Abstract
Continuous time series observations of seawater carbon dioxide partial pressure ( p CO 2 ) are crucial for documenting temporal variations in air-sea CO 2 fluxes. To examine the seawater p CO 2 variation and its influence factors at Qingdao coastal waters, a high-resolution observation of seawater p CO 2 near the Xiaomaidao Island was conducted from May 29 to July 25 in 2024. Sea surface p CO 2 varied from 519 µatm to 717 µatm during this monitoring period, with an obvious decline and rise from July 12 to 21. The variation of seawater p CO 2 was mainly affected by the increasing sea surface temperature, except for the period of p CO 2 decrease which was caused by Ulva prolifera bloom. Accompanied by the increase of U. prolifera , sea surface p CO 2 decreased to 563 µatm, then the coverage of U. prolifera decreased and sea surface p CO 2 rose to 669 µatm during period of July 12 to 21. The observation site acted as a source for atmospheric CO 2 throughout the monitoring period, with air-sea CO 2 flux ranging from less than 1 mmol m -2 d -1 to over 100 mmol m -2 d -1 , resulting in a total CO 2 release of 334 mmol m -2 . Thus, it is essential for high-resolution measurement of p CO 2 in coastal areas.