s.d.brenner

Floe-scale variablility in sea ice-ocean coupling

by Samuel Brenner

Within the marginal ice zone (MIZ), sea ice is comprised of a mosaic of individual floes that span a wide range of horizontal scales—from meters to tens of kilometers across.

However, when considering air-sea coupling at climate model scales, the role of sea ice variability is typically collapsed to a single metric: the sea ice concentration. As a result, the spatial heterogeniety in surface properities that is an inherent feature of the floe-covered MIZ is not resolved or accounted for. Yet, there is an increasing awareness that sea ice melt rates and atmosphere/ocean boundary layer dynamics are impacted by floe-scale effects.

Explicitly representing sea ice floes—rather than treating the ice cover as a continuum—introduces a range of new physical effects, as floe-scale features imprint on upper-ocean dynamics. For example, because individual floes move as rigid bodies, their motion is subject to geometric and dynamical constraints that differ from continuum behaviour. Because ice-ocean fluxes are driven by differences between sea ice and ocean velocity, these velocity constraints can impact the transfers of momentum and energy across the atmosphere-ice-ocean boundary in a way that depends on the relative horizontal scales of floes and the scales of ocean variablity (fig. 1).

fig. 1 (Reproduced from Brenner et al., 2023 ): A schematic showing how scale mismatches between ocean flow (blue colourmap and background vectors) and ice velocity (vector arrows over ice floes) contribute to boundary-layer turbulent production (cyan/red colourmap).

During my postdoctoral work at Brown University, I made use of a high-resolution, discrete element model (DEM) of sea ice that explicitly resolves individual sea ice floes (see video) in order to investigate the joint roles of floe-floe interactions and flow-floe interactions in mediating ice-ocean exchanges (Brenner et al., 2023). I also considered the role of individual ice floes in a surface-gravity-wave model to understand geometric constraints on local wave growth (Brenner & Horvat, 2024).

My ongoing postdoctoral work at Caltech continues investigating these effects using a combination of methods, including a sea ice DEM coupled to an ocean large-eddy-simulation (LES) model in order to understand how sea ice floe scales imprint on the scales associated with the underlying dynamics associated with energy transfers in the upper ocean.

  • Brenner, S., Horvat, C., 2024. Scaling simulations of local wind-waves amid sea ice floes. J. Geophys. Res. Oceans., 129, e2024JC021629. doi:10.1029/2024JC021629.

  • Brenner, S., Horvat, C., Hall, P., Lo Piccolo, A., Fox-Kemper, B. Labbé, S., Dansereau, V. 2023. Scale-dependent air-sea exchange in the polar oceans: floe-floe and floe-flow coupling in the generation of ice-ocean boundary layer turbulence. Geophys. Res. Lett., 50, e2023GL105703. doi:10.1029/2023GL105703.