Classic Article: Steady flow in a frictionless homogenous ocean

A mathematical model is developed to study the free (frictionless) steady horizontal flow which can occur in a homogeneous ocean of constant depth. The flow satisfies the dynamic constraint that the vertical component of absolute vorticity is constant along a streamline. The conclusion is reached that in an enclosed ocean a free steady circulation cannot have any slow broad eastward currents. The eastward currents must occur as narrow streams of high velocity and high relative vorticity. Intensified currents are present along the eastern and western coasts. The theory which is developed for the homogeneous ocean of constant depth can be applied to the two-layer ocean if the horizontal divergence of flow is negligible. If the horizontal divergence is not negligible, then the intensification of poleward currents is more pronounced and that of equatorward currents less pronounced as compared with the homogeneous ocean

Nonlinear limits to ocean thermal structure

The nonlinear volume changes associated with diffusion and mixing of different seawater types produce significant conversions of gravitational potential energy to kinetic energy to maintain and enhance mixing processes and to limit the magnitudes of temperature gradients that can persist in the ocean. Several examples are given to illustrate these critical temperature gradients beyond which conversion exceeds local energy consumption by mixing. The vertical temperature gradients in the Gulf Stream reduce downstream from Cape Hatteras to the critical limit found in the North Atlantic thermocline. The limiting gradients are also seen in surface thermoclines and in staircase structures. Although the theoretical interpretation of the nonlinear limiting processes is still incomplete, the observational evidence is compelling for further study of these mechanisms

Steady flow in a frictionless homogeneous ocean

A mathematical model is developed to study the free (frictionless) steady horizontal flow which can occur in a homogeneous ocean of constant depth. The flow satisfies the dynamic constraint that the vertical component of absolute vorticity is constant along a streamline...

Specific gravity and density of seawater at atmospheric pressure

Four independent sets of specific gravity measurements are intercompared relative to a least squares polynomial in temperature and salinity over the range - 2 to 30°C and 8 to 40‰. Within this range, individual measurements have a standard deviation of 7.1 ppm about the regression polynomial. Over most of the range, the polynomial formula has a standard deviation of 1 to 3 ppm. The data sets are marginal in defining specific gravity below 0°C and above 25°C and inadequate below 10‰ salinity

Oceanic flow over varying bottom topography

A study has been made of steady barotropic flows on the β plane over a bottom topography that varies in a direction inclined to the circles of latitude. The solutions obtained, starting with both the Eulerian and the Lagrangian systems of equations, are shown to be identical in the case of flow over a single-depth discontinuity...

Ensemble inequivalence, bicritical points and azeotropy for generalized Fofonoff flows

We present a theoretical description for the equilibrium states of a large class of models of two-dimensional and geophysical flows, in arbitrary domains. We account for the existence of ensemble inequivalence and negative specific heat in those models, for the first time using explicit computations. We give exact theoretical computation of a criteria to determine phase transition location and type. Strikingly, this criteria does not depend on the model, but only on the domain geometry. We report the first example of bicritical points and second order azeotropy in the context of systems with long range interactions.Comment: 4 pages, submitted to Phys. Rev. Let

Characterizing horizontal variability and energy spectra in the Arctic Ocean halocline

Energy transfer from the atmosphere into the upper Arctic Ocean is expected to become more efficient as summer sea-ice coverage decreases and multiyear ice thins due to recent atmospheric warming. However, relatively little is known about how energy is transferred within the ocean by turbulent processes from large to small scales in the presence of ice and how these pathways might change in future. This study characterises horizontal variability in several regions of the Eurasian Arctic Ocean under differing sea-ice conditions. Historic along track CTD data collected by a Royal Navy submarine during summer 1996 allows a unique examination of horizontal variability and associated wavenumber spectra within the Arctic Ocean halocline. Spectral analysis indicates that potential energy variance under perennial sea-ice in the Amundsen Basin is O(100) less than within the Marginal Ice Zone (MIZ) of Fram Strait. Spectra from all regions show a transition in scaling at wavelengths of approximately 5 to 7 km. At scales greater than the transition wavelength to 50 km, energy spectra are consistent with a k-3 scaling (where k is wavenumber) and interior quasi-geostrophic dynamics. The scaling of spectra at these scales is extremely similar between regions suggesting similar dynamics and energy exchange pathways. The k-3 scaling is steeper than typically found in regions of mid latitude open ocean. At scales below the transition wavelength to 300 m, spectra are close to a k-5/3 scaling or flatter, indicating a change in dynamics, which is potentially due to internal waves dominating variability at small scales

Topographic Control of Southern Ocean Gyres and the Antarctic Circumpolar Current: A Barotropic Perspective

In the Southern Ocean the Antarctic Circumpolar Current is significantly steered by large topographic features, and sub-polar gyres form in their lee. The geometry of topographic features in the Southern Ocean is highly variable, but the influence of this variation on the large-scale flow is poorly understood. Using idealised barotropic simulations of a zonal channel with a meridional ridge, it is found that the ridge geometry is important for determining the net zonal volume transport. A relationship is observed between ridge width and volume transport that is determined by the form stress generated by the ridge. Gyre formation is also highly reliant on the ridge geometry. A steep ridge allows gyres to form within regions of unblocked geostophic ( f /H) contours, with an increase in gyre strength as the ridge width is reduced. These relationships between ridge width, gyre strength, and net zonal volume transport emerge in order to simultaneously satisfy the conservation of momentum and vorticity

Diversity and patterns of marine non‐native species in the archipelagos of Macaronesia

Aims The present study is the first attempt to grasp the scale and richness of marine biological invasions in Macaronesia. We pioneered a comprehensive non-native species (NNS), inventory in the region to determine their diversity patterns and native distribution origins. NNS were defined here as the result of both introductions and range expansions. We also used statistical modelling to examine relationships among NNS richness, anthropogenic activities, demographic and geographical variables across Macaronesia. Location Macaronesia. Methods A comprehensive literature search was conducted for marine NNS records in Macaronesia, registering the first record's location and year from 1884 to 2020. We used univariate and multivariate analyses to evaluate differences and similarities in community composition. By applying a Generalized Linear Model (GLM), we tested hypotheses regarding NNS richness as a function of anthropogenic activities, demographic and geographical variables. Results A total of 144 marine non-native species (NNS) were recorded for the whole of Macaronesia. The highest NNS richness was registered in the Canary Islands (76 NNS), followed by the Azores (66 NNS), Madeira (59 NNS) and finally Cabo Verde (18 NNS). Some differences amongst archipelagos were observed, such as the high number of non-native macroalgae in the Azores, fishes in the Canary Islands and tunicates in Cabo Verde. Overall, macroalgae, tunicates and bryozoans were the predominant taxonomic groups in the Macaronesian archipelagos. Madeira and Canary Islands were the archipelagos with more similarity in marine NNS, and Cabo Verde the most divergent. Finally, GLM suggested that non-native richness patterns across Macaronesia were dependent on the considered archipelago and strongly affected by (1) minimum distance to the mainland, (2) the total number of ports and marinas and (3) total marinas area (km2). Conclusions The model results and NNS listing in the present study will likely raise the awareness and response regarding marine NNS in the whole Macaronesia region, serving as a baseline for future research as well as implementing and enforcing regulations related to the introduction of marine NNS in oceanic islands