High‐frequency time‐series autonomous observations of sea surface pCO₂ and pH

Abstract

Carbon dioxide partial pressure (pCO 2) in surface water was continuously measured every 3 h from July 2012 to June 2013 using an autonomous pCO 2 system (MAPCO 2) deployed on a moored buoy on the East China Sea shelf (31 N, 124.5 E). Sea surface pCO 2 and pH had the largest variations in summer, ranging from 215 to 470 μatm, and 7.941 to 8.263 (averagely 8.084 ± 0.080), respectively. They varied little in winter, ranging from 328 to 395 μatm, and 8.003 to 8.074 (averagely 8.052 ± 0.010), respectively. The seasonal average sea surface pCO 2 was respectively 335 ± 70 μatm, 422 ± 43 μatm, 362 ± 11 μatm, and 311 ± 59 μatm in summer, autumn, winter, and spring, and was overall undersaturated with respect to atmosphere on a yearly basis. Although the average sea surface pCO 2 in summer was below the atmospheric level, the net CO 2 flux has suggested a CO 2 source status due to the influence of typhoon. Our observation thus demonstrated the significant, even dominant impact of episodic typhoon events on surface ocean CO 2 chemistry and air-sea CO 2 gas exchange, which would be impossible to capture by shipboard observation. The high wind stress and curl associated with the northward movement of typhoon induced complex sea surface water movement, vertical mixing, and subsequent biological drawdown, which differed in pre-, onset, and post-typhoon stages. Based on our estimates, the degassing fluxes during typhoon reached as high as 82 mmol m −2 CO 2 and 242 mmol m −2 CO 2 in summer and autumn, respectively, accounting for twice as large as the summer CO 2 sink during non-typhoon period, and 28% of the total CO 2 source in autumn.

Variations in Seawater pCO2 Associated With Vertical Mixing During Tropical Cyclone Season in the Northwestern Subtropical Pacific Ocean

“…However, this conclusion may not be valid in other regions. For example, unlike our study area (a subtropical area with a relatively deep nutricline), the East and South China seas showed enhancements in the chlorophyll-a concentration of approximately five times after TC passage (Ye et al, 2013;Wu et al, 2020). This difference may be due to regional variations of the vertical chlorophyll-a and nutrient profiles, and especially due to the shallower nutricline of the shelf regions (the East and South China seas), where NO 3 − concentration is one order of magnitude greater than in our study region at 50 m depth.…”

“…This compensatory effect is welldocumented; however, regional differences in the physical and chemical properties of subsurface water result in large variability in the surface pCO 2 in response to TC passage (Mahadevan et al, 2011;Lévy et al, 2012;Ye et al, 2020). Phytoplankton CO 2 fixation, which is fueled by the supply of subsurface nutrients, is also highly variable in space and time (Lin, 2012;Ye et al, 2013;Wu et al, 2020;Chai et al, 2021;Zhang et al, 2021). Furthermore, the magnitude and direction of air-sea CO 2 flux during and after TC passage strongly depend on pre-storm pCO 2 conditions and the intensities of individual TCs (Lévy et al, 2012).…”

A Portable Tunable Diode Laser Absorption Spectroscopy System for Dissolved CO2 Detection Using a High-Efficiency Headspace Equilibrator

“…The at equilibration temperature ( ) can be expressed in terms of partial pressure in the gas-phase ( ) while under equilibrium state using Equation (2) [ 35 ]: where was the mole fraction in dry air that equilibrated with the water sample and barometric pressure ( ) in the equilibrator after correcting for the vapor pressure ( ) at 100% relative humidity [ 36 ]. The was the function of the amplitude of the 2f-signal ( ).…”

Biological CO2 Uptake and Upwelling Regulate the Air-Sea CO2 Flux in the Changjiang Plume Under South Winds in Summer

“…Similar to the Mississippi River plume, the Changjiang plume is a strong carbon sink in summer due to intense biological production. The biological uptake of CO 2 and the air-sea CO 2 flux in the Changjiang plume have large temporal variations associated with episodic wind events (Li et al, 2018(Li et al, , 2019Wu et al, 2020). Typhoon winds cause Changjiang plume waters to become a strong carbon source through the upward transport of high-CO 2 bottom waters (Li et al, 2019) or cause the waters to become carbon sinks by in situ biological production or the advection of undersaturated-CO 2 waters (Zhang et al, 2018;Wu et al, 2020).…”

“…The biological uptake of CO 2 and the air-sea CO 2 flux in the Changjiang plume have large temporal variations associated with episodic wind events (Li et al, 2018(Li et al, , 2019Wu et al, 2020). Typhoon winds cause Changjiang plume waters to become a strong carbon source through the upward transport of high-CO 2 bottom waters (Li et al, 2019) or cause the waters to become carbon sinks by in situ biological production or the advection of undersaturated-CO 2 waters (Zhang et al, 2018;Wu et al, 2020). Unlike typhoons, southerly or southwesterly winds prevail in summer in the East China Sea and are associated with offshore advection and even the detachment of Changjiang plume waters (Lie et al, 2003;Xuan et al, 2012).…”