We investigated sediments from the tropical Indian Ocean to study water column structure and carbon cycling during the mid-Piacenzian Warm Period, about 3 million years ago, when atmospheric carbon dioxide levels were similar to today. Our findings reveal persistent upper ocean stratification and niche separation among plankton groups, which limited nutrient mixing and carbon export to the deep ocean. These results highlight how ocean layering can influence climate feedback in a warmer world.

Coccolithophores are important marine CaCO₃ producers and their biominerals, the coccoliths, partly dissolve in the upper water column where dissolution is unexpected. Studying coccolith dissolution in field samples is hampered by a paucity of experimental studies describing dissolution morphologies. Here we fill this gap by experimentally dissolving different coccolithophores and applying our results to field samples.

Planktonic foraminifera are marine plankton that have a long and continuous fossil record. They are used for correlating and dating ocean sediments and studying evolution and past climates. This paper presents new information about Pulleniatina, one of the most widespread and abundant groups, from an important site in the Pacific Ocean. It also brings together a very large amount of information on the fossil record from other sites globally.

Coccolithophores are an important group of phytoplankton that produce intricate skeletons of calcium carbonate. They contribute to the base of the marine food web and are important drivers of the global carbon cycle. Here, we describe novel coccolithophores and novel life cycle combinations detected by electron microscopy in samples collected in the Red Sea and the western Mediterranean. Our study advances our understanding of coccolithophore diversity and life cycle complexity.