Late Neogene evolution of modern deep-dwelling plankton

Abstract. The fossil record of marine microplankton provides insights into the evolutionary drivers which led to origin modern deep-water plankton, one largest components ocean biomass. We use global abundance and biogeographic data, combined with depth habitat reconstructions, determine environmental mechanisms behind speciation in two groups pelagic microfossils over past 15 Myr. compare our microfossil datasets water column profiles simulated an Earth system model. show that deep-living planktonic foraminiferal (zooplankton) calcareous nannofossil (mixotroph phytoplankton) species were virtually absent globally during peak middle Miocene warmth. evolution deep-dwelling foraminifera started from subpolar–mid-latitude species, late cooling, via allopatry. Deep-dwelling subsequently spread towards lower latitudes further diversified sympatry, establishing communities stratified hundreds metres down column. Similarly, sub-euphotic zone specialist nannofossils become a major component tropical sub-tropical assemblages latest early Pliocene. Our model simulations suggest increased organic matter oxygen availability for foraminifera, nutrients light penetration nannoplankton, favoured new niches. These conditions resulted cooling associated increase efficiency biological pump last