Figure 4. Shows both time series and seasonal inventories of SRP and N+N. a. Seasonal distribution of MAGIC-SRP (mmol P m-2; 0-100 m; n=228. b. Seasonal distribution of the mixed layer depth. c. Seasonal distribution of N+N (mmol m-2; 0-100 m; n=200). Box plot boundaries are the 10th and 90th percentile (whiskers), the 25th and 75th percentile (box edges) and the mean and median values. d. Time series of depth-integrated (0-100 m) N+N and (0-100 m) SRP with the mixed layer also shown.

Analyses of Inorganic Nutrient Pools by the Hawai’i Ocean Time-series (HOT) Program: Methods, Procedures, and Standardization

Susan E. Curless,1 Karin M. Björkman,1 John E. Dore,3 Claire Mahaffey,2 Mariona Segura-Noguera,1 Brett Updyke,1

David M. Karl,1 Matthew J. Church1

1 School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa 2 School of Environmental Sciences, University of Liverpool

3 Department of Land Resources and Environmental Sciences, Montana State University

Introduction: Nutrient biogeochemistry is a hallmark component of the Hawaii Ocean Time-series (HOT) program. At Station ALOHA, the field site for HOT, nutrient concentrations range from (sub)nanomolar in the upper (<100 m) oligotrophic waters to micromolar in the nutrient enriched deep ocean. Such large

gradients in inorganic nutrient concentrations challenge routine analyses. Consequently, HOT has developed methodologies specific for quantification of the large range of nutrient concentrations observed throughout the water column (~0-4800 m) at Station ALOHA.

Table 1. The limits of detection for full ocean depth (0-4800 m) and upper ocean (0-200 m) nutrient analysis. The limits of detection were calculated using the protocol outlined in Chapter 5 of the EPA Revised Assessment of Detection and Quantification Approaches, 2004.

Nutrient Concentration Range Limit of DetectionNO2 + NO3 0-45 µM 0.066 µMNO2 + NO3 0-5 µM 0.010 µM

SRP 0-3 µM 0.0047 µMSRP 0-1 µM 0.0040 µM

Silicate 0-160 µM 0.016 µMSilicate 0-5 µM 0.013 µM

Poster #2461

Acknowledgements: The authors would like to thank the National Science Foundation for their continued support of the HOT program. Thank you to Erika Wasner Designs for the HOT logo, and to Lance Fujieki for the preparation of the QC charts.

Manual High Sensitivity Soluble Reactive Phosphorus: This analysis uses the MAGnesium Induced Co-precipitation (MAGIC) method (Karl and Tien, 1992). The detection limit is ~2 nM-P for the routine HOT protocol. Figure 2 depicts the steps of the MAGIC-SRP analysis. Figures 3 and 4 shows the seasonal inventories, and depth distribution of SRP in the surface ocean.

Figure 2. High sensitivity analysis SRP (MAGIC-SRP). NaOH (1 N) is added to seawater samples forming (Mg(OH)2) precipitate. Samples are pelleted by centrifugation and supernatants removed; SRP content of pellets are analyzed by traditional colorimetric methods.

Manual High Sensitivity Nitrogen: This analysis is performed using the chemiluminescent method of Cox (1980) as modified for seawater by Garside (1982). The limit of detection for this method is ~2 nM (Dore et al. 1996). Seasonal inventories and depth distribution of nitrogen in the surface ocean can be seen in Figures 3 and 4.

High Sensitivity Nutrient Analysis: In the upper water column (0-200 m), ambient concentrations of nitrite, nitrate, urea, ammonium, and SRP are often below limits of detection for analysis on the AA3. High sensitivity automated and manual methods have been developed for nanomolar concentration levels. Automated nanomolar analyses of ammonium, urea, and nitrite, are performed on a hybrid instrument system. SEAL Analytical AA3 pumps and manifolds are coupled with a 2 m LWCC for nanomolar concentration detection. For more information and to see data of ammonium, urea, and nitrite distribution at Station ALOHA, please see Poster #2441.

