Gf f filter

Seawater for nutrients (NO₃, NO₂, NH₄, PO₄, and SiO₄) was filtered through GF/F filters (Whatman, United States) and frozen at −20°C until analyzed by an AA3 auto-analyzer (SEAL, Germany). Dissolved inorganic nitrogen (DIN) concentrations were the sum of NO₃, NO₂, and NH₄ concentrations (Grasshoff et al., 1999 ).
For Chl a samples, 1 L seawater was filtered onto the GF/F filters (Whatman, United States) and then the filters were kept at −20°C. Chl a concentrations were measured with a fluorometer (Turner Designs Trilogy, United States) after acetone extraction at 4°C for 24 h (Parsons, 1985 ).
Water samples for Dissolved organic carbon (DOC) were filtered through pre-combusted (450°C for 4 h) GF/F filters (Whatman, United States) and stored in pre-combusted glass vials at −20°C. DOC concentrations were analyzed with an auto-analyzer (Shimadzu TOC-VCPH, Japan) (Alvarez-Salgado and Miller, 1998 (link)).
Bioavailable dissolved organic carbon at the end of the incubation in mesocosm experiments was determined by the declined DOC concentrations over the 30-day incubation at room temperature.

The physical and chemical parameters of these sites (i.e., temperature, conductivity and pH) were measured in situ with a Thermo Scientific Orion Star multiparameter device (model A329). To determine nitrate, nitrite, phosphate and silicic acid, water samples (60 mL) were taken in triplicate, filtered through a GF/F filter (Whatman^®, Buckinghamshire, UK) and stored at −20°C. These nutrient samples were analyzed using colorimetric methods (Strickland and Parsons, 1972 ) with an automatic nutrient analyzer (Atlas et al., 1971 ). To determine chlorophyll-a concentration, 200 mL water samples were filtered through a GF/F filter (Whatman^®, Buckinghamshire, UK). The filters were stored at −20°C to then be analyzed using the fluorometric method (Caspers, 1970 (link)) in a Turner A10 fluorometer.

Particulate carbon was collected on pre-combusted GF/F filters (25 mm, Whatman Nuclepore), which were stored at -20°C until analysis. The filtration volume (80–380 mL) was adjusted to the particle loading of the seawater. Filters were treated with 200 μL of carbon-free HCl (0.2 N) to remove inorganic carbon and dried at 60°C for approximately 48 h. After drying, filters were packed into small Zn-cartridges and analyzed using an elemental analyzer (Euro EA 3000, EuroVector Instruments & Software, Italy).
For analysis of DOC concentration, seawater was filtered through combusted (400°C, 4 h) GF/F filters (0.7 μm, Whatman), and 15 mL was sealed in combusted glass ampoules. Samples were stored at -80°C in the dark. Some of the ampoules were damaged during transport to the mainland, resulting in reduced temporal resolution. Acidified samples (pH 2, HCl) were analyzed using high-temperature catalytic oxidation (Sugimura and Suzuki, 1988 (link)) on a Shimadzu total organic carbon (TOC)-VCPH instrument with analytical precision better than 5% for three replicate samples. Accuracy was tested in each run against deep Atlantic seawater reference material (D.A. Hansell, University of Miami, FL, USA) and was better than 5%.
Total organic carbon (TOC) was calculated as the sum of particulate organic carbon (POC) and DOC.