California Current Ecosystem LTER

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Size fractionation of total Chl a larger and smaller than 8 μm

Title
Size fractionation of total Chl a larger and smaller than 8 μm data generated by Mike Mullin of the Marine Life Research Group, aboard CalCOFI (California Cooperative Oceanic Fisheries Investigations) cruises of the coast of California, January 1994 - October 1996.

Abstract
Based on twelve quarterly cruises over three years, the relative importance and absolute biomass of phytoplankton retained on an 8 mu m-pore membrane filter increased as the depth of the nitricline decreased, even though biomass of macrozooplankton (potential grazers) also increased as the nitricline shoaled. The relative importance of greater than or equal to 8 mu m cells was inversely related to a proxy for their biomass-specific mortality (biomass of macrozooplankton/biomass of greater than or equal to 8 mu m cells), as was their "residual" biomass not predicted from the nitricline depth
Keywords
measurements, communities, phytoplankton, chlorophyll a, seawater, depth

LTER Data System Record
http://dx.doi.org/10.6073/pasta/02183db3ad041992304d26757f1b25f9
Projects
Marine Life Research Group

Creators
Mullin, Michael ()

Contact
CCE LTER Information Manager (ccelter.im@gmail.com)

Data

table SizeFractionatedChl
Main data table for dataset 		Rows: 422
Columns: 7 		View / Download

Methods

General Methods
At approximately half of the locations sampled on twelve quarterly cruises by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) from January 1994 through November 1996, samples were taken to estimate the biomass of phytoplankton ≥ 8 μm, defined as chlorophyll retained on a membrane filter of this nominal pore diameter (filter type). On these cruises, samples were routinely taken from several depths with closing water bottles on a rosette with a CTD, and the seston from each bottle retained on a GF/F glass fiber was extracted for chlorophyll, determined fluorometrically. From each of the shallowest ten of these water bottles (representing samples from the surface to approximately 100 m or shallower), an additional 140 ml sample was withdrawn; these were combined and filtered through the 8 pm membrane filter, which was then extracted and analyzed as were the ten GF/F filters representing the same sampled depths. Biomasses of chlorophyll per unit volume were then integrated to 100 m for both the total phytoplankton (GF/F filters, ten samples integrated algebraically) and the ≥ 8 μm phytoplankton (membrane filter, one physically integrated sample) to give biomass in mg chlorophyll. m-2. The biomass of cells <8 μm was calculated as the difference between total and ≥ 8 μm chlorophyll, although this procedure means that <8 μm chlorophyll is not an independent variable for statistical analysis. In a few cases, the measured biomass of ≥ 8 μm cells as chlorophyll exceeded that of total chlorophyll, presumably due to subsampling or analytical variability. In these cases, the biomass of large cells was taken to be 100% that of the total.

References

Mullin, M.M. (1998) Biomasses of large-celled phytoplankton and their relation to the nitricline and grazing in the California Current system off Southern California, 1994 - 1996. CalCOFI Reports 39, 117 - 123

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