Hawaii Ocean Time-series (HOT)
in the School of Ocean and Earth Science and Technology at the University of Hawai'i at Manoa
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Primary Production

Primary Production array
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To assist in the interpretation of the data, it can be displayed using the Hawaii Ocean Time-series Data Organization & Graphical System (HOT-DOGS©).

Sampling Procedure

Photosynthetic production of organic matter was measured by the 14C tracer method. All incubations from 1990 through mid-2000 were conducted in situ at eight depths (5, 25, 45, 75, 100, 125, 150 and 175m) over one daylight period using a free-drifting array as described by Winn et al. (1991). From HOT-119 to HOT-319 (October 2000 - January 2020), we collected samples from only the upper six depths & modeled the lower two depths based on the monthly climatology. During 2022, all incubations were conducted in situ on a free floating, surface tethered array. Integrated carbon assimilation rates were calculated using the trapezoid rule with the shallowest value extended to 0 meters and the deepest extrapolated to a value of zero at 200 meters.


Cruise Incident
Irradiance 		Pigments
(mg m-2) 		Incubation
Duration 		Light Assimilation
Rates
(E m-2 d-1) Chl a Pheo (hrs) (mg C m-2 d-1)
335 47.60 22.6 41.7 15.00 590
336 50.59 18.0 27.7 15.25 653
337 46.84 31.4 53.8 15.00 NA
338 53.48 24.8 43.0 15.75 639
339 47.00 22.6 47.9 15.00 NA

Results

The depth-integrated (0-200m) results of the 14C incubations and pigment determinations for samples collected from CTD casts in 2022 are presented in the Table above. Also included for each cruise is the incubation duration and the total incident irradiance (400-700 nm) measured on the deck of the ship during the incubation period. Integrated primary production rates measured over all 34 years of the program are shown in Figure 54. A contour plot is shown in Figure 55. Depth-integrated rates of primary production vary seasonally, with summer maxima and winter minima. Overall, primary production varies by approximately a factor of five, ranging from ~200 to 1000 mg C/m2/d. The mean (± sd) depth integrated primary production for the entire 34 year data set is 537 ± 135 mg C/m2/d. Although this value is higher than historical measurements for the oceanic central gyres (Ryther 1969), it is consistent with more recent measurements (Martin et al. 1987; Laws et al. 1989; Knauer et al. 1990).