Role of wind in regulating phytoplankton blooms on the Mid-Atlantic Bight

Mixing has long been recognized as having an important role in influencing underwater light and nutrient budgets and thus regulating phytoplankton bloom. Mixing related to stratification and de-stratification is a key parameter of the physical environment that can control the timing and magnitude of blooms. Here we use a high-resolution three-dimensional biogeochemical model in the Mid-Atlantic Bight (MAB) to study phytoplankton bloom dynamics for the years 2004–2007. We present a simulated fall-winter bloom in the shelf region and spring bloom in the shelf-break front region. The ratio of light over mixed layer depth (MLD) was used to determine the trade-off effects of mixing (increase mixing will increase nutrients availability but decrease light availability). We find that the critical light value (I′chl mas) is around 60 (W m−2) for the shelf region and 150 (W m−2) for the shelf-break front region. There is a predictable linear regression relationship between I′chl mas and depth. A sensitivity run with no wind forcing was used to test the role of wind-induced mixing on the balance between light and nutrient terms and its influence on timing and magnitude of the bloom. The phytoplankton dynamics in the shelf-break front region are found to be more sensitive to the wind-induced mixing.

► Based on satellite SeaWiFS observation, there is annual fall-winter phytoplankton bloom in the middle.
► And outer shelf of MAB but spring and fall bloom in the shelf-break region.
► Our coupled bio-physical model can capture such bloom.
► The balance between light and nutrient limitation is analyzed by calculate the mixing light term.
► Phytoplankton bloom is sensitive to the wind mixing especially in the shelf-break front region.