Gravity current propagation up a valley

The advance of the front of a dense gravity current propagating in a rectangular channel and V-shaped valley both horizontally and up a low slope is examined through theory, full-depth lock-release laboratory experiments and hydrostatic numerical simulations. Consistent with theory, experiments and simulations show that the front speed is relatively faster in the valley than in the channel. The front speed measured shortly after release from the lock is 5% to 22% smaller than theory with greater discrepancy found in up-sloping V-shaped valleys. By contrast, the simulated speed is about 6% larger than theory showing no dependence on slope for rise-angles up to θ = 8◦. Unlike gravity currents in a channel, the current head is observed in experiments to be more turbulent when propagating in a V-shaped valley. The turbulence is presumably enhanced due to the lateral flows down the sloping sides of the valley. As a consequence, lateral momentum transport contributes to the observed lower initial speeds. A WKB-like theory predicting the deceleration of the current as it runs upslope agrees remarkably well with simulations and with most experiments, within errors.The authors gratefully acknowledge the National Science Foundation (grant OCE-0824636) and the Office of Naval Research (grant N00014-09 1-0844) for their support of the 2013 WHOI Geophysical Fluid Dynamics Summer School, where much of the research presented in this paper was performed

Novel Application of Laboratory Instrumentation Characterizes Mass Settling Dynamics of Oil-Mineral Aggregates (OMAs) and Oil-Mineral-Microbial Interactions

AbstractIt is reasonable to assume that microbes played an important role in determining the eventual fate of oil spilled during the 2010 Deepwater Horizon disaster, given that microbial activities in the Gulf of Mexico are significant and diverse. However, critical gaps exist in our knowledge of how microbes influence the biodegradation and accumulation of petroleum in the water column and in marine sediments of the deep ocean and the shelf. Ultimately, this limited understanding impedes the ability to forecast the fate of future oil spills, specifically the capacity of numerical models to simulate the transport and fate of petroleum under a variety of conditions and regimes.By synthesizing recent model developments and results from field- and laboratory-based microbial studies, the Consortium for Simulation of Oil-Microbial Interactions in the Ocean (CSOMIO) investigates (a) how microbial biodegradation influences accumulation of petroleum in the water column and in marine sediments and (b) how biodegradation can be influenced by environmental conditions and impact forecasts of potential future oil spills.</jats:p

Increasing the Depth of Current Understanding: Sensitivity Testing of Deep-Sea Larval Dispersal Models for Ecologists

Larval dispersal is an important ecological process of great interest to conservation and the establishment of marine protected areas. Increasing numbers of studies are turning to biophysical models to simulate dispersal patterns, including in the deep-sea, but for many ecologists unassisted by a physical oceanographer, a model can present as a black box. Sensitivity testing offers a means to test the models' abilities and limitations and is a starting point for all modelling efforts. The aim of this study is to illustrate a sensitivity testing process for the unassisted ecologist, through a deep-sea case study example, and demonstrate how sensitivity testing can be used to determine optimal model settings, assess model adequacy, and inform ecological interpretation of model outputs. Five input parameters are tested (timestep of particle simulator (TS), horizontal (HS) and vertical separation (VS) of release points, release frequency (RF), and temporal range (TR) of simulations) using a commonly employed pairing of models. The procedures used are relevant to all marine larval dispersal models. It is shown how the results of these tests can inform the future set up and interpretation of ecological studies in this area. For example, an optimal arrangement of release locations spanning a release area could be deduced; the increased depth range spanned in deep-sea studies may necessitate the stratification of dispersal simulations with different numbers of release locations at different depths; no fewer than 52 releases per year should be used unless biologically informed; three years of simulations chosen based on climatic extremes may provide results with 90% similarity to five years of simulation; and this model setup is not appropriate for simulating rare dispersal events. A step-by-step process, summarising advice on the sensitivity testing procedure, is provided to inform all future unassisted ecologists looking to run a larval dispersal simulation

High interannual variability in connectivity and genetic pool of a temperate clingfish matches oceanographic transport predictions

