Daniel Kamykowski

Semianalytic Moderate-Resolution Imaging Spectrometer Algorithms for Chlorophyll A and Absorption with Bio-Optical Domains Based on Nitrate-Depletion Temperatures

This paper describes algorithms for retrieval of chlorophyll a concentration and phytoplankton and gelbstoff absorption coefficients for the Moderate-Resolution Imaging Spectrometer (MODIS) or sensors with similar spectral channels. The algorithms are based on a semianalytical, bio-optical model of remote sensing reflectance, Rrs(λ). The Rrs(λ) model has two free variables, the absorption coefficient due to phytoplankton at 675 nm, aϕ(675), and the absorption coefficient due to gelbstoff at 400 nm, ag(400). The Rrs model has several parameters that are fixed or can be specified based on the region and season of the MODIS scene. These control the spectral shapes of the optical constituents of the model. Rrs(λi) values from the MODIS data processing system are placed into the model, the model is inverted, and aϕ(675), ag(400), and chlorophyll a are computed. The algorithm also derives the total absorption coefficients a(λi) and the phytoplankton absorption coefficients aϕ(λi) at the visible MODIS wavelengths. MODIS algorithms are parameterized for three different bio-optical domains: (1) high photoprotective pigment to chlorophyll ratio and low self-shading, which for brevity, we designate as “unpackaged”; (2) low photoprotective pigment to chlorophyll ratio and high self-shading, which we designate as “packaged”; and (3) a transitional or global-average type. These domains can be identified from space by comparing sea-surface temperature to nitrogen-depletion temperatures for each domain. Algorithm errors of more than 45% are reduced to errors of less than 30% with this approach, with the greatest effect occurring at the eastern and polar boundaries of the basins.

Hypoxia in the world ocean as recorded in the historical data set

Abstract As of December 1986, the National Oceanographic Data Center (NODC), Washington, DC, listed over 2 million observations of dissolved oxygen concentratiions in the world ocean (including adjacent seas) collected between 1905 and 1982. Hypoxia, defined as concentrations below 0.2 ml l−1, accounts for 27,413 of the recorded oxygen observations. The spatial distribution of this NODC-based hypoxia is more extensive than previous compilations suggest. Although the more isolated data points may represent spurious data, the great majority of the observations fall within the ocean regions bounded by contours of oxygen concentrations ml l −1 or of oxygen saturation in published contour maps of the oxygen minimum surface. In the eastern Pacific, the contour boundary reduces to 0.5 ml l−1 or 7.5% saturation. Some seasonality is detected, especially at high latitudes. The depth distribution of hypoxia exhibits a typical marine ( ≥28 ppt ) range from near-surface to about 1500 m depth but with occasional occurrences at greater depths; the estuarine ( ppt ) range extends from near-surface to the bottom of the basin in question. The apparent oxygen utilization leading to hypoxia varies widely (4.0–9.5 ml l−1) in the world ocean. The highest values occur at higher latitudes in coastal environments. Nitrate deficits ( >10 μ m ) calculated for restricted marine areas (28–38 ppt) generally occupy subzones nested within the major historically identified hypoxic regions in the world ocean, but the data are inadequate for a definitive comparison in all areas. These marine nitrate deficits occur in water with a somewhat more restricted range of apparent oxygen utilization than marine hypoxia.

Predicting plant nutrient concentrations from temperature and sigma-t in the upper kilometer of the world ocean

A National Oceanographic Data Center data set comprised of 230,202 oceanographic stations representing all regions of the world ocean was analyzed statistically for temperature and sigma-t (σt) relationships with nitrate, phosphate or silicic acid concentrations in the upper kilometer of the water column. Six cubic regressions were computed for each 10° square of latitude and longitude containing adequate data. World maps display the locations that allow the prediction of plant nutrient concentrations from temperature or σt within the limits of selected subjective and objective criteria. Geographic coverage improves along the sequence: nitrate, phosphate and silicic acid, and is better for σt than for temperature. A percentile analysis of the temperature or σt at which less a selected amount of plant nutrient occurs provided a method to examine incipient nutrient limitation. Contour maps display the approximate temperatures above or σt values below which nitrate, phosphate or silicic acid routinely approach unmeasurable concentrations in the world ocean as determined by classical plant nutrient analyses. The results summarize the global potential to predict plant nutrient concentrations from remotely sensed temperature or σt and emphasize the latitudinally and longitudinally changing phytoplankton growth environment based on temperature, σt and plant nutrients in present and past oceans.

