The contribution of submesoscale over mesoscale eddy iron transport in the open Southern Ocean

Abstract

In order to examine the roles of ocean dynamics in supplying iron, the limiting nutrient in the open Southern Ocean, to the surface where it can be effectively utilized for photosynthesis, we run a flat-bottom zonally re-entrant channel model configured to represent the Antarctic Circumpolar Current region and couple it to a full biogeochemical model. The model was forced with monthly varying physical and biogeochemical boundary conditions to incorporate seasonality. Much focus on previous studies on iron pathways in the open ocean region has been on mixed-layer entrainment and diapycnal fluxes of iron. The Southern Ocean, however, is a region with strong meso- and submeso-scale turbulence and we would expect eddy fluxes to transport tracers including iron. Spatial resolution is, therefore, chosen as the parameter to control the effect of eddy transport. We utilize cross spectral analysis and the generalized Omega equation to temporally and spatially decompose the vertical transport attributable to meso- and submeso-scale motions. Our results suggest that the mesoscale vertical fluxes provide a first-order pathway for transporting iron across the mixing-layer base where diapycnal mixing is weak and must be included in modelling the open-Southern-Ocean iron budget.

Iron Supply Pathways Between the Surface and Subsurface Waters of the Southern Ocean: From Winter Entrainment to Summer Storms

“…On the seasonal scale, in addition to the “once‐off” winter DFe supply to the surface by convective mixing (Tagliabue et al, ), this study shows that enhanced eddy activity contributes to a DFe supply of similar magnitude over the year (Figure c) and is thus an important supply mechanism for SO productivity (supporting 14% annual and 25% spring‐summer production). Our estimate of the eddy DFe flux is likely underestimated as the horizontal resolution used (~5 km or 1/24°) is not sufficient to represent submesoscale iron fluxes (Rosso et al, ; Uchida et al, ).…”

The Seasonality of Submesoscale Energy Production, Content, and Cascade

“…Dynamically, submesoscales are defined to have Rossby and Richardson numbers that are order unity: Ro~1, Ri~1. Submesoscale processes make a significant contribution to the vertical ocean heat and material transports (Lévy et al, 2012;Su et al, 2018;Uchida et al, 2019), and occasionally significant horizontal transports (Capet et al, 2008;Pearson et al, 2019;Zhong et al, 2012). Submesoscales can be generated by a number of mechanisms, including mixed layer instability (Boccaletti et al, 2007;Fox-Kemper et al, 2008), frontogenesis (Capet et al, 2008a;Hoskins, 1982;McWilliams, 2016), symmetric instability (Bennetts & Hoskins, 1979;Hoskins, 1974; Thomas et al, 2013), and topographic interactions (Gula et al, 2016).…”

“…Dynamically, submesoscales are defined to have Rossby and Richardson numbers that are order unity: Ro~1, Ri~1. Submesoscale processes make a significant contribution to the vertical ocean heat and material transports (Lévy et al, 2012;Su et al, 2018;Uchida et al, 2019), and occasionally significant horizontal transports (Capet et al, 2008;Pearson et al, 2019;Zhong et al, 2012).…”

Eddy‐Mean Flow Interaction With a Multiple Scale Quasi Geostrophic Model

“…Cessi (2008) and Eden and Greatbatch (2008), on the other hand, try to constrain the rectification based on the eddy energetics. It is also a well know issue that the rectification is sensitive to how the adiabaticity is relaxed near the surface and bottom boundaries (e.g., Ferrari et al., 2008, 2010; Uchida, 2019, his Appendix D). A synthesis of the different approaches appears in Gent (2011) and references therein.…”