Multidecadal polynya formation in a conceptual (box) model

Abstract

Abstract. Maud Rise polynyas (MRPs) form due to deep convection, which is caused by static instabilities of the water column. Recent studies with the Community Earth System Model (CESM) have indicated that a multidecadal varying heat accumulation in the subsurface layer occurs prior to MRP formation due to the heat transport over the Weddell Gyre. In this study, a conceptual MRP box model, forced with CESM data, is used to investigate the role of this subsurface heat accumulation in MRP formation. Cases excluding and including multidecadal varying subsurface heat and salt fluxes are considered, and multiple polynya events are only simulated in the cases where subsurface fluxes are included. The dominant frequency for MRP events in these results, approximately the frequency of the subsurface heat and salt accumulation, is still visible in cases where white noise is added to the freshwater flux. This indicates the importance and dominance of the subsurface heat accumulation in MRP formation.

Coastal Polynyas Enable Transitions Between High and Low West Antarctic Ice Shelf Melt Rates

“…Simply put, κ P is a smoothed step function that transitions from a small diffusive end member κ diff when the thermocline is buoyant to a large convective end member κ conv when the thermocline approaches the density of the underlying mCDW. The effect is analogous to rapid transitions to vertical homogeneity triggered by static instability in simple models of open ocean polynyas (Boot et al., 2021; Martinson et al., 1981). Functionally, we define κ P as, $$${\kappa }_{\mathrm{P}}({\Delta }b)=\frac{{\kappa }_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{v}}-{\kappa }_{\mathrm{d}\mathrm{i}\mathrm{ff}}}{2}\left(1-\mathrm{tanh}\left(\phi \left({\Delta }b-{\Delta }{b}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}\right)\right)\right)+{\kappa }_{\mathrm{d}\mathrm{i}\mathrm{ff}},$$$ where κ conv (10 −2 m 2 s −1 ) and κ diff (10 −4 m 2 s −1 , taken from Pine Island Ice Front observations, Garabato et al., 2017) are vertical diffusivities, Δ b crit (5 × 10 −4 m s −2 ) is a small stratification strength at which turbulent convection onsets, and ϕ (5 × 10 4 ) is a parameter determining the steepness of the onset of convection.…”

“…Simply put, κ P is a smoothed step function that transitions from a small diffusive end member κ diff when the thermocline is buoyant to a large convective end member κ conv when the thermocline approaches the density of the underlying mCDW. The effect is analogous to rapid transitions to vertical homogeneity triggered by static instability in simple models of open ocean polynyas (Boot et al, 2021;Martinson et al, 1981). Functionally, we define κ P as,…”

Coastal polynyas enable transitions between high and low West Antarctic ice shelf melt rates

“…a small diffusive end member κ diff when the thermocline is buoyant to a large convective end member κ conv when the thermocline approaches the density of the underlying mCDW. The effect is analogous to rapid transitions to vertical homogeneity triggered by static instability in simple models of open ocean polynyas (Martinson et al, 1981;Boot et al, 2021). Functionally, we define κ P as,…”