Seasonal-to-decadal scale variability in primary production and particulate matter export at Station ALOHA

Station ALOHA (A Long-term Oligotrophic Habitat Assessment) was established in the North Pacific Subtropical Gyre (22°45′N, 158°W) as an oligotrophic ocean benchmark to improve our understanding of processes that govern fluxes carbon (C) into and from surface ocean. At approximately monthly intervals, measurements primary production particulate C (PC) using 14C method, export PC nitrogen (PN) surface-tethered sediment traps deployed at 150 m have been made along with a host complementary physical, biological, biogeochemical measurements. Euphotic zone depth-integrated (0–200 m) ranged 220.2 (standard deviation, SD, 10.8) mg m−2 d−1 Feb 2018 1136.5 (SD = 17.1) Jun 2000, 30-yr (1989–2018) mean 536.8 135.0) (n 271). Although climatology fairly well constrained, we observed substantial sub-decadal variability significant 0–125 increasing trend 4.0 (p < 0.01; 95% confidence interval, CI, 2.1–5.9) (mg d−1) yr−1 since 1989, displaying large relative increase 37% (CI 18–55%) lower portion (75–125 euphotic zone. Chlorophyll (Chl) suspended PN concentrations also displayed 0.01) increases 75–125 region exhibited both short-term (monthly) longer-scale 27.9 9.7, n 265) d−1. extended, multi-year periods significantly or higher values compared mean. These anomalously low high particle export, absence contemporaneous variations production, probably reflect periodic changes remineralization efficiencies. The ratio (e-ratio; ÷ 0–150 14C-based production) low, 0.054 0.021, 248), long-term decreasing over observation period. (~37%), Chl a, (~17%, 8%, respectively) water column are hypothesized result enhanced supply nutrients past three decades.