Diatom abundance index and biogenic opal content for ODP Leg 175 holes

This maximum is centered around 2.0-2.6 Ma, and follows a rapid increase of diatom deposition near 3.1 Ma.

Within the MDM, we recognized intervals dominated by the antarctic/subantarctic species Thalassiothrix antarctica which have the aspect of diatom mats. The MDM (and the mats) developed during a time of sustained Southern Ocean influence (3.2-1.6 Ma), probably reflecting a period of seasonally-pulsed continuous advection of subantarctic waters into the Benguela Oceanic Current. The onset and cessation of the MDM raises questions about modes in the operation of the silica cycle and the relation of these to major oceanographic events.