The Chixulub bolide impact 66 million years ago drove near-instantaneous oceanic ecosystem collapse. Devastating diversity loss at the base of ocean food-webs likely triggered cascading extinctions across all trophic levels 1-3 and caused severe disruption of ocean biogeochemical function, especially the cycling of carbon between the surface and deep sea 4,5. The absence of sufficiently detailed biotic data spanning the postextinction interval has limited our understanding of how ecosystem resilience and biochemical function was restored, with estimates of 'recovery' varying from <100 years to 10 million years 6-8. Using a 13-million-year long nannoplankton time-series we show that post-extinction communities exhibited 1.8 million years of exceptional volatility before a more stable equilibrium community emerged displaying hallmarks of resilience. The transition to this new equilibrium-state community with a broader cellsize spectrum coincides with indicators of carbon cycle restoration and a fully functioning biological pump 9. This finding implies a fundamental link between 93 perturbation (i.e., the significant linear trend between carbon isotope excursion and variance) 94 and rapid recoveries following each event (return of variance to the background state within 95 <200 kyrs of the excursion, Fig. 1c and ref 21). 96 Tantalisingly, the shift to more stable communities approximately 64.2 Myr ago (the end of 97 Regime 1) also falls towards the top of the interval of biological pump recovery 9 (Fig. 3f). 98 Ocean biogeochemical function was profoundly disrupted by the end-Cretaceous mass 99 extinction, most obviously through weakening of the biological pump 2,5,9. The scale and duration of this productivity reduction is contentious, ranging from scenarios of a lifeless Strangelove Ocean to a partially functioning Living Ocean state 4 , but the long, multimillionyear delay in restoration of the biological pump is well established 2,22 , and indicated by both the gradual increase in vertical carbon isotope gradient to pre-extinction values 9 and changing community structures of benthic primary-consumer communities (benthic foraminifera) 23. Carbon isotope gradients finally returned to pre-extinction values by ~1.77 Myrs after the event 9 providing an upper limit on full recovery of the biological pump. This broad
Past global warming events such as the Palaeocene–Eocene Thermal Maximum (PETM—56 Ma) are attributed to the release of vast amounts of carbon into the ocean, atmosphere and biosphere with recovery ascribed to a combination of silicate weathering and organic carbon burial. The phytoplanktonic nannoplankton are major contributors of organic and inorganic carbon but their role in this recovery process remains poorly understood and complicated by their contribution to marine calcification. Biocalcification is implicated not only in long-term carbon burial but also both short-term positive and negative climatic feedbacks associated with seawater buffering and responses to ocean acidification. Here, we use exceptional records of preserved fossil coccospheres to reconstruct cell size distribution, biomass production (particulate organic carbon, POC) and (particulate) inorganic carbon (PIC) yields of three contrasting nannoplankton communities (Bass River—outer shelf, Maud Rise—uppermost bathyal, Shatsky Rise—open ocean) through the PETM onset and recovery. Each of the sites shows contrasting community responses across the PETM as a function of their taxic composition and total community biomass. Our results indicate that nannoplankton PIC:POC had no role in short-term climate feedback and, as such, their importance as a source of CO2 to the environment is a red herring. It is nevertheless likely that shifts to greater numbers of smaller cells at the shelf site in particular led to greater carbon transfer efficiency, and that nannoplankton productivity and export across the shelves had a significant modulating effect on carbon sequestration during the PETM recovery.This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.
The end-Cretaceous bolide impact triggered the devastation of marine ecosystems. However, the specific kill mechanism(s) are still debated, and how primary production subsequently recovered remains elusive. We used marine plankton microfossils and eco-evolutionary modeling to determine strategies for survival and recovery, finding that widespread phagotrophy (prey ingestion) was fundamental to plankton surviving the impact and also for the subsequent reestablishment of primary production. Ecological selectivity points to extreme post-impact light inhibition as the principal kill mechanism, with the marine food chain temporarily reset to a bacteria-dominated state. Subsequently, in a sunlit ocean inhabited by only rare survivor grazers but abundant small prey, it was mixotrophic nutrition (autotrophy and heterotrophy) and increasing cell sizes that enabled the eventual reestablishment of marine food webs some 2 million years later.
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