Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Unfiltered seawater samples were collected from the Niskin bottles in acid-washed plastic tubes. The stored samples were immediately analyzed for silicate in triplicate using the pFI assay protocol outlined in Hatta et al. (2021). One key modification was adjusting the holding coils’ temperatures to 25ºC instead of the originally specified 50ºC. In tandem with this temperature change, the stop flow time in the flow cell was extended to 60 seconds to ensure the absorbance of the silicomolybdenum blue at 810 and 660 nm product reached a steady state. 

We used a miniSIA-2 instrument (miniSIA2, GlobalFIA, Fox Island, USA) equipped with a 8-port LOV unit and a 20 cm flow cell furnished with a Tungsten Halogen light source and UV-VIS spectrophotometer (Ocean Insight, USA) and a 14 position auto sampler (GlobalFIA, USA). The entire system was controlled with FloZF software (v 5.2, GlobalFIA). The system was calibrated using silicate working standards prepared in low nutrient seawater (LNSW, (0-119 µmol L-1 Si)). 

To accommodate the analysis of Si samples from full depth ocean profiles within the constraints of a 20 cm flow cell, a dual measurement wavelength approach was adopted. For low Si samples (< 40 µmol L-1), the difference between the baseline corrected absorbances at 810 nm and the 1050 nm reference was used. For high Si samples (> 40 µmol L-1), a singular, baseline corrected measurement wavelength at 660 nm was employed. Silicate concentrations were calculated using the mean absorbances (660 nm for Si > 40 µmol L-1 and 810-1050 nm for Si <  40 µmol L-1) and the intercept and slope of the corresponding calibrations curves (660 nm calibration curve for Si > 40 µmol L-1 and 810-1050 nm calibration curve  for Si <  40 µmol L-1 ). 

- Units removed from parameter names in primary data file
- Spaces in parameter names replaced with underscores ("_")

NSF Award Abstract:

Progress and discovery in the understanding of the chemical processes that regulate the growth of phytoplankton in the marine environment is limited by the ability of oceanographers to measure nutrients and trace metals at relevant spatial and temporal scales. This project aims to develop a new generation of autonomous and highly sensitive nutrient and trace metal analyzers for shipboard use and deployment at coastal monitoring stations, with potential for incorporation into existing autonomous observing platforms (e.g., gliders, autonomous underwater vehicles). Such a development will generate new insights into nutrient dynamics at a range of spatial and temporal scales and provide a new capability to obtain high resolution data sets for nutrients and trace metals in remote areas and environments where sample volumes are limited (e.g., brines, pore waters).

This project will develop novel automated methods for nutrients (phosphate and silicate) and trace metals (aluminium, manganese) using a technology called programmable Flow Injection (pFI). pFI is a microfluidic technique, which allows to automate conventional wet chemical analysis using microliter volumes of sample and reagents while significantly reducing the generation waste. In order to bring low levels of trace metals and nutrients that characterize remote ocean regions into the analytical window of pFI, concentration techniques will also be developed and coupled to spectrophotometric and fluorescence detection. The developed methodologies will be intercalibrated with standard oceanographic methods by participating in a GO-SHIP research cruise and a Hawaii Ocean Time-series cruise of opportunity. The long-term, unattended operation of the pFI analyzers will be evaluated at the Central California Ocean Observing System (CenCOOS) Moss Landing Shore station, where autonomous pFI analyzers will be deployed to undertake a year-long, hourly time series of phosphate and silicate. The data obtained from the shore station will be made publicly available and will complement existing monitoring data from this location, illuminating the connection between deep ocean nutrient dynamics and biological activity in coastal upwelling systems. The newly developed pFI analyzers will be assembled using commercially available components and open source software to facilitate uptake of this new methodology by the chemical oceanography community at large. This project will also support the training and exchange of at least two graduate students at the University of Hawaii at Mānoa and the Moss Landing Marine Laboratories, who will represent the next generation of specialists in the development and application of pFI methodologies to chemical oceanography.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.