Research ReportDiurnal global ocean surface p CO 2 and air-sea CO 2 flux reconstructed from spaceborne LiDAR data.

The ocean absorbs a significant amount of carbon dioxide (CO 2 ) from the atmosphere, helping regulate Earth's climate. However, our knowledge of ocean CO 2 sink levels remains limited. This research focused on assessing daily changes in ocean CO 2 sink levels and air-sea CO 2 exchange, using a new technique. We used LiDAR technology, which provides continuous measurements during day and night, to estimate global ocean CO 2 absorption over 23 years. Our model successfully reproduced sea surface partial pressure of CO 2 data. The results suggest the total amount of CO 2 absorbed by oceans is higher at night than during the day. This difference arises from a combination of factors like temperatures, winds, photosynthesis, and respiration. Understanding these daily fluctuations can improve predictions of ocean CO 2 uptake. It may also help explain why current carbon budget calculations are not fully balanced-an issue scientists have grappled with. Overall, this pioneering study highlights the value of LiDAR's unique day-night ocean data coverage. The findings advance knowledge of ocean carbon cycles and their role in climate regulation. They underscore the need to incorporate day-night variability when assessing the ocean's carbon sink capacity.