.3 Continental Shelf Processes

Quantifying the oceanographic processes on the continental shelf and slope of South East Australia is a key research area of the NSW-IMOS Node.

The Eat Australian Current (EAC) accelerates off northern New South Wales where the continental shelf off Smoky Cape (~31ºS) narrows by half in less than 0.5º latitude, to just 16 km wide.  The acceleration pushes up cool nutrient rich water.  Further uplifting is facilitated by the strength of the EAC, the eddies, topography and summer north-easterly winds (Roughan and Middleton 2002).  In addition to the EAC inducing mixing through interactions with topographic features, tides interact with these features generating internal tides and waves, which are a significant source of mixing.  These structures are complex and an understanding of these processes is essential for development of an understanding of the regional physical oceanography, for future physical model developments and as a supporting science for other marine disciplines and for atmospheric studies.

Key Science Questions

  • Examine the coastal wind and wave climate in driving nearshore currents and the northward sediment transport.
  • Quantify the biogeochemical cycling of carbon (nutrients and phytoplankton composition).
  • Determine the transport and dispersal of passive particles (e.g. larvae, eggs, spores) and the degree of along coast connectivity and trophic linkages.

3.4 Ecosystem Responses

A key research focus for the NSW-IMOS Node is to integrate ecosystem responses with oceanographic processes. The East Australia Current (EAC) is the key oceanographic feature off Australia’s east coast and is likely to be a major factor influencing the distributions of benthic organisms.  This warm water current is known to vary substantially among years in its strength and southward extension and is forecast to change further given climate change.  The coast of southeastern Australia comprises species-rich and diverse habitats across eastern Australia’s tropical-subtropical and temperate transitions.  This, together with the pervasive influence of the EAC on marine connectivity is a challenge for managers as they strive to understand the mechanisms underlying resident biodiversity.  The net effect of physical oceanographic changes on the biological connectivity of coastal populations is a critical concern for coastal management. 

Key Scientific Questions

  • Quantify the daily to decadal variation of planktonic communities in relation to oceanographic and climate-driven changes in physical and chemical ocean properties.
  • Quantify rocky reef biota variables (kelp distribution and abundance) associated with climate variability, at deep reefs along the NSW to Tasmanian coast.
  • Relationship of the EAC, its eddies and oceanographic conditions on fisheries, and movements by fish and sharks.
  • Quantify the seasonal and yearly variation of upper-predator (fish and marine mammal) communities.

4. Research: How will the key science questions be addressed?

4.1 Multi-decadal Ocean Change

To determine the variability in EAC strength from its source in the Coral Sea, the seasonal and spatial variability in the separation of the EAC from central NSW, and the EAC’s southward extension.

The NSW-IMOS alongshore mooring array is designed to allow monitoring of the temperature gradients in the EAC along the coast of NSW, north (Coffs) and south (Sydney) of the separation zone.  Combined with the proposed mooring arrays of SE Qld (Q-IMOS) and the BWC end point array we will gain valuable information in seasonal and decadal changes in the EAC and its extension along the coast of southern NSW.  This data set complements the data being collected at the Maria Island NRS (Tas-IMOS).  Together these data will inform the large scale changes along Australia’s eastern continental shelf.  This data will also be combined with crucial biological data (such as kelp distribution and abundance, CPR plankton) providing information on range shifting which is indicative of changes in the flow field.  Future emphasis on instigating quantitative and sustained biological and chemical time-series data streams from physical properties moorings at Coffs Harbour, Eden and Maria Island, will necessitate new scientific aims from the 3 eastern state IMOS nodes (NSW-IMOS, Q-IMOS and Tas-IMOS).

Contribute to monitoring the Bass Strait outflow and the northward coastally trapped wave propagation.

The deployment of a mooring pair in southern NSW will monitor the Bass Strait outflow and the addition of pressure sensors on each of the mooring pairs will allow for the measurement of coastally trapped wave propagation northward along the coast of NSW.

Contribute to the national backbone through the National Reference Station network and the supplementation of Satellite Remote Sensing products with local data.

Three of the NRS incorporate the long-term (~70 y) hydrographic sampling locations on the continental shelf (Port Hacking, Maria Island, Rottnest Island) and will provide biogeochemical data on the effect of boundary current changes.  An IMOS-appointed bio-optical working group containing members of NSW-IMOS are using the NRS data in a national effort to validate bio-optical signals from the moored time-series at each NRS.

4.2 Major Boundary Currents and Inter-basin Flows

A key research focus for the NSW-IMOS Node is to investigate the East Australian Current (EAC), its separation from the coast, and the resultant eddy field along the coast of South East Australia.

The East Australian Current (EAC) is the major western boundary current of the South Pacific Gyre, flowing from the southern Coral Sea and along the northern NSW coast (Ridgway & Dunn 2003). The EAC is Australia’s largest current and is typically 30 km wide, 200 m deep and travelling up to 4 knots. 

The core of the EAC is centred over the continental slope, although its coastal presence is felt by eddy encroachment.  Our knowledge of processes at the shelf break is very limited.  By comparison to the knowledge of the behaviour and variability of other western boundary currents there has been a significant lack of investigation into the EAC and its eddy field, for a current renowned for its mesoscale variability.

Key Science Questions

  • To determine the frequency, form and function (horizontal and vertical) of EAC eddies.
  • To understand air sea interactions, particularly to determine the development of East Coast Lows and severe winter storms in relation to warm core eddies.
  • Quantify the impact of key physical processes such as onshore encroachment of the EAC, slope water intrusions, upwelling, downwelling and internal waves.

