High-energy reef and terrigenous sedimentation, Boulder Reef, Great Barrier Reef
Authors / CoAuthors
Sediment and water flux were monitored at Boulder Reef, in the Northern Great Barrier Reef, before, during, and after the passage of Tropical Cyclone Dominic. Rainfall at Cooktown as a result of Dominic amounted to 430 mm in 3 days, this effecting a record discharge in the Endeavour River of nearly 50 000 megalitres/day. At Boulder Reef, conditions prior to Dominic of 10-20 knot winds effected average water velocities of 11 cm/s across the reef, which generated a substantial reef-derived sediment load with particulate organic material up to ten times greater than particulate inorganic carbon by weight. During the high-energy event, winds in excess of 50 knots generated water movements of up to 40 cm/s and sediment loads two to five times greater than before the event. In addition, the sediment contained a substantial terrestrial component (illite and kaolinite), probably originating from the Endeavour River. Three days after the passage of Dominic, water velocities across the reef were still rapid (up to 60 cm/s) and sediment loads still high, although now only reef-derived. However, further monitoring indicated a second pulse of terrigenous material reaching Boulder Reef four days after Dominic. Large amounts of reef-derived carbonate and organic material are lost daily from the system to the inter-reef areas. Conversely, large quantities of terrestrially derived clay are added to the reef every five years or so, in amounts within the range 135- 228 tonnes: this has probably occurred at this periodicity for the past 5000 years. Cores through the Holocene section confirmed that clay deposition has occurred throughout its growth.