Diadinoxanthin cycle of the bottom ice algal community during spring in McMurdo Sound,Antarctica

Using the ice algal community growing at the bottom of the annual sea ice in McMurdo Sound Antarctica, the response of the photoprotective diadinoxanthin (DD)-cycle to exposure to light was investigated. Changes in pigment concentration were detected using high-performance liquid chromatography. A light mixing simulator (LMS) was developed and used to simulate the pigment response to mixing in the upper water column. No DD-cycle was detected under the sea ice under natural light conditions. The DD-cycle was activated after exposure to surface natural light conditions and artificial light conditions. The first-order kinetic rates of the DD-cycle under constant artificial irradiance, natural irradiance and simulations with the LMS were found to be similar to other studies suggesting that ice algae do not vary the rate of deepoxidation depending on light history. Simulations under natural light using the LMS demonstrated that the response of the DD-cycle to static incubations and when subject to vertical mixing was not similar, and that static incubations overestimate DD-cycle activity over the long term. Algae in a simulated vertically mixed environment were able to increase the pool of xanthophyll pigments compared to static conditions where the pool remained the same or decreased. The recovery of DD in the dark or under low light was found to be significantly faster than in temperate algal communities. These results suggest that ice algae at the sea ice bottom can activate the photoprotective DD-cycle to regulate excess thermal energy. Unlike temperate species of diatoms, ice algae can rapidly reconstruct the pigment pool under low light or in the dark and is likely a particular adaptation to the unique light environment in Antarctica.