scholarly journals On the treatment of particulate organic matter sinking in large-scale models of marine biogeochemical cycles

2007 ◽  
Vol 4 (4) ◽  
pp. 3005-3040
Author(s):  
I. Kriest ◽  
A. Oschlies
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Water Column ◽  
Size Distribution ◽  
Power Law ◽  
Particulate Organic Matter ◽  
Large Scale ◽  
Regional Patterns ◽  
Size Dependent ◽  
Biogeochemical Models

Abstract. Various functions have been suggested and applied to represent the sedimentation and remineralisation of particulate organic matter (POM) in numerical ocean models. Here we investigate some representations commonly used in large-scale biogeochemical models: a constant sinking speed, a sinking speed increasing with depth, a spectrum of particles with different size and different size-dependent sinking velocities, and a model that assumes a power-law particle size distribution everywhere in the water column. The analysis is carried out for an idealised one-dimensional water column, under stationary boundary conditions for surface POM. It focuses on the intrinsic assumptions of the respective sedimentation function and their effect on POM mass, mass flux, and remineralisation profiles. A constant and uniform sinking speed does not appear appropriate for simulations exceeding a few decades, as the sedimentation profile is not consistent with observed profiles. A spectrum of size classes, together with size-dependent sinking and constant remineralisation, causes the sinking speed of total POM to increase with depth. This increase is not strictly linear with depth. Its particular form will further depend on the size distribution of the POM ensemble at the surface. Assuming a power-law particle size spectrum at the surface, this model results in unimodal size distributions in the ocean interior. For the size-dependent sinking model, we present an analytic integral over depth and size that can explain regional variations of remineralisation length scales in response to regional patterns in trophodynamic state.

scholarly journals On the treatment of particulate organic matter sinking in large-scale models of marine biogeochemical cycles

2008 ◽  
Vol 5 (1) ◽  
pp. 55-72 ◽  
Author(s):  
I. Kriest ◽  
A. Oschlies
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Water Column ◽  
Size Distribution ◽  
Power Law ◽  
Particulate Organic Matter ◽  
Large Scale ◽  
Regional Patterns ◽  
Size Dependent ◽  
Biogeochemical Models

Abstract. Various functions have been suggested and applied to represent the sedimentation and remineralisation of particulate organic matter (POM) in numerical ocean models. Here we investigate some representations commonly used in large-scale biogeochemical models: a constant sinking speed, a sinking speed increasing with depth, a spectrum of particles with different size and different size-dependent sinking velocities, and a model that assumes a power law particle size distribution everywhere in the water column. The analysis is carried out for an idealised one-dimensional water column, under stationary boundary conditions for surface POM. It focuses on the intrinsic assumptions of the respective sedimentation function and their effect on POM mass, mass flux, and remineralisation profiles. A constant and uniform sinking speed does not appear appropriate for simulations exceeding a few decades, as the sedimentation profile is not consistent with observed profiles. A spectrum of size classes, together with size-dependent sinking and constant remineralisation, causes the sinking speed of total POM to increase with depth. This increase is not strictly linear with depth. Its particular form will further depend on the size distribution of the POM ensemble at the surface. Assuming a power law particle size spectrum at the surface, this model results in unimodal size distributions in the ocean interior. For the size-dependent sinking model, we present an analytic integral over depth and size that can explain regional variations of remineralisation length scales in response to regional patterns in trophodynamic state.

scholarly journals A mechanistic particle flux model applied to the oceanic phosphorus cycle

2014 ◽  
Vol 11 (19) ◽  
pp. 5381-5398 ◽  
Author(s):  
T. DeVries ◽  
J.-H. Liang ◽  
C. Deutsch
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Particle Flux ◽  
Particle Sizes ◽  
Biogeochemical Models ◽  
Wide Range ◽  
Flux Model ◽  
Surface Particle

Abstract. The sinking and decomposition of particulate organic matter are critical processes in the ocean's biological pump, but are poorly understood and crudely represented in biogeochemical models. Here we present a mechanistic particle remineralization and sinking model (PRiSM) that solves the evolution of the particle size distribution with depth. The model can represent a wide range of particle flux profiles, depending on the surface particle size distribution, the relationships between particle size, mass and sinking velocity, and the rate of particle mass loss during decomposition. The particle flux model is embedded in a data-constrained ocean circulation and biogeochemical model with a simple P cycle. Surface particle size distributions are derived from satellite remote sensing, and the remaining uncertain parameters governing particle dynamics are tuned to achieve an optimal fit to the global distribution of phosphate. The resolution of spatially variable particle sizes has a significant effect on modeled organic matter production rates, increasing production in oligotrophic regions and decreasing production in eutrophic regions compared to a model that assumes spatially uniform particle sizes and sinking speeds. The mechanistic particle model can reproduce global nutrient distributions better than, and sediment trap fluxes as well as, other commonly used empirical formulas. However, these two independent data constraints cannot be simultaneously matched in a closed P budget commonly assumed in ocean models. Through a systematic addition of model processes, we show that the apparent discrepancy between particle flux and nutrient data can be resolved through P burial, but only if that burial is associated with a slowly decaying component of organic matter such as might be achieved through protection by ballast minerals. Moreover, the model solution that best matches both data sets requires a larger rate of P burial (and compensating inputs) than have been previously estimated. Our results imply a marine P inventory with a residence time of a few thousand years, similar to that of the dynamic N cycle.

