Figure - available from: Elementa: Science of the Anthropocene
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Reaction norms of phytoplankton growth rates and (PIC:POC)cocco ratios. Point markers indicate normalized phytoplankton growth rates and (PIC:POC)cocco ratios from laboratory experiments (see references in Tables 2 and S1–S4), and lines indicate fitted functions for growth rates of coccolithophores, diatoms, and small phytoplankton, as well as (PIC:POC)cocco ratios. They are exemplarily displayed for a carbonate system ranging from 3 to 5500 μatm pCO2 and a constant alkalinity of 2300 μmol kg⁻¹ (computed with ScarFace web version 1.3.0, https://raitzsch.shinyapps.io/scarface_web/ as in Gattuso et al. [2019], and Raitzsch and Gattuso [2020], assuming surface pressure, salinity of 35, temperature of 20°C, and zero silicate and phosphate concentrations). Root mean square errors reveal the reproducibility of the data by the fitted functions. Vertical lines denote pCO2 levels of the simulations (280, 420, and 750 μatm). The black inset in the main plot indicates the area enlarged on the right side. PIC = particulate inorganic carbon; POC = particulate organic carbon.
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Atmospheric and oceanic CO2 concentrations are rising at an unprecedented rate. Laboratory studies indicate a positive effect of rising CO2 on phytoplankton growth until an optimum is reached, after which the negative impact of accompanying acidification dominates. Here, we implemented carbonate system sensitivities of phytoplankton growth into our...
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Lower pH and elevated temperature alter phytoplankton growth and biomass in short-term incubations, but longer-term responses and adaptation potential are less well-studied. To determine the future of the coccolithophore Emiliania huxleyi , a mixed genotype culture from subantarctic water was incubated for 720 days under present-day temperature and...
Citations
... Kroeker et al., 2013;Meyer and Riebesell, 2015;Seifert et al., 2020) -especially for planktonic calcifiers, calcifying algae and corals -uncertainties are high due to potential decoupling between growth and calcification in response to environmental stressors (e.g. light and nutrient availability, as well as carbonate chemistry; Zondervan et al., 2001;Seifert et al., 2022). In addition, biological studies often focus on coccolithophores, and in particular Emiliania huxleyi, which may not be representative of wider pelagic calcifiers (Ridgwell et al., 2007), which exhibit diverse responses to environmental change (e.g. ...
... On paleoclimatic timescales, especially for the study of glacial-interglacial transitions, the oceanic CaCO 3 cycle is often invoked to explain changes in the global carbon cycle and, in particular, variability in the concentration of atmospheric CO 2 of about 80-100 ppm (Sigman and Boyle, 2000). Changes in the carbonate pump magnitude, in particular through shallow water coral reef surface availability, could partly drive large variations in the concentration of atmospheric CO 2 (e.g. ...
... In addition, in response to a perturbation in carbonate chemistry, the carbonate compensation feedback tends to restore the balance between river input of Alk and CaCO 3 burial through fluctuations in the lysocline depth -the upper limit of the transition zone, where sinking and sedimentary CaCO 3 starts to substantially dissolve -at a timescale of about 10 4 years (e.g. Broecker and Peng, 1987;Sigman and Boyle, 2000;Sarmiento and Gruber, 2006;Boudreau et al., 2018;Kurahashi-Nakamura et al., 2022). This mechanism alleviates an initial perturbation in atmospheric CO 2 from an external source to the ocean (negative feedback; e.g. for an imbalance in the terrestrial carbon cycle) and amplifies it when resulting from an internal ocean process (positive feedback; e.g. for a change in the organic matter or CaCO 3 production; Sarmiento and Gruber, 2006). ...
Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedback on anthropogenic carbon uptake and ocean acidification has received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from −74 % to +23 % under a high-emission scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on 21st century ocean carbon uptake and acidification. However, we highlight a potentially abrupt shift, between 2100 and 2300, in the dissolution of CaCO3 from deep to subsurface waters when the global-scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900–1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air–sea carbon fluxes, particularly in the Southern Ocean.
