scholarly journals Minor Contribution by Biomineralizing Phytoplankton to Surface Ocean Biomineral Pools in the Late Stratified Period

Oceans ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 489-507
Author(s):  
Stuart C. Painter
Keyword(s):  
Mixed Layer ◽  
Inorganic Carbon ◽  
Late Summer ◽  
Euphotic Zone ◽  
Surface Mixed Layer ◽  
Surface Ocean ◽  
Minor Contribution ◽  
Vertical Distributions ◽  
Adequate Nutrient ◽  
Particulate Inorganic Carbon

Vertical distributions of biogenic silica (bSi), particulate inorganic carbon (PIC) and key biomineral-forming phytoplankton indicate vertical zoning, or partitioning, during the late summer stratified period in the northeast Atlantic. Coccolithophores were generally more numerous in the surface mixed layer, whilst PIC concentrations were more homogenous with depth throughout the euphotic zone. Diatoms were notably more abundant and more diverse in the lower euphotic zone beneath the mixed layer in association with subsurface maxima in chlorophyll-a, bSi and oxygen concentrations. The four dominant coccolithophore species (Emiliania huxleyi, Gephyrocapsa muellerae, Syracosphera spp., and Rhabdosphaera clavigera) represented 78 ± 20% (range 31–100%) of the observed community across all sampled depths yet simultaneously contributed an average of only 13% to measured PIC pools. The diatom community, which was dominated by Pseudo-nitzschia spp. and by a species tentatively identified as Nanoneis longta, represented only ~1% of the bSi pool on average, with contributions increasing within the chlorophyll maximum. Despite a slow gradual deepening of the surface mixed layer in the period prior to observation, and adequate nutrient availability beneath the mixed layer, biomineral pools at this time consisted largely of detrital rather than cellular material.

scholarly journals Niche partitioning by photosynthetic plankton as a driver of CO2-fixation across the oligotrophic South Pacific Subtropical Ocean

2021 ◽  
Author(s):  
Julia Duerschlag ◽  
Wiebke Mohr ◽  
Timothy G. Ferdelman ◽  
Julie LaRoche ◽  
Dhwani Desai ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Niche Partitioning ◽  
Euphotic Zone ◽  
South Pacific ◽  
Niche Differentiation ◽  
Surface Mixed Layer ◽  
The South ◽  
The Core ◽  
Photosynthetic Eukaryotes ◽  
Phytoplankton Communities

AbstractOligotrophic ocean gyre ecosystems may be expanding due to rising global temperatures [1–5]. Models predicting carbon flow through these changing ecosystems require accurate descriptions of phytoplankton communities and their metabolic activities [6]. We therefore measured distributions and activities of cyanobacteria and small photosynthetic eukaryotes throughout the euphotic zone on a zonal transect through the South Pacific Ocean, focusing on the ultraoligotrophic waters of the South Pacific Gyre (SPG). Bulk rates of CO2 fixation were low (0.1 µmol C l−1 d−1) but pervasive throughout both the surface mixed-layer (upper 150 m), as well as the deep chlorophyll a maximum of the core SPG. Chloroplast 16S rRNA metabarcoding, and single-cell 13CO2 uptake experiments demonstrated niche differentiation among the small eukaryotes and picocyanobacteria. Prochlorococcus abundances, activity, and growth were more closely associated with the rims of the gyre. Small, fast-growing, photosynthetic eukaryotes, likely related to the Pelagophyceae, characterized the deep chlorophyll a maximum. In contrast, a slower growing population of photosynthetic eukaryotes, likely comprised of Dictyochophyceae and Chrysophyceae, dominated the mixed layer that contributed 65–88% of the areal CO2 fixation within the core SPG. Small photosynthetic eukaryotes may thus play an underappreciated role in CO2 fixation in the surface mixed-layer waters of ultraoligotrophic ecosystems.

Seasonal characteristics of the surface mixed layer in the Australasian region: implications for primary production regimes and biogeography

2006 ◽  
Vol 57 (6) ◽  
pp. 569 ◽  
Author(s):  
Scott A. Condie ◽  
Jeff R. Dunn
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Biological Properties ◽  
Supplementary Information ◽  
Nutrient Concentrations ◽  
Surface Mixed Layer ◽  
Surface Ocean ◽  
Seasonal Characteristics ◽  
Long Term Trends ◽  
Australasian Region

