Abstract:
The optical absorption spectra from seawater’s particulate and dissolved components can be used to compute the penetration of light to various depths, estimate the proportion of living to non-living particulate matter, assess photosynthetic light availability and the type of phytoplankton present, and the validate of satellite or airborne ocean color measurements. Chlorophyll and phaeopigment concentrations are often used to estimate the amount of phytoplankton present, and to allow extrapolation of in situ fluorometric measurements. Water was collected using a CTD rosette near the surface and from several depths at each sampling station occupied by the DEEPEND cruises DP03 & DP04 (see GRIIDC dataset R4.x257.226:0012 and R4.x257.226:0013). A variable amount (<1 to 5 l) of this water was filtered through glass-fiber filter pads. The filter pads were stored for subsequent analysis. Some of the filtrate was passed through an additional nylon membrane (0.2 µm) filter, and also retained for shore based analysis. Optical absorption of the particulate material on the filter pads was determined on shore, using the quantitative filter technique (Yentsch, 1962; Kiefer and SooHoo, 1982). The spectral transmission of light (400-800nm) passing through each filter pad was measured, both before and after the phytoplankton pigments are extracted from the particles retained on the filter pad using methanol (Kishino et al., 1985). These techniques allow the optical absorption spectra of the particles in the water to be determined, as well as the proportion of absorption due to pigmented or detrital material. The extraction of pigments allows the chlorophyll a and phaeopigment concentration to be determined fluorometrically using an acidification technique (Holm-Hansen et al., 1965; Holm-Hansen and Riemann, 1978). The filtrate from the at sea filtration was analyzed using a spectrophotometer to determine the absorption spectra (200-800nm) of the colored dissolved material (CDOM) in the water sample. This data was collected during the same cruise as GRIIDC CTD datasets R4.x257.230:0011 and R4.x257.230:0012.
Suggested Citation:
Chuanmin Hu, Jennifer Cannizzaro, David English. 2017. Chlorophyll concentration and optical absorption spectra of particulate and dissolved material, collected at several depths on DEEPEND cruises DP03 and DP04 from January-December 2016. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7ZP44GF
Purpose:
Chlorophyll concentrations and the spectral absorption of particulates and dissolved material was measured from selected water samples to validate in situ fluorometers, for comparison with remote sensing reflectance and optical properties, and to aid estimates of the distribution of light.
Data Parameters and Units:
for Chl data file: time (in UTC, Coordinated Universal Time), latitude (° North), longitude (-° are West), Station name, Cast name, sample depth (meters), USF sample bottle ID, Chlorophyll_a concentration (mg per m^3) determined using the Welschmeyer method, Chlorophyll_a concentration (mg per m^3) determined usng the 1978 Holm-Hansen and Riemann method, phaeophytin concentration (mg per m^3) determined usng the 1978 Holm-Hansen and Riemann method. for particulate absorption files: time (in UTC, Coordinated Universal Time), location (°, North and East positive), Station ID (in file name), cast ID, sample depth (m), sample ID, and reliability flag for each sample. Spectral (wavelength in nanometers) absorption values are given as absorption per meter. for dissolved absorption files: time (in UTC, Coordinated Universal Time), latitude and longitude (°, North and East positive), StationID (in file name), cast ID, sample depth (m), sample ID. Spectral (wavelength in nanometers) absorption values are given as absorption per meter.
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