Implications of sea-ice biogeochemistry for oceanic production and emissions of dimethyl sulfide in the Arctic

Abstract

Abstract. Sea ice represents an additional oceanic source of the climatically active gas dimethyl sulfide (DMS) for the Arctic atmosphere. To what extent this source contributes to the dynamics of summertime Arctic clouds is, however, not known due to scarcity of field measurements. In this study, we developed a coupled sea ice-ocean ecosystem-sulfur cycle model to investigate the potential impact of bottom-ice DMS and its precursor dimethylsulfoniopropionate (DMSP) on the oceanic production and emissions of DMS in the Arctic. The results of the 1-D model simulation were compared with field data collected during May and June of 2010 in Resolute Passage. Our results reproduced the accumulation of DMS and DMSP in the bottom ice during the development of an ice algal bloom. The release of these sulfur species took place predominantly during the earlier phase of the melt period, resulting in an increase of DMS and DMSP in the underlying water column prior to the onset of an under-ice phytoplankton bloom. Production and removal rates of processes considered in the model are analyzed to identify the processes dominating the budgets of DMS and DMSP both in the bottom ice and the underlying water column. When openings in the ice were taken into account, the simulated sea-air DMS flux during the melt period was dominated by episodic spikes of up to 8.1 µmol m −2 d −1 . Further model simulations were conducted to assess the effects of the incorporation of sea-ice biogeochemistry on DMS production and emissions, as well as the sensitivity of our results to changes of uncertain model parameters of the sea-ice sulfur cycle. The results highlight the importance of taking into account both the sea-ice sulfur cycle and ecosystem in the flux estimates of oceanic DMS near the ice margins and identify key uncertainties in processes and rates that should be better constrained by new observations.

A model-based analysis of physical and biological controls on ice algal and pelagic primary production in Resolute Passage

“…When ice algae were excluded from the simulation (Figure 7b), the onset of the under-ice bloom was delayed by a few days. This delay in the bloom onset is due to the lack of seeding by ice algae in the exclusion run (Hayashida et al, 2017). Despite the delay in the development of the underice bloom, the exclusion run simulated a higher peak in Chl a (with a concentration difference of about 7 mg Chl a m -3 ) than the standard run.…”

CSIB v1: a sea-ice biogeochemical model for the NEMO community ocean modelling framework

“…The ocean sulfur 15 cycle is one-way coupled to CanOE as sulfur cycle processes depend on the state of the ecosystem, but not vice versa. The ocean sulfur-cycle model is based on Hayashida et al (2017) with the following two modifications. First, the cellular DMSP content of modelled phytoplankton is derived from their carbon content as opposed to the chlorophyll content as in Hayashida…”

“…The submodel for sea-ice biogeochemistry is a modified version of a three-compartment (ice algae, nitrate, and ammonium) ecosystem based on Mortenson et al (2017) and a two-compartment (DMS and DMSPd) sulfur cycle based on Hayashida et al (2017).…”

“…Equation 3 neglects the density difference between sea ice and seawater, and therefore violates mass conservation. However, this simplification has negligible effect on ocean biogeochemistry given the relatively-thin sea-ice biogeochemical layer as demonstrated in Hayashida et al (2017). For ice algae only, a minimum biomass threshold is set at 10 mmol C m −3 in order to mimic reasonable overwintering biomass (Mortenson et al, 2017).…”

“…The biological and chemical processes represented as sources and sinks of the sea-ice biogeochemical state variables are described in detail in Mortenson et al (2017) and Hayashida et al (2017). For the ecosystem component, these processes include photosynthesis, mortality, and remineralization of dead organic matter.…”