Adults of most marine benthic and demersal fish are site-attached, with the dispersal of their larval stages ensuring connectivity among populations. In this study we aimed to infer spatial and temporal variation in population connectivity and dispersal of a marine fish species, using genetic tools and comparing these with oceanographic transport. We focused on an intertidal rocky reef fish species, the shore clingfish Lepadogaster lepadogaster, along the southwest Iberian Peninsula, in 2011 and 2012. We predicted high levels of self-recruitment and distinct populations, due to short pelagic larval duration and because all its developmental stages have previously been found near adult habitats. Genetic analyses based on microsatellites countered our prediction and a biophysical dispersal model showed that oceanographic transport was a good explanation for the patterns observed. Adult sub-populations separated by up to 300 km of coastline displayed no genetic differentiation, revealing a single connected population with larvae potentially dispersing long distances over hundreds of km. Despite this, parentage analysis performed on recruits from one focal site within the Marine Park of Arrabida (Portugal), revealed self-recruitment levels of 2.5% and 7.7% in 2011 and 2012, respectively, suggesting that both long-and short-distance dispersal play an important role in the replenishment of these populations. Population differentiation and patterns of dispersal, which were highly variable between years, could be linked to the variability inherent in local oceanographic processes. Overall, our measures of connectivity based on genetic and oceanographic data highlight the relevance of long-distance dispersal in determining the degree of connectivity, even in species with short pelagic larval durations

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Gulf Stream separation in numerical ocean models

This chapter summarizes our present knowledge of Gulf Stream separation in numerical ocean models. High horizontal resolution ocean numerical models are now capable of simulating quite realistically the separation and path of the Gulf Stream, and significant advances have been made in the last decade in our understanding of western boundary current separation. However, the Gulf Stream separation in numerical models continues to be a challenge because it remains very sensitive to the choices made for subgrid scale parameterizations.</p

Gulf Stream separation in numerical ocean models

This chapter summarizes our present knowledge of Gulf Stream separation in numerical ocean models. High horizontal resolution ocean numerical models are now capable of simulating quite realistically the separation and path of the Gulf Stream, and significant advances have been made in the last decade in our understanding of western boundary current separation. However, the Gulf Stream separation in numerical models continues to be a challenge because it remains very sensitive to the choices made for subgrid scale parameterizations.</p

Evolution of land surface air temperature trend

The global climate has been experiencing significant warming at an unprecedented pace in the past century(1,2). This warming is spatially and temporally non-uniform, and one needs to understand its&nbsp;evolution&nbsp;to better evaluate its potential societal and economic impact. Here, the&nbsp;evolution&nbsp;ofglobal&nbsp;land&nbsp;surface&nbsp;air&nbsp;temperature&nbsp;trend&nbsp;in the past century is diagnosed using the spatial-temporally multidimensional ensemble empirical mode decomposition method(3). We find that the noticeable warming (&gt;0.5 K) started sporadically over the global&nbsp;land&nbsp;and accelerated until around 1980. Both the warming rate and spatial structure have changed little since. The fastest warming in recent decades (&gt;0.4 K per decade) occurred in northern mid-latitudes. From a zonal average perspective, noticeable warming (&gt;0.2 K since 1900) first took place in the subtropical and subpolar regions&nbsp;of&nbsp;the Northern Hemisphere, followed by subtropical warming in the Southern Hemisphere. The two bands&nbsp;of&nbsp;warming in the Northern Hemisphere expanded from 1950 to 1985 and merged to cover the entire Northern Hemisphere.</span

Validating ocean general circulation models via Lagrangian particle simulation and data from drifting buoys

Drifting Fish Aggregating Devices (dFADs) are small drifting platforms with an attached solar powered buoy that report their position with daily frequency via GPS. We use data of 9,440 drifting objects provided by a buoys manufacturing company, to test the predictions of surface current velocity provided by two of the main models: the NEMO model used by Copernicus Marine Environment Monitoring Service (CMEMS) and the HYCOM model used by the Global Ocean Forecast System (GOFS)