Dutkiewicz
Stephanie
Dutkiewicz
Stephanie
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ArticleDiel light cycles affect phytoplankton competition in the global ocean(Wiley, 2022-07-02) Tsakalakis, Ioannis ; Follows, Michael J. ; Dutkiewicz, Stephanie ; Follett, Christopher L. ; Vallino, Joseph J.Aim Light, essential for photosynthesis, is present in two periodic cycles in nature: seasonal and diel. Although seasonality of light is typically resolved in ocean biogeochemical–ecosystem models because of its significance for seasonal succession and biogeography of phytoplankton, the diel light cycle is generally not resolved. The goal of this study is to demonstrate the impact of diel light cycles on phytoplankton competition and biogeography in the global ocean. Location Global ocean. Major taxa studied Phytoplankton. Methods We use a three-dimensional global ocean model and compare simulations of high temporal resolution with and without diel light cycles. The model simulates 15 phytoplankton types with different cell sizes, encompassing two broad ecological strategies: small cells with high nutrient affinity (gleaners) and larger cells with high maximal growth rate (opportunists). Both are grazed by zooplankton and limited by nitrogen, phosphorus and iron. Results Simulations show that diel cycles of light induce diel cycles in limiting nutrients in the global ocean. Diel nutrient cycles are associated with higher concentrations of limiting nutrients, by 100% at low latitudes (−40° to 40°), a process that increases the relative abundance of opportunists over gleaners. Size classes with the highest maximal growth rates from both gleaner and opportunist groups are favoured by diel light cycles. This mechanism weakens as latitude increases, because the effects of the seasonal cycle dominate over those of the diel cycle. Main conclusions Understanding the mechanisms that govern phytoplankton biogeography is crucial for predicting ocean ecosystem functioning and biogeochemical cycles. We show that the diel light cycle has a significant impact on phytoplankton competition and biogeography, indicating the need for understanding the role of diel processes in shaping macroecological patterns in the global ocean.
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ArticleReviews and syntheses: the biogeochemical cycle of silicon in the modern ocean(European Geosciences Union, 2021-02-18) Tréguer, Paul J. ; Sutton, Jill N. ; Brzezinski, Mark A. ; Charette, Matthew A. ; DeVries, Timothy ; Dutkiewicz, Stephanie ; Ehlert, Claudia ; Hawkings, Jon ; Leynaert, Aude ; Liu, Su Mei ; Llopis Monferrer, Natalia ; López-Acosta, María ; Maldonado, Manuel ; Rahman, Shaily ; Ran, Lihua ; Rouxel, OlivierThe element silicon (Si) is required for the growth of silicified organisms in marine environments, such as diatoms. These organisms consume vast amounts of Si together with N, P, and C, connecting the biogeochemical cycles of these elements. Thus, understanding the Si cycle in the ocean is critical for understanding wider issues such as carbon sequestration by the ocean's biological pump. In this review, we show that recent advances in process studies indicate that total Si inputs and outputs, to and from the world ocean, are 57 % and 37 % higher, respectively, than previous estimates. We also update the total ocean silicic acid inventory value, which is about 24 % higher than previously estimated. These changes are significant, modifying factors such as the geochemical residence time of Si, which is now about 8000 years, 2 times faster than previously assumed. In addition, we present an updated value of the global annual pelagic biogenic silica production (255 Tmol Si yr−1) based on new data from 49 field studies and 18 model outputs, and we provide a first estimate of the global annual benthic biogenic silica production due to sponges (6 Tmol Si yr−1). Given these important modifications, we hypothesize that the modern ocean Si cycle is at approximately steady state with inputs =14.8(±2.6) Tmol Si yr−1 and outputs =15.6(±2.4) Tmol Si yr−1. Potential impacts of global change on the marine Si cycle are discussed.