scholarly journals A mechanistic particle flux model applied to the oceanic phosphorus cycle

2014 ◽  
Vol 11 (3) ◽  
pp. 3653-3699 ◽  
Author(s):  
T. DeVries ◽  
J.-H. Liang ◽  
C. Deutsch
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Particle Flux ◽  
Particle Model ◽  
Particle Sizes ◽  
Phosphorus Cycle ◽  
Biogeochemical Models ◽  
Wide Range

Abstract. The sinking and decomposition of particulate organic matter are critical processes in the ocean's biological pump, but are poorly understood and crudely represented in biogeochemical models. Here we present a mechanistic model for particle fluxes in the ocean that solves the evolution of the particle size distribution with depth. The model can represent a wide range of particle flux profiles, depending on the surface particle size distribution, the relationships between particle size, mass and velocity, and the rate of particle mass loss during decomposition. Spatially variable flux profiles are embedded in a data-constrained ocean circulation model, where the most uncertain parameters governing particle dynamics are tuned to achieve an optimal fit to the global distribution of phosphate. The resolution of spatially variable particle sizes has a significant effect on modeled organic matter production rates, increasing production in oligotrophic regions and decreasing production in eutrophic regions compared to a model that assumes spatially uniform particle sizes and sinking fluxes. The mechanistic particle model can reproduce global nutrient distributions better than, and sediment trap fluxes as well as, other commonly used empirical formulas. However, these independent data constraints cannot be simultaneously matched in a closed P budget commonly assumed in ocean models. Through a systematic addition of model processes, we show that the apparent discrepancy between particle flux and nutrient data can be resolved through P burial, but only if that burial is associated with a slowly decaying component of organic matter as might be achieved through protection by ballast minerals. Moreover, the model solution that best matches both datasets requires a larger rate of P burial (and compensating inputs) than have been previously estimated. Our results imply a marine PO4 inventory with a residence time of a few thousand years, similar to that of the relatively dynamic N cycle.

scholarly journals Effects of CO<sub>2</sub> on particle size distribution and phytoplankton abundance during a mesocosm bloom experiment (PeECE II)

2008 ◽  
Vol 5 (2) ◽  
pp. 509-521 ◽  
Author(s):  
A. Engel ◽  
K. G. Schulz ◽  
U. Riebesell ◽  
R. Bellerby ◽  
B. Delille ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Large Scale ◽  
Phytoplankton Community ◽  
Co2 Enrichment ◽  
Suspended Particles ◽  
Phytoplankton Abundance ◽  
General Importance ◽  
Co2 Treatment

Abstract. The influence of seawater carbon dioxide (CO2) concentration on the size distribution of suspended particles (2–60 μm) and on phytoplankton abundance was investigated during a mesocosm experiment at the large scale facility (LFS) in Bergen, Norway, in the frame of the Pelagic Ecosystem CO2 Enrichment study (PeECE II). In nine outdoor enclosures the partial pressure of CO2 in seawater was modified by an aeration system to simulate past (~190 μatm CO2), present (~370 μatm CO2) and future (~700 μatm CO2) CO2 conditions in triplicates. Due to the initial addition of inorganic nutrients, phytoplankton blooms developed in all mesocosms and were monitored over a period of 19 days. Seawater samples were collected daily for analysing the abundance of suspended particles and phytoplankton with the Coulter Counter and with Flow Cytometry, respectively. During the bloom period, the abundance of small particles (<4 μm) significantly increased at past, and decreased at future CO2 levels. At that time, a direct relationship between the total-surface-to-total-volume ratio of suspended particles and DIC concentration was determined for all mesocosms. Significant changes with respect to the CO2 treatment were also observed in the phytoplankton community structure. While some populations such as diatoms seemed to be insensitive to the CO2 treatment, others like Micromonas spp. increased with CO2, or showed maximum abundance at present day CO2 (i.e. Emiliania huxleyi). The strongest response to CO2 was observed in the abundance of small autotrophic nano-plankton that strongly increased during the bloom in the past CO2 mesocosms. Together, changes in particle size distribution and phytoplankton community indicate a complex interplay between the ability of the cells to physiologically respond to changes in CO2 and size selection. Size of cells is of general importance for a variety of processes in marine systems such as diffusion-limited uptake of substrates, resource allocation, predator-prey interaction, and gravitational settling. The observed changes in particle size distribution are therefore discussed with respect to biogeochemical cycling and ecosystem functioning.

scholarly journals Global variability of phytoplankton functional types from space: assessment via the particle size distribution

2010 ◽  
Vol 7 (3) ◽  
pp. 4295-4340 ◽  
Author(s):  
T. S. Kostadinov ◽  
D. A. Siegel ◽  
S. Maritorena
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Power Law ◽  
Seasonal Succession ◽  
Remote Sensing Data ◽  
Good Correspondence ◽  
Size Classes ◽  
Functional Types ◽  
Phytoplankton Size

