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. This dataset contains measurements of chlorophyll concentrations and optical absorption spectra derived from particulate filtrations of water samples and the particle-free filtrate. The water samples were collected between 02-08 May and 09-12 August, 2015 during the DP01 and DP02 cruises, as was the GRIIDC CTD datasets R4.x257.230:0004 and R4.x257.230:0010.
Suggested Citation:
Chuanmin Hu, David English, Jenifer CannizzaroCharles Kovach. 2016. Chlorophyll concentration and optical absorption spectra of particulate and dissolved material, collected at several depths on DEEPEND cruises DP01 and DP02, May 2015 - Aug 2015. Distributed by: Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC), Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7319T92
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, 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, cast ID, sample depth (m), sample ID. Spectral (wavelength in nanometers) absorption values are given as absorption per meter.
Methods:
Water is collected using a CTD rosette near the surface and from several depths at each sampling station occupied by the DEEPEND cruises (DP01 and DP02, see GRIIDC dataset R4.x257.226:0003 and R4.x257.226:0011). A variable amount (<1 to 5 l) of this water is filtered through glass-fiber filter pads. The filter pads are stored for subsequent analysis. Some of the filtrate is 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 is determined on shore, using the quantitative filter technique (Yentsch, C.S. 1962. Measurement of visible light absorption by particulate matter in the ocean. Limnology and Oceanography 7, 207-217.) (Kiefer, D.A. and J.B. SooHoo. 1982. Spectral absorption by marine particles of coastal waters of Baja California. Limnology and Oceanography 27(3), 492-499). The spectral transmission of light (400-800nm) passing through each filter pad is 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 pheopigment concentration to be determined fluorometrically using an acidification technique (Holm-Hansen, O., C.J. Lorenzen, R.W. Holmes, and J.D.H. Strickland. 1965. Fluorometric determination of chlorophyll. J. Conseil, Conseil Perm. Intern. Exploration Mer., 30: 3-15.) (Holm-Hansen, O. and B. Riemann. 1978. Chlorophyll a Determination: Improvements in Methodology. Oikos 30(3), 438-447). The filtrate from the at sea filtration is analyzed using a spectrophotometer to determine the absorption spectra (200-800nm) of the colored dissolved material (CDOM) in the water sample.
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