Decreasing influence of Subantarctic Mode Water north of the Tasman Front over the past 150 kyr

A positive relationship between the population size of Globorotalia truncatulinoides in deep-sea sediments and thermostad thicknesses in mode waters of both the northern and the southern hemispheres is documented. In cores RC12-113, DSDP 588 and DSDP 591 (located north of the Tasman Front) G. truncatulinoides shows a decreasing trend in abundance from oxygen isotope stages 6 to 1, suggesting a progressive reduction of Subantarctic Mode Water (SAMW) thermostads in the northern Tasman Sea. Heating, seasonality and/or a more dynamic East Australian Current are suggested as possible mechanisms that cause the piling up of isotherms that distort thermostads in the northern Tasman Sea. Alternatively, a more vigorous mixing of the ocean (by convection and overturning) may have been in operation south of the Subtropical Convergence during glacial stage 6. Palaeoceanographic conditions during glacial stages 6 and 2 appear to be significantly different.