Cara Nissen

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Nissen

First Name

Cara

ORCID

0000-0001-5804-3191

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Publications 1 - 10 of 23

Southern Ocean coccolithophore biogeography – controlling factors and implications for global biogeochemical cycles
Nissen, Cara; Vogt, Meike; Münnich, Matthias; et al. (2017)
Geophysical Research Abstracts
MOBYDICK: Potential contribution of ETHZ
Vogt, Meike; Gruber, Nicolas; Righetti, Damiano; et al. (2017)
Strengthening of the Southern Ocean Carbon Sink through Recent Changes in Freshwater Forcing
Haumann, Alexander; Gruber, Nicolas; Münnich, Matthias; et al. (2016)
Coccolithophore controls on the Southern Ocean biogeochemistry
Nissen, Cara; Vogt, Meike; Münnich, Matthias; et al. (2018)
Coccolithophore controls on the Southern Ocean carbon cycle
Nissen, Cara; Vogt, Meike; Münnich, Matthias; et al. (2018)
Coccolithophore Growth and Calcification in an Acidified Ocean: Insights From Community Earth System Model Simulations
Krumhardt, Kristen M.; Lovenduski, Nicole S.; Long, Matthew C.; et al. (2019)
Journal of Advances in Modeling Earth Systems
Anthropogenic CO2 emissions are inundating the upper ocean, acidifying the water, and altering the habitat for marine phytoplankton. These changes are thought to be particularly influential for calcifying phytoplankton, namely, coccolithophores. Coccolithophores are widespread and account for a substantial portion of open ocean calcification; changes in their abundance, distribution, or level of calcification could have far‐reaching ecological and biogeochemical impacts. Here, we isolate the effects of increasing CO2 on coccolithophores using an explicit coccolithophore phytoplankton functional type parameterization in the Community Earth System Model. Coccolithophore growth and calcification are sensitive to changing aqueous CO2. While holding circulation constant, we demonstrate that increasing CO2 concentrations cause coccolithophores in most areas to decrease calcium carbonate production relative to growth. However, several oceanic regions show large increases in calcification, such the North Atlantic, Western Pacific, and parts of the Southern Ocean, due to an alleviation of carbon limitation for coccolithophore growth. Global annual calcification is 6% higher under present‐day CO2 levels relative to preindustrial CO2 (1.5 compared to 1.4 Pg C/year). However, under 900 μatm CO2, global annual calcification is 11% lower than under preindustrial CO2 levels (1.2 Pg C/year). Large portions of the ocean show greatly decreased coccolithophore calcification relative to growth, resulting in significant regional carbon export and air‐sea CO2 exchange feedbacks. Our study implies that coccolithophores become more abundant but less calcified as CO2 increases with a tipping point in global calcification (changing from increasing to decreasing calcification relative to preindustrial) at approximately ∼600 μatm CO2.
Biotic versus abiotic controls on Southern Ocean coccolithophore biogeography
Nissen, Cara; Vogt, Meike; Münnich, Matthias; et al. (2017)
Book of Abstracts, XIIth SCAR Biology Symposium
Southern Ocean phytoplankton biogeography is important for the biogeochemical cycling of carbon, silicate, and the transport of macronutrients to lower latitudes. With the discovery of the ‘Great Calcite Belt’, revealing an unexpectedly high prevalence of calcifying phytoplankton in this ocean basin, the relative importance of Southern Ocean coccolithophores for phytoplankton biomass and net primary productivity, the factors controlling their biogeography, and their impact on the carbon cycle need to be revisited. Using a mechanistic regional high-resolution model (ROMS-BEC) for the Southern Ocean (24-78°S) that has been extended to include an explicit representation of coccolithophores, we assess controlling factors of Southern Ocean coccolithophore biogeography over the course of the growing season, with a particular focus on biotic interactions and the relative role of top-down versus bottom-up factors. In our simulation, coccolithophores are an important member of the Southern Ocean phytoplankton community, contributing ~13% to annually integrated net primary productivity south of 30°S. Coccolithophore biomass is highest in February and March in a latitudinal band between 40-55°S, when diatoms become heavily silicate limited. This region is characterized by a number of divergent fronts with a low Si:Fe ratio of waters supplied to the mixed layer, supporting an increased growth of coccolithophores relative to diatoms. Furthermore, we find top down controls to be a major control on the relative abundance of diatoms and coccolithophores in the Southern Ocean. Consequently, when assessing potential future changes in Southern Ocean coccolithophore abundance, both physical (temperature, light, nutrients) and chemical (ocean acidification) changes, but also biotic interactions need to be considered.
Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018
DeVries, Tim; Yamamoto, Kana; Wanninkhof, Rik; et al. (2023)
Global Biogeochemical Cycles
This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation-based products. The mean sea-air CO₂ flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr⁻¹ based on an ensemble of reconstructions of the history of sea surface pCO₂ (pCO₂ products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO₂, which is estimated at −2.1 ± 0.3 PgC yr⁻¹ by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr⁻¹ of terrestrially derived CO₂, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO₂ products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr⁻¹ decade⁻¹, while biogeochemical models and inverse models diagnose an anthropogenic CO₂-driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr⁻¹ decade⁻¹, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO₂-forced variability by 2–3 times. These results suggest that anthropogenic CO₂ dominates the ocean CO₂ sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.
Factors controlling the competition between Phaeocystis and diatoms in the Southern Ocean
Nissen, Cara; Vogt, Meike (2020)
Biogeosciences Discussions
The high-latitude Southern Ocean phytoplankton community is shaped by the competition between Phaeocystis and silicifying diatoms, with the relative abundance of these two groups controlling primary and export production, the production of dimethylsulfide, the ratio of silicic acid and nitrate available in the water column, and the structure of the food web. Here, we investigate this competition using a regional physical-biogeochemical-ecological model (ROMS-BEC) configured at eddy-permitting resolution for the Southern Ocean south of 35° S. We extended ROMS-BEC by an explicit parameterization of Phaeocystis colonies, so that the model, together with the previous addition of an explicit coccolithophore type, now includes all biogeochemically relevant Southern Ocean phytoplankton types. We find that Phaeocystis contribute 46 % and 40 % to annual NPP and POC export south of 60° S, respectively, making them an important contributor to high-latitude carbon cycling. In our simulation, the relative importance of Phaeocystis and diatoms is mainly controlled by the temporal variability in temperature and iron availability. The higher light sensitivity of Phaeocystis at low irradiances promotes the succession from Phaeocystis to diatoms in more coastal areas, such as the Ross Sea. Still, differences in the biomass loss rates, such as aggregation or grazing by zooplankton, need to be considered to explain the simulated seasonal biomass evolution.
Controlling factors of Southern Ocean Coccolithophore Biogeography
Nissen, Cara (2017)

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Cara Nissen

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