Figure F32. Conceptual model of the Matuyama Diatom Maximum (MDM) between 2.6 and 2.1 Ma. The input parameter is the system state x, represented by deepwater oxygen isotopes (18O of benthic foraminifers from Site 849, eastern equatorial Pacific; Mix et al., 1995), greatly smoothed. A frontal zone optimum is defined as those numbers of x that lie within the interval MDM. The model depends on x itself (taken as a proxy for upwelling) and on the absolute difference of x to the nearest value within the frontal zone optimum. All such difference values are increased by 0.5 and then inverted to write the two-dimensional equation (see "Early Matuyama Diatom Maximum: Search for Mechanisms" in "Lüderitz Site (Site 1084)"). The Site 1084 diatom abundance index (DAI) data are from Lange et al. (1999); the sea-surface temperature (SST) index (y-axis) is based on transforming x to the mean and range of the Site 1084 alkenone SST of Marlow et al. (2000).