A simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated. The theory is based on two competing mechanisms that move the buoyant fluid offshore: 1) the radial spread of the lighter water over the ambient water, being deflected by the Coriolis force and producing an anticyclonic cyclostrophic plume, and 2) offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom. The surface expression of the cyclostrophic plume moves offshore a distance y s ϭ 2(3gЈh 0 ϩ)/(2gЈh 0 ϩ) 1/2 f, 2 2 i i where gЈ is reduced gravity based on the inflow density anomaly, h 0 is the inflow depth, i is the inflow velocity, and f is the Coriolis parameter. The plume remains attached to the bottom to a depth given by h b ϭ (2L i h 0 f /gЈ) 1/2 , where L is the inflow width. Both scales are based solely on parameters of the buoyant inflow at its source. There are three possible scenarios. 1) If the predicted h b is shallower than the inflow depth, then the bottom boundary layer does not transport buoyancy offshore, and a purely surface-advected plume forms, which extends offshore a minimum of more than four Rossby radii. 2) If the h b isobath is farther offshore than y s , then transport in the bottom boundary layer dominates and a purely bottom-advected plume forms, which is trapped along the h b isobath. 3) If the h b isobath is deeper than the inflow depth but shoreward of y s , then an intermediate plume forms in which the plume detaches from the bottom at h b and spreads offshore at the surface to y s. The theory is tested using a primitive equation numerical model. All three plume types are reproduced with scales that agree well with the theory. The theory is compared to a number of observational examples. In all cases, the prediction of plume type is correct, and the length scales are consistent with the theory.

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The efficiency of shelf/basin exchange (SBE) in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography. Numerical model calculations suggest that upwelling‐favorable winds generate very little SBE so long as the ice edge remains shoreward of the shelf break, but an abrupt onset of shelf‐break upwelling takes place when the ice edge retreats beyond the shelf break. A climatology (1968–2000) of ice conditions from the Canadian Shelf of the Beaufort Sea shows large interannual variability in ice edge extent and duration of ice‐free conditions in summer. Similarly, available hydrographic data reflect a corresponding variability in water mass properties. Under scenarios of climate warming associated with greenhouse gas build‐up, both the extent and duration of summer melt‐back are predicted to increase, and this may have dramatic impacts on SBE and biological productivity.

A simple theory is proposed for steady, two-dimensional, wind-driven coastal upwelling that relates the dynamics and the structure of the cross-shelf circulation to the stratification, bathymetry, and wind stress. The new element is an estimate of the nonlinear cross-shelf momentum flux divergence due to the wind-driven cross-shelf circulation acting on the vertically sheared geostrophic alongshelf flow. The theory predicts that the magnitude of the cross-shelf momentum flux divergence relative to the wind stress depends on the Burger number S = αN/f, where α is the bottom slope, N is the buoyancy frequency, and f is the Coriolis parameter. For S ≪ 1 (weak stratification), the cross-shelf momentum flux divergence is small, the bottom stress balances the wind stress, and the onshore return flow is primarily in the bottom boundary layer. For S ≈ 1 or larger (strong stratification), the cross-shelf momentum flux divergence balances the wind stress, the bottom stress is small, and the onshore return flow is in the interior. Estimates of the cross-shelf momentum flux divergence using moored observations from four coastal upwelling regions (0.2 ≤ S ≤ 1.5) are substantial relative to the wind stress when S ≈ 1 and exhibit a dependence on S that is consistent with the theory. Two-dimensional numerical model results indicate that the cross-shelf momentum flux divergence can be substantial for the time-dependent response and that the onshore return flow shifts from the bottom boundary layer for small S to just below the surface boundary layer for S ≈ 1.5–2.

We demonstrate a compact, single-mode quantum cascade laser source continuously tunable between 8.7 and 9.4 m. The source consists of an array of single-mode distributed feedback quantum cascade lasers with closely spaced emission wavelengths fabricated monolithically on a single chip and driven by a microelectronic controller. Our source is suitable for a variety of chemical sensing applications. Here, we use it to perform absorption spectroscopy of fluids.