... In the Northern Hemisphere, the deepest MLD (> 1000 m) is found in the Labrador and Greenland-Iceland-Norwegian seas. The magnitude is larger than in Sallée et al. (2021a) but is in the same range as in other modelling studies (Griffies et al., 2009;Sidorenko et al., 2011). In the Southern Hemisphere, winter deep mixing in high latitudes is also overestimated compared to the observations, especially in the Pacific sector of the Southern Ocean. ...
... This model set-up provides the basis for further model development, for example, the inclusion of coccolithophores as an additional phytoplankton functional type and the sensitivity of phytoplankton growth to rising CO 2 (Seifert et al., 2022) and the separation of the generic small zooplankton group into micro-and mesozooplankton that reduces model biases in nutrient fields, increases net primary production, and better captures the top-down control on phytoplankton bloom phenology (Karakuş et al., 2022). We further plan to incorporate more detailed iron biogeochemistry, as developed in REcoM coupled to MITgcm (e.g. ...
The cycling of carbon in the oceans is affected by feedbacks driven by changes in climate and atmospheric CO2. Understanding these feedbacks is therefore an important prerequisite for projecting future climate. Marine biogeochemistry models are a useful tool but, as with any model, are a simplification and need to be continually improved. In this study, we coupled the Finite-volumE Sea ice–Ocean Model (FESOM2.1) to the Regulated Ecosystem Model version 3 (REcoM3). FESOM2.1 is an update of the Finite-Element Sea ice–Ocean Model (FESOM1.4) and operates on unstructured meshes. Unlike standard structured-mesh ocean models, the mesh flexibility allows for a realistic representation of small-scale dynamics in key regions at an affordable computational cost. Compared to the previous coupled model version of FESOM1.4–REcoM2, the model FESOM2.1–REcoM3 utilizes a new dynamical core, based on a finite-volume discretization instead of finite elements, and retains central parts of the biogeochemistry model. As a new feature, carbonate chemistry, including water vapour correction, is computed by mocsy 2.0. Moreover, REcoM3 has an extended food web that includes macrozooplankton and fast-sinking detritus. Dissolved oxygen is also added as a new tracer. In this study, we assess the ocean and biogeochemical state simulated with FESOM2.1–REcoM3 in a global set-up at relatively low spatial resolution forced with JRA55-do (Tsujino et al., 2018) atmospheric reanalysis. The focus is on the recent period (1958–2021) to assess how well the model can be used for present-day and future climate change scenarios on decadal to centennial timescales. A bias in the global ocean–atmosphere preindustrial CO2 flux present in the previous model version (FESOM1.4–REcoM2) could be significantly reduced. In addition, the computational efficiency is 2–3 times higher than that of FESOM1.4–REcoM2. Overall, it is found that FESOM2.1–REcoM3 is a skilful tool for ocean biogeochemical modelling applications.
... Kroeker et al., 2013;Meyer and Riebesell, 2015;Seifert et al., 2020) -especially for planktonic calcifiers, calcifying algae and corals -uncertainties are high due to potential decoupling between growth and calcification in response to environmental stressors (e.g. light and nutrient availability, as well as carbonate chemistry, Zondervan et al., 2001;Seifert et al., 2022). In addition, biological studies often focus on coccolithophores, and in particular Emiliane huxleyi, which may not be representative of wider pelagic calcifiers 55 (Ridgwell et al., 2007), which exhibit diverse responses to environmental change (e.g. ...
Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedbacks on anthropogenic carbon uptake and ocean acidification have received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from -74 % to +23 % under a high-emissions scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on twenty-first century ocean carbon uptake and acidification. However between 2100 and 2300, we highlight a potentially abrupt shift in the dissolution of CaCO3 from deep to subsurface waters when the global scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900 to 1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air-sea carbon fluxes, particularly in the Southern Ocean.
