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- Title
Effects of Biological Production and Vertical Mixing on Sea Surface pCO<sub>2</sub> Variations in the Changjiang River Plume During Early Autumn: A Buoy‐Based Time Series Study.
- Authors
Li, Dewang; Chen, Jianfang; Ni, Xiaobo; Wang, Kui; Zeng, Dingyong; Wang, Bin; Jin, Haiyan; Huang, Daji; Cai, Wei‐Jun
- Abstract
A monthlong, high‐resolution buoy time series from the surface ocean of the Changjiang River plume in early autumn 2013 (30‐min sampling frequency) shows great variability in the partial pressure of carbon dioxide (pCO2) and other physical and biogeochemical parameters. Early in the deployment, surface pCO2 decreased by ~117 μatm in a single day (11–12 September, from an initial value of ~527 μatm); a similar decline of 62 μatm occurred five days later (to ~378 μatm). Both drawdown events were associated with strong vertical stratification, high chlorophyll a concentrations, and oxygen supersaturation. A one‐dimensional mass balance model suggests that biological production was responsible for more than half the pCO2 decrease observed during 10–23 September. Subsequently, in association with strong winds, the mixed layer rapidly deepened and surface pCO2 increased sharply (by about 108 μatm in late September and again in early October). Vertical mixing accounted for more than half of this pCO2 increase, which offset more than the earlier biologically driven CO2 drawdown. In the presence of such strong temporal variations of pCO2, sampling frequency exerts a substantial influence on air‐sea CO2 flux calculations for the Changjiang River plume and similar coastal areas. Compared to daily sampling, even weekly sampling would result in a bias of up to ±4.7 mmol C · m−2 · day−1 or ±63% error. Key Points: A 31‐day high‐resolution buoy time series from the Changjiang River plume shows large temporal variations of sea surface pCO2 and other biogeochemical parametersIn early autumn, the dominant process regulating sea surface pCO2 in the river plume shifted from biological production to vertical mixingSampling frequency exerts a substantial influence on air‐sea CO2 flux calculations for the Changjiang plume and similarly variable coastal sites Plain Language Summary: Determining the mechanisms that control sea surface pCO2 and its variability in coastal waters is an important step toward estimating global air‐sea CO2 fluxes and projecting future atmospheric CO2 levels. In this study, a 31‐day high‐resolution buoy time series from the surface ocean of the Changjiang River plume in early autumn 2013 show great variability in the partial pressure of carbon dioxide (pCO2) and other parameters. Early in the deployment, surface pCO2 decreased sharply in short period (one to five days). The pCO2 drawdown events were associated with strong vertical stratification, high chlorophyll a concentrations, and oxygen supersaturation. A mass balance model suggests that biological production was responsible for more than half the pCO2 decrease observed. Subsequently, in association with strong northeast winds, the mixed layer rapidly deepened and surface pCO2 increased sharply. Vertical mixing accounted for more than half of this pCO2 increase. In the presence of such strong temporal variations of pCO2, sampling frequency exerts a substantial influence on air‐sea CO2 flux calculations for the Changjiang River plume and similar coastal areas.
- Subjects
OCEAN; BIOGEOCHEMISTRY; CHLOROPHYLL; BODIES of water; GEOCHEMISTRY
- Publication
Journal of Geophysical Research. Oceans, 2018, Vol 123, Issue 9, p6156
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2017JC013740