Dataset: beaconII_bgc

Samples for dissolved oxygen were collected in 140 ml Pyrex iodine flasks, stored in a dark location and the necks of the flasks were sealed with seawater. Samples were analyzed after 6-8 hours, based on the Strickland and Parsons (1968) modification of the Winkler (1888) method. Analysis was performed on an automated titration system using an UV light endpoint detection system as designed by the late Robert Williams of SIO. Prior to running the samples, a series of standards (6-8) and blanks (3-4) were run for determination of the thiosulphate normality value. Precision was typically <0.5 µmol kg-1.  

TA and DIC samples were collected according to standard protocols (Dickson et al., 2007) using 250-mL Kimax brand glass sample bottles. Samples were immediately poisoned with 100 μL saturated solution of HgCl2. DIC was analyzed coulometrically using a UIC CM5011 CO2 coulometer combined with a VINDTA3C (Marianda Inc) or SOMMA system, alternatively based on infrared absorption using an AIRICA (Marianda, Inc) and a Li-Cor 7000 as the detector. TA was analyzed based on potentiometric acid titrations (∼0.1 N HCl) using a VINDTA3S (Marianda Inc). Performance and precision of the instruments were regularly verified using certified reference material (CRM) prepared by A. Dickson at Scripps Institution of Oceanography (SIO). The accuracy and precision of replicate CRMs on any given day of analyses were typically in the range of ±2–4 μmol kg−1 for both TA and DIC.

Samples for nitrate+nitrite, nitrite, phosphate, silicic acid and ammonia were filtered through 0.8 µm Nuclepore filters then frozen (-20°C) in HDPE bottles until analysis. Samples were analyzed on a four channel SEAL AutoAnalyzer III using modified methods from Knap et al. (1996).   Analytical precision for triplicate nutrient measurements was approximately 0.03-0.05 µmoles kg-1. Certified standards from Ocean Scientific International were analyzed on a regular interval to maintain data quality.

Particulate Organic Carbon and Nitrogen (POC/PON) samples (2L) were filtered onto pre-combusted (450ºC, 5 hours) Whatman GF/F glass fiber filters (nominal pore size 0.7µm), and stored at -20°C.  Dried acidified samples were be combusted at 980 ºC on an Exeter Analytical Elemental Analyzer as described in Knap et al. (1996). Field blanks and acetanilide standards were run with each batch of samples. 

Phytoplankton pigment samples (4L) were filtered onto 25mm Whatman GF/F glass fiber filters, frozen in liquid nitrogen, and analyzed by both standard fluorometric and high performance liquid chromatography (HPLC) techniques. Samples were analyzed using the method of Bidigare et al. (2005) on an Agilent 1100 series HPLC. Samples were calculated based upon instrument response and retention times that were standardized annually with pigment standards obtained from Danish Hydraulic Institute.

Samples for bacterial abundance were collected in 50ml Falcon tubes then preserved with 0.2μm filtered formalin and stored at -80 °C. Direct counts of DAPI (4,6-Diaminino-2-phenylidole) stained cells were conducted using an epifluorscence microscope to determine abundance (Knap et al., 1996).

Salinity samples were collected in 250 ml borosilicate glass bottles (Ocean Scientific, UK) and analyzed using a Guildline Autosal 8400B. The salinometer were calibrated with standard seawater provided by Ocean Scientific, UK. Salinity was calculated based on the mean sample conductivity ratio from two separate measurements averaged over 5 seconds and computed according to the 1978 definition of Practical salinity (UNESCO, 1978). The precision of replicate samples was typically less than 0.001 psu.

Dissolved calcium samples were analyzed using a titration system developed by J. Ballard and Dr. T. Martz at SIO. Samples were collected in 100 ml plastic bottles. The dissolved calcium concentration was determined by EGTA titration with Zn-zincon as an indirect photometric indicator (Anfält and Granéli, 1976) using a custom photometric cell with a white LED, 620 nm filter, and photodiode. The voltage of the cell was monitored with Labview software and a 24-bit analog to digital converter (NI-9219). In the first step, 1 M borate buffer was added to 25 g of sample and diluted 10 fold. Zincon indicator (0.1%, 1ml) and equimolar Zn-EGTA (0.01 M, 2.5ml) were then added prior to an EGTA (0.02 M) gravimetric addition (~11 g) and software controlled volumetric additions (~0.1 ml).  Accuracy and precision of IAPSO standard seawater was in the range of 2-5 mol kg-1.