3.2.1 Currents

Ocean currents can be driven by tides, winds and gradients in temperature, salinity and sea surface height. Currents on the Reef are influenced mostly by the westward-flowing South Equatorial Current and prevailing winds. Along the continental slope, the South Equatorial Current enters the Region and splits into the East Australian Current flowing south and the Gulf of Papua Current (made up of the North Queensland Current and the Hiri Gyre) flowing north 525,526 (Figure 3.2). The South Equatorial Current influences the Region at multiple locations 527 and controls the relative strength of the North Queensland Current and the East Australian Current.525 South-easterly trade winds are the main driver of currents on the continental shelf and closer to the coast. Driven by wind and the Coriolis Effect, most river plumes in the Region are primarily dispersed northwards along the coast.528

The far northern Great Barrier Reef shows little connectivity with the rest of the Reef; it operates as a semi-enclosed sea that is poorly flushed.530 The Gulf of Papua Current does not directly flow into the lagoon, and most of the northwards water movement within the lagoon is wind driven. The North Queensland Current can provide cooler waters and protection from marine heatwave events.246 However, this current slows down when the prevailing winds stop and localised heating can contribute to bleaching in this region.530,531 Some research suggests the North Queensland Current may have decelerated since 1980.532 

Currents continue to connect and transport species and nutrients but are changing

Currents in the Region continue to connect and transport species and nutrients. However, some changes are occurring. The offshore East Australian Current has intensified since 1980, and both current strength and the frequency of its southward extensions have increased.356,533,534 How climate change will affect long-shore and cross-shelf transport of seawater through potentially altered wind directions and current strengths is not well understood.535 If the strength of the East Australian Current continues to increase as expected,536 the Reef could be exposed to an increasing frequency of marine heatwaves. 

Although changes are occurring, currents in the Region continue to connect species and habitats and transport nutrients. Longer-term changes to currents due to climate change are expected.

Satellite photo showing the different coloured waters: lighter blue on the left to the darker blues of deeper water on the right, with additional eddy patterns arising in the lee of the islands as the water, and suspended particles, move around them.
Suspended particles in the water make flow lines from tidal currents and eddies readily visible around islands east of Mackay. © Landsat 8 | NASA Ocean Color Image Gallery 2020
Figure 3.2
Seasonal prevailing surface currents and oceanic upwelling within the Region

Prevailing surface currents are shown for both trade winds (left) and monsoon (right) seasons. Variations due to weather and eddies are not depicted. GPC = Gulf of Papua Current, NGCC = New Guinea Coastal Current, SEC = South Equatorial Current, EAC = East Australian Current. The Gulf of Papua Current includes the North Queensland Current and the Hiri Gyre. During the trade winds season (usually in winter), consistent south-easterly winds boost northward-flowing currents and slow southward-flowing currents. In the monsoon season (during summer), there is very little effect on currents from surface winds. Source: eAtlas 529 attribution: Craig Steinberg, Eric Lawrey, CC BY

Figure is of two maps, side by side, both depicting the Eastern Australian coast down to Brisbane and up to the base of Papua New Guinea, focusing on the Coral Sea and Great Barrier Reef. The Queensland and Marion Plateaus are named, positioned centrally, and arrows are draw over the ocean region: narrow lines depicting weak currents and thick dark lines depicting strong current areas.
  • 246. Huang, Z., Feng, M., Dalton, S.J. and Carroll, A.G. 2024, Marine heatwaves in the Great Barrier Reef and Coral Sea: their mechanisms and impacts on shallow and mesophotic coral ecosystems, Science of The Total Environment 908: 1-20.
  • 525. Schiller, A., Herzfeld, M., Brinkman, R., Rizwi, F. and Andrewartha, J. 2015, Cross-shelf exchanges between the Coral Sea and the Great Barrier Reef lagoon determined from a regional-scale numerical mode, Continental Shelf Research 109: 150-163.
  • 526. Burrage, D.M., Steinberg, C.R., Skirving, W.J. and Kleypast, J.A. 1996, Mesoscale circulation features of the Great Barrier Reef region inferred from NOAA satellite imagery, Remote Sensing of Environment 56(1): 21-41.
  • 527. Woanski, E., Kingsford, M., Lambrechts, J. and Marmorino, G. 2024, The physical oceanography of the Great Barrier Reef: a review, in Oceanographic processes of coral reefs: physical and biological links in the Great Barrier Reef, eds E. Wolanski and M.J. Kingsford, 2nd edn, CRC Press, Boca Raton, Florida, pp. 9-34.
  • 528. Devlin, M.J. and Brodie, J. 2005, Terrestrial discharge into the Great Barrier Reef Lagoon: nutrient behavior in coastal waters, Marine Pollution Bulletin 51(1-4): 9-22.
  • 529. Steinberg, C. 2023, eAtlas: Circulation and upwelling, <https://eatlas.org.au/ne-aus-seascape-connectivity/circulation-upwelling>.
  • 530. Wolanski, E. and Lambrechts, J. 2020, The net water circulation in the far Northern Great Barrier Reef, Estuarine, Coastal and Shelf Science 235: 106569.
  • 531. Wolanski, E., Andutta, F., Deleersnijder, E., Li, Y. and Thomas, C.J. 2017, The Gulf of Carpentaria heated Torres Strait and the Northern Great Barrier Reef during the 2016 mass coral bleaching event, Estuarine, Coastal and Shelf Science 194: 172-181.
  • 532. DeCarlo, T.M. and Harrison, H.B. 2019, An enigmatic decoupling between heat stress and coral bleaching on the Great Barrier Reef, PeerJ 7: e7473.
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