Station ALOHA

Karl, D.M., J.R. Christian, J.E. Dore, D.V. Hebei, R.M. Letelier, L.M. Tupas, and C.D. Winn. 1996. Seasonal and interannual variability in primary production and particle flux at Station ALOHA. Deep-Sea Research II 43 1270-1286. 

Depth profiles of Ne, N2, Ar, Kr, and Xe supersaturations (in %) measured at station ALOHA (22°45 N 158°W) in August 2004. Station ALOHA is located in the central region of fhe North Pacific Subtropical Gyre, about 100 km north of Oahu. Equilibrium with the atmosphere is indicated by the vertical line at 0%. Points indicate individual samples while the lines are the average of duplicates. Source After Hamme, R. C., and J. P. Severinghaus (2007). Deep Sea Research Part I Oceanographic Research Papers 54, 939-950. 

Station ALOHA (see Figure 23.4 for location information). Three-point running mean observations of N/P molar ratios in (a) total dissolved inorganic plus organic pool, (b) total suspended particulate matter in the upper 0-100 m, (c) in exported particulate matter at 150 m depth, and (d) cycling in nutrient limitation (described in text). Source From Karl, D. M. (2002). Trends in Microbiology 10(9), 410-418. 

Figure 11.2. Normalized vertical profile of the concentrations of DOC, DON, and DOP at Station ALOHA.

The average molar C/N ratio (over all depths) for the HOT data set from Station ALOHA is 16.4 2.5. From the compilation of Bronk (2002), the average molar... 

Sannigrahi, P., Ingall, E. D., and Benner, R. (2005). Cycling of dissolved and particulate organic matter at station Aloha Insights from 13C NMR spectroscopy coupled with elemental, isotopic and molecular analyses. Deep-Sea Res. 152,1429-1444. 

Landry, M.R., Al-Mutairi, H., Selph, K.E., Christensen, S., and Nunnery, S., Seasonal patterns of mesozooplankton abundance and biomass at Station ALOHA, Deep Sea Res. II, in press. 

Karl, D.M., Tien, G., Dore, J., and Winn, C.D. (1993) Total dissolved nitrogen and phosphorus concentrations at United States-JGOFS station ALOHA—Redefield reconciliation. Mar. Chem. 41, 203-208. 

Several reports in varied locations have now provided quantification of N input in the small size fraction of the plankton. Montoya ei a/. (2004) found highly variable but at times, extremely high, rates of N2 fixation in studies in the sub-tropical N. Pacific and along the north coast of Australia (Tables 4.4 and 4.5). Average rates (excluding one extreme value) for 10 stations on the North Pacific transect north of the Hawaiian Islands were about 520 pmol N m day. Curiously, rates were considerably and consistently lower at station ALOHA in the vicinity of the Hawaiian Islands. This was also concordant with an earlier study (Dore et al., 2002) and another recent effort that employed plankton concentrates (Falc6n et al., 2004). 

Station ALOHA Tricho Cyano 4 7 Marine Church et at., 2004... 

Karl, D. M., et al. (2001b). Ecological nitrogen-to-phosphorus stoichiometry at station ALOHA. Deep Sea Res. II. 48(8-9), 1529-1566. 

Scharek, R., Tupas, L. M., and Karl, D. M. (1999b). Diatom fluxes to the deep sea in the oligotrophic North Pacific gyre at Station ALOHA. Mar. Ecol. Prog. Ser. 182, 55-67. 

Dore,. E., and Karl, D. M. (1996). Nitrification in the euphoric zone as a source for nitrite, nitrate, and nitrous oxide at station ALOHA. Limnology and Oceanography 41, 1619—1628. 

Al-Mutairi, H., and Landry, M. R. (2001). Active export of carbon and nitrogen at Station ALOHA by diel migrant zoooplankton. Deep Sea Res. II48, 2083—2103. 

Figure l6.6 Representative upper ocean profile of NO3, DON and PON at Station ALOHA based on 17-year time-series observations. Note accumulation of reduced N, especially DON in near-surface and decreases with depth. In the near-surface waters at Station ALOHA, DON accounts for nearly 95 % of the total fixed N inventory. 

Figure 16.7 Seasonal and interannual variations in NOs concentrations at Station ALOHA. Shown are (A) the 16-year data set on NOs (nM) in the upper 200 m as well as the summer vs. winter climatologies. Note the log scale in both graphs. (B) integrated (0-100 m) inventories of NO3 showing aperiodic irgections of NO3 into the upper euphotic zone. Note the lower graph presents the data on a log scale to emphasize the extreme temporal variability in N03 inventory which exceeds a factor of300 over the 16-year observation period,...

The concentrations and dynamics of the near-surface DON and PON pools have been studied at Station ALOHA since 1988. Church et al (2002) reported that the 0—175 m dissolved organic C (DOC) and DON (but not dissolved organic P) increased at rates of 303 and 33 mmol m year respectively, for the period 1993—1999. The accumulated DOM had a mean C N molar ratio of 27.5. By comparison, the C N ratio of isolated HMW-DOM in the North Pacific trades biome is 14—15, suggesting that the highly aged (based on C content) LMW-DOM is more carbon rich (Loh et al, 2004). However, the true C N ratio of the DON pool (as opposed to bulk DOM) is neither known nor easily determined because the DOC and DOC-N, DOC-N-P and DOC-P sub-pools cannot currently be separated. For example, the N content of HMW-DOM isolated from Station ALOHA varied between 0.95 and 1.69 wt% with no clear depth trends between 20 and 4000 m molecular analyses identified carbohydrate and amino acids as major compound classes (Sannigrahi et al, 2005). 

Figure 16.10 (A) Nitrous oxide (N2O) concentrations and isotopic composition for water samples collected at Station ALOHA. [Left] Depth profile of N2O showing a distinct mid-depth maximum of 60 nM coincident with the dissolved oxygen minimum. [Center] N isotope composition of N2O. [Right] 0 isotope composition of N2O. Data from Dore et al. (1998) and B. Popp and J. Dore (unpublished). (B) N2O saturation state, expressed as a percentage of air saturation, for the upper portion of the water column at Station ALOHA during the period September 1992— September 1994. The vertical dashed line indicates equilibrium (100% saturation) with atmospheric N2O. With the exception of one measured value on cruise HOT-45, all determinations indicate significant N2O saturation relative to the atmosphere which implies both a local source and a net ocean-to-air gas flux.From Dore and Karl (1996a).

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