Introduction – the importance of pre-Quaternary diatoms in paleoceanography
The marine system is vast, involving a highly diverse range of habitats; from coastal lagoons, fjords, bays, and estuaries, out over the shelf to the open ocean thousands of kilometers from any landmass. The Pacific Ocean alone covers an area of nearly 170 million km2. In total, the world's oceans cover approximately two-thirds of the Earth's surface and since marine diatoms are the dominant marine primary producers, contributing about 40% of the total primary production in the modern oceans (Tréguer et al., 1995) and over 50% of organic carbon burial in marine sediments (Falkowski et al., 2004), they are key players in the marine biological carbon pump. Therefore, the study of both living and fossil marine diatoms is important for many reasons other than just their intrinsic interest – from understanding (past) marine ecological systems, through biogeochemical cycling, to links with carbon dioxide (CO2) (e.g. Harrison, 2000), and the causes and effects of rapid climate change (e.g. Pollock, 1997).
Diatoms preserved in marine sediments are commonly used to reconstruct paleoenvironments and paleoceanographic events for the Holocene and Quaternary, but they are equally as valuable for paleoceanographic reconstructions of time periods much earlier than this – in fact for as far back as their fossil record allows, i.e. the Early Cretaceous (Gersonde & Harwood, 1990; Harwood & Gersonde, 1990).