The net water circulation in the far Northern Great Barrier Reef

The 500 km long Far Northern Great Barrier Reef (FNGBR) is a semi-enclosed sea with little connectivity with the rest of the GBR further South. Its mean circulation is controlled by the prevailing southeasterly (northwestward) wind that generates a wind-driven mean longshore flow that is enabled by an inflow of oceanic water in the South. From an examination of single-point, mid-depth current meter data at ten sites over one year, it appears that there is no net current during calm weather, which implies that the northward North Queensland Coastal Current in the adjoining Coral Sea does not intrude in the FNGBR. Only about 20–40% of the wind-driven longshore transport continues northward to exit the FNGBR through Torres Strait because of blockage by reefs, shoals and islands and by the tidal friction effect in shallow waters. The remaining 60–80% of the flow appears to be deflected seaward to the Coral Sea in the North, an observation that appears to be supported by oceanographic modelling. This situation differs from that in the central and southern Great Barrier Reef where the southward flowing East Australian Current intrudes on the shelf and generates a net current even during calm weather. •The 500 km long Far Northern Great Barrier Reef (FNGBR) is a semi-enclosed sea that is flushed very slowly.•The FNGBR is little connected with the rest of the Great Barrier Reef.•During southeasterly winds, there is an inflow from the Coral Sea in the South of the FNGBR and apparently an outflow to the Coral Sea in the North.