Abstract:
The dataset contains the results of roller tank experiments designed to measure detailed properties of diatom aggregates, including cell and aggregate size, carbon content, size-dependent sinking velocity and fractal dimension. Such measurements are useful for aggregation model parameterizations.
Suggested Citation:
Uta Passow and Simone Francis. 2017. Properties of diatom aggregates formed in laboratory roller tanks. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7H70D81
Purpose:
The primary mechanism by which dispersed oil in the ocean is transported to the seafloor is via incorporation into marine snow aggregates, which sink rapidly through the water column. This dataset contains detailed information on the characteristics and properties of one common type of marine snow—diatom aggregates—providing parameter values that are essential for various marine-oil-snow modeling efforts.
Data Parameters and Units:
Species (SKEL 775 – Skeletonema Grethae 775 diatom species, SKEL 776 – Skeletonema Grethae 776 diatom species, or OTO 816 – Odontella 816 diatom species) Tank number Type of sample (SSW – surrounding seawater, no aggregates included in sample or Agg slurry – sample containing a mixture of 10 randomly selected aggregates and minimal SSW) Number of replicates for TEP measurements Average TEP – transparent exopolymer particles (μg GXeq/L or μg GXeq/aggregate) Standard deviation TEP - transparent exopolymer particles (μg GXeq/L or μg GXeq/aggregate) Gxeq – Gum Xanthan equivalent Number of replicates for DW measurements Average DW – dry weight (mg/L or mg/aggregate) Standard deviation DW - dry weight (mg/L or mg/aggregate) Number of replicates for POC and PON measurements Average POC – particulate organic carbon (μg/L or μg/aggregate) Standard deviation POC – particulate organic carbon (μg/L or μg/aggregate) Average PON – particulate organic nitrogen (μg/L or μg/aggregate) Standard deviation PON – particulate organic nitrogen (μg/L or μg/aggregate) Average POC:PON – molar ratio of particulate organic carbon to particulate organic nitrogen Average # cells/agg – number of cells per aggregate Standard deviation # cells/agg – number of cells per aggregate Average # chains/agg – number of cell chains per aggregate Standard deviation # chains/agg – number of cell chains per aggregate Average Cell length – cell longest dimension (μm) Standard deviation Cell length – cell longest dimension (μm) Average Cell width – cell shortest dimension (μm) Standard deviation Cell width – cell shortest dimension (μm) Average Cell volume – volume of cell assuming cylindrical shape (μm3) Cell ESD – cell equivalent spherical diamter (μm) Average Agg area – cross-sectional area of aggregate (mm2) Standard deviation Agg area – cross-sectional area of aggregate (mm2) Average Agg volume – volume of aggregate, assuming third dimension is equal to Agg width (mm3) Standard deviation Agg volume – volume of aggregate, assuming third dimension is equal to Agg width (mm3) Average Agg ESD – aggregate equivalent spherical diameter (mm) Standard deviation Agg ESD – aggregate equivalent spherical diameter (mm) Agg number - aggregate number Agg area – cross-sectional area of aggregate (mm2) Agg length – aggregate longest dimension (mm) Agg width – aggregate shortest dimension (mm) Agg ESD – aggregate equivalent spherical diameter (mm) Sinking time – time required for aggregate to sink over a distance of 142 mm (s) Sinking velocity – rate at which aggregate sinks (m/d) Comments Number of cells measured for average length and width Agg ESR – aggregate equivalent spherical radius (mm) Average Cell ESR – cell equivalent spherical radius (μm) Agg fractal dimension – aggregate fractal dimension
Methods:
Two strains of the diatom Skeletonema grethae (strains CCMP 775 and CCMP 776), both native to the Gulf of Mexico, were incubated in rolling tanks to allow aggregate formation. For each strain, two replicate, 4-liter rolling tanks were filled bubble-free with the culture in late exponential/early senescent phase and incubated in the dark at 19˚C for 2-4 days. When aggregates had formed, 20 individual aggregates per tank were isolated and sized. Ten of these were used for microscopical enumeration of abundance, cell size and chain length. Diatom cells were counted and sized using a hemocytometer (Olympus CX41); at least 6 subsamples and 100 cells each were counted per sample. The other ten aggregates were used to determine size-specific sinking velocities using the settling column method (Ploug et al., 2010). Additionally, four sets of ten aggregates each were collected to determine the average POC, PON and TEP content per aggregate. Duplicate filters (GF/F) prepared for POC/PON analysis were measured in a CEC44OHA elemental analyzer (Control equipment). TEP concentrations were determined in triplicate using the colorimetric method and are expressed in Gum Xanthan equivalents (GXeq) (Passow and Alldredge, 1995). We estimated the fractal dimension of the aggregates using the relationship between cell size, aggregate size and the number of cells per aggregate as given by Jokulsdottir (2011). An additional diatom species, Odontella aurita (strain CCMP 816) was incubated in the same manner as the Skeletonema species, in two replicate roller tanks. Four sets of ten aggregates each were collected to determine the average POC, PON and TEP content per aggregate for the Odontella species as for the Skeltonema, but cell counts and sizes, aggregate sizes and sinking velocities were not determined for these samples. Jokulsdottir, T. (2011) Sinking biological aggregates in the ocean – a modeling study. PhD Dissertation, Department of Geophysical Sciences, The University of Chicago, Chicago, IL. Passow, U and Alldredge, A.L. (1995) A dye-binding assay for the spectrophotometric measurement of transparent exopolymer particles (TEP). Limnology and Oceanography (40) 7:1326-1335. Ploug, H., Terbrüggen, A., Kaufmann, A., Wolf-Gladrow, D. and Passow, U. (2010) A novel method to measure particle sinking velocity in vitro, and its comparison to three other in vitro methods. Limnology and Oceanography: Methods (8) 8: 386-393.
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