A dynamic marine iron cycle module coupled to the University of Victoria Earth System Model: the Kiel Marine Biogeochemical Model 2 (KMBM2) for UVic 2.9

Abstract

Abstract. Marine biological production and the associated biotic uptake of carbon in many ocean regions depend on the availability of nutrients in the euphotic zone. While large areas are limited by nitrogen and/or phosphorus, the micronutrient iron is considered the main limiting nutrient in the North Pacific, equatorial Pacific and Southern Ocean. Changes in iron availability via changes in atmospheric dust input are discussed to play an important role in glacial/interglacial cycles via climate feedbacks caused by changes in biological ocean carbon sequestration. Although many aspects of the iron cycle remain unknown, its incorporation into marine biogeochemical models is needed to test our current understanding and better constrain its role in the Earth system. In the University of Victoria Earth System Climate Model (UVic) iron limitation in the ocean was, until now, simulated pragmatically with an iron concentration masking scheme that did not allow a consistent interactive response to perturbations of ocean biogeochemistry or iron cycling sensitivity studies. Here, we replace the iron masking scheme with a dynamic iron cycle and compare the results to available observations and the previous marine biogeochemical model. Sensitivity studies are also conducted with the new model to test the importance of considering the variable solubility of iron in dust deposition, the importance of considering high resolution bathymetry for the sediment release of iron, the effect of scaling the sedimentary iron release with temperature and the sensitivity of the iron cycle to a climate change scenario.

Explicit planktic calcifiers in the University of Victoria Earth System Climate Model

“…Ocean during glaciation leading to the expansion of diatoms at the expense of coccolithophores (Matsumoto, Sarmiento, & Brzezinski, 2002) can be tested using the prognostic iron cycle of Nickelsen et al (2014) once diatoms and silicate are implemented (currently underway). Increased calcifier concentration with increased ocean alkalinity driving sawtooth-shaped global CO 2 time series (Omta, van Voorn, Rickaby, & Follows, 2013) can be tested with the implementation of increased calcifier growth or advantage with increasing carbonate saturation state.…”

“…Iron limitation is calculated from the concentration of iron prescribed in interpolated monthly-mean fields using an iron half-saturation approximation constant (k Fe ) (Galbraith, Gnanadesikan, Dunne, & Hiscock, 2010;Keller et al, 2012). A prognostic iron cycle was recently implemented in the UVic ESCM (Nickelsen, Keller, & Oschlies, 2014), though it adds computational expense. However, accounting for iron limitation on growth rates by means of a limitation mask improves phytoplankton biogeography without additional computational cost (Keller et al, 2012).…”

Riverine nutrient impact on global ocean nitrogen cycle feedbacks and marine primary production in an Earth System Model

“…The model represents iron including a static concentration mask. Therefore no interactive response to perturbations of ocean biogeochemistry are possible and iron availability and limitation will not change during the simulations (Nickelsen et al, 2014). N 2 -fixation is influenced by P only.…”