Warm plankton soup and red herrings: calcareous nannoplankton cellular communities and the Palaeocene–Eocene Thermal Maximum

Abstract

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’.

Low‐Latitude Calcareous Nannofossil Response in the Indo‐Pacific Warm Pool Across the Eocene‐Oligocene Transition of Java, Indonesia

“…This is not to say that there is no longer‐term p CO 2 control on coccolithophore cell size through the Paleogene, as by the late Eocene the very large early to middle Eocene taxa are mostly absent. In other words, the cell size distribution present during the late Eocene appears to have been insensitive to p CO 2 , but this cell size distribution might have already been strongly selected by earlier cooling and p CO 2 declines between the middle and late Eocene (Gibbs et al, ; Hendriks & Pagani ).…”

Placing our current ‘hyperthermal’ in the context of rapid climate change in our geological past

“…Both phenomena enhance organic carbon burial-a significant sink of carbon dioxide [59]. Here Gibbs et al [60] pick apart the mechanisms of this process further by examining the size of coccolithophorid cells across the PETM. They conclude that, in response to the warming across the event, cell size decreases at shelf sites.…”

A 15-million-year-long record of phenotypic evolution in the heavily calcified coccolithophore <i>Helicosphaera</i> and its biogeochemical implications

“…2b). Age models are based on calcareous nannoplankton biostratigraphy (this study; Backman et al, 1988;Moore et al, 1984;Suchéras-Marx and Henderiks, 2014), updated to the most recent geological timescale (Gradstein et al, 2012; Table S1 in the Supplement). Linear sedimentation rates were estimated between age-depth tie points.…”