Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change

Abstract

Marine planktonic diatoms export carbon to the deep ocean, playing a key role in the global carbon cycle. Although commonly thought to have diversified over the Cenozoic as global oceans cooled, only two conflicting quantitative reconstructions exist, both from the Neptune deep-sea microfossil occurrences database. Total diversity shows Cenozoic increase but is sample size biased; conventional subsampling shows little net change. We calculate diversity from a separately compiled new diatom species range catalog, and recalculate Neptune subsampled-in-bin diversity using new methods to correct for increasing Cenozoic geographic endemism and decreasing Cenozoic evenness. We find coherent, substantial Cenozoic diversification in both datasets. Many living cold water species, including species important for export productivity, originate only in the latest Miocene or younger. We make a first quantitative comparison of diatom diversity to the global Cenozoic benthic ∂18O (climate) and carbon cycle records (∂13C, and 20-0 Ma pCO2). Warmer climates are strongly correlated with lower diatom diversity (raw: rho = .92, p<.001; detrended, r = .6, p = .01). Diatoms were 20% less diverse in the early late Miocene, when temperatures and pCO2 were only moderately higher than today. Diversity is strongly correlated to both ∂13C and pCO2 over the last 15 my (for both: r>.9, detrended r>.6, all p<.001), but only weakly over the earlier Cenozoic, suggesting increasingly strong linkage of diatom and climate evolution in the Neogene. Our results suggest that many living marine planktonic diatom species may be at risk of extinction in future warm oceans, with an unknown but potentially substantial negative impact on the ocean biologic pump and oceanic carbon sequestration. We cannot however extrapolate our my-scale correlations with generic climate proxies to anthropogenic time-scales of warming without additional species-specific information on proximate ecologic controls.

Accelerated diversification is related to life history and locomotion in a hyperdiverse lineage of microbial eukaryotes (Diatoms, Bacillariophyta)

“…2a). These results were in agreement with recent paleontological studies based on similar data (Lazarus et al ., 2014; Cermeño et al ., 2015). …”

“…Most shifts occurred within the past c . 70 Myr, and upward shifts tended to be more recent, consistent with the Cenozoic increase in diatom diversity as a whole (Rabosky & Sorhannus, 2009; Lazarus et al ., 2014; Cermeño et al ., 2015), as well as many lineages of both ON (Alverson, 2014) and AM (Edwards, 1991) diatoms (Fig. 4a).…”

“…This approach used the first and last occurrence of fossil species binned into discrete, nonoverlapping time intervals to calculate the instantaneous rates of speciation and extinction. Fossil data were taken from the Barron Diatom Catalog of first and last occurrences of Cenozoic diatoms (Lazarus et al ., 2014). To obtain a single estimate of relative extinction for the entire set of fossils spanning the Cenozoic, we binned the data into discrete time intervals, calculated rates of speciation and extinction, and then averaged over time intervals.…”

Continental erosion and the Cenozoic rise of marine diatoms

“…Marine diatoms exhibit two major pulses of diversification and geographic expansion during the Cenozoic (13)(14)(15) (Fig. 2A).…”

“…The abrupt midMiocene emplacement of the Columbia River Flood Basalt province (34) would also boost silicate weathering, and an uptick in this parameter is noted by Li and Elderfield (20). Although time-calibrated molecular phylogenies situate the origin of marine diatoms in the early Jurassic ∼200 Ma (35), it was not until the mid-Cenozoic that this group of marine microalgae rose to ecological and biogeochemical prominence, suggesting that factors other than accelerated silicate weathering were important (13,36). Unlike other phytoplankton, diatoms are equipped with large intracellular vacuoles (about 40% of the volume of the cell), which they use for the storage of inorganic nutrients.…”