Airborne Lidar Measurements of Ice and Phytoplankton in the Arctic Ocean

Nathan Marshall, Stanford, CA, United States and James H Churnside, NOAA Boulder, Boulder, CO, United States
As Arctic sea ice breaks up earlier, declines in extent, and moves more rapidly, it affects phytoplankton distribution and abundance. Satellite measurements of surface chlorophyll cannot measure vertically integrated phytoplankton abundance, which is important for understanding carbon sequestration rates and fisheries recruitment. However, airborne lidar can penetrate at least 10 meters into the ocean and can be used to determine both sea ice fraction and chlorophyll concentration. In late May 2019, airborne lidar was flown over the Beaufort and Chukchi Seas surrounding Utqiagvik, Alaska, taking vertical optical backscattering profiles to study the relationship between sea ice and phytoplankton. This study followed similar lidar deployments in July 2014 and 2017. Though the 2019 study occurred two months earlier than the prior studies, the Chukchi Sea May sea ice extent was comparable to the July sea ice extent from previous years. However, instead of intense subsurface plankton layers, as the lidar found in 2014 and 2017, there was an exceptionally high concentration of chlorophyll dispersed evenly throughout the water column in May 2019. Chlorophyll concentration decreased with distance from ice and increased closer to the Alaskan coast, but pockets of high chlorophyll concentration were detected even near and amongst pack ice. Primary productivity was calculated from chlorophyll using published models. As Chukchi Sea ice continues to decrease, we expect primary productivity to continue increasing. This has major implications for carbon transfer to the deep ocean, the rate of secondary production, and the viability of commercial fisheries. Amid astonishingly rapid changes in sea ice, it is critical to continue monitoring the Arctic’s increasing primary productivity and studying the consequences of this change.