Life-forms of phytoplankton as survival alternatives in an unstable environment

The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teramole = 10(12) moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years.

https://science.sciencemag.org/content/sci/268/5209/375.full.pdf

The silica balance in the world ocean: a reestimate.

We estimate the global rate of biogenic silica production in the ocean to be between 200 and 280 × 1012 mol Si yr−1. The upper limit is derived from information on the primary productivity of the oceans, the relative contribution of diatoms to primary production and diatom Si/C ratios. The lower limit is derived independently using a multi-compartment model of nutrient transport and biogenic particle flux, and field data on the balance between silica production and dissolution in the upper ocean. Our upper limit is 30–50% lower than several previous estimates, due to new data indicating lower values for both the relative contribution of diatoms to primary productivity and their Si/C ratios. Globally, at least 50% of the silica produced by diatoms in the euphotic zone dissolves in the upper 100 m, resulting in an estimated export of 100–140 × 1012 mol Si yr−l to the deep ocean. Our estimates correspond to a global mean rate of biogenic silica production between 0.6 and 0.8 mol Si m−2 yr−1. Incubation experiments indicate that silica production rates exceed that mean by a factor of 3–12 in coastal areas and are 2–4 times less than the global average in the oligotrophic mid-ocean gyres. The mean silica production rate in waters overlying diatomaceous sediments (approximately 10–12% of the surface area of the oceans) is 0.7–1.2 mol Si m−2 yr−1. That rate is only slightly higher than the global average, indicating that the silica produced in those regions is only 10–25% of the global total. The estimated production of biogenic silica in surface waters of the mid-ocean gyres is approximately equal to that for all major areas of opal sediment accumulation combined. Regional comparison of silica production and accumulation rates suggests a strongly bimodal character in the efficiency of opal preservation in the sea. In waters overlying diatom-rich sediments 15–25% of the silica produced in the surface layer accumulates in the seabed, while virtually none of the silica produced in other areas is preserved. The global burial/production ratio of ˜ 3% is a composite of those two very different systems. The mechanisms leading to more efficient opal preservation in regions of silica accumulation are presently unknown, but they have no simple relationship to primary productivity. Regional differences in opal preservation appear to be controlled by factors such as low surface temperature, selective grazing and aggregate formation, which diminish the rate of silica dissolution in surface waters and/or accelerate its transport to the seafloor.

Production and dissolution of biogenic silica in the ocean: Revised global estimates, comparison with regional data and relationship to biogenic sedimentation

Production and dissolution of biogenic silica in the ocean: revised global estimates, comparison with regional data and relationship to biogenic sedimentation

Classically, the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the ‘Stokes’ sedimentation rates, for the fine fractions. Results from the two methods are compared with results from laser diffraction size analysis, which is based on the forward scattering of monochromatic coherent light. From a point of view of laboratory efficiency, the laser sizing technique is far superior. Accuracy and reproducibility are shown by measurements on certified materials. It appears that laser grain size measurements of certified materials correspond very well with the certificated measurements. Tests were also done on a set of randomly selected sediments of fluvial, aeolian and lacustrine origin. Except for the (<2 μm) clay fraction, there is a coarsening of the mean diameter of one to two size classes (0.25 ɛ), caused by the non-sphericity of the particles. The platy form of the clay particles induces considerable differences (eight size classes) between pipette and laser measurements: the <2 μm grain size, defined by the pipette method corresponds with a grain size of 8 μm defined by the Laser Particle Sizer for the studied sediments. Using a higher grain size level for the clay fraction, when laser analysis is applied, enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique.

Comparison of laser grain size analysis with pipette and sieve analysis: a solution for the underestimation of the clay fraction

I. Principles of Studying Suspended Material and Its Settling Velocities.- Principles of Studying Suspended Materials in Water.- Stokes' Settling and Chemical Reactivity of Suspended Particles in Natural Waters.- II. Principles of Optical Techniques.- Beam Transmissometers for Oceanographic Measurements.- Volume-Scattering Functions in Ocean Waters.- Mie Theory Models of Light Scattering By Ocean Particulates.- Spatial Distribution of the Index of Refraction of Suspended Matter in the Ocean.- Absolute Calibration of a Scatterance Meter.- III. Nearshore Studies.- Effects of Tropical Storm Agnes on the Suspended Solids of the Northern Chesapeake Bay.- Distribution and Transport of Suspended Particulate Matter in Submarine Canyons Off Southern California.- Continuous Light-Scattering Profiles and Suspended Matter Over Nitinat Deep-Sea Fan.- Physical, Chemical, and Optical Measures of Suspended-Particle Concentrations: Their Intercomparisons and Application to the West African Shelf.- The Distribution of Particulate Matter in a Northwest African Coastal Upwelling Area.- The Suspended Material of the Amazon Shelf and Tropical Atlantic Ocean.- IV. Offshore Studies.- Turbidity Distribution in the Deep Waters of the Western Atlantic Trough.- Variations in Benthic Boundary Layer Phenomena: Nepheloid Layer in the North American Basin.- Distribution of Suspended Particles in the Equatorial Pacific Ocean.- Suspended Matter and the Stability of the Water Column: Central Caribbean Sea.- Light-Scattering Measurements and Chemical Analysis of Suspended Matter in the Near-Bottom Nepheloid Layer of the Gulf of Mexico.- Light Scattering and Suspended Particulate Matter on a Transect of the Atlantic Ocean at 11 N.- List of Contributors and Participants.

Suspended solids in water.

Equations are given for the Stokes settling velocities of the following particle shapes: the sphere, oblate spheroid, prolate spheroid, circular cylinder, elliptic cylinder, disc, and hemispherical cap. Dissolution of calcareous and silicate particles settling through ocean water, based on literature data, is analyzed in terms of a model for dissolution rate independent of the particle surface area, and a model for dissolution rate dependent on a surface reaction. The settling of dissolving particles in the presence of a countercurrent of upwelling water may lead to formation of thin nepheloid layers. Settling of calcite crystals through a stratified water column is treated as a case of variable nucleation (production) rates, dissolution and agglomeration of crystals en route to the bottom. A stochastic model presented in the paper gives a reasonably simple method for treating transient transport of particles in a physically heterogeneous water column.

Stokes’ Settling and Chemical Reactivity of Suspended Particles in Natural Waters

For calcareous and siliceous biogenic particles in the micron size range, the Stokes' settling velocities are sufficiently small such that appreciable dissolution may be expected in transit through a vertical column of ocean water. In the course of settling the rate of addition of dissolved biogenic carbon and silicon to seawater at all depths is nearly constant provided the macroscopic rate of dissolution is a phenomenon dependent on the surface area and invariant with depth. Settling and dissolution of particles in the presence of upwelling water result in the formation of layers of high particle concentrations. Possible coagulation of the submicron-size particles in such layers does not lead to a significant reduction of the particle concentrations. Upper-limit estimates of the rates of addition to ocean water (depths of 1–4 km), owing to dissolution of settling particles, are: carbon, (3–60) × 10−9 g cm−3 yr−1, and silicon, 4 × 10−7 g cm−3 yr−1.

Devendra Lal

Papers

Suspended solids in water.

Stokes’ Settling and Chemical Reactivity of Suspended Particles in Natural Waters

Dissolution and behavior of particulate biogenic matter in the ocean: Some theoretical considerations

Regeneration rates in the ocean

Suspended solids in water.