The seasonal cycle of physical, chemical, and biological properties of the surface ocean mixed layer in the Australasian region (0 to 50°S, 90 to 180°E) were described on the basis of a range of data products, some of which are described for the first time. They include seasonal fields of temperature, salinity, mixed layer depth, nitrate, phosphate and silicate from the CSIRO Atlas of Regional Seas (CARS), as well as estimates of chlorophyll from SeaWiFS ocean colour data, and a range of supplementary information taken from published studies. Seasonal chlorophyll cycles were interpreted within the context of variability in nutrient concentrations and mixed layer depths. This interpretation included a biogeographical description, which was compared with related regional and global products. Such descriptions provide a baseline for future investigations of interannual variability and long-term trends in mixed layer properties, as well as contributing to the development of spatial frameworks for management of the region’s resources.

scholarly journals Vertically migrating phytoplankton drive seasonal formation of subsurface negative preformed nitrate anomalies in the subtropical North Pacific and North Atlantic

2018 ◽  
Author(s):  
Robert T. Letscher ◽  
Tracy A. Villareal
Keyword(s):  
Organic Matter ◽  
Mixed Layer ◽  
North Atlantic ◽  
North Pacific ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Euphotic Zone ◽  
The North ◽  
Station Aloha ◽  
Biological Nitrogen

Abstract. Summertime drawdown of dissolved inorganic carbon in the absence of measurable nutrients from the mixed layer and subsurface negative preformed nitrate (preNO3) anomalies observed for the ocean's subtropical gyres are two biogeochemical phenomena that have thus far eluded complete description. Many processes are thought to contribute including biological nitrogen fixation, lateral nutrient transport, carbon overconsumption or non-Redfield C : N : P organic matter cycling, heterotrophic nutrient uptake, and the actions of vertically migrating phytoplankton. Here we investigate the seasonal formation rates and potential contributing mechanisms for negative preformed nitrate anomalies (oxygen consumption without stoichiometric nitrate release) in the subsurface and positive preformed nitrate anomalies (oxygen production without stoichiometric nitrate drawdown) in the euphotic zone at the subtropical ocean time series stations ALOHA in the North Pacific and BATS in the North Atlantic. Non-Redfield −O2 : N stoichiometry for dissolved organic matter (DOM) remineralization is found to account for up to ~ 15 mmol N m−2 yr−1 of negative preNO3 anomaly formation at both stations. Residual negative preNO3 anomalies in excess of that which can be accounted for by non-Redfield DOM cycling are found to accumulate at a rate of ~ 32–46 mmol N m−2 yr−1 at station ALOHA and ~ 46–87 mmol N m−2 yr−1 at the BATS station. These negative anomaly formation rates are in approximate balance with positive preNO3 anomaly formation rates from the euphotic zone located immediately above the nutricline in the water column. Cycling of transparent exopolymer particles (TEP) and heterotrophic nitrate uptake can contribute to the formation of these preNO3 anomalies, however a significant fraction, estimated at ~ 50–95 %, is unexplained by the sum of these processes. Vertically migrating phytoplankton possess the necessary nutrient acquisition strategy and biogeochemical signature to quantitatively explain both the residual negative and positive preNO3 anomalies as well as the mixed layer dissolved inorganic carbon drawdown at stations ALOHA and BATS. TEP production by the model Rhizosolenia mat system could provide accelerated vertical transport of TEP as well as link the three processes together. Phytoplankton vertical migrators, although rare and easily overlooked, may play a large role in subtropical ocean nutrient cycling and the biological pump.

scholarly journals Rapid formation of large aggregates during the spring bloom of Kerguelen Island: observations and model comparisons

2014 ◽  
Vol 11 (3) ◽  
pp. 4949-4993 ◽  
Author(s):  
M.-P. Jouandet ◽  
G. A. Jackson ◽  
F. Carlotti ◽  
M. Picheral ◽  
L. Stemmann ◽  
...  
Keyword(s):  
Particle Size ◽  
Mixed Layer ◽  
Late Summer ◽  
Surface Mixed Layer ◽  
Particle Volume ◽  
Kerguelen Island ◽  
Underwater Vision ◽  
Rapid Formation ◽  
Total Particle ◽  
Spherical Diameter

Abstract. We recorded vertical profiles of particle size distributions (PSD, sizes ranging from 0.052 to several mm in equivalent spherical diameter) in the natural iron-fertilized bloom southeast of Kerguelen Island (Southern Ocean) from pre-bloom to early bloom stage. PSD were measured by the Underwater Vision Profiler during the Kerguelen Ocean and Plateau Compared Study cruise 2 (KEOPS 2, October–November 2011). The total particle numerical abundance was more than 4 fold higher during the early bloom phase compared to pre-bloom conditions as a result of the 2-weeks bloom development. We witnessed the rapid formation of large particles and their accumulation at the base of the mixed layer within a two days period, as indicated by changes in total particle volume (VT) and particle size distribution. The VT profiles suggest sinking of particles from the mixed layer to 200 m, but little export deeper than 200 m during the observation period. The results of a one dimensional particles dynamic model support coagulation as the mechanism responsible for the rapid aggregate formation and the development of the VT subsurface maxima. Comparison with KEOPS1, which investigated the same area during late summer, and previous iron fertilization experiments highlights physical aggregation as the primary mechanism for large particulate production during the earlier phase of iron fertilized bloom and its export from the surface mixed layer.

