Ja-Myung Kim1, Kitack Lee1*, Miok Kim1, Ju-Hyoung Kim2, HyunKyum Kim3, and Byung Hee Jeon3
1Division of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, Korea
2College of Ocean Science and Engineering, Kunsan National University, Gunsan 54150, Korea
3Ecological Restoration Division, Korea Fisheries Resources Agency, Busan 46041, Korea
Ocean biological activity tends to shift the dynamics of surface pCO2 from effects primarily controlled by changes in the sea surface temperature (thermodynamic cause). The biological activity in a macroalgal habitat of coastal Korea contributed 4.4 g C m–2 month–1 of the net C uptake during the growing period (the cooling period, September-May), and changed the thermodynamic-induced seasonal dynamics such that the air-sea equilibrium of pCO2 was impeded by the increased magnitude of disequilibrium. The surface pCO2 dynamics during the cooling period was significantly affected 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 from the thermodynamic drivers (i.e., changes in sea surface temperature). In contrast to the phytoplankton-dominated off-shore waters, in which phytoplankton populations are typically 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 thermal-driven changes. Moreover, the distinctive features of the nearshore vegetated habitat—large seasonal temperature extremes (~18oC), massive anthropogenic nutrient inputs, and active macroalgal metabolisms—intensified the seasonal decoupling of seawater and air pCO2 dynamics.