We plan to collect Soutar box cores at all of the U.S. JGOFS EqPac benthic lander stations. These corers will recover about 20 KY of sedimentation at the Equator and about 50 KY of sedimentation at the ends of the transect due to decreases in sedimentation rate.
We have been funded to carry out an ancillary aerosol collection program. Aerosol collections will be made during the steam to the first station, during the transit between each station, and during the steam to port. Such sampling will provide long-duration samples within each of the trade wind systems, as well as several short duration samples.
We propose to analyze C and CaCO by coulometry and/or by Carlo-Erba analyzer (depending on the outcome of intercalibrations still being completed) and biogenic SiO by spectrophotometry [see Methods section] in at least one box, spade, and gravity [trigger] core collected at each coring site by the program [an estimated total of about 20 box cores, 20 spade cores and 12 gravity cores]. We have designed a sampling and analysis program for our own studies as well as to meet the needs of PI's proposing benthic flux and process studies. We have settled on a sampling interval of 1 mm in the upper 3 cm [for cores at lander sites only], 1 cm for the next 5 cm, every 2 cm thereafter to a depth of 15 cm, and every 5 cm thereafter to the total depth of the cores. We estimate a total of about 2,000 analyses for each component from the benthic cruise. We can provide analyses of CaCO, C and biogenic SiO in lander sediment samples if requested.
Because of the time delays of curation and sampling of the cores and the length of time necessary for the measurements, we cannot provide all of the measurements by six months post-cruise. Our first priority is to provide analyses of CaCO, C and stratigraphic information on box cores and spade cores being used for analysis of benthic processes and fluxes by 6 months post-cruise. Our second priority for sediment composition will be analyses of biogenic SiO and other sediment components [aluminosilicates, elements]. We expect to provide completed analyses by one year post-cruise, or the time frame of the post-cruise science meeting.
The mineralogy of the sample is determined by low temperature ashing of the filter followed by analysis on zero-background quartz mounts. The samples are also inspected by SEM/EDAX for grain size, mineral content, and identification of other particle types.
The C content of equatorial Pacific sediments is small and averages less than 1--2 wt %. Small errors in the measured value can, therefore, have a large impact on calculated accumulation rates and benthic fluxes. The simple technique for determining C described above works well when the CaCO content of the samples is low. When CaCO exceeds about 50 % of the sediment, however, the small error on replicate inorganic carbon analyses can exceed the total concentration of C in the sample. Therefore, we will determine C using a sample preparation method developed by Curry and modified in our laboratory. We determine C on a separate split of sample. The sample is weighed and CaCO is removed by treating the sample with 50 ml of phorphoric acid. The solution is filtered through a pre-combusted Whatman GF/F fine filter and the remaining sediment is washed on the filter with 50 ml of deionized distilled water. The filter is dried and folded into a precombusted aluminum foil square for insertion into the coulometer. The precision of the method based on the average % difference of replicate measurements of over 400 samples is ±5 % of measured value or about ±5µgC.
Several investigators have recently found that the loss of C during acid dissolution of CaCO in sediment trap samples and margin sediments can be large. We tested our technique for dissolution of C by acid predigestion: the filtrate was analyzed using the coulometer attachment for TOC in water. We found no C in the solution. The filtered solutions from sediment samples at 5° N and the Equator [also therefore high CaCO and low CaCO sediments] were also analyzed for dissolved C by E. Peltzer at Woods Hole Oceanographic Institution using the technique of Suzuki as modified by Peltzer. Insignificant amounts of C were present in the solution. We believe that this is because the C in sediments from the central equatorial Pacific has undergone considerable degradation and is fairly refractory. This would not be the case in sediment trap material and may not be the case in margin sediments.
The mineralogy of the clay and silt-sized fractions will be determined by x-ray diffraction using preparation, standardization, and data analysis methods outlined in Leinen, 1989.
I plan to conduct mineralogical and XRF analyses of samples from the spade cores. These analyses were not proposed by DeMaster et al. I plan to conduct analyses of biogenic constituents as requested by the lander group.