ABSTRACT 1296 | POSTER 222

IMPACTS OF MARINE HEATWAVES ON PHYTOPLANKTON COMMUNITY DYNAMICS AND SURFACE CO₂ EXCHANGE IN THE NORTH PACIFIC

Changes in marine environments caused by global warming can significantly affect the carbon cycle by altering the abundance, community structure, and productivity of phytoplankton, the main primary producers. In the North Pacific, which is considered one of the world’s largest biological carbon dioxide (CO₂) sinks, there has also been growing concern in recent years about the frequent, prolonged, and widespread occurrence of marine heatwaves (MHWs). Therefore, understanding how MHWs alter phytoplankton communities and the CO₂ exchange between the atmosphere and the ocean has become an urgent issue. In this study, we conducted in situ observations using a merchant vessel in the North Pacific from 2014 to evaluate the impact of MHWs on the partial pressure of seawater CO₂ (pCO₂) and phytoplankton dynamics, including their photosynthetic activity measured with active chlorophyll fluorometry. By analyzing seawater samples associated with MHWs, we found that the concentrations of chlorophyll a, nitrate + nitrite, and silicic acid were significantly lower in the mid-latitudes of the eastern North Pacific during a strong spring MHW event. We successfully developed the world’s first in situ dataset that simultaneously captures seasonal variations in seawater pCO₂ and phytoplankton photosynthetic activity in the North Pacific related to MHWs.

Shintaro Takao, National Institute for Environmental Studies, [email protected], https://orcid.org/0000-0002-0118-6447

Koji Suzuki, Hokkaido University, [email protected], https://orcid.org/0000-0001-5354-1044

Toru Hirawake, National Institute of Polar Research, [email protected], https://orcid.org/0000-0003-0274-6642

Shin-Ichiro Nakaoka, National Institute for Environmental Studies, [email protected], https://orcid.org/0000-0002-3870-1721

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