Dataset: GP15 Be-7 Leg 2
Deployment: RR1815

Be-7 Aerosol:
Aerosol samples were collected between Sept 20, 2018 and Nov 23, 2018 during the U.S. GEOTRACES PMT cruise, R/V Roger Revelle (RR1814), 18 September 2018 - 24 November 2018, Seattle, Washington - Papeete, Tahiti, French Polynesia (with a port stop in Hilo, Hawaii, 21-25, October 2018). Aerosol samples were obtained with a Tisch TE-5170V-BL high volume aerosol sampler, modified to collect 12 replicate samples on acid-washed (Wallace et al, 1977; Baker et al., 2006) 47mm diameter Whatman-41 (W-41) filters, using procedures of the US GEOTRACES aerosol program (Morton et al., 2013). In order to minimize the filter blanks for our experiment, the W-41 filters were pre-cleaned before deployment using three cycles of leaching with 0.5M HCl (Optima) then rinsing with ultra-high purity water (UHP water) according to trace element protocols in a HEPA-filtered laminar flow hood (Morton et al., 2013; similar to Baker et al., 2006).

For 7Be, three of the 47mm aerosol samples were stacked in a plastic Petri dish and counted by gamma spectroscopy. Be-7 has a readily identifiable gamma peak at 478 keV. The counting system was calibrated for all samples by preparing a commercial standard in geometry identical to the samples.

Be-7 Seawater:
A weighted sampling hose, attached to a submersible pump with a portable ctd was deployed over the aft of the ship to collect seawater for Be-7 analysis. The seawater was collected in plastic 700 liter holding tanks and then passed through iron-oxide impregnated acrylic fiber filters (adsorbs Be-7). The efficiency of the fiber for extraction of Be from seawater was determined by adding stable Be atomic absorption standards to a drum containing seawater, pumping the water through an iron fiber cartridge, and at every 100 L measuring the Be content of the cartridge effluent. Based on several trials, it was found that for sample volumes in the range 400-700L, extraction efficiencies are respectively, 82 ± 3% to 76 ± 2%. 

All fibers were returned to the lab where they were dried and ashed. Fiber samples were pressed into pellets. All samples were then placed over a low background germanium gamma detector. 7Be has a readily identifiable peak at 478keV. The detector is calibrated for these samples by adding a commercially prepared mixed solution of known gamma activities to ashed fiber and counting in the appropriate geometry.