Enhanced sensitivity of oceanic CO2 uptake to dust deposition by iron‐light colimitation

Abstract

AbstractThe iron hypothesis suggests that in large areas of the ocean phytoplankton growth and thus photosynthetic CO2 uptake is limited by the micronutrient iron. Phytoplankton requires iron in particular for nitrate uptake, light harvesting, and electron transport in photosynthesis, suggesting a tight coupling of iron and light limitation. One important source of iron to the open ocean is dust deposition. Previous global biogeochemical modeling studies have suggested a low sensitivity of oceanic CO2 uptake to changes in dust deposition. Here we show that this sensitivity is increased significantly when iron‐light colimitation, i.e., the impact of iron bioavailability on light‐harvesting capabilities, is explicitly considered. Accounting for iron‐light colimitation increases the shift of export production from tropical and subtropical regions to the higher latitudes of subpolar regions at high dust deposition and amplifies iron limitation at low dust deposition. Our results reemphasize the role of iron as a key limiting nutrient for phytoplankton.