Quantifying subtropical North Pacific gyre mixed layer primary productivity from Seaglider observations of diel oxygen cycles

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 4032–4039, doi:10.1002/2015GL063065.
Using autonomous underwater gliders, we quantified diurnal periodicity in dissolved oxygen, chlorophyll, and temperature in the subtropical North Pacific near the Hawaii Ocean Time-series (HOT) Station ALOHA during summer 2012. Oxygen optodes provided sufficient stability and precision to quantify diel cycles of average amplitude of 0.6 µmol kg−1. A theoretical diel curve was fit to daily observations to infer an average mixed layer gross primary productivity (GPP) of 1.8 mmol O2 m−3 d−1. Cumulative net community production (NCP) over 110 days was 500 mmol O2 m−2 for the mixed layer, which averaged 57 m in depth. Both GPP and NCP estimates indicated a significant period of below-average productivity at Station ALOHA in 2012, an observation confirmed by 14C productivity incubations and O2/Ar ratios. Given our success in an oligotrophic gyre where biological signals are small, our diel GPP approach holds promise for remote characterization of productivity across the spectrum of marine environments.
The authors acknowledge support from the National Science Foundation (NSF) through an NSF Science and Technology Center, the Center for Microbial Oceanography Research and Education (C-MORE; NSF EF-0424599). D.N. also was supported by NSF (OCE-1129644) and an Independent Study Award from the Woods Hole Oceanographic Institution (WHOI). D.M.K. was also supported by the Gordon and Betty Moore Foundation. WHOI Summer Student Fellow Cole Stites-Clayton, Stanford University, contributed to early stages of Seaglider data analysis and was supported by an NSF REU grant to WHOI (OCE-1156952).