SEASONAL AND INTERANNUAL VARIABILITY IN PRIMARY PRODUCTION AND PARTICLE-FLUX AT STATION ALOHA

A 5-year time-series study of primary production and euphotic-zone par ticle export in the subtropical North Pacific Ocean near Hawaii (Sta. ALOHA, 22 degrees 45'N, 158 degrees W) with measurements collected at approximately monthly intervals has revealed significant variability i n both ecosystem processes. Depth-integrated (0-200 m) primary product ion averaged 463 mg C m(-2) day(-1) (s = 156, n = 54) or 14.1 mol C m( -2) year(-1). This mean value is greater than estimates for the North Pacific Ocean gyre made prior to 1984, but conforms to data obtained s ince the advent of trace metal-clean techniques. Daily rates of primar y productivity at Sta. ALOHA exhibited interannual variability includi ng a nearly 3-year sustained increase during the period 1990-1992 that coincided with a prolonged El Nino-Southern Oscillation (ENSO) event. Export production, defined as the particulate carbon (PC) flux measur ed at the 150 m reference depth, also varied considerably during the i nitial 5 years of the ongoing field experiment. The PC flux averaged 2 9 mg C m(-2) day(-1) (s = 11, n = 43) or 0.88 mol C m(-2) year(-1). A 5-fold variation between the minimum and maximum fluxes, measured in a ny given year, was observed. During the first 3 years of this program (1989-1991), a pattern was resolved that included two major export eve nts per annum one centered in late winter and the other in late summer . After 1991, export production exhibited a systematic decrease with t ime during the prolonged ENSO event. When expressed as a percentage of the contemporaneous primary production, PC export ranged from 2 to 16 .9%, with a 5-year mean of 6.7% (s = 3.3, n = 40). Contrary to existin g empirical models, contemporaneous primary production and PC Aux were poorly correlated, and during the ENSO period they exhibited a signif icant inverse correlation. This unexpected decoupling of particle prod uction and flux has numerous implications for oceanic biogeochemical c ycles and for the response of the ocean to environmental perturbations . Copyright (C) 1996 Elsevier Science Ltd