Practical MAGICAdd

NaOH (1 N)2.5% v/v

Centrifuge @ 1000xg,

60’, RT

Remove supernatant

Add acid(0.2 N HCl)

Add reagentsAs red

Mo-mix

Developcolor

triplicate 50 ml subsamples

Inve

rt to

mix

supernatant

pellet

Vortex todissolve pellet

Read on spectrophotometer

Abs 880 nm

pH up;Mg(OH)2 floc

forms

Auto Analyzer Nutrients: The SEAL Analytical AA3 is used for the analysis of full ocean depth nutrient profiles. The chemistries used for Nitrate + Nitrite, Soluble Reactive Phosphorus, and Reactive Silicate are based on Strickland and Parsons (1972). The AA3 manifold is configured for either full ocean depth analyses (0-4800 m: Figure 1) or for upper ocean (0-200 m: Figure 3) nutrient analysis. Detection limits for both configurations of analyses are shown in Table 1.

Figure 1. Full ocean depth profiles of a. Nitrate + Nitrite, b. Soluble Reactive Phosphorus, and c. Reactive Silicate at Station ALOHA.

Reference Materials: To evaluate the analytical reproducibility of nutrient measurements, HOT relies on routine use of reference materials. Two independent reference materials are used for each nutrient channel and analysis run to validate analytical performance. The OSIL Nutrient Standard Solutions are commercially prepared in deionized water and are diluted into low nutrient seawater for analysis. The Wako CSK’s are commercially prepared in NaCl (30.5‰) and are analyzed without manipulation. Quality control charts for each reference material used can be seen in Figure 5. We have observed that the PO4 Wako CSK returns an ~7% lower than expected value, similar to what has been reported by Yuzuru et al. (2001). Hence, we also rely on the OSIL Nutrient Standard Solutions as secondary checks in all analyses.

c. e.

b. d. f.

Figure 5.a-f. Quality Control Charts for WAKO and OSIL reference materials. a. Wako - 40.0 μM in NaCl:30.5‰, measured directly. b. OSIL - 1000 μM stock in DIW, diluted

in LNSW to be 40 μM. c. Wako - 2.0 μM in NaCl:30.5‰,

measured directly. Literature shows value of CSK can be up to ~7% low return, so concentration of ~1.8 µM is acceptable.

d. OSIL - 100 μM stock in DIW, diluted in LNSW to be 2 μM.

e. Wako - 100.0 μM in NaCl:30.5‰, measured directly.

f. OSIL - 1000 μM stock in DIW, diluted in LNSW to be 100 μM.

a.

Mean (± stdev, n=267) is 100.215 ± 0.509 μM

Mean (± stdev, n=150) is 1.889 ± 0.031 μM

Mean (± stdev, n=351) is 1.985 ± 0.022 µM

Mean (± stdev, n=288) is 39.880 ± 0.300 μM

Mean (± stdev, n=143) is 39.855 ± 0.277 μM Mean (± stdev, n=166) is 100.469 ± 0.754 μM

Figure 3.a. Upper ocean depth profile of MAGIC-SRP (µM; 0-200 m; mean ± se; n=40). 3.b. Upper ocean depth profile of N+N (nM; 0-200 m; mean ± se; n=40).

3.a. 3.b.

4.a.

4.b.

4.c.

References: Cox, R. D. 1980. Determination of nitrate at the parts per billion level by chemiluminescence. Analytical Chemistry, 52, 332-335. Dore, J.E. and Karl, D.M., 1996. Nitrite distributions and dynamics at Station ALOHA. Deep Sea Research. Part 2 43: 385-402. Garside, C. 1982. A chemiluminescent technique for the determination of nanomolar concentrations of nitrate and nitrite in seawater. Marine Chemistry, 11, 159-167. Karl, D. M. and G. Tien. 1992. MAGIC: A sensitive and precise method for measuring dissolved phosphorus in aquatic environments. Limnology and Oceanography 37: 105-116. Strickland, J.D.H. and T.R. Parsons. 1972. A Practical Handbook of Seawater Analysis. Fisheries Research Board of Canada. Yuzuru, N., Hideaki, S., Takashi, N., Hiroshi, H., Yoshitaka, Y. 2001. Analytical Studies of Standard Solution for Nutrients in the Ocean. Journal of the Faculty of Science and Technology, Kinki University, 37, 37-40.

4.d.

µmol

P m

-2

1.a. 1.b. 1.c.

Corresponding author: curless@hawaii.edu