During the Gibraltar Experiment in 1985–1986, observations of shear, stratification, microstructure, and acoustic backscatter revealed a complex mixing regime at Camarinal Sill in the Strait of Gibraltar. The mixing is forced by strong semidiurnal tidal currents and weaker, but more steady, baroclinic flows. Flows are characterized as outflow or inflow, nearly equivalent to westward or eastward. Rising water at Gibraltar coincides with outflow at all depths. We observed two modes of outflow at the sill. In May 1986 the transition layer separating Atlantic and Mediterranean water was between 0.75 MPa and 1 MPa when we sampled east of the sill near neap tide. The transition turned down just before reaching the sill crest, where the flow became critical. Increasing shear soon destabilized the transition, producing billows which grew to 30–75 m on the west flank of the sill. The overturning generated intense turbulence, with peak dissipation rates, ε, exceeding 10−2 W kg−1. This turbulence rapidly thickened the transition from Δz = 30–50 m east of the sill to Δz = 130–150 m within 1–2 km west of the sill. From the rate of thickening, we estimate the rate of formation of new transitional water during neap tide as (0.8–1.2) × 105 m3 s−1. This outflow mode did not release eastward‐propagating internal bores when outflow turned to inflow, but the inflow did appear to arrest the deep outflow. In May, the largest average dissipation rate over and just west of the sill had the same magnitude as estimates of the net energy lost by adjustment of velocity and mass across the sill during outflow. Other averages are smaller than the energy loss, presumably because the limited sampling severely underestimates the average dissipation rate. During outflow, strong shears were observed to rise to 100 times those in the background internal wave field. However, probably owing to spatial offsets between the ship's acoustic Doppler current profiler and our tethered free‐fall profiler, the only statistically significant correlations were found between overturning scales measured directly and those estimated from ε in the same profile. We observed the other outflow mode in October 1985, when we profiled over the sill near spring tide and the transition was east of the sill, centered near 1.5 MPa. After encountering the sill, the transition rose sharply and remained within 10–20 m of the surface across the sill, plunging steeply downward just past the west edge of the sill. This was accompanied by intense turbulence and at least one rebound of the transition. We did not observe release of eastward propagating bores when inflow turned to outflow, but observations by Armi and Farmer (1988) in April 1986 found bores released at spring tide in regimes similar to the one we observed in October 1985.

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Ocean surface roughness plays an important role in air–sea interaction and ocean remote sensing. Its primary contribution is from surface waves much shorter than the energetic wave components near the peak of the wave energy spectrum. Field measurements of short-scale waves are scarce. In contrast, microwave remote sensing has produced a large volume of data useful for short-wave investigation. Particularly, Bragg resonance is the primary mechanism of radar backscatter from the ocean surface and the radar serves as a spectrometer of short surface waves. The roughness spectra inverted from radar backscatter measurements expand the short-wave database to high wind conditions in which in situ sensors do not function well. Using scatterometer geophysical model functions for L-, C-, and Ku-band microwave frequencies, the inverted roughness spectra, covering Bragg resonance wavelengths from 0.012 to 0.20 m, show a convergent trend in high winds. This convergent trend is incorporated in the surface roughness spectrum model to improve the applicable wind speed range for microwave scattering and emission computations.

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.

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Turbulent mixing adjacent to the Velasco Reef and Kyushu–Palau Ridge, off northern Palau in the western equatorial Pacific Ocean, is examined using shipboard and moored observations. The study focuses on a 9-day-long, ship-based microstructure and velocity survey, conducted in November–December 2016. Several sections (9–15 km in length) of microstructure, hydrographic, and velocity fields were acquired over and around the reef, where water depths ranged from 50 to 3000 m. Microstructure profiles were collected while steaming slowly either toward or away from the reef, and underway current surveys were conducted along quasi-rectangular boxes with side lengths of 5–10 km. Near the reef, both tidal and subtidal motions were important, while subtidal motions were stronger away from the reef. Vertical shears of currents and mixing were stronger on the northern and eastern flanks of the reef than on the western flanks. High turbulent kinetic energy dissipation rates, 10−6–10−4 W kg−1, and large values of eddy diffusivities, 10−4–10−2 m2 s−1, with strong turbulent heat fluxes, 100–500 W m−2, were found. Currents flowing along the eastern side separated at the northern tip of the reef and generated submesoscale cyclonic vorticity of about 2–4 times the planetary vorticity. The analysis suggests that a torque, imparted by the turbulent bottom stress, generated the cyclonic vorticity at the northern boundary. The northern reef is associated with high vertical transports resulting from both submesoscale flow convergences and energetic mixing. Even though the area around Palau represents a small footprint of the ocean, vertical velocities and mixing rates are several orders magnitude larger than in the open ocean.

Abstract-The results from two field experiments in the Mediterranean Sea are used to study the wind speed dependence of brightness temperature at L-band. During the EuroSTARRS airborne experiment, an L-band radiometer made measurements across a large wind speed gradient, enabling us to study this dependence at high wind speed. We compare our results with a two-scale emissivity model using several representations of the sea state spectrum. While the results are encouraging, unfortunately the accuracy of the measurements does not permit us to distinguish between the so-called twice Durden and Vesecky spectrum and the Elfouhaily spectrum above 7 m s 1 . The effect of foam is certainly small. During the WISE 2001 field experiment carried on an oil rig, we studied this dependence at low wind speed, finding an abrupt decrease of the wind speed effect on the brightness temperature below 3 m s 1 .

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