Observed patterns of wind stress curl and air-sea heat flux associated with the North Atlantic oscillation (NAO) are used to discuss the response of ocean gyres and thermohaline circulation to NAO forcing and their possible feedback on the NAO. The observations motivate, and are interpreted in the framework of, a simple mathematical model that couples Ekman layers, ocean gyres, and thermohaline circulation to the atmospheric jet stream. Meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres, and north-south dipoles in air-sea flux drive anomalous thermohaline circulation. Both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence, through air-sea interaction, the overlying jet stream. The model, which can be expressed in the form of a delayed oscillator with ocean gyres and/or thermohaline circulation providing the delay, identifies key nondimensional parameters that control whether the ocean responds passively to NAO forcing or actively couples. It suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales.

We review recent observations and models concerning the dynamics of Cryogenian global glaciation and their biological consequences.

Simulations of frigid Neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally. We have constructed a simple model of the production and flow of marine ice on a planetary scale, and determined ice thickness and flow in two situations: when the ocean is globally ice‐covered (“hard snowball”) and when the tropical waters remain open (“soft snowball”). In both cases, ice flow strongly affects the distribution of marine ice. Flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a Snowball Earth climate. We speculate that flowing marine ice, rather than continental ice sheets, may be the erosive agent that created some Neoproterozoic glacial deposits.

Recent observations of the south pole of Saturn's moon Enceladus by the Cassini spacecraft have revealed an active world, powered by internal heat. In this paper, we propose that localized subsurface melting on Enceladus has produced an internal south polar sea. Evidence for this localized sea comes from the shape of Enceladus, which does not match a differentiated body at its current orbital position. We show that melting induced by the observed heat flow at the south pole produces a large enough pit to match the shape of Enceladus with a differentiated rock and ice interior. Numerical modeling of melting and ice flow shows that the sea produced beneath the south pole is stable against inflow of ductile ice from its surroundings for the duration of the heating. The shape modification due to melting also produces a negative degree-two gravity anomaly, which can reorient the spin axis of Enceladus in order to place the sea at the pole.

[1] Hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from Europa's rocky interior through a liquid ocean to the base of its ice shell. This process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer. In contrast to earlier work, we argue that Europa's ocean should be treated as an unstratified fluid. We have adapted and expanded upon existing work describing buoyant plumes in a rotating, unstratified environment. We discuss the scaling laws governing the flow and geometry of plumes on Europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a Europa-like parameter regime. We predict that hydrothermal plumes on Europa are of a lateral scale (at least 25-50 km) comparable to large chaos regions; they are too broad to be responsible for the formation of individual lenticulae. Plume heat fluxes (0.1-10 W/m 2 ) are too weak to allow complete melt-through of the ice layer. Current speeds in the plume (3-8 mm/s) are much slower than indicated by previous studies. The observed movement of ice blocks in the Conamara Chaos region is unlikely to be driven by such weak flow.