Comparison of sinking velocity, swimming velocity, rotation and path characteristics among six marine dinoflagellate species

Six marine dinoflagellate species representing a range of equivalent spherical diameters between 12 and 36 μm were examined for several characteristics that influence their translation velocity. Sinking velocities estimated by three independent techniques and applied to swimming and narcotized cells generally agreed, and followed the cell-size relationships previously reported for diatoms. Dinokont sinking and swimming velocities both decreased with increasing surface area: volume ratio, but a small desmokont deviated from the dinokont relationships. Sinking velocities influenced the relative ascent/descent capabilities of a species. The swim:sink ratio decreased as equivalent spherical diameter increased to 25 μm and then remained constant at 7.6, despite further increases in cell size. This relationship suggests a minimum required swimming capability relative to cell size. The swim:sink ratio increased with increasing surface area:volume ratio for all the surveyed species. Out observations of decreasing cell rotation:translation ratio and increasing cell drag with increasing cell size supported the hypothesis that the dinoflagellate flagellar apparatus generates maximum swimming velocity at intermediate cell sizes. However, an alternate analysis supported the hypothesis that swimming velocity increases with cell size and that variations among genera are due to subtle differences in the basic dinoflagellate propulsion system. A three-dimensional helical path index provided a more realistic estimate of the actual translation velocity (along the helix axis) during diel vertical migration when applied as a correction factor to the more typically measured helix velocity (along the helix) of a given dinoflagellate.

The vertical trajectories of motile phytoplankton in a wind-mixed water column

Abstract Motile phytoplankton representing a diatom, two dinoflagellates and a ciliate were studied using a random walk model in a dynamically active mixing layer where turbulence was driven by a range of wind speeds acting on a weakly stratified water column. The simulations extend the results reported in Yamazaki and Osborn (1989) by incorporating a broad range of more complex phytoplankton behavior and by examining the differential Photosynthetically Active Radiation (PAR) exposure of different individuals within a species population under a range of mixing conditions. The respective motility capabilities of the modeled species clearly influence their vertical distributions under the same mixing conditions even at the highest wind condition considered. The wind energy required to distort the diel vertical migration significantly is related directly to their swimming capability. The portion of the initial phytoplankton population that is mixed to the bottom of the Ekman layer can experience PAR stress. The simulations show that turbulence in the mixing layer does not necessarily create a physiologically uniform state after 24 h; this differs from the conventional wisdom concerning the effect of turbulence in mixed layers. The difference reflects depth-dependent turbulence intensity inferred from the Ekman layer model, as well as the definition of the Lagrangian diffusion coefficient discussed in our study.

TRAJECTORIES OF AUTOTROPHIC MARINE DINOFLAGELLATES

Flagellated cells, separated into approximately 1 0 major botanical taxonomic categories (classes or phyla), are a prominent component of the phytoplankton (Cox 1980). The different phytoflagellate body types represented in each taxonomic category typically extend over a characteristic size range (Cox 1980) and exhibit characteristic flagellar number, external structure and insertion (Sleigh 1991), and unique flagellar beat patterns (Goldstein 1992). These attributes combine to provide a broad range of different propulsion systems with various degrees of effectiveness (Goldstein 1992). Although marine dinoflagellates, whose motility is described only qualitatively (Levandowsky and Kaneta 1987), are the focus of this review, many aspects of the discussion generally apply to all flagellated autotrophs. The subsequent discussion of dinoflagellate motility in an environmental context begins with a consideration of the group’s flagellar propulsion system. Next, the two components of cell velocity, swimming speed and swimming direction, are considered with respect to environmental sensitivity and to the cell’s biosynthetic cycle. Finally the cell’s motility is discussed in the context of vertical water motions in the upper ocean.

A preliminary biophysical model of the relationship between temperature and plant nutrients in the upper ocean

Abstract A biophysical model was constructed to examine the relationship between temperature increases and plant nutrient decreases (represented by nitrate) in an upper ocean mixed layer and in underlying 2 m thick strata throughout the remainder of the euphotic zone. The formulation combines the dual effect of solar radiation on the water column heat budget and on nitrate uptake based on photosynthesis to simulate field observations of the nitrate-temperature relationship. The present model examines how the predicted nitrate-temperature relationships respond to changes in available solar radiation, the thickness of the upper mixed layer, the optical water type and the changes in biological efficiency throughout the euphotic zone. Required improvements include a more realistic treatment of inter-layer mixing in the physical model and of the phytoplankton radiation utilization efficiency in the biological model. Future models can be combined with improved global data sets to yield realistic descriptions of how the latitudinal patterns of water column temperatures and plant nutrient concentrations are determined.

Benthic nutrient regeneration in South Texas coastal waters

Abstract Because of the variable, unpredictable nature of many potential nutrient sources for coastal phytoplankton primary production needs in the north-western Gulf of Mexico, benthic regeneration was investigated as a more constant source of nutrients to this ecosystem. Water column ammonia profiles taken at several locations on the south Texas inner-shelf in the last seven years showed peak concentrations in bottom waters. Benthic chamber measurements verified the presence of ammonia fluxes at the mud-water interface in south Texas coastal waters. These fluxes were related to benthic faunal activity as measured by sediment metabolism. Laboratory experiments, designed to test the effect of benthic faunal removal on nutrient regeneration, suggested that the fauna play a role in regulating this process. How this regulation may occur is discussed. It was estimated that annual benthic regeneration rates can supply 69% of the nitrogen required to support phytoplankton primary production in these coastal waters.

The simulation of a Southern California red tide using characteristics of a simultaneously-measured internal wave field

Abstract Temperature data obtained from NUC Tower, San Diego, California during May–June 1968 provide input to a three-wave period version of MOVER, a computer model that simulates organism diurnal vertical migration through an internal wave field. The locally characteristic wave periods are 21.50 h, 12.50 h and 0.42 h. The phase of the modeled interval wave spectrum matches the field observations for a 10-day period preceding and including a red tide. MOVERs output shows a rapid aggregation of representative phytoplankton under all modeled conditions. The aggregation or red tide occurs at the geographic location of NUC Tower under certain organism behavioral regimes. Whether these conditions actually occurred at NUC Tower in May 1968 is not certain from the available data.

GEOTAXIS/PHOTOTAXIS AND BIOCHEMICAL PATTERNS IN HETEROCAPSA (=CACHONINA) ILLDEFINA (DINOPHYCEAE) DURING DIEL VERTICAL MIGRATIONS

Two separate experiments with Heterocapsa (=Cachonina) illdefina Herman et Sweeney, one with and the other without water volume replacement, were performed in a 250‐L laboratory mesocosm (45‐cm diameter × 150‐cm height) to examine how diel vertical migration (DVM) relates to taxis sign and strength and to cellular biochemical state. Although only the cell population grown with water volume replacement maintained a division per day over the course of the experiment, periodic measurements during both experiments demonstrated that cells aggregating at the surface during the light period generally were deficient in all measured biochemical constituents compared to cells obtained from a midcolumn depth. More specifically, H. illdefina cells that aggregated at the surface during the light period in both experiments exhibited weakened positive geotaxis but strengthened positive phototaxis and were very deficient in lipid and free amino acid compared to midcolumn cells. Cells sampled at midcolumn during the light period exhibited similar but weaker taxes changes compared to surface samples, and geotaxis strength was inversely correlated with cell diameter, cellular DNA and protein content, and RNA/DNA ratio. In comparison, published data on Gymnodinium breve Davis, a harmful algal bloom species, showed that cells aggregating at the surface during the light period generally exhibited weakened negative geotaxis and strengthened positive phototaxis and were very deficient in lipid and chl a compared to midcolumn cells. Although the persistent tendency toward negative geotaxis was weaker in midcolumn subpopulations throughout the day, its strength was inversely correlated with cell diameter and cellular lipid content. The combined results for both species support a revised conceptual model of optimized DVM in autotrophic marine dinoflagellates incorporating generalized expressions of taxis and biochemical state of individual cells.