DID PHYTOPLANKTON EVOLUTION FUEL THE DIVERSIFICATION OF THE MARINE BIOSPHERE? NEW EVIDENCE

Tectonic oscillations like those proposed by Fischer & Arthur (1) impacted the quantity (primary productivity) and quality (stoichiometry) of phytoplankton at the base of marine food pyramids and their fueling of the diversification of the marine biosphere. Based on the theory of ecological stoichiometry (2), we hypothesize that increasing nutrient runoff to the oceans through the Phanerozoic resulted from orogeny and the emplacement of Large Igneous Provinces (LIPs) coupled to the evolution of deep-rooting forests and the appearance of more easily decomposable angiosperm organic matter that enhanced weathering.

Marine generic diversity is paralleled by strontium isotope ratios, phosphorus and selenium data (3) indicating continental weathering, and δ¹³C indicating primary productivity (4). The relatively subdued marine biodiversity of the Paleozoic corresponds to a time of relatively low phosphorus availability and poor food quality of green phytoplankton lineages dominated by acritarchs, whereas diversification of the Modern Fauna through the Meso-Cenozoic occurred during the diversification of phosphorus-rich phytoplankton: coccolithophorids, dinoflagellates, and diatoms.

We assess our suppositions against recently-published biogeochemical models for geologic time scales (5). Major peaks of marine diversity often occur near rising or peak fluxes of silica, phosphorus and dissolved reactive oceanic phosphorus; either major or minor ⁸⁷Sr/⁸⁶Sr peaks; and frequently in the vicinity of major (e.g., the Circum-Atlantic Magmatic Province) and minor volcanic events, some of which are associated with Oceanic Anoxic Events.

References: (1) Fischer, A.G. & Arthur, M.A. 1977. Secular variations in the pelagic realm. In Cook, H.E. & Enos, P. (eds.): Deep-Water Carbonate Environments, 19. SEPM (Society for Sedimentary Geology) Spec. Publ. 25.; (2) Sterner, R.W. & Elser, J.J. 2002. Ecological Stoichiometry. Princeton U. Press, Princeton, 439 p.; (3) Large, R.R. et al. 2015. Gond. Res. 28: 1282; (4) Martin, R. E., & Servais, T. 2019. Did phytoplankton evolution fuel the diversification of the marine biosphere? Lethaia. DOI:10.1111/let.12343; (5) Arvidson, R.S. et al. 2013. Geologic history of seawater: A MAGic approach to carbon chemistry and ocean ventilation. Chem. Geol. 362: 287.