Preprints
https://doi.org/10.5194/bg-2022-9
https://doi.org/10.5194/bg-2022-9

  13 Jan 2022

13 Jan 2022

Review status: this preprint is currently under review for the journal BG.

Observing intermittent biological productivity and vertical carbon transports during the spring transition with BGC Argo floats in the western North Pacific

Chiho Sukigara1, Ryuichiro Inoue2, Kanako Sato2, Yoshihisa Mino3, Takeyoshi Nagai1, Andrea J. Fassbender4,5, Yuichiro Takeshita5, Stuart Bishop6, and Eitarou Oka7 Chiho Sukigara et al.
  • 1Tokyo University of Marine Science and Technology, Tokyo, 1088477, Japan
  • 2Japan Agency for Marine-Earth Science and Technology, Yokosuka, 2370061, Japan
  • 3Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, 4648601, Japan
  • 4NOAA/OAR Pacific Marine Environmental Laboratory, Washington, 98115, USA
  • 5Monterey Bay Aquarium Research Institute, California, 95039, USA
  • 6North Carolina State University, Raleigh, North Carolina, 27695, USA
  • 7Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, 2778564, Japan

Abstract. To investigate changes in ocean structure during the spring transition and responses of biological activity, two BGC-Argo floats equipped with oxygen, fluorescence (to estimate chlorophyll a concentration – Chl a), backscatter (to estimate particulate organic carbon concentration – [POC]), and nitrate sensors conducted daily vertical profiles of the water column from a depth of 2000 m to the sea surface in the western North Pacific from January to April of 2018. Data for calibrating each sensor were obtained via shipboard sampling that occurred when the floats were deployed and recovered. During the float-deployment periods, repeated meteorological disturbances passed over the study area and caused the mixed layer to deepen. After deep-mixing events, the upper layer restratified and nitrate concentrations decreased while Chl a and POC concentrations increased, suggesting that spring mixing events promote primary productivity through the temporary alleviation of nutrient and light limitation. At the end of March, POC accumulation rates and nitrate decrease rates within the euphotic zone (0–70 m) were the largest of the four events observed, ranging from +84 to +210 mmol C m−2 d−1 and –28 to –49 mmol N m−2 d−1, respectively. The subsurface consumption rate of oxygen (i.e., the degradation rate of organic matter) after the fourth event (the end of March) was estimated to be –0.62 micromol O2 kg−1 d−1. At depths of 300–400 m (below the mixed layer), the POC concentrations increased slightly throughout the observation period. The POC flux at a depth of 300 m was estimated to be 1.1 mmol C m−2 d−1. Our float observation has made it possible to observed biogeochemical parameters, which previously could only be estimated by shipboard observation and experiments, in the field and in real time.

Chiho Sukigara et al.

Status: open (until 24 Feb 2022)

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Chiho Sukigara et al.

Chiho Sukigara et al.

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Short summary
To investigate the physical changes in the ocean from winter to spring and the corresponding biological activities, two automated floats were used to conduct observations in the western North Pacific from January to April 2018. During the observation, repeated storms passed and mixed the ocean surface layer. Afterwards, active biological activity was observed. Using data from the float, we observed the formation, decomposition, and settling of particulate organic matter.
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