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The bathymetry (bottom structure) of Sydney Harbour is complex, with dredged channels for shipping, deep holes, and shallow shoals. Within the estuary, large and shallow bays adjacent to the main channel allow the influx and collection of tidal waters.
The benthic environments within the harbour are also varied, from the harbour entrance (marine flood-tide delta sands), lower estuary (sands), central estuary (muddy sands) and upper estuary (muds), to the off-channel embayments (muds).
These differences constitute six environmental or sedimentological units within the harbour.
Check out the OzCoasts site
to fully explore the complex bottom of Sydney Harbour.
The East Australian Current (EAC) that flows poleward off the coast of Sydney is generally warmer and less rich in nutrients than the other waters around the coast. The EAC forms an eddy zone off Sydney Harbour that delivers these nutrient-poor waters to the harbour.
Current speeds offshore can be very fast (p to 1.5 m/s) in relatively shallow waters (up to 65m depth), meaning that water flowing past the entrance to the harbour is continually being renewed and replenished. Oceanic temperatures range 12–25ºC in February but winter temperature variations are more moderate, ranging 16–20ºC in June.
Salinity in the harbour ranges from 35.2 to 35.6 PSU (Practical Salinity Units) and is regulated through a combination of evaporation, precipitation and freshwater inflows.
Three dominant wind patterns affect Sydney Harbour:
Read more here about the physical attributes of Sydney Harbour in our 2014 review.