Polynya

A polynya is a persistent or recurrent area of open water or relatively thin ice within surrounding sea ice. Wind can maintain it by transporting ice away; an oceanic heat flux can prevent freezing. Open-water width supplies an open-water fetch over which wind waves can grow.

In a uniformly wind-forced polynya with normalized heat loss $f$, let $H=L+c_{p}m{C}_{\infty }$, $K=f/H$, $J=3S/(4\rho )$ and $r=\rho -{\rho }_s$. The dilute equilibrium model gives $b{u}^2=Jx$, $\varphi bu=Kx$ and $rg\varphi b{b}^{\prime }=S/4$. Hence $u=(rgKx/\rho {)}^{1/3}$, $b=Jx/u^2$ and $\varphi =(K/J)u$. This similarity solution is valid only while the frazil ice volume fraction is small and no exported crystal flux has been neglected improperly.

The simplest Pease polynya model balances offshore ice export at speed $U$ against production of new ice at thickness rate $F$ within an open strip of width $L$. Newly formed ice is collected into an edge of prescribed thickness $H$, with negligible residence time. Per unit coastline length, conservation gives $H(U-\dot{L})=FL$. For constant positive parameters,Thus the equilibrium width is $HU/F$ and the relaxation time is $H/F$. If warming reduces $F$ while $U,H$ stay fixed, both increase. With $F\le 0$ the positive-freezing equilibrium ceases to apply. Finite frazil ice residence, variable atmospheric forcing and alongshore transport require extensions of the model.

The North Water Polynya, also called Pikialasorsuaq, lies between northern Greenland and the Canadian Arctic in the Smith Sound and northern Baffin Bay region. An upstream ice arch can restrict replenishment of drifting Arctic ice while winds and currents export newly formed ice. Ocean heat contributes in some parts of the polynya.

The Northeast Water Polynya is a recurrent open-water region off northeast Greenland. Ice barriers, local currents and winds organize ice divergence; summer opening and winter new-ice export need not have the same dominant forcing. Its regional northward coastal flow must not be confused with assuming that every current along east Greenland flows southward.

A sensible-heat polynya is maintained by ocean heat delivered through currents, mixing or upwelling, sufficient to inhibit local sea ice growth. Mechanical export and sensible heating may act together, so this classification identifies a dominant mechanism rather than an exclusive geographical class.

A latent-heat polynya remains relatively open because winds or currents remove newly formed sea ice. Sustained cooling can produce large amounts of ice even while local ice concentration remains low. Opening is maintained by export, not by latent heat warming the ocean enough to prevent freezing.