Dataset: Multitracers Biogenic Concentration Data

Sample collection
During the Multitracers Project (September 1987 to July 1991) bottom-moored sediments traps were deployed at three stations (Nearshore, Midway, and Gyre) in the Northeast Pacific Ocean.

Each mooring had sediment traps deployed at 500 m (Year 1 only), 1000 m, 1500 and/or 1750 m, and 500 m above the bottom (~2300 m at the Nearshore and Midway stations and ~3200 m at the Gyre site). Most traps, with the exception of the 1500 m trap, had 6 sample cups. The 1500 m traps, referred to as Whizbang (WzB) traps, had 13 sample cups. Data for cup opening dates and the number of days each cup was open are provided in this dataset.

The trap sample cups were filled with unfiltered seawater collected from the near-bottom trap depth at each site and poisoned with 15g/L of sodium azide. To compare the effects of different "preservatives" a pair of traps were deployed at the Nearshore site (1750 m water depth) in Year 3; one set of cups was poisoned with sodium azide and the others preserved with formalin. No special trace metal clean sampling procedures were utilized during the Mulitracers Project; however, the traps were constructed out of plastic and fiberglass thus reducing possible trace metal contamination.

When the sediment traps were recovered the sample cups were removed, sealed, and not opened until they were ready to be processed in the laboratory. Once back at the lab the samples were allowed to sit undisturbed until the particulate material had settled. Once opened the supernatant was poured off and then used to rinse the particulate fraction through a 2 mm sieve. The ≥2 mm size-fraction was transferred to a bottle containing formalin and refrigerated for future use. The <2 mm size-fraction, which was used in this study, was split into 10 aliquots. Between 1 and 4 aliquots were frozen for future use. The other 6 to 9 aliquots were centrifuged and the supernatant was discarded. These samples were then rinsed with buffered distilled water and centrifuged; this step was carried out twice. Finally, the samples were freeze-dried and then homogenized using either an agate pestle and mortar or a Wig-L-Bug grinding mill with plastic vials.

Analytical methods
Particulate organic carbon (POC) concentrations were determined by measuring the total carbon using an elemental analyzer and then subtracting the percent carbonate carbon that was measured by coulometry. The amount of organic matter (OM) is 2.5 x the %Corg and the amount of carbonate (i.e., CaCO3) is 8.33 x %Ccarb. The opal concentration was determined by Na2CO3 extraction of the opal followed by Atomic Adsorption Spectrophotometry analysis of the extracted Si (% Opal = Si x 2.59; Collier pers. comm.).

Known problems/issues
In Year 1, the 500 m trap at the Nearshore station failed after the third cup, presumably due to clogging during a high flux event. There is also evidence that the 500 m trap at the Gyre site under-collected material (i.e., lower fluxes at 500 m compared to 1000 m). The 1500 m trap, which was only deployed at the Nearshore station in Year 1, appears to have failed partway through or was programmed incorrectly. Other failed traps are indicated by MTT (column 1) and a sample description of "bulk" (column 2).

The Gyre mooring deployed in Year 3 was not recovered until Year 4 and is therefore named Gyre-4. However, the Date the Cup Opened (column 10) clearly shows these samples were collected between 9/21/89 and 6/25/90 (i.e., Year 3 and much of Year 4).