Spring blooms and seasonal light responses in phytoplankton in the Eastern Bering Sea

Phytoplankton communities in the Eastern Bering Sea are a prime example of spring blooms in high latitude environments. This project studies the role of changing light responses in regulating spring bloom development. Seasonality was observed in the light response curves of phytoplankton samples taken in the Eastern Bering Sea shortly before and during the spring bloom. Underice samples were found to have lower values of both the maximum nutrient uptake rate vm and the initial slope ɑ of the photosynthesis-irradiance curve. This trend in ɑ was also noted in a literature review. A trade-off is proposed linking ɑ and maintenance respiration such that below the compensation intensity EC it becomes advantageous to decrease ɑ A seasonal NPZD model reected this trade-off with a seasonal transition from low to high ɑ and μ0 , at the point where available light is greater than EC. A parameter analysis found that with this seasonal plasticity the model could accurately reproduce the timing and magnitude of the 2009 spring bloom using parameter combinations within realistic ranges. Without this seasonality, no parameter set could be found that reasonably reproduced the observations. Inter-annual variations applying the model to 2014, 2015, and 2016, when the EBS experienced warmer temperatures and significantly less ice cover. Seasonal light response has been experimentally observed in the Eastern Bering Sea and is found to be an important factor for inclusion in numerical models that aim to capture timing of the spring bloom.Phytoplankton communities in the Eastern Bering Sea are a prime example of spring blooms in high latitude environments. This project studies the role of changing light responses in regulating spring bloom development. Seasonality was observed in the light response curves of phytoplankton samples taken in the Eastern Bering Sea shortly before and during the spring bloom. Underice samples were found to have lower values of both the maximum nutrient uptake rate vm and the initial slope ɑ of the photosynthesis-irradiance curve. This trend in ɑ was also noted in a literature review. A trade-off is proposed linking ɑ and maintenance respiration such that below the compensation intensity EC it becomes advantageous to decrease ɑ A seasonal NPZD model reected this trade-off with a seasonal transition from low to high ɑ and μ0 , at the point where available light is greater than EC. A parameter analysis found that with this seasonal plasticity the model could accurately reproduce the timing and magnitude of the 2009 spring bloom using parameter combinations within realistic ranges. Without this seasonality, no parameter set could be found that reasonably reproduced the observations. Inter-annual variations applying the model to 2014, 2015, and 2016, when the EBS experienced warmer temperatures and significantly less ice cover. Seasonal light response has been experimentally observed in the Eastern Bering Sea and is found to be an important factor for inclusion in numerical models that aim to capture timing of the spring bloom