BGD

Biogeosciences Discussions

BGD

Biogeosciences Discuss.

1810-6285

Göttingen, Germany

10.5194/bg-2022-9

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

Sukigara

Chiho

¹ Inoue

Ryuichiro

² Sato

Kanako

² Mino

Yoshihisa

³ Nagai

Takeyoshi

¹ Fassbender

Andrea J.

https://orcid.org/0000-0002-5898-1185

⁴ ⁵ Takeshita

Yuichiro

⁵ Bishop

Stuart

⁶ Oka

Eitarou

⁷

Tokyo University of Marine Science and Technology, Tokyo, 1088477, Japan

Japan Agency for Marine-Earth Science and Technology, Yokosuka, 2370061, Japan

Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, 4648601, Japan

NOAA/OAR Pacific Marine Environmental Laboratory, Washington, 98115, USA

Monterey Bay Aquarium Research Institute, California, 95039, USA

North Carolina State University, Raleigh, North Carolina, 27695, USA

Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, 2778564, Japan

Japan Society for the Promotion of Science

JP15H05818

JP15K21710

JP16H01590

JP18H04914

JP19H01965

JP20K20634

13 01 2022

2022 1 52

2022

This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/

This article is available from https://bg.copernicus.org/preprints/bg-2022-9/

The full text article is available as a PDF file from https://bg.copernicus.org/preprints/bg-2022-9/bg-2022-9.pdf

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.