Shine a light: Under-ice light and its ecological implications in a changing Arctic Ocean

Abstract

The Arctic marine ecosystem is shaped by the seasonality of the solar cycle, spanning from 24-h light at the sea surface in summer to 24-h darkness in winter. The amount of light available for under-ice ecosystems is the result of different physical and biological processes that affect its path through atmosphere, snow, sea ice and water. In this article, we review the present state of knowledge of the abiotic (clouds, sea ice, snow, suspended matter) and biotic (sea ice algae and phytoplankton) controls on the underwater light field. We focus on how the available light affects the seasonal cycle of primary production (sympagic and pelagic) and discuss the sensitivity of ecosystems to changes in the light field based on model simulations. Lastly, we discuss predicted future changes in under-ice light as a consequence of climate change and their potential ecological implications, with the aim of providing a guide for future research.

Pelagic and ice‐associated microalgae under elevated light and pCO2: Contrasting physiological strategies in two Arctic diatoms

“…M. arctica is typically not exposed to high or strongly fluctuating light in its sub‐ice habitat, where it forms long, mucilaginous threads that grow into the underlying water column (Melnikov et al 2002). Therefore, its physiology is tuned for optimal light harvest under stable LL conditions, often even far below the here applied irradiance (Castellani et al 2021). High or fluctuating light situations would mainly be found in a breakup or melt‐pond scenario, when the ice disintegrates and the heavy algae mats sink quickly, leading to massive, pulsed carbon export (Boetius et al 2013).…”

Comparison of macroalgae meadows in warm Atlantic versus cold Arctic regimes in the high-Arctic Svalbard

“…The amount of radiation reaching the sea surface would be affected solely by local cloud cover, which is similar in both investigated regions (Figure 1). On the way through the water column to the bottom, sunlight might be partially attenuated by the sea ice cover (Perovich et al, 1993) and absorbed by particles suspended in the water (Castellani et al, 2022). At the CA site, turbidity is slightly higher than at the WA site, possibly due to higher meltwater runoff, yet differences are not very pronounced.…”

A changing Arctic Ocean

“…The main biotic and abiotic factors which drive the extent and spatial variability of light under ice are discussed by Castellani et al (2022), who also used model simulations to evaluate the effects of available light on the seasonal variability of primary production. Moreover, the authors discuss potential consequences of future changes in underice light for a wide range of marine ecosystems within the framework of ongoing climate change.…”