Estimating underwater light regime under spatially heterogeneous sea ice in the Arctic

• Published in: Applied Sciences
• Main Authors: Massicotte, Philippe, Babin, Marcel, Bécu, Guislain, Lambert Girard, Simon, Leymarie, Edouard
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: geo; envir; Arctic; Arctique*; ice pack; Phytoplankton; Sea ice
• Online Access: https://hdl.handle.net/20.500.11794/34896; https://doi.org/10.3390/app8122693

Abstract: The vertical diffuse attenuation coefficient for downward plane irradiance (Kd ) is an apparent optical property commonly used in primary production models to propagate incident solar radiation in the water column. In open water, estimating Kd is relatively straightforward when a vertical profile of measurements of downward irradiance, Ed, is available. In the Arctic, the ice pack is characterized by a complex mosaic composed of sea ice with snow, ridges, melt ponds, and leads. Due to the resulting spatially heterogeneous light field in the top meters of the water column, it is difficult to measure at single-point locations meaningful Kd values that allow predicting average irradiance at any depth. The main objective of this work is to propose a new method to estimate average irradiance over large spatially heterogeneous area as it would be seen by drifting phytoplankton. Using both in situ data and 3D Monte Carlo numerical simulations of radiative transfer, we show that (1) the large-area average vertical profile of downward irradiance, Ed(z), under heterogeneous sea ice cover can be represented by a single-term exponential function and (2) the vertical attenuation coefficient for upward radiance (KLu), which is up to two times less influenced by a heterogeneous incident light field than Kd in the vicinity of a melt pond, can be used as a proxy to estimate Ed(z) in the water column.