Geophysical Laboratory, Carnegie Institution of Washington, 5152 Broad Branch Road, NW Washington DC, 20015-1305, US

Changes in environmental conditions, including the concentration of atmospheric CO₂, disturbance, temperature, aridity and salinity, can influence the competitive balance between C₃ and C₄ plants. C₃ and C₄ plants posses diagnostic carbon stable isotope ratios, and d ¹³C data from dated sediments are frequently used to reconstruct C₃ and C₄ vegetation dynamics. Records of this type are lacking from Northern and Western Australia. A Late-Quaternary record from Wolfe Creek Meteorite Crater in Western Australia shows d ¹³C_organic values between -25 and -16‰. The present vegetation at the crater’s center consists of species tolerating saline (15-19 ppt) conditions, including Acacia ampliceps (d ¹³C = -25.9‰), Flaveria australasica (d ¹³C -13.0‰), Atriplex sp. (d ¹³C -11.0‰), sedges (d ¹³C = -9.6‰) and halophytic microbes (-14‰), while that at the outer edge is related to aridity and includes the C₄ grass Triodia pungens (-11.8‰). In addition to salinity and aridity the present species distribution is related to the nutrient (nitrogen) status of the subrate. d ¹⁵N values from plants at the crater’s center are high (~10‰) relative to those values from plants at the edge (~0‰). These findings illustrate how complicated both modern and past C₃ and C₄ dynamics can be and highlight the need for additional habitat proxies, for example phytoliths, to distinguish C₄-like d ¹³C values from saline, arid and microbial habitats.