Data for continuous and discrete measurements of carbonate parameters in a productive coastal region in the Northwestern Pacific (36°09'13.5''N, 129°24'04.9''E) from January to September in 2019 and from March to December in 2020

Photosynthetic organisms shift the dynamics of surface pCO2 driven by the
sea surface temperature change (thermodynamic driver) by assimilating C
from seawater. Here we measured net C uptake in a macroalgal habitat of
coastal Korea for two years (2019–2020) and found that the macroalgal
habitat contributed 5.8 g C m-2 month-1 of the net C uptake during the
growing period (the cooling period, September-May). This massive C uptake
changed the thermodynamics-driven seasonal dynamics such that the air-sea
equilibrium of pCO2 was pushed into disequilibrium. The surface pCO2
dynamics during the cooling period were mostly influenced by the seasonal
decrease in temperature and the proliferation of macroalgae, while the
dynamics during the warming period (the stagnant period, June-August)
closely followed that predicted based solely on the change in sea surface
temperature only (thermodynamic driver). In contrast to the
phytoplankton-dominated offshore waters (where phytoplankton populations
are large in spring and summer), the impact of coastal water macroalgae on
surface pCO2 dynamics was most pronounced during the cooling period, when
the magnitude of pCO2 change was as much as twice that resulting from
temperature change. Our study shows that the distinctive features of the
macroalgal habitat—in particular the seasonal temperature extremes (~18°C
difference), the active macroalgal metabolism, and anthropogenic nutrient
inputs—collectively influenced the seasonal decoupling of seawater and air
pCO2 dynamics.