... For varying single bottom-up environmental drivers, phytoplankton growth responses in models are commonly described by mechanistic approaches such as the Arrhenius curve for temperature (Arrhenius, 1889), the Michaelis-Menten, Monod, or Droop functions for different nutrients (Droop, 1973;Michaelis & Menten, 1913;Monod, 1942Monod, , 1949, photosynthesis-irradiance curves for light (Geider et al., 1996;Geider & Osborne, 1992), and functions that describe growth responses to the carbonate system Gafar et al., 2018;Paul & Bach, 2020;Seifert et al., 2022). Subsequently, the applied growth descriptions in models usually consist of the multiplication of these single driver effects; ...
... While not sufficient data was available from other driver interactions to obtain robust results, increasing partial pressure of carbon dioxide (CO 2 ) was found to profusely dampen the growth-enhancing effects of high temperature and high light (Seifert et al., 2020). Here, we develop and implement a new parameterization of the dual driver interactions of CO 2 with temperature and light into the global ocean biogeochemistry model FESOM-REcoM (Hauck et al., 2013;Karakuş et al., 2021;Seifert et al., 2022). In the first step, both the initial model setup without driver interactions and the newly developed model setup with driver interactions are used to assess changes in biomass, NPP, and individual driver limitations between present-day and future conditions. ...
... We briefly introduce REcoM and the relevant model equations here but refer the reader to the Supporting Information (Text S.1) for a more detailed description of the model. The structure of REcoM mainly follows Hauck et al. (2013), Karakuş et al. (2021), and Seifert et al. (2022) including two detritus groups (slow-sinking and fast-sinking particles), two zooplankton groups (small, fast-growing zooplankton and slow-growing polar macrozooplankton), and three phytoplankton groups (diatoms, coccolithophores, and small-sized phytoplankton). ...
Phytoplankton growth is controlled by multiple environmental drivers, which are all modified by climate change. While numerous experimental studies identify interactive effects between drivers, large-scale ocean biogeochemistry models mostly account for growth responses to each driver separately and leave the results of these experimental multiple-driver studies largely unused. Here, we amend phytoplankton growth functions in a biogeochemical model by dual-driver interactions (CO2 and temperature, CO2 and light), based on data of a published meta-analysis on multiple-driver laboratory experiments. The effect of this parametrization on phytoplankton biomass and community composition is tested using present-day and future high-emission (SSP5-8.5) climate forcing. While the projected decrease in future total global phytoplankton biomass in simulations with driver interactions is similar to that in control simulations without driver interactions (5%-6%), interactive driver effects are group-specific. Globally, diatom biomass decreases more with interactive effects compared with the control simulation (-8.1% with interactions vs. no change without interactions). Small-phytoplankton biomass, by contrast, decreases less with on-going climate change when the model accounts for driver interactions (-5.0% vs. -9.0%). The response of global coccolithophore biomass to future climate conditions is even reversed when interactions are considered (+33.2% instead of -10.8%). Regionally, the largest difference in the future phytoplankton community composition between the simulations with and without driver interactions is detected in the Southern Ocean, where diatom biomass decreases (-7.5%) instead of increases (+14.5%), raising the share of small phytoplankton and coccolithophores of total phytoplankton biomass. Hence, interactive effects impact the phytoplankton community structure and related biogeochemical fluxes in a future ocean. Our approach is a first step to integrate the mechanistic understanding of interacting driver effects on phytoplankton growth gained by numerous laboratory experiments into a global ocean biogeochemistry model, aiming toward more realistic future projections of phytoplankton biomass and community composition.
