Site summaries (continued)

Site NWS-5A

Priority: Primary
Position: 27.3749°S, 112.9250°E
Water depth (m): 214
Target drilling depth (mbsf): 366
Approved maximum penetration (mbsf): 366
Survey coverage (track map; seismic profile): Track map (Fig. AF1)
Seismic profiles (Figs. AF4, AF5)
Objective(s): This site, at the northern edge of the modern winter-dominated rainfall zone of southwestern Australia, is targeted to chart the timing of this regime; it is not likely to yield an orbital-scale climate record due to slope erosional processes. However, it will complement Site NWS-4A, as it is south of a climatic divide between the Australian monsoon–dominated north and the westerly wind-driven, winter rainfall–dominated south. It is also near the southern end of the north-south latitudinal transect and may provide a shelf to shelf-edge record of the tropical–subtropical transition related to Leeuwin Current activity. It is influenced by the anticlockwise, colder West Australian Current gyre, and the relative influence of this gyre versus the Leeuwin Current produces variations in paleoproductivity that may be documented over millions of years. Subsidence rates in this region are estimated to be significantly less than in the Carnarvon Basin further north because of variations in mantle dynamic subsidence between the Perth and Carnarvon Basins. Paleobathymetric analyses may produce the first detailed greater than million year subsidence record for this part of the West Australian margin, where previous subsidence estimates only extend to 125 ka.
Drilling program: Triple APC, double XCB
Logging program or downhole measurements program: Triple combo, FMS, VSP
Nature of rock anticipated: Calcarenites, calcilutites