Late Neogene evolution of modern deep-dwelling plankton

Abstract

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

Novel adaptation increases resilience in Planktic Foraminifera

“…1d). The slight deviation in values at ∼10 Ma could be the colonization of the twilight zone [47], but we are not inclined to interpret such a small change in values in this study.…”

Paleoecology and evolutionary response of planktonic foraminifera to the mid-Pliocene Warm Period and Plio-Pleistocene bipolar ice sheet expansion

“…This may reflect regional thermocline shoaling similar to patterns observed at DSDP Site 84 in the proximal Panama Basin (Lutz, 2010). Other geological intervals associated with significant global cooling such as the Eocene-Oligocene transition and late Miocene cooling exhibit similar patterns of gradual, successive turnover of warm-water dwellers by cold-water taxa potentially associated with contractions and expansions in their respective ecospaces (Keller, 1983;Boersma and Premoli Silva, 1991;Keller et al, 1992;Molina et al, 1993;Wade and Pearson, 2008;Ezard et al, 2011;Lowery and Fraass, 2019;Lowery et al, 2020;Boscolo-Galazzo and Crichton et al, 2021;Boscolo-Galazzo et al, 2022;Woodhouse and Swain et al, 2023).…”

“…Major Antarctic ice sheet expansion (Shevenell et al, 2004;Holbourn et al, 2015;Frigola et al, 2018;Westerhold et al, 2020) following the Miocene Cli-matic Optimum (∼ 17-15 Ma; Methner et al, 2020) initiated global cooling, intensifying meridional gradients (Gaskell et al, 2022). This triggered unprecedented mean size increases in low-latitude planktonic foraminifera (Schmidt et al, 2004a, b) and higher efficiency of the biological carbon pump, promoting greater endemism and exploitation of new deep-water niches in calcifying plankton (Olsson, 1982;Scott, 1982;Keller, 1985;Malmgren and Berggren, 1987;Scott et al, 1990;Norris et al, 1993Norris et al, , 1994Norris et al, , 1996Norris, 1999Norris, , 2000Rögl, 1999;Chaisson, 2003;Kucera and Schönfeld, 2007;Ezard et al, 2011;Crundwell, 2018;Rosenthal et al, 2018;Spezzaferri et al, 2018;Lam and Leckie, 2020;Boscolo-Galazzo and Crichton et al, 2021;Boscolo-Galazzo et al, 2022;Woodhouse and Swain et al, 2023). From ∼ 6.5 Ma, the equatorial Pacific shows meridionally distinct planktonic foraminiferal faunal provinces that display a turnover in dominance from Miocene species to more Recent taxa ∼ 4 Ma (Chaisson, 1995;Chaisson and Ravelo, 2000) linked with the closure of the CAS (Haug et al, 2001).…”

“…Woodhouse et al: Paleoecology and evolutionary response of planktonic foraminifera formation is less essential than the repercussions of the gradual shoaling and restriction of the Central American Seaway (CAS), which triggered significant global paleoceanographic effects fundamental to the evolution of the present climate state. The gradual restriction of consistent throughflow between the tropical Atlantic and Indo-Pacific Oceans via isthmus formation (O'Dea et al, 2016) was coupled with bipolar cryosphere development that significantly restructured global vertical and meridional temperature gradients (Schmidt et al, 2004a, b;Mudelsee and Raymo, 2005;Boscolo-Galazzo and Crichton et al, 2021;Boscolo-Galazzo et al, 2022;Ford et al, 2022;Gaskell et al, 2022), altering marine ecosystems and trophic structure (Woodhouse and Swain et al, 2023). The recorded effects on global paleoceanography and biodiversity are of particular importance, as this ice sheet expansion was preceded by the sustainedly warmer world of the Pliocene.…”

Globorotalia truncatulinoides in the Mediterranean Basin during the Middle–Late Holocene: Bio-Chronological and Oceanographic Indicator

“…G. truncatulinoides originated 2.82 Ma in the Southwest Pacific [85][86][87][88]. The species later appeared in the Atlantic Ocean between 2.544 and 2.525 Ma [89], before finally colonizing other ocean basins ~2.0 Ma ago [8,86,89].…”