Ocean Carbon and Biogeochemistry Data System

VERTIGO multi-ship
PI notes for Barium VUB - Dissolved Ba; particulate Ba, Sr, Ca, Al from Niskins

12 November 2008: Prepared for OCB data system by Steve Gegg, BCO DMO (WHOI)
from documentation contributed by data set PI.

Original data were contributed by PI as a single multi sheet Excel file (Barium_ALOHA_and_K2_VUB.xls).

Contact: Frank Dehairs (VUB)

Sampling and Analytical Methodology

Dissolved Ba

15 ml of unfiltered seawater were sampled in polypropylene vials (Nalgene), rinsed three times with the seawater sample. Samples were acidified using Suprapur HCl (15 µl) and stored at room temperature till analysis. At ALOHA and K2 6 casts (0-1000m) were sampled during the site occupation. Dissolved barium was measured using an isotope dilution ICP-QMS (ID-ICP-QMS) as described by Klinkhammer and Chan (1990) and Freydier et al. (1995). Sample preparation is as follows: 1 g of seawater is spiked with 0.7 g of ¹³⁵Ba-spike solution yielding a ¹³⁸Ba/¹³⁵Ba ratio between 0.7 and 1 to minimize error propagation [Webster, 1960; Klinkenberg et al., 1996]. Subsequently the sample is diluted with Milli-Q grade water to a final weight of 30 g. Blanks consist of acidified (nitric acid) Milli-Q water. Quantities of sample, spike and dilution water were accurately assessed by weighing.

Isotope ratios were measured with a SF-ICP-MS (Element 2 Thermo Finnigan). Reproducibility of our method is ± 1.5% (RSD) as tested on repeat preparations of reference solutions. Average Ba values obtained for reference waters SLRS-3 and an in house standard (i.e. a Mediterranean Sea standard prepared by C. Jeandel, OMP, Toulouse) were 13.48 ± 0.21 µg l^-1 (1δ) with RSD of 1.55% and 10.49 ± 0.29 µg l^-1 (1δ) with RSD of 2.75% respectively, in good agreement with certified values (SLRS-3: 13.4 ± 0.6 µg l-1 and OMP: 10.4 ± 0.2 µg l^-1). For the ALOHA site characterized by very stable hydrographic conditions over the duration of the investigation, overall precision (including sampling precision) based on the 6 dissolved Ba profiles is ± 0.3 µg l^-1 (1δ) with an RSD of 5%.

Ba, Sr, Ca, Al in Suspended matter

Suspended matter was sampled from 5 casts at ALOHA (Julian days 178, 182, 186, 188, 191) and 6 casts at K2 (Julian days 209, 212, 214, 219, 223, 225) using a CTD rosette equipped with 10L Niskin bottles. Suspended matter was sampled at 14 depths between surface and 1000m. Between 3 and 10 L of seawater was filtered through 47mm diameter, 0.4µm pore size Nuclepore membranes, under pressure of filtered (0.4 µm) air. Suspended matter profiles were also sampled by in-situ filtration using filter holders (holding 47 mm Nuclepore membranes of 0.4 µm porosity) mounted on side arms of Multiple Unit Large Volume Filtration Systems (MULVFS; Bishop et al., 1985). In-situ pumping lasted between 3 and 5 hours and seawater volumes filtered through the side arm filter holders ranged between 1.5 (upper water column) and 40 liter (at 1000m).

Particulate material was completely digested in sealed Teflon beakers using a HCl/HNO₃/HF mixture (1.5 mL/1 mL/0.5 mL respectively; Merck Suprapur grade) heated at 90°C, in a pressurized clean room. After evaporation to dryness, the residue was dissolved in 3 mL of 2% HNO₃ and made to volume in 10 mL with Milli-Q grade water. Filter blanks were processed using the same conditions as for the samples and their analytical signals subtracted. Ba and Sr were analysed by Inductively Coupled Plasma – Quadrupole Mass Spectrometry (ICP-QMS, VG Instruments, Plasma PQ2+) using 4 internal standards (Ru, In, Re and Bi) for matrix and instrumental drift corrections. Ca and Al were analysed by Inductively Coupled Plasma – Atomic Emission Spectroscopy (ICP-AES, Thermo-Optics, IRIS) using Y and Au as internals standards to correct for instrumental drift.

Calibrations were performed using artificial standard solutions and dilute mineralized natural rock standards (BHVO-1, SGR-1, CCH-1, DWA; Govindaraju, 1994). Accuracy of Ba measurements was within 5% as monitored by analyses of the above-mentioned standards.

References

Freydier R., B. Dupre and M. Polve (1995). Analyses by Inductively-Coupled Plasma- Mass Spectrometry of Ba Concentrations in Water and Rock Samples - Comparison between Isotope-Dilution and External Calibration with or without Internal Standard. European Mass Spectrometry, 1(3): 283-291

Govindaraju K. (1994). Compilation of Working Values and Sample Description for 383 Geostandards. Geostandards Newsletter 18.

Jacquet, S., (2007). Barium in the Southern Ocean: Towards an estimation of twilight zone carbon mineralization, PhD Thesis; Vrije Universiteit Brussel, 234pp.

Klinkenberg H., W. VanBorm and F. Souren (1996). A theoretical adaptation of the classical isotope dilution technique for practical routine analytical determinations by means of inductively coupled plasma mass spectrometry. Spectrochimica Acta Part B-Atomic Spectroscopy, 51(1): 139-153.

Klinkhammer G.P. and L.H. Chan (1990). Determination of Barium in Marine Waters by Isotope-Dilution Inductively Coupled Plasma Mass-Spectrometry. Analytica Chimica Acta, 232(2): 323-329. Webster, Methods in Geochemistry, in: A.A. Smales, L.R. Wagner (Eds), Interscience, New York, 1960, pp 202-246.

Modifications to Original Data

date reformatted to YYYYMMDD
column headers edited to BCO-DMO convention

Cruise_ID added manually to both KM0414 and RR_K2 data

date, event, ev_code, lon, lat from cruise logs merged with original data
one single multi-ship dataset generated for both KM0414 and RR_K2 data

Used common "cast" id from these data to determine sample position, date and event code for Niskin data

(KM0414 event log)
(RR_K2 event log)