Paleozoic-Mesozoic turnover of marine biological pump and Mesozoic plankton revolution

Abstract

<p indent="0mm">The evolution of deep-time marine biological pumps (BPs) is critical to our understanding of the processes and mechanisms of the present-day carbon cycle. The Late Paleozoic-Early Mesozoic was a key period for the formation of modern marine biological pumps. Two types of Phanerozoic biological pump have been recognized: Paleozoic (Paleozoic-Middle Triassic) and Modern (Late Triassic-Modern). The Paleozoic-type pump comprises benthic algae and acritarch, whereas the Modern-type pump consists mainly of pelagic plankton. Geological records show that the Permian-Triassic extinction event destroyed the Paleozoic BP. Then, a special BP composed of cyanobacteria and other autotrophic bacteria, briefly appeared during the Permian-Triassic extinction interval. The Modern-type BP consists primarily of pelagic nannoplankton that originated in the Late Triassic. Fossil records suggest that the origin and rapid radiation of nannoplankton (coccoliths and dinoflagellates) during the Late Triassic to Early Jurassic promoted the establishment of modern plankton ecosystem. The rise of pelagic plankton such as dinoflagellates, coccolithophores, and planktonic foraminifers in the Mesozoic is summed up as the Mesozoic plankton revolution. The Mesozoic plankton revolution changed the patterns of marine material cycling and energy flow. The proliferation of nannoplankton accelerated the transfer of material and energy from primary producers to larger consumers and higher trophic levels, increasing the resources available to mesotrophic levels of marine ecosystems. The increased availability of energy resulted in rapid changes in composition, spatial structure, and food chain structures of marine fauna. The resulting “biological arms race” is summarized as the Mesozoic marine animal revolution. The Mesozoic plankton revolution was also the key driver of the Mid-Mesozoic revolution in terms of the regulation of ocean chemistry. Before the Early Jurassic, fluctuations in sea level, ocean area, continental weathering rates, and oceanic calcium ion concentrations produced large perturbations in carbonate deposition and the oceanic carbon cycle, which were only weakly buffered by the ocean. After the Early Jurassic, seawater chemistry changed—With the decrease and stabilization of carbonate saturation due to the transfer of biogenic carbonate from the shallow to the deep marine deposits—Mainly as a result of the rise of nannoplankton and tectonic movement. Changes in seawater chemistry are also reflected in the increased oxygen concentration therein. The oxygen concentration was higher on the Jurassic shelf, likely due to pelagic planktonic algal blooms. The occurrence of phytoplankton increased the efficiency of pelagic biological and carbonate pumps, and the accumulation and dissolution of deep-sea carbonates began to emerge as an important link in the carbon cycle; this improved the buffering capacity of ocean against environmental disturbances. It also provided a stable environment for the creation of modern marine ecosystem, and several oceanic anoxic events that occurred in the Mesozoic did not directly lead to mass extinctions of marine animals, causing only small fluctuations in the diversity of some taxa. Therefore, the Mesozoic plankton revolution is a critical link between the animal and chemical revolutions, and these three processes make up the Mesozoic marine revolution. The origin and evolution of key marine producers and their controlling factors are important topics that need to be studied. However, there are few high-precision studies on the evolution of primary producers and biological pumps during the Late Paleozoic-Early Mesozoic. In addition, the timeline and mechanisms driving the origin of pelagic phytoplankton are key questions that need to be addressed. To solve these problems, the evolution of photosynthetic pigment lineages and the paleogeographic distribution of algae, along with the changes in the size of plankton during the early Mesozoic, require further research attention.