Abstract. We present a comparison of Arctic Ocean hydrographic data sets from the 1990s, with a focus on changes in the upper few hundred meters of the Eurasian Basin. The most recent observations discussed here were collected during the spring 1995 Scientific Ice Expedition (SCICEX'95), the second in a series of scientific cruises to the Arctic Ocean aboard U.S. Navy nuclear submarines. Although the 1990s have seen an abundance of synoptic cruises to the Arctic, this was the only one to take place in winter/spring conditions. Other data considered here were collected during the first SCICEX cruise in summer 1993 (SCICEX'93) and during an icebreaker cruise to the Eurasian Basin in summer 1991 (Oden'91). A new Russian-American winter climatology is also used as a reference. These comparisons reveal that the Eurasian Basin "cold halocline layer" has retreated during the 1990s to cover significantly less area than in previous years. Specifically, we find a retreat from the Amundsen Basin back into the Makarov Basin; the latter is the only region with a true cold halocline layer during SCICEX'95. Changes are also seen in other halocline types and in the Atlantic Water layer heat content and depth. Since the cold halocline layer insulates the surface layer (and thus the overlying sea ice) from the heat contained in the Atlantic Water layer, this should have profound effects on the surface energy and mass balance of sea ice in this region. Using a simple mixing model, we calculate maximum iceocean heat fluxes of 1-3 W m -2 in the Eurasian Basin, where during SCICEX'95 the surface layer lay in direct contact with the underlying Atlantic Water layer. The overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s, which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the Arctic Ocean. Finally, we discuss two different mechanisms that have been proposed for cold halocline water formation, and we propose a compromise that best fits these data.

Evidence of a warm, salty surface current flowing poleward along the Iberian Peninsula is presented using a sequence of satellite infrared images and concomitant in situ hydrographic data obtained during the winter of 1983–1984. The current, which flows over 1500 km along the upper continental slope‐shelf break zone off western Portugal, northwest and northern Spain, and southwest France, is 25–40 km wide, about 200 m deep, and characterized by velocities of 0.2–0.3 m s−1. According to the hydrographic data acquired during late November and early December 1983, the current's salinity signal off Portugal is about 0.2 practical salinity units, and its waters are ∼0.5°C warmer than the surrounding ones. The satellite observations, however, which span a longer time period and cover a much larger area, indicate that the current's typical thermal signature is 1°–1.5°C. The current's associated geostrophic volume transports show an increase from about 300×103 m3 s−1 near 38°3′N to 500–700×103 m3 s−1 at 41°–42°N. The origin of this poleward flow and the causes for its increasing transport off western Iberia are investigated. Onshore Ekman convergence induced by southerly winds along the Portuguese west coast provides about one fifth of the computed transports in the correct direction. A mechanism giving better quantitative agreement with the observations is the geostrophic adjustment of the eastward oceanic flow driven by the large‐scale meridional baroclinic pressure gradient in the eastern North Atlantic as the flow reaches the continental slope of the western Iberian Peninsula. Topographic trapping by the bathymetric step existing along the shelf break explains both the width and the path of the observed current. The role of “dam break” type mechanisms is discarded owing to strong discrepancies between the available models and the present observations. Since satellite images reveal that similar situations occurred during many winters, the flow identified here appears as a characteristic feature of the winter circulation off southwest Europe. Furthermore, the occurrence of analogous poleward flows in eastern boundary layers of the subtropical and mid‐latitude oceans suggests that these currents are typical features of those regions' winter circulation.

A high-resolution primitive equation model simulation is used to form an energy budget for the principal semidiurnal tide (M 2 ) over a region of the Hawaiian Ridge from Niihau to Maui. This region includes the Kaena Ridge, one of the three main internal tide generation sites along the Hawaiian Ridge and the main study site of the Hawaii Ocean Mixing Experiment. The 0.01°-horizontal resolution simulation has a high level of skill when compared to satellite and in situ sea level observations, moored ADCP currents, and notably reasonable agreement with microstructure data. Barotropic and baroclinic energy equations are derived from the model's sigma coordinate governing equations and are evaluated from the model simulation to form an energy budget. The M 2 barotropic tide loses 2.7 GW of energy over the study region. Of this, 163 MW (6%) is dissipated by bottom friction and 2.3 GW (85%) is converted into internal tides. Internal tide generation primarily occurs along the flanks of the Kaena Ridge and south of Niihau and Kauai. The majority of the baroclinic energy (1.7 GW) is radiated out of the model domain, while 0.45 GW is dissipated close to the generation regions. The modeled baroclinic dissipation within the 1000-m isobath for the Kaena Ridge agrees to within a factor of 2 with the area-weighted dissipation from 313 microstructure profiles. Topographic resolution is important, with the present 0.01°resolution model resulting in 20% more barotropic-to-baroclinic conversion compared to when the same analysis is performed on a 4-km resolution simulation. A simple extrapolation of these results to the entire Hawaiian Ridge is in qualitative agreement with recent estimates based on satellite altimetry data.

The cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing. We investigated this cascade along the Hawaiian Ridge using observations and numerical models. A divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models. Large internal tidal waves with peak-to-peak amplitudes of up to 300 meters occur on the ridge. Internal-wave energy is enhanced, and turbulent dissipation in the region near the ridge is 10 times larger than open-ocean values. Given these major elements in the tides-to-turbulence cascade, an energy budget approaches closure.