Abstract. A new method of retrieving the parameters of a power-law particle size distribution (PSD) from ocean color remote sensing data was used to assess the global distribution and dynamics of phytoplankton functional types (PFT's). The method retrieves the power-law slope, ξ, and the abundance at a reference diameter, N0, based upon the shape and magnitude of the particulate backscattering coefficient spectrum. Relating the PSD to PFT's on global scales assumes that the open ocean particulate assemblage is biogenic. The retrieved PSD's can be integrated to define three size-based PFT's by the percent volume concentration contribution of three phytoplankton size classes – picoplankton (0.5–2 μm in equivalent spherical diameter), nanoplankton (2–20 μm) and microplankton (20–50 μm). Validation with in-situ HPLC diagnostic pigments results in satisfactory match-ups for the pico- and micro-phytoplankton size classes. Global climatologies derived from SeaWiFS monthly data reveal PFT and particle abundance spatial patterns that are consistent with current understanding. Oligotrophic gyres are characterized by lower particle abundance and higher contribution by picoplankton-sized particles than transitional or eutrophic regions. Seasonal succession patterns for size-based PFT's reveal good correspondence between increasing chl and percent contribution by microplankton, as well as increasing particle abundance. Long-term trends in particle abundances are generally inconclusive yet are well correlated with the MEI index indicating increased oligotrophy (i.e. lower particle abundance and increased contribution of picoplankton-sized particles) during the warm phase of an El Niño event. This work demonstrates the utility and future potential of assessing phytoplankton functional types using remote characterization of the particle size distribution.

scholarly journals Modelling the biogeochemical effects of heterotrophic and autotrophic N<sub>2</sub> fixation in the Gulf of Aqaba (Israel), Red Sea

2018 ◽  
Vol 15 (24) ◽  
pp. 7379-7401 ◽  
Author(s):  
Angela M. Kuhn ◽  
Katja Fennel ◽  
Ilana Berman-Frank
Keyword(s):  
Water Column ◽  
Red Sea ◽  
N2 Fixation ◽  
Large Scale ◽  
Gulf Of Aqaba ◽  
Nutrient Concentrations ◽  
Nutrient Ratios ◽  
Biogeochemical Models ◽  
Deep Waters ◽  
Direct Measurements

Abstract. Recent studies demonstrate that marine N2 fixation can be carried out without light by heterotrophic N2 fixers (diazotrophs). However, direct measurements of N2 fixation in aphotic environments are relatively scarce. Heterotrophic as well as unicellular and colonial photoautotrophic diazotrophs are present in the oligotrophic Gulf of Aqaba (northern Red Sea). This study evaluates the relative importance of these different diazotrophs by combining biogeochemical models with time series measurements at a 700 m deep monitoring station in the Gulf of Aqaba. At this location, an excess of nitrate, relative to phosphate, is present throughout most of the water column and especially in deep waters during stratified conditions. A relative excess of phosphate occurs only at the water surface during nutrient-starved conditions in summer. We show that a model without N2 fixation can replicate the observed surface chlorophyll but fails to accurately simulate inorganic nutrient concentrations throughout the water column. Models with N2 fixation improve simulated deep nitrate by enriching sinking organic matter in nitrogen, suggesting that N2 fixation is necessary to explain the observations. The observed vertical structure of nutrient ratios and oxygen is reproduced best with a model that includes heterotrophic as well as colonial and unicellular autotrophic diazotrophs. These results suggest that heterotrophic N2 fixation contributes to the observed excess nitrogen in deep water at this location. If heterotrophic diazotrophs are generally present in oligotrophic ocean regions, their consideration would increase current estimates of global N2 fixation and may require explicit representation in large-scale models.

Observations of the Particle Size Distribution and Concentration in a Coastal System using an In Situ Laser Analyzer

2002 ◽  
Vol 36 (1) ◽  
pp. 59-69 ◽  
Author(s):  
Teresa Serra ◽  
Xavier Casamitjana ◽  
Jordi Colomer ◽  
Timothy C. Granata
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Water Column ◽  
Size Distribution ◽  
Posidonia Oceanica ◽  
High Energy ◽  
Suspended Particles ◽  
Energy Conditions ◽  
Coastal System

An in situ laser particle size analyzer (LISST-100, Sequoia Scientific, Inc.) has been used to study the particle size distribution and concentration of biological and non biological particles in the water column of a Mediterranean coastal system. Two field campaigns have been carried out during low and high energy conditions of the flow, caused by the passage of a storm front. For the low energy period, the water column remained stratified, whereas for the high energetic period the water column was warmer and well mixed. The first study dealt with the distribution of particles near the bottom of the coastal area. Here, two regions were taken into account. The first region was a sea-grass meadow of Posidonia oceanica and the second region was a barren sand area. The second study dealt with the determination of the vertical distribution of suspended particles in the whole water column of the system. The results showed a decrease in the vertical concentration of suspended particles in the water column with the passage of the storm front, which was associated with advection of warm water mass rather than by vertical mixing. In contrast, vertical resuspension determined the fate of suspended particles at the bottom of the water column and an increase of their concentration was found.

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