The Sea-Bird Electronic Carousel Water Sampler (SBE 32) uses an electromagnetically activated lanyard release system to close 24 ten-liter plastic (PVC) bottles equipped with epoxy-coated springs and Viton O-rings. Each cast typically samples ~20 depths to a maximum sampling depth of 515 meters, bottom depth permitting. Four deeper CTD casts are performed at sta 90.90 (3500m), 80.90 (3500m), Santa Monica Basin (770m), & Santa Barbara Basin (570m). Some stations have multiple bottles tripped at the same depth to provide additional water for ancillary measurements. The bottle sample depths are based on the chlorophyll maximum & mixed layer depths profiled during the CTD downcast. Using the CTD down cast fluorometer profile to determine the chlorophyll max depth, 10m bottle spacing shifts up or down. Distributing the higher resolution 10m bottle spacing around the chl max. Salinity, oxygen, and nutrients analyses are done at-sea for all depths sampled. Chlorophyll-a and phaeopigments are also analyzed at-sea on samples from the upper 200 meters, bottom depth permitting.
On each station, seawater salinity samples of ~225 mL are drawn from all CTD-rosette bottles closed during the cast. A Guildline Instruments Portasal™ Salinometer (8410A) measures the seawater sample conductivity precisely, comparing it to a reference seawater standard. From these comparisons, salinities are calculated and logged using Windows-PC based software that averages data that meet replicate criteria. Concurrent with the water sampling, a Sea-Bird Electronics CTD equipped with dual conductivity meters profiles in situ data. Data processing software is then used to compare the bottle salts to in situ CTD measurements. These are used to confirm bottle closures at target depths, monitor CTD sensor performance, and helps select the best salinity data for future comparison and publication.
The amount of dissolved oxygen in seawater is measured using the Carpenter modification of the Winkler method. Carpenters modification (1965) was designed to increase the accuracy of the original method devised by Winkler in 1889. Using Carpenters modification, the significant loss of iodine is reduced and air oxidation of iodide is minimized. Rather than using the visible color of the iodine-starch complex as an indicator of the titration end-point, we use an automated titrator that measures the absorption of ultraviolet light by the tri-iodide ion, which is centered at a wavelength of 350 nm.
The phytoplankton macro nutrients nitrate, nitrite, silicate, phosphate and ammonium are analyzed in seawater using a colorimetric assay in which light absorbance is measured versus known standards. To analyze for nutrients a Seal Analytical continuous-flow AutoAnalyzer 3 (AA3) is used. After each run, the charts are reviewed for any problems, any blank is subtracted, and final concentrations (micro moles/liter) are calculated.
Complete methods for nutrient determination can be found here.
Chlorophyll a is cold-extracted in a 90% acetone solution for ~24 hours. Chlorophyll and phaeopigments are then measured fluorometrically using an acidification technique. The method used today is based on those developed by Yentsch and Menzel (1963), Holm-Hansen et al. (1965) and Lorenzen (1967). Note that concentrations of 'phaeopigments' are not a good measure of Chl a degradation products present in the sample since Chl b present in the sample will be measured as 'phaeopigments'.
Complete methods of chlorophyll-a determination can be found here.
Primary productivity samples are taken each day shortly before local apparent noon (LAN). Primary production is estimated from 14C uptake using a simulated in-situ technique. Light penetration is estimated from the Secchi depth (assuming that the 1% light level is three times the Secchi depth). The depths with ambient light intensities corresponding to light levels simulated by the on-deck incubators are identified and sampled on the rosette upcast. Occasionally an extra bottle or two are tripped in addition to the usual 20 levels sampled in the combined rosette-productivity cast in order to maintain the normal sampling depth resolution. Triplicate samples (two light and one dark control) are drawn from each productivity sample depth into 250 ml polycarbonate incubation bottles.
Complete methods for primary productivity determination can be found here.
The CalCOFI group collects samples for the characterization of the inorganic carbon system at selected locations along the cruise track. Total inorganic carbon and alkalinity are measured which allows the calculation of pH and pCO2. The objectives of these measurements are: first, the long-term characterization of the inorganic carbon system and its response to changing ocean climate, and second, measurements of pH in the coastal zone in order to monitor the impact of 'corrosive' waters on benthic ecosystems in the Southern California Bight.
Standard depths in meters are:
0 (surface), 10, 20, 30, 50, 75, 100, 125, 150, 200, 250, 300, 400, 500
Additional standard depths when deep casts are performed may include: 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000, 3200, 3400, 3600...
Bottle Cast-Types: typical bottle depths in meters with 10m-spacing centered around the chlorophyll max, are:
CalCOFI casts are typically to 515m, with a 3500m deep cast on sta 90.90 (& sometimes 80.90) if ship time & winch wire-length permits.
If additional bottles are available, standard depth bottle spacing can continue at 200m intervals till terminal depth. But normally, due to seawater demands that require duplicate bottle closures, standard level data may be interpolated and/or taken from the CTD sensors.
During the daily primary productivity cast, bottle depths and spacing are based on light level percentages. So shallower bottle depths may not be standard since the target specific, calculated light levels. On casts where bottle closures miss standard depths, data will be interpolated and/or come from the CTD sensors. Refer to the primary productivity methods web page and the table below for more info on the bottle depth determination.
DNA & RNA samples are collected daily on the noontime primary productivity station, typically at 4 depths - 10m, chl max, 170m, & 515m. Additional NCOG DNA & RNA samples are collected on CCE-LTER cardinal stations (refer to NCOG Sampling Method for station list). The samples collected for DNA and RNA analyses are for studies examining the diversity, biogeography, and activity of planktonic microbes. DNA samples are collected in conjunction with CCE-LTER particulate organic carbon and nitrogen (POC/PON) samples on NCOG stations and will be used to assay the diversity and distribution of microbes and other planktonic organisms. POC and PON measurements provide information on the spatial and temporal variability, and relative carbon:nitrogen (C:N) ratio, of the standing crop of biomass in the CCE. By linking analyses of microbial community and structure and diversity directly to measurements of ecosystem productivity we can evaluate microbial population and community dynamics in context with other indictors of ecosystem productivity. NCOG Sampling Method is outlined here.