Evaluation of iron sources in the Ross Sea

A one-dimensional numerical model that includes the complex life cycle of Phaeocystis antarctica, diatom growth, dissolved iron (dFe) and irradiance controls, and the taxa's response to changes in these variables is used to evaluate the role of different iron sources in supporting phytoplankton blooms in the Ross Sea. Simulations indicate that sea ice melt accounts for 20% of total dFe inputs during low light conditions early in the growing season (late November-early December), which enhances blooms of P. antarctica in early spring. Advective inputs of dFe (60% of total inputs) maintain the P. antarctica bloom through early January and support a diatom bloom later in the growing season (early to mid-January). In localized regions near banks shallower than 450 m, suspension of iron-rich sediments and entrainment into the upper layers contributes dFe that supports blooms. Seasonal dFe budgets constructed from the simulations show that diatom-associated dFe accounts for the largest biological reservoir of dFe. Sensitivity studies show that surface input of dFe from sea ice melt, a transient event early in the growing season, sets up the phytoplankton sequencing and bloom magnitude, suggesting that the productivity of the Ross Sea system is vulnerable to changes in the extent and magnitude of sea ice.