Polar oceans are crucial in the global carbon cycle, and sea ice melt significantly modulates the variation characteristics of surface seawater CO₂ partial pressure (pCO₂). During the melt season, pCO₂ fluctuations exhibit complex patterns under the synergistic effects of thermodynamics (temperature), air–sea gas exchange, vertical mixing, and biological activity. Moreover, the pronounced time lags among these different mechanisms lead to a non‑instantaneous response of pCO₂ to changing sea ice conditions, manifesting instead as a phased evolution. To date, studies on how high‑frequency (daily‑scale) events, such as sea ice ablation and marginal ice‑zone algal blooms, affect pCO₂ remain insufficient. Leveraging high‑temporal‑resolution satellite remote sensing and continuous underway observations to systematically elucidate the underlying mechanisms by which polar sea surface pCO₂ is influenced by such high‑frequency events is therefore of great significance for accurately assessing the trajectory of the Arctic carbon sink under rapid environmental change.
This study integrates multi‑source satellite remote sensing data, and extensive underway pCO₂ measurements from 2003 to 2024 to examine the dynamic evolution of pCO₂ in the high‑latitude ice‑covered Arctic Ocean. We define the Melt Onset Date (MOD) for each grid cell as the date when the sea ice concentration (SIC) first drops below specified thresholds (0.15, 0.25, 0.40, and 0.50) in a given year. The time interval between the field observation date and the MOD is defined as InMOD (observation date minus MOD), which quantifies the temporal phase of the data collection relative to the onset of sea ice melt.
Taking the Beaufort Sea, a marginal sea of the Arctic Ocean, as a typical study area, our preliminary results show that when the SIC threshold is 0.15 and InMOD ∈ (−50, 0) (i.e., observations precede melt onset), the sea ice has not yet retreated, and strong photosynthetic carbon fixation by under‑ice ice algae keeps pCO₂ below 300 μatm. In contrast, when InMOD ∈ (0, 50), pCO₂ exhibits a sustained increasing trend, coinciding with enhanced warming and air–sea gas exchange, which dominate the pCO₂ rise. Overall, during the ice‑covered period, biological processes primarily govern pCO₂ variability and maintain low values, whereas after ice retreat, physical processes gradually become dominant and drive pCO₂ upward. These findings provide important insights into the dynamic evolution and future trajectory of the polar ocean carbon sink.