Dataset: Dinitrogen fixation rates and nifH community structure
Deployment: KM1110

Rates of ¹⁵N₂ fixation were assessed using the ¹⁵N isotopic tracer technique.  Whole seawater samples from six discrete depths (5, 25, 45, 75, 100, and 125 m) were withdrawn into acid-washed duplicate 4.3 L polycarbonate bottles and sealed with caps fitted with a silicone septa. Three mL of ¹⁵N₂ gas (98 %; Isotech Laboratories ©) was injected into each polycarbonate bottle through the silicone septum using a gas-tight syringe fitted with a stainless steel needle. The bottles were attached to a free drifting array, deployed before dawn and incubated at in situ light and temperature for ~24 hours.  After recovery of the array, the entire volume of each bottle was filtered onto pre-combusted glass microfiber (GF/F) filters (25 mm diameter) for whole seawater N₂-fixation estimates.  All GF/F filters were placed on combusted foil pieces in Petri dishes and stored frozen at -20 °C for transport.