Abstract
Abstract. Oceanic primary production forms the basis of the marine food web and provides a pathway for carbon sequestration. Despite its importance, spatial and temporal variations of primary production are poorly observed, in large part because the traditional measurement techniques are laborious and require the presence of a ship. More efficient methods are emerging that take advantage of miniaturized sensors integrated into autonomous platforms such as gliders and profiling floats. One such method relies on determining the diurnal cycle of dissolved oxygen in the mixed layer and has been applied successfully to measurements from gliders and mixed-layer floats. This study is the first documented attempt to estimate primary production from diurnal oxygen changes measured by Argo-type profiling floats, thus accounting for the whole euphotic zone. We first present a novel method for correcting measurement errors that result from the relatively slow response time of the oxygen optode sensor. This correction relies on an in situ determination of the sensor's effective response time. The method is conceptually straightforward and requires only two minor adjustments in current Argo data transmission protocols: (1) transmission of measurement time stamps and (2) occasional transmission of downcasts in addition to upcasts. Next, we present oxygen profiles collected by 10 profiling floats in the northern Gulf of Mexico, evaluate whether community production and respiration can be detected, and show evidence of internal oscillations influencing the diurnal oxygen signal. Our results show that profiling floats are capable of measuring diurnal oxygen variations although the confounding influence of physical processes does not permit a reliable estimation of biological rates in our dataset. We offer suggestions for recognizing and removing the confounding signals.
Highlights
Oceanic primary production forms the basis of the oceanic food web and is a major component of the global carbon cycle by providing a pathway for carbon sequestration in the ocean interior
In the Introduction, we posed two sets of questions relevant for the estimating of NCP and R from the diurnal oxygen cycle measured by continuously profiling autonomous floats
Addressing the first led to the development of a novel method for determining the effective in situ time constant of an oxygen optode deployed on a profiling float, without needing to characterize the physical flow around that sensor
Summary
Oceanic primary production forms the basis of the oceanic food web and is a major component of the global carbon cycle by providing a pathway for carbon sequestration in the ocean interior. Primary production is intrinsic to understanding biogeochemical dynamics in the ocean, its temporal and spatial variations are not well observed It has been estimated by performing 12 to 24 h bottle incubations using 14C (Steeman-Nielsen, 1952; Marra, 2009). Satellites estimate production on the global scale but rely on assumptions about the photosynthesis–irradiance relationship, the vertical structure of biomass, and global regressions of observed productivity with sea surface temperature, all with inherent limitations. Both of the above methods quantify net primary production (NPP), defined as the total rate of photosynthetically fixed carbon minus autotrophic respiration. The balance between GPP and R is referred to as net com-
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