Secular increase in nutrient levels through the Phanerozoic; implications for productivity, biomass, and diversity of the marine biosphere

Approximately three decades ago, Helen Tappan began a series of classic papers on the interaction of the marine and terrestrial realms, and their influence on nutrient input to the oceans, marine productivity, and plankton evolution and extinction. Unfortunately, many of her assertions conflicted with the fossil record, and her papers have been treated in recent accounts as being largely of historical interest only. Based on recent δ13C, lithologic, and paleontologic evidence (including a reinterpretation of plankton diversity patterns), I reassess the role of nutrients and productivity in the evolution of the biosphere through the Phanerozoic. Cambrian-to-Devonian seas were characterized by extremely low nutrient ("superoligotrophic") conditions. By the Permo-Carboniferous, nutrient levels and marine productivity had increased toward intermediate ("submesotrophic") concentrations via glaciation, sea level fall, and enhanced deep-ocean overturn and continental weathering. Following end-Permian extinctions, bioturbation rates increased above Paleozoic levels, thereby recycling nutrients back to surface waters (fully "mesotrophic" conditions) and enhancing marine productivity as pelagic habitats expanded (via sea level rise). Increased rates of ocean circulation, continental erosion, and bioturbation further heightened nutrient levels ("eutrophic" conditions) and productivity in the Neogene. Rising nutrient levels and marine productivity may have fueled a secular increase in marine biomass and diversity, and the accompanying decline in background extinction rates, through the Phanerozoic.