Modelling a simple mechanism for the formation of phytoplankton thin layers using large-eddy simulation: in situ growth

2020 ◽  
Vol 653 ◽  
pp. 77-90
Author(s):  
A Brereton ◽  
Y Noh ◽  
S Raasch
Keyword(s):  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Light Availability ◽  
Euphotic Zone ◽  
Thin Layers ◽  
Biophysical Model ◽  
Surface Mixed Layer ◽  
Eddy Simulation ◽  
Phytoplankton Communities ◽  
Large Eddy

A curious phenomenon found in phytoplankton communities is the forming of socalled thin layers, wherein phytoplankton biomass can stretch out kilometres in the horizontal but only a few metres in the vertical. These layers are typically found at the pycnocline, just below the surface mixed layer. Thin layers are usually attributed to a range of complex environmental and species-dependent factors. However, we believe that, given the frequency at which this phenomenon is observed, a simpler mechanism is at play. In this study, we found that phytoplankton thin layers can be attributed simply to a decreasing light availability with depth, when there is an abundance of nutrients in the euphotic zone and below the mixed layer. This mechanism was ascertained using a number of modelling approaches ranging in complexity from analytical solutions of a simple 1-dimensional plankton model to a 3-dimensional biophysical model incorporating large-eddy simulation. The conditions which, according to the results of our study, allow thin layers to form are ubiquitous in the coastal ocean and are therefore a likely candidate explanation as to why planktonic thin layers are so frequently observed.

Mixed Layer Models and Their Application to Water Quality Problems

1994 ◽  
Vol 29 (2-3) ◽  
pp. 221-232
Author(s):  
M.J. McCormick
Keyword(s):  
Water Quality ◽  
Mixed Layer ◽  
Thermal Structure ◽  
Mass Conservation ◽  
Eddy Diffusion ◽  
Rate Of Change ◽  
Surface Mixed Layer ◽  
Storm Events ◽  
Quality Model ◽  
Mixing Processes

Abstract Four one-dimensional models which have been used to characterize surface mixed layer (ML) processes and the thermal structure are described. Although most any model can be calibrated to mimic surface water temperatures, it does not imply that the corresponding mixing processes are well described. Eddy diffusion or "K" models can exhibit this problem. If a ML model is to be useful for water quality applications, then it must be able to resolve storm events and, therefore, be able to simulate the ML depth, h, and its time rate of change, dh/dt. A general water quality model is derived from mass conservation principles to demonstrate how ML models can be used in a physically meaningful way to address water quality issues.

scholarly journals Simulation of diurnal variability in vertical density structure using a coupled model

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Yadidya ◽  
A. D. Rao ◽  
Sachiko Mohanty
Keyword(s):  
Mixed Layer ◽  
3D Model ◽  
Coupled Model ◽  
Wave Model ◽  
Andaman Sea ◽  
Surface Mixed Layer ◽  
Diurnal Variability ◽  
Rama Buoy ◽  
Vertical Displacements ◽  
Primary Advantage

AbstractThe changes in the physical properties of the ocean on a diurnal scale primarily occur in the surface mixed layer and the pycnocline. Price–Weller–Pinkel model, which modifies the surface mixed layer, and the internal wave model based on Garrett–Munk spectra that calculates the vertical displacements due to internal waves are coupled to simulate the diurnal variability in temperature and salinity, and thereby density profiles. The coupled model is used to simulate the hourly variations in density at RAMA buoy (15° N, 90° E), in the central Bay of Bengal, and at BD12 (10.5° N, 94° E), in the Andaman Sea. The simulations are validated with the in-situ observations from December 2013 to November 2014. The primary advantage of this model is that it could simulate spatial variability as well. An integrated model is also tested and validated by using the output of the 3D model to initialize the coupled model during January, April, July, and October. The 3D model can be used to initialize the coupled model at any given location within the model domain to simulate the diurnal variability of density. The simulations showed promising results which could be further used in simulating the acoustic fields and propagation losses which are crucial for Navy operations.

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