AMMONIUM CONCENTRATIONS AT STATION ALOHA – IMPROVED METHODOLOGY ALLOWS FOR FULL OCEAN DEPTH ANALYSIS.
Ammonium in the oligotrophic waters of Station ALOHA has not routinely been a part of the measurements of the Hawaii Ocean Time-series (HOT) due to difficulties associated with sampling and laboratory methodologies. However, in 2012 we adopted the use of a Liquid Waveguide Capillary Cell (LWCC) to allow for lower method detection limit and the ability to measure this nutrient in the full ocean depth at Station ALOHA. More recently, we improved on this method by coupling the SEAL AA3 with the 2 m LWCC cell, and to further eliminate contamination from the surroundings, the auto sampler and samples are enclosed in an airtight plexi-glass box with a tray of acidified silica gel to provide an ammonium sink for the air inside the box. All reagent containers are equipped with air clean-up devices consisting of acidic silica gel. Low nutrient seawater is used as a carrier and the samples are mixed with reagents to form an indophenol blue dye which is measured at 640 nm. The limit of detection for this method is 3.7nM with a precision of ± 1.2nM, and linear range of 500nM. A HOT time-series of full ocean depth ammonium at Station ALOHA began in 2015 and shows an ammonium increase in the upper euphotic zone around the nitrite maximum. A larger peak in ammonium was consistently observed around 800 m. This increase is mirrored in N2O concentration and at depths where nitrate is at a maximum and nitrite and dissolved oxygen are at a minimum.
Curless, S. E., Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai'i, USA, email@example.com
Church, M. J., University of Montana, Flathead Lake Biological Station, USA, firstname.lastname@example.org
Segura-Noguera, M., University of Sheffield, United Kingdom, email@example.com
Karl, D. K., Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai'i, USA, firstname.lastname@example.org
Time: 15:30 - 16:30
Location: Poster/Exhibit Hall
Presentation is given by student: No