Natural values of the Solitary Islands Marine Park - Marine Parks ...

2 Physical environment2.1 ClimateThe Solitary Islands Marine Park is situated on the north coast of NSW. The climateis subtropical, with average air temperatures ranging from 13.9°C in winter to 23.2°Cin summer. Easterly trade winds are dominant and regulate the temperature fromSeptember to March, providing warm humid conditions (Zann 2000a). Average rainfallfor the area is 1700 millimetres, with most rainfall occurring between December andMay (Copeland et al 1993).Figure 2.Sea surface temperatureimage of the NSW andsouthern Queenslandregion in January, showingthe EAC influence inthe marine park. Imagetaken 19 September1991, Copyright 1999,CSIRO Division of MarineResearch, Hobart.Coffs Harbour2.2 Ocean currentsThe oceanography of the region’s shelf waters is determined by a combinationof large-scale oceanographic circulation, local wind stress and bathymetry(underwater depth). It is dominated by the warm, stratified, nutrient-poor waterof the East Australian Current (EAC), and cooler, well-mixed water from the south.The EAC brings tropical and subtropical waters down from the Coral Sea, GreatBarrier Reef and southern Queensland into the more temperate areas of thecontinental shelf (Zann 2000b).Sea surface temperature images indicate that thewarm waters of the EAC generally dominate thewaters of the marine park, particularly those on themid and outer continental shelf, between Januaryand March. During the cooler months, the marinepark is dominated by cooler inshore currents,although these can also occur in summer due toupwelling (Zann 2000b).The influence of the EAC often extends onto thecoast, creating a southward flowing current inshore(Figure 2). The presence of the EAC near the coastfrequently results in complex currents downstreamof headlands and reefs, and cooler northwardflowingcounter currents.In the marine park, annual maximum and minimumsea temperatures range from about 17°C duringwinter to 27°C during summer (Malcolm 2007),although slightly lower and higher values have beenrecorded in some years, mostly due to variations inthe dominance of the EAC.Sites near the shore such as Muttonbird Island havea lower annual average sea temperature (about20.9°C) than offshore sites such as North SolitaryIsland (about 21.8°C). During summer, the watertemperature at North Solitary Island is on averageabout 0.5–1°C warmer than the water temperatureat North West Solitary Island, and 1–1.5°C warmerthan at inshore sites (Figure 3), although thetemperature differences are reduced slightlyover winter.