The ocean is responsible for taking up approximately 25% of anthropogenic CO2 emissions and stores >50 times more carbon than the atmosphere. Biological processes in the ocean play a key role, maintaining atmospheric CO2 levels approximately 200 ppm lower than they would otherwise be. The ocean's ability to take up and store CO2 is sensitive to climate change, however the key biological processes that contribute to ocean carbon storage are uncertain, as are how those processes will respond to, and feedback on, climate change. As a result, biogeochemical models vary widely in their representation of relevant processes, driving large uncertainties in the projections of future ocean carbon storage. This review identifies key biological processes that affect how ocean carbon storage may change in the future in three thematic areas: biological contributions to alkalinity, net primary production, and interior respiration. We undertook a review of the existing literature to identify processes with high importance in influencing the future biologically‐mediated storage of carbon in the ocean, and prioritized processes on the basis of both an expert assessment and a community survey. Highly ranked processes in both the expert assessment and survey were: for alkalinity—high level understanding of calcium carbonate production; for primary production—resource limitation of growth, zooplankton processes and phytoplankton loss processes; for respiration—microbial solubilization, particle characteristics and particle type. The analysis presented here is designed to support future field or laboratory experiments targeting new process understanding, and modeling efforts aimed at undertaking biogeochemical model development.
The ocean is responsible for taking up approximately 25% of anthropogenic CO2 emissions and stores > 50 times more carbon than the atmosphere. Biological processes in the ocean play a key role, maintaining atmospheric CO2 levels 200 ppm lower than they would otherwise be. The ocean’s ability to take up and store CO2 is sensitive to climate change, however the key biological processes that contribute to ocean carbon storage are uncertain, as are their response and feedbacks to climate change. As a result, biogeochemical models vary widely in their representation of relevant processes, driving large uncertainties in the projections of future ocean carbon storage. This review identifies key biological processes that affect how carbon storage may change in the future in three thematic areas: biological contributions to alkalinity, net primary production, and interior respiration. We undertook a review of the existing literature to identify processes with high importance in influencing the future biologically-mediated storage of carbon in the ocean, and prioritised processes on the basis of both an expert assessment and a community survey. Highly ranked processes in both the expert assessment and survey were: for alkalinity – high level understanding of calcium carbonate production; for primary production – resource limitation of growth, zooplankton processes and phytoplankton loss processes; for respiration – microbial solubilisation, particle characteristics and particle type. The analysis presented here is designed to support future field or laboratory experiments targeting new process understanding, and modelling efforts aimed at undertaking biogeochemical model development.
The cycling of carbon in the oceans is affected by feedbacks driven by changes in climate and atmospheric CO2. Understanding these feedbacks is therefore an important prerequisite for projecting future climate. Marine biogeochemical models are a useful tool there, but as any model is a simplification, need to be continually improved. In this study, we coupled the Finite-volumE Sea ice-Ocean Model (FESOM2.1) to the Regulated Ecosystem Model version 3 (REcoM3). FESOM2.1 is an update of the Finite Element Sea ice-Ocean Model (FESOM1.4) and operates on variable mesh resolution. Unlike standard structured-mesh ocean models, the mesh flexibility allows for a realistic representation of small-scale dynamics in key regions at affordable computational cost. Compared to the previous coupled model version FESOM1.4-REcoM2, the model FESOM2.1-REcoM3 utilizes a new dynamical core based on a finite volume discretization instead of finite elements, but retains central parts of the biogeochemistry model. As a new feature, carbonate chemistry including water vapor correction is computed by mocsy-2.0. Moreover, REcoM3 has an extended food web that includes macrozooplankton and fast-sinking detritus. Dissolved oxygen is added as a new tracer. In this study we assess the ocean and biogeochemical state simulated with FESOM2.1-REcoM3 in a global setup at relatively low spatial resolution forced with JRA55-do atmospheric reanalysis. The focus is on the recent period 1958–2021, to assess how well the model can be used for present-day and future climate change scenarios on decadal to centennial timescales. A bias in global ocean-atmosphere preindustrial CO2 flux present in the previous model version FESOM1.4-REcoM2 could be significantly reduced. In addition, the computational efficiency is 2–3 times higher than that of FESOM1.4-REcoM. Overall, it is found that FESOM2.1-REcoM3 is a skillful tool for ocean biogeochemical modelling applications.