4.3 Continental Shelf Processes

Examine the coastal wind and wave climate in driving nearshore currents and the northward sediment transport.

The NSW-IMOS Node will investigate the utility of HF Radar to provide directional wave spectra over a large spatial area, as opposed to the current 7 point records at buoys along the coast.  The WERA HF radar array has the ability to measure wave frequency period and directional wave spectra across the entire radar domain.  A deployment scheduled for Coffs Harbour is designed to overlap the domain of the Coffs Harbour waverider buoy to allow for an assessment of the accuracy of the wave measurements derived from the HF radar.  As an additional contribution to IMOS it is anticipated that we will trial a WAMOS wave measurement system which has the ability to provide directional wave spectra in high resolution in the near shore zone.  This system also has the potential to provide measurements of sea bed topography which can be used in the enhancement of wave models.

Quantify the biogeochemical cycling of carbon (nutrients and phytoplankton composition).

The water quality monitor at the Port Hacking NRS currently provides estimates of turbidity and fluorescence at one depth, which in combination with dissolved nutrients and oxygen, provides data to understand biogeochemical cycling.  In co-ordination with SRS nutrient and plankton observations, and SOOP carbon measurements, gliders quantify the biogeochemical state of the water column.  Oxygen, coloured dissolved organic matter (CDOM) and fluorescence indicate the state of carbon in the system, and hence can aid calculations of carbon fluxes.  The observations by glider deployments over 4 years will provide an archive of vertical profiles of oxygen, CDOM and even fluorescence that dwarf the number presently available.

Determine the transport and dispersal of passive particles (e.g. larvae, eggs, spores) and the degree of along coast connectivity and trophic linkages.

The Solitary Islands Marine Park (SIMP) is both a state and federal marine reserve and it is in this region that we have focused our upstream East Australian Current (EAC) observations.  The combination of HF Radar giving spatial coverage of the flow patterns at the surface and the moorings giving resolution throughout the water column will help answer the question of the dispersion of passive particles in and around SIMP.  AATAMS lines are also focused through SIMP which will provide insight into the nature of the connectivity between fish populations in the region.  These data will inform modelling studies of connectivity along the NSW coastline and both within and among marine reserves.

4.4 Ecosystem Responses

Quantify the daily to decadal variation of planktonic communities in relation to oceanographic and climate-driven changes in physical and chemical ocean properties.

The current time series of plankton observations/samples in the East Australian Current (EAC) (1997 to 2009 archive) is too short to reliably detect a climate change signal from natural patterns of climate variability.  However, by examining the physical and biological responses to contemporary climate variations, we will determine responses that may be indicative of future climate change.  We will address temporal variability by making high-frequency measurements of phytoplankton using the ANMN, ANFOG and AUV facilities.  Additionally we will use the SOOP-CPR data from Brisbane-Sydney-Melbourne, and the corresponding bio-acoustic transect. To assess spatial dynamics, we will use a multi-faceted approach: synoptic views of ocean colour using the SRS facility, quasi-synoptic assessments of chl-a fluorescence and particle backscatter using ocean gliders, and the development of a regional ocean model so that single-point observations such as those at moorings can be placed into a spatial context.

Quantify rocky reef biota variables (kelp distribution and abundance) associated with climate variability, at deep reefs along the NSW to Tasmanian coast.

We will use the AUV facility to document changes in kelp among depths and among latitudes throughout the distribution of kelp in NSW.  On each dive, associated AUV-based measurements of temperature, light levels and samples for nitrate analysis will enable interpretation of the biological signal in the context of local environmental conditions.  Observations in NSW will form part of a set of sites on the east coast, where reefs will be monitored in SE Qld, NSW, Victoria and Tasmania using AUV technology.

Relationship of the EAC, its eddies and oceanographic conditions on fisheries, and movements by fish and sharks.

Observations are designed as a set of cross-shelf receivers to ensure that data on fish movement covers the necessary geographic extents and ranges of conditions and is overlaid by oceanographic monitoring.  The observations across a broad spectrum of conditions will give new insight into role of ocean dynamics on movements, habitat use and site fidelity for predatory fish in the coastal zone.  Simultaneous and sustained monitoring will indicate links between hydrography and fish migration, facilitated by observations from the ocean moorings, coastal radar, BLUElink, SOOP, and cross shelf data collected via proposed fine scale temperature recorders positioned on the bottom and surface of existing AATAMS line mooring arrays.  

Quantify the seasonal and yearly variation of upper-predator (fish and marine mammal) communities.

Passive acoustic observatories will capture vocalisations of great whales and nearby fish at scales of km’s (fish) to many tens of km’s (great whales).  The passive acoustic array was designed specifically to allow source tracking for sources which arrive coherently on all receivers.  This will not only record the presence of cetaceans and fish in the absence of visual detection but will also allow us to track animal movements, seasonal occurrence, distribution, and behaviour, including dive and migratory patterns, particularly for cetaceans.  These trends can then be related to larger scale physical features for elucidation of how the physical environment impacts on the respective animal population.

5. Collaborators

Lead Institution

Collaborating Institutions

 

6. Contact Details

Moninya Roughan

Sydney Institute for Marine Science/University of New South Wales

+61 2 9385 7067

mroughan(at)unsw.edu.au

 

Martina Doblin

Sydney Institute for Marine Science/University of Technology Sydney

+61 2 9514 8307

Martina.doblin(at)uts.edu.au

--

To view NSW-IMOS mooring locations visually please see the Moorings page

--