PLIOCENE GLACIATIONS SEND PLANKTONIC SNOWBIRDS TO THE TROPICS

Foraminifera and other pelagic microfossils are generally regarded as being capable of very wide dispersal and having extremely large, even global, distributions. Here we show that the foraminifer, Truncorotalia truncatulinoides does, indeed, spread very rapidly, but does so only by tracking the global expansion of its favored habitat. Therefore, T. truncatulinoides populations tend to rise and fall very rapidly outside its core range and are frequently absent through much of its total range for long periods of time. G. truncatulinoides originates in the subtropical SW Pacific 2.8 Ma, and soon spreads to other subtropical waters nearby. In the tropical western Pacific we observe six distinct peaks in G. tosaensis and G. truncatulinoides abundances between 2.4 and 2.7 Ma, almost all of which coincided with distinct glacial periods. Intervening interglacials are characterized by almost the complete absence of both species in the tropical Pacific. In the tropical Atlantic, T. Truncatulinoides makes a very brief appearance in the that coincides with a large glacial event at 2.55 Ma equivalent with its first appearance in the tropical Pacific. The complete absence of T. truncatulinoides in a subtropical South Atlantic core suggests that the tropical Atlantic populations were established by the dispersal of very small numbers of individuals that dispersed from the Pacific to reach distant areas of the ocean. Our results provide evidence of a very strong correlation between climate change and invasion of the tropical latitudes from subtropical regions. Furthermore, the intermittent dispersal of subtropical populations into the tropics in both the Pacific and Atlantic suggest that the oceanography of the glacial tropical waters came to resemble the interglacial subtropics during at least a few periods of the late Pliocene.

Dispersal clearly depends on the climate of the time, and can establish viable populations in favorable habitats wherever these exist around the world. particularly glacial versus interglacial periods, and gives an idea as to how much distance plays a factor in global distribution. Perhaps this can provide insight into the factors influencing the distribution of many other types of plankton and what ancient waters were like.