Velocity variability in a cross-section of a well-mixed estuary

North Inlet, South Carolina, is a well-mixed, tidally driven, high-salinity, shallow type IA estuary consisting of winding creeks that intersect a 30 km2 Spartina alterniflora salt marsh. An intensive spring tide field sampling in a 320 m wide cross-section during three consecutive tidal cycles in November 1977 resulted in detailed information on the cross-sectional net and rootmean-square (r.m.s.) velocity distributions...

Construction of net isopleth plots in cross-sections of tidal estuaries

Construction of isopleth plots of net velocity, material concentration, or material flux in cross-sections of tidal estuaries is not a trivial matter. To construct a flux-preserving isopleth plot requires that each instantaneous measure is weighted by the subarea for which the measure is representative. This area-weighted averaging procedure is outlined. Without area-weighting, net isopleth plots typically yield misleading results in tidal estuaries. In our example, net fluxes of total nitrogen are over-estimated without area-weighting

On the Sensitivity of the West Caribbean Sea Circulation to Tides, Wind, and Mesoscale Ocean Eddies: A Three-Dimensional Ocean Model Study

A three-dimensional, primitive equation ocean model is used to study the circulation in the West Caribbean Sea (WCS) region, and to test the sensitivity of the coastal flow to various forcing fields such as tides, climatological wind, and Caribbean eddies. The model domain is bordered by latitudes 15 – 22 degrees N and longitudes 76 – 87 degrees W, with the MesoAmerican Barrier Reef System (MBRS, along the coasts of Mexico, Belize, Guatemala, and Honduras) and the southern coast of Cuba as land boundaries. The WCS is open to the Caribbean Sea in the southeast and the Yucatan Channel in the northwest, with a prescribed 25 Sv flow-through from southeast to northwest. The results show that the base flow is highly variable even without time dependent forcing and without assimilation of eddies. The interaction of the base flow with the bathymetry gives rise to frequent westward propagating cyclonic eddies with diameters of 50-150 km in the Gulf of Honduras, and an anticyclonic eddy southeast of the Yucatan Channel with diameter of 200 km. When mesoscale eddies are included in the initial condition through assimilation of altimeter data, the WCS model simulates the propagation of those eddies, so that the eddy field is quite realistic even after 45 days from the initialization. Moreover, eddies were found to influence the coastal flow, such that when a cyclonic or an anticyclonic eddy is propagating through the WCS, the velocity field along the MBRS is either attenuated or enhanced, respectively. The area-averaged mean surface kinetic energy is influenced mostly by the 25 Sv flow-through and climatological winds, while the area- averaged eddy surface kinetic energy is influenced mostly by the mesoscale Caribbean eddies

Mesoamerican Reef Spawning Aggregations Help Maintain Fish Population: A Review of Connectivity Research and Priorities for Science Management

The life history of most marine organisms includes an obligate period of pelagic larval dispersal. Migration to spawning areas and pelagic dispersal is often well beyond the home range of these organisms. Designing marine protected areas to include a broad range of taxa and their various dispersal patterns is an important and daunting challenge. This paper addresses the issue of connectivity for one set of species in a limited geographic area. We focus on transient spawning reef fish within the Mesoamerican