Katherine A. Kilpatrick

Overview of the NOAA/NASA advanced very high resolution radiometer Pathfinder algorithm for sea surface temperature and associated matchup database

The National Oceanic and Atmospheric Administration (NOAA)/NASA Oceans Pathfinder sea surface temperature (SST) data are derived from measurements made by the advanced very high resolution radiometers (AVHRRs) on board the NOAA 7, 9, 11, and 14 polar orbiting satellites. All versions of the Pathfinder SST algorithm are based on the NOAA/National Environmental Satellite Data and Information Service nonlinear SST operational algorithm (NLSST). Improvements to the NLSST operational algorithm developed by the Pathfinder program include the use of monthly calibration coefficients selected on the basis of channel brightness temperature difference (T4–T5). This channel difference is used as a proxy for water vapor regime. The latest version (version 4.2) of the Pathfinder processing includes the use of decision trees to determine objectively pixel cloud contamination and quality level (0–7) of the SST retrieval. The 1985–1998 series of AVHRR global measurements has been reprocessed using the Pathfinder version 4.2 processing protocol and is available at various temporal and spatial resolutions from NASAs Jet Propulsion Laboratory Distributed Active Archive Center. One of the highlights of the Pathfinder program is that in addition to the daily global area coverage fields, a matchup database of coincident in situ buoy and satellite SST observations also is made available for independent algorithm development and validation.

Calcification, photosynthesis and growth of the bloom-forming coccolithophore, Emiliania huxleyi

Measurements were made of photosynthesis and calcification in a bloom of coccolithophores in the Gulf of Maine as well as in laboratory batch cultures of the Emiliania huxleyi strain 88E. The14C technique for measuring calcification was evaluated with calcifying and noncalcifying coccolithophore strains. Shipboard bloom observations showed physiological evidence of stratification between surface and deep populations within the surface mixed layer. Photosynthesis and calcification rates were enhanced within hours of addition of KNO3 or nitrate-rich deep water (to the same final concentration). Such rates were strongly temperature dependent in laboratory cultures, decreasing over a factor of two from 15 to 20°C. Calcification was considerably less light-dependent than photosynthesis and consistently had a measurable dark rate. In culture, maximum calcification rates and degree of cell plating were limited to logarithmic growth phase. This was followed by rapid increase in the coccolith shedding rate 1 day prior to the onset of stationary phase which continued several days after cell division stopped. The regional significance of these features to total organic and inorganic carbon production as well as calcite burial is discussed.

Calcification rates in the equatorial Pacific along 140°W

Abstract The calcite standing stock, calcification rate, concentrations of detached coccoliths and plated coccolithophore cells were determined in the equatorial Pacific along 140°W, between 12°N and 12°S latitude, during August and September 1992. Continuous surface optical and fluorescence measurements were also taken along this transect. Integrated calcification ranged between 3 and 12% of the total carbon fixed into particulate matter. Calcification exceeded 50% of the total fixed carbon (per unit volume) at specific depths from the northern-most oligotrophic stations. A pronounced subsurface peak in suspended calcite was noted near the equator. Calcification was considerably more patchy than photosynthesis. Normalizing the calcification rates to the surface area of calcite-producing species provided an estimate of the extracellular calcite flux rates. These results showed that the populations from the equator to 3°N at 60 m depth, and near the surface from the equator to 9°S were the most active calcite producers. Underway estimates of light scattering showed the importance of upwelling for bringing cold, clear, relatively particle-free water to the surface, followed by growth and calcite production as the water warmed. When temperatures reached their upper range (about 28.8°C), light scattering decreased again, presumably as growth slowed and particles sank. Integrated calcification estimates averaged over the equatorial region were compared to sediment trap data: the results suggest significant disappearance of calcite particles in the top 1000 m, above the lysocline. One hypothesis to explain this is that dissolution occurred in microzones where decomposition of reduced organic matter lowered the pH sufficiently to dissolve calcite.

Methane oxidation in Saanich Inlet during summer stratification

Abstract Saanich Inlet, British Columbia, a fjord on the southeast coast of Vancouver Island, typically stratifies in summer, leading to the formation of an oxic-anoxic interface in the water column and accumulation of methane in the deep water. We present the results of methane concentration measurements in the water column of the inlet at various times throughout the summer months in 1983. Methane gradients and calculated diffusive fluxes across the oxic-anoxic interface increased as the summer progressed. Methane distribution and consumption in Saanich Inlet were studied in more detail during August 1986. At this time, a typical summer stratification with an oxic-anoxic interface around 140 m was present. At the interface, steep gradients in nutrient concentrations, bacterial abundance and methane concentration were observed. Methane oxidation was detected in the aerobic surface waters and in the anaerobic deep layer, but highest rates occurred in a narrow layer at the oxic-anoxic interface. Estimated methane oxidation rates were sufficient to consume 100% of the methane provided by diffusive flux from the anoxic layer. Methane oxidation is thus a mechanism whereby atmospheric flux from anoxic waters is minimized.

Relationship between substrate concentration and oxidation of ammonium and methane in a stratified water column

Abstract Distributions and oxidation rates of methane and ammonium were investigated during two cruises in Saanich Inlet, British Columbia in late summer. Distributions of inorganic nutrients were related to oxygen distribution, exhibiting large gradients associated with the oxic-anoxic interface. The depth distributions of oxidation rates were also defined by the oxic-anoxic interface: ammonium oxidation occurred at variable rates (up to 120 nM day−1) between the photic zone and the oxic-anoxic interface. Methane oxidation occurred throughout the oxic layer and increased near the interface. The possibility of interactions such as inhibition and competition between the two substrates, methane and ammonium, were investigated in kinetic experiments. Ammonium oxidation rate was independent of both ammonium and methane concentrations. Methane oxidation rates were linearly related to methane concentration, both in manipulation experiments, and in relation to ambient methane concentrations. There was no evidence of interaction between methane and ammonium as alternative substrates for methanotrophic and ammonium oxidizing populations, which were both present in the environment. In September, we observed a bolus-type mixing event, which introduced oxygenated deep water into the inlet beneath a wedge of anoxic, methane-rich water. This kind of event is probably important in determining the rate of methane loss, due to increased microbial oxidation at the boundaries of the anoxic wedge.

Optical backscattering by calcifying algae : Separating the contribution of particulate inorganic and organic carbon fractions

Light scattering properties of biogenic CaCO3 particles [particulate inorganic carbon (PIC)] were determined on cultured calcifying algae and field-derived CaCO3 particles. The particles were separated from particulate organic carbon (POC) with a flow cytometer, volume-scattering functions were measured with a laser light-scattering photometer, and particle composition was measured using atomic absorption spectrometry. Small calcite coccoliths were best sorted by gating on the ratio of horizontally polarized forward light scattering and vertically polarized forward light scattering; plated coccolithophores could be sorted by gating on side scattering and forward angle light scattering. Normalized volume-scattering functions for the culture-derived calcite particles varied by a factor of 2 for the different species. Backscattering cross sections (m2 particle−1) for calcite particles varied by ∼35 times and were generally a function of size. Backscattering efficiencies were ∼2–4 times higher for cells with CaCO3 than without it. CaCO3-specific backscattering showed much less variability across various species; the calcite-specific backscattering coefficient varied by only ∼38% for both cultured coccolithophores and field-derived CaCO3 particles. Organic carbon-specific backscattering of “naked” coccolithophores was highly consistent within all coccolithophores used in our experiments, as well as with values in the literature. Our results suggest that both POC and PIC can be optically estimated, the former by measuring backscattering of decalcified phytoplankton as well as their size distribution, and the latter is proportional to acid-labile backscattering. These results show the feasibility of a rapid optical technique for measuring two biogeochemically important carbon fractions in the sea.

COCCOLITH PRODUCTION AND DETACHMENT BY EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)

Laboratory experiments were performed with the prymnesiophyte Emiliania huxleyi (Lohm.) Hay and Mohler, strain 88E, to quantify calcification per cell, coccolith detachment, and effects of coccolith production on optical scattering of individual cells. 14C incorporation into attached and detached coccoliths was measured using a bulk filtration technique. 14C‐labeled cells also were sorted using a flow cytometer and analyzed for carbon incorporation into attached coccoliths. The difference between the bulk and flow cytometer analyses provided a 14C‐based estimate of the rate of production of detached coccoliths. Coccolith production and detachment were separated in time in batch cultures, with most detachment happening well after calcification had stopped. Accumulation of coccoliths was maximum at the end of logarithmic growth with 50–80 coccoliths per cell (three to five complete layers of coccoliths around the cells). Net accretion rates of coccoliths were on the order of 7 coccoliths· cell−1·d−1 while net detachment rates were as high as 15 coccoliths· cell−1·d−1 for stationary phase cells. Equal numbers of coccoliths were attached and detached early in logarithmic growth, and as cells aged, the numbers of detached coccoliths exceeded the attached ones by a factor of 6. Our results demonstrate pronounced charges of forward angle light scatter and 90° light scatter of cells as they grow logarithmically and enter stationary phase. Counts of loose coccoliths in batch cultures are consistent with the detachment of coccoliths in layers rather than individual coccoliths.

Methane oxidation associated with mid-depth methane maxima in the Southern California Bight

Methan e concentration in the water column of the Southern California Bight exhibits two or more maxima. In the upper water column, a subsurface concentration maximum is often observed, usually near the bottom of the euphoric zone. Deeper maxima are often detected, well below the euphotic zone and separated from the sediments, which suggests an advective source from continental slope sediments. We measured methane concentrations and oxidation rates in an attempt to quantify the biological loss term for methane throughout the water column in the Santa Monica Basin, one of the semi-enclosed basins in the Southern California Borderland. The study site was in the central basin at a water depth of 900 m, which was sampled several times over 4 years, and an offshore transect of three stations, which was sampled once. Layers of methane rich water were detected in the mid water column (500-800 m depth) at the deeper stations, with concen- trations exceeding those found in the subsurface maximum. Oxidation rates in these layers greatly exceeded rates associated with the subsurface maximum and represented turnover times on the order of a few months. The source of the methane at mid-depth is probably advection from petroliferous sediments in the margin of the borderland, rather than diffusion from underlying anoxic sediments in the basin. Relatively rapid oxidation rates and resulting turnover rates at depth imply the presence of a community adapted for the utilization of methane as a carbon source, a community which is not found in surface waters.

Antibody and DNA probes for detection of nitrite reductase in seawater

A polyclonal antiserum was produced by immunization with nitrite reductase (NiR) purified from Pseudomonas stutzeri (ATCC 14405) and tested for specificity among known denitrifying strains. The antiserum was nearly strain-specific, identifying NiR only in some, but not all, other P. stutzeri strains. Denitrifying isolates from water column and sediment environments were also screened; several isolates from an intertidal microbial mat reacted with the NiR antiserum. Activity assays for NiR in polyacrylamide gels demonstrated that strains with apparently very similar NiR proteins did not react with the antiserum. These results imply that the NiR protein is more variable even among closely related strains than previously suspected. A DNA probe for a 721 bp region of the NiR structural gene was obtained by PCR amplification of P. stutzeri (ATCC 14405) DNA and used to screen denitrifying strains and isolates. The probe hybridized with a greater variety of strains than did the antiserum, implying that the DNA probe may be a more broadly useful and functional probe in environmental samples, whilst the NiR antiserum is nearly strain- or, at most, species-specific. Limits for detection of the enzyme and gene in seawater were estimated and NiR DNA was detected in DNA extracted from natural seawater. The hybridization data imply that in the order of 1-10 in 1000 cells in natural seawater possess homology with the NiR gene probe.

Nitrogen Transformations in the Oxic Layer of Permanent Anoxic Basins: The Black Sea and the Cariaco Trench

Transformations of inorganic nitrogen (nitrification and nitrate reduction) are considered in the context of small scale nutrient distributions in the oxic and oxygen deficient zones of two permanently anoxic basins. The distribution of nitrification rates apparently was bounded by light inhibition in surface waters and by anoxic waters below. Nitrite concentration maxima in the oxic/anoxic transition region are suggested to result from uncoupled rates of nitrite production and consumption by nitrification and nitrate reduction/denitrification.