Carbon Air–Sea Flux in the Arctic Ocean from CALIPSO from 2007 to 2020

• Published in: Remote Sensing
• Main Authors: Siqi Zhang, Peng Chen, Zhenhua Zhang, Delu Pan
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: diurnal variation; air–sea carbon flux; CALIPSO; LiDAR; remote sensing; Science; Q; Arctic; Arctic Ocean; Pacific; Atlantic Arctic; Atlantic-Arctic; Phytoplankton; Sea ice
• Online Access: https://doi.org/10.3390/rs14246196; https://doaj.org/article/ef6fe73821594603918a54e07332aa2c

Quantified research on the Arctic Ocean carbon system is poorly understood, limited by the scarce available data. Measuring the associated phytoplankton responses to air–sea CO 2 fluxes is challenging using traditional satellite passive ocean color measurements due to low solar elevation angles. We constructed a feedforward neural network light detection and ranging (LiDAR; FNN-LID) method to assess the Arctic diurnal partial pressure of carbon dioxide ( p CO 2 ) and formed a dataset of long-time-series variations in diurnal air–sea CO 2 fluxes from 2001 to 2020; this study represents the first time spaceborne LiDAR data were employed in research on the Arctic air–sea carbon cycle, thus providing enlarged data coverage and diurnal p CO 2 variations. Although some models replace Arctic winter Chl- a with the climatological average or interpolated Chl- a values, applying these statistical Chl- a values results in potential errors in the gap-filled wintertime p CO 2 maps. The CALIPSO measurements obtained through active LiDAR sensing are not limited by solar radiation and can thus provide ‘fill-in’ data in the late autumn to early spring seasons, when ocean color sensors cannot record data; thus, we constructed the first complete record of polar p CO 2 . We obtained Arctic FFN-LID-fitted in situ measurements with an overall mean R 2 of 0.75 and an average RMSE of 24.59 µatm and filled the wintertime observational gaps, thereby indicating that surface water p CO 2 is higher in winter than in summer. The Arctic Ocean net CO 2 sink has seasonal sources from some continental shelves. The growth rate of Arctic seawater p CO 2 is becoming larger and more remarkable in sectors with significant sea ice retreat. The combination of sea surface partial pressure and wind speed impacts the diurnal carbon air–sea flux variability, which results in important differences between the Pacific and Atlantic Arctic Ocean. Our results show that the diurnal carbon sink is larger than the nocturnal carbon sink in the Atlantic Arctic ...