Plankton functional group models – An assessment

This Discussant’s Report provides a summary of the discussions that followed presentation of the approaches and ideas described in Thingstad et al. (this volume). The discussions, which addressed aspects of conceptual understanding and parameterization that are relevant to development of ecosystem models capable of emergent behavior at a range of scales, the benefits of functional group modeling, and some of the limitations of this approach, provide insights that are relevant to setting directions for future research efforts. One important point emerging from the discussions was that reconciling the requirements of simplicity versus complexity with the desire to obtain predictive capability is an important area where biogeochemical and ecosystem models can be improved

Plankton dynamics on the outer southeastern U.S. continental shelf. Part III: A coupled physical-biological model

Gulf Stream frontal eddies and bottom intrusions provide an almost continuous input of nutrients to the waters of the outer southeastern U.S. continental shelf. However, the two types of upwelling differ in physical dynamics, frequency of occurrence and duration. To investigate the effect of these differences on biological production associated with the two upwellings, a ten-component biological model was coupled to circulation and temperature fields constructed from an optimal interpolation of current meter data obtained from moorings deployed on the mid- to outer southeastern U.S. continental shelf as part of GABEX I (February to June, 1980) and GABEX II (June to September, 1981). Model output gives the spatial and temporal distributions of nitrate, ammonium, phytoplankton, and a copepod in an alongshore plane located at a nominal depth of 37 m. These distributions were used to investigate the flux of properties to and from the outer southeastern U.S. shelf and the role of upwelling features in the formation of large-scale plankton patches on the outer southeastern U.S. continental shelf. The simulated distributions show basic differences in the biological response to frontal eddy and bottom intrusion upwelling. For frontal eddies most of the upwelled nitrate is advected northward along the outer shelf, with only occasional transport of the upwelled nitrate across the shelf to the 40-m isobath. The primary production resulting from this upwelling is also transported northward. The net transport of primary production at the 75-m isobath is offshore. Copepod densities associated with the frontal eddies are low. Bottom intrusions have time scales that are longer than those associated with the frontal eddies and bottom intrusions tend to move onshore rather than remaining only on the outer shelf. Consequenlty, these events result in a net onshore flux of nitrate and phytoplankton at the 75-m isobath over the region included in the model. The longer lifetime of these events results in the development of copepod blooms that are characterized by a biomass that is approximately twice that associated with frontal eddies. A large portion of the primary production resulting from bottom intrusions is consumed by the shelf zooplankton community. Also, much of the primary and secondary production associated with bottom intrusions is transported across the shelf to onshore areas. These results imply a strong seasonal signal in the carbon and nitrogen fluxes on the outer southeastern U.S. continental shelf

Biology of the Southern Ocean

The article reviews the book Biology of the Southern Ocean, by George Knox

NetCDF model output of the entire state of the surface layer, including simulated dFe dyes, of the circum-Antarctic

Dataset: Antarctic dFe model dyesFor a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/782848NSF Office of Polar Programs (formerly NSF PLR) (NSF OPP) OPP-1643652, NSF Office of Polar Programs (formerly NSF PLR) (NSF OPP) OPP-164361

Simulations of Phytoplankton Species and Carbon Production in the Equatorial Pacific Ocean 2. Effects of Physical and Biogeochemical Processes

A one-dimensional multi-component lower trophic level ecosystem model that includes detailed algal physiology is used to investigate the response of phytoplankton community and carbon production and export to variations in physical and biochemical processes in the Cold Tongue region of the equatorial Pacific Ocean at ON, 140W. Results show that high-frequency variability in vertical advection and temperature is an important mechanism driving the carbon export. Filtering out low frequency physical forcing results in a 30% increase in primary production and dominance of high-light adapted Prochlorococcus and autotrophic eukaryotes. Sensitivity studies show that iron availability is the primary control on carbon export and production; whereas, algal biomass concentration is largely regulated by zooplankton grazing. Recycled iron is an important component of the ecosystem dynamics because sustained growth of algal groups depends on remineralized iron which accounts for 4.0% of the annual primary production in the Cold Tongue region. Sensitivity studies show that although all algal groups have a considerable effect on simulated phytoplankton carbon biomass, not all have a strong effect on primary production and carbon export. Thus, these sensitivity studies indicate that it may not be necessary to represent a broad spectrum of algal groups in carbon cycle models, because a few key groups appear to have a large influence on primary production and export variability. Combining the low-light adapted Prochlorococcus, high-light adapted Prochlorococcus and Synechococcus groups as a single group and using a three algal group model may be sufficient to simulate primary production and export variability in the tropical Pacific waters. The results from this modeling study suggest that the net effect of increased stratification and temperature conditions is a decrease in carbon export in the Cold Tongue region and a shift in the phytoplankton community towards smaller algal forms (e.g., Prochlorococcus spp. and Synechecoccus). Increased stratification can result in decreased iron concentration and reduced vertical velocities, both of which contribute to decreased carbon export. Also, stratified conditions enhance the remineralization rate of nutrients (e.g., iron), which enhances carbon production. Thus, inclusion of iron dynamics in climate models may be needed to fully represent the effect of climate variability on equatorial Pacific ecosystems

Plankton dynamics on the outer southeastern U.S. continental shelf. Part I: Lagrangian particle tracing experiments

The residence time and flow patterns of plankton populations on the outer southeastern U.S. continental shelf were studied with Lagrangian particle tracing experiments. Flow and temperature fields used for these experiments were constructed by applying optimal interpolation methods to current meter data obtained during the Georgia Bight Experiment I and II which took place 25 February to 18 June 1980 and 10 June to 24 September 1981, respectively. The interpolated fields reproduced the flow and temperature structures associated with Gulf Stream frontal eddies and bottom intrusions, which are the upwelling mechanisms of interest in this region. The general particle tracing results showed that plankton residence time and flow trajectory are controlled primarily by the Gulf Stream location and wind direction. During times when the Gulf Stream is located near the shelf break, plankton are transported rapidly to the north with little onshore flow. Residence times are short, being on the order of three to four days. When the Gulf Stream is located offshore of the shelf break and wind patterns are variable, particle transport shows no preferred direction and residence times on the outer southeastern U.S. shelf are long; sometimes in excess of thirty days. Tracing of particles in waters upwelled in frontal eddies and bottom intrusions showed considerable differences in the fate of plankton associated with these features. Residence times of waters and particles upwelled in frontal eddies are short, four to six days, and transport is northward with the Gulf Stream. Bottom intrusion waters, by contrast, remain on the continental shelf for more than twenty days and transport of these waters and of associated particles is across the shelf to the inshore regions. The particle tracing experiments showed that the different upwelling regimes and changing physical environment greatly affect the transport of material from and across the outer southeastern U.S. continental shelf. This in turn implies that these physical processes are a major component influencing the structure of plankton communities of this region

Simulations of Phytoplankton Species and Carbon Production in the Equatorial Pacific Ocean 1. Model Configuration and Ecosystem Dynamics

The primary objective of this research is to investigate phytoplankton community response to variations in physical forcing and biological processes in the Cold Tongue region of the equatorial Pacific Ocean at 0N, 140W. This research objective was addressed using a one-dimensional multicomponent lower trophic level ecosystem model that includes detailed algal physiology, such as spectrally-dependent photosynthetic processes and iron limitation on algal growth. The ecosystem model is forced by a one-year (1992) time series of spectrally-dependent light, temperature, and water column mixing obtained from a Tropical Atmosphere-Ocean (TAO) Array mooring. Autotrophic growth is represented by five algal groups, which have light and nutrient utilization characteristics of low-light adapted Prochlorococcus, high-light adapted Prochlorococcus, Synechococcus, autotrophic eukaryotes, and large diatoms. The simulated distributions and rates are validated using observations from the 1992 U. S. Joint Global Ocean Flux Study Equatorial Pacific cruises. The modeldata comparisons show that the simulations successfully reproduce the temporal distribution of each algal group and that multiple algal groups are needed to fully resolve the variations observed for phytoplankton communities in the equatorial Pacific. The 1992 simulations show seasonal variations in algal species composition superimposed on shorter time scale variations (e.g., 8–20 days) that arise from changes in the upwelling/downwelling environmental structure. The simulated time evolution of the algal groups shows that eukaryotes are the most abundant group, being responsible for half of the annual biomass and 69% of the annual primary production and organic carbon export

An Introduction to Ecology of Infectious Diseases - Oysters and Estuaries

Infectious diseases are recognized as an important factor regulating marine ecosystems (Harvell et al., 1999, 2002, 2004; Porter et al., 2001; McCallum et al., 2004; Ward and Lafferty, 2004; Stewart et al., 2008; Bienfang et al., 2011). Many of the organisms affected by marine diseases have important ecological roles in estuarine and coastal environments and some are also commercially important. Outbreaks of infectious diseases in these environments, referred to as epizootics, can produce significant population declines and extinctions, both of which threaten biodiversity, food web interactions, and ecosystem productivity (Harvell et al., 2002, 2004)

Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 3. Lagrangian Drifters

Two types of numerical Lagrangian drifter experiments were conducted, using a set of increasingly complex and sophisticated models, to investigate the processes associated with the plankton distributions in the California coastal transition zone (CTZ). The first experiment used a one-dimensional (1-D; vertical) time-dependent physical-bio-optical model, which contained a nine-component food web. Vertical velocities, along the track of simulated Lagrangian drifters, derived from a three-dimensional (3-D), primitive equation circulation model developed to simulate the flow observed within the CTZ; were used to parameterize the upwelling and downwelling processes. The second experiment used 880 simulated Lagrangian drifters from a 3-D primitive equation circulation model which was coupled to the same food web and bio-optical model used in the first experiment. Parameterization of the biological processes in both experiments were based upon data obtained during the CTZ field experiments. Comparison of simulations with data provided insight into the role of the biological and physical processes in determining the development of the subsurface chlorophyll maximum and other related features. In both studies, the vertical velocities experienced by a simulated Lagrangian drifter as it was advected offshore while entrained within a filament played a major role in determining the depth to which the euphotic zone and the chlorophyll maximum developed. Also, as the drifters moved offshore, the food web changed from a coastal, neritic food web to an offshore, oligotrophic food web due to the decrease in nutrient availability. The temporal development of the food web constituents following the simulated drifters was dependent upon the environment to which the drifter was exposed. For example, the amount of time upwelled or downwelled and the initial location in the CTZ region greatly affected the development of the food web

Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 1. A Time- and Depth-Dependent Model

A time- and depth-dependent, physical-bio-optical model was developed for the California coastal transition zone (CTZ) with the overall objective of understanding and quantifying the processes that contribute to the vertical and temporal development of nutrient and plankton distributions in the CTZ. The model food web components included silicate, nitrate, ammonium, two phytoplankton size fractions, copepods, doliolids, euphausiids, and a detritus pool. The wavelength-dependent subsurface irradiance field was attenuated by sea water and phytoplankton pigments. The one-dimensional (1-D) model adequately simulated the development and maintenance of a subsurface chlorophyll maximum in different regions within the CTZ. An analysis of the individual terms in the model governing equations revealed that phytoplankton in situ growth was primarily responsible for the creation and maintenance of the subsurface chlorophyll maximum at both coastal and oceanic regions in the CTZ. The depth to which the maximum in situ growth occurred was controlled by the combined effect of light and nutrient limitation. Also, the simulated bio-optical fields demonstrated the effect of nonlinear couplings between food web components and the subsurface irradiance field on vertical biological distributions. In particular, the epsilon-folding scale of the subsurface photosynthetically available radiation (PAR) was influenced by the level of zooplankton grazing