期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：1
DOI：10.1073/pnas.2113263118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
The elemental composition of marine phytoplankton reflects their quality as a food source and regulates the flow of carbon, oxygen, and nutrients between the ocean, atmosphere, and rock reservoirs. Despite this importance, no systematic estimate exists of the geologic history of phytoplankton elemental composition, which is often regarded to have been constant through time, limiting our understanding of evolutionary patterns and global biogeochemistry. Here, using a biogeochemical model forced by geologic and evolutionary events (e.g., the colonization of the continents by plants), we find that the nutrient content of phytoplankton has increased over the last 550 million y of Earth history. This increase in the organic matter nutrient content has likely been important for the evolution of marine fauna.
Planktonic organic matter forms the base of the marine food web, and its nutrient content (C:N:P
org) governs material and energy fluxes in the ocean. Over Earth history, C:N:P
org had a crucial role in marine metazoan evolution and global biogeochemical dynamics, but the geologic history of C:N:P
org is unknown, and it is often regarded constant at the “Redfield” ratio of ∼106:16:1. We calculated C:N:P
org through Phanerozoic time by including nutrient- and temperature-dependent C:N:P
org parameterizations in a model of the long-timescale biogeochemical cycles. We infer a decrease from high Paleozoic C:P
org and N:P
org to present-day ratios, which stems from a decrease in the global average temperature and an increase in seawater phosphate availability. These changes in the phytoplankton’s growth environment were driven by various Phanerozoic events: specifically, the middle to late Paleozoic expansion of land plants and the Triassic breakup of the supercontinent Pangaea, which increased continental weatherability and the fluxes of weathering-derived phosphate to the oceans. The resulting increase in the nutrient content of planktonic organic matter likely impacted the evolution of marine fauna and global biogeochemistry.
