Return to the light: Evolution of photosymbiosis after the end-Cretaceous mass extinction

• The Cretaceous/Paleogene (K/Pg) mass extinction seriously affected the marine pelagic ecosystem causing >90% loss of planktonic foraminifera species. Surface to deep-ocean foraminiferal d13C gradients and carbonate accumulation show that the extinctions coincided with a crash in organic matter flux to the sea floor that disrupted carbon cycling and took 3Myr to recover. Establishing the evolutionary and ecological response of the plankton through this recovery is important for understanding the role of the pelagic ecosystem in marine carbon cycling. Here we present new multispecies foraminiferal stable isotope data and planktic shell size distributions from a new, well-dated and continuous Atlantic deep sea core. The data document the evolution and diversification of photosymbiosis (thought to be an adaptation to low nutrient pelagic environments) in Paleocene planktonic species 3 million years after the K/Pg extinction when the pelagic carbon system recovered to a pre-K/Pg state and Oligotropic conditions returned. The data show that the geochemical signature of photosymbiosis evolved in an initially thermocline dwelling species, Preamurica pseudoinconstans, that started migrating to the shallower photic levels during later life stages. Initially appearing less than 1 myr after the K/ Pg extinction, symbiosis as an ecological strategy did not become important for a further 2 million years when the genus Morozevlla underwent major diversification, probably in response to an expanding ecologic opportunity that in turn resulted from final recovery of the marine carbon cycle.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Paleocene

planktonic foraminifera

mass extinction

evolution

carbon system

symbiosis

Earth sciences

Geovetenskap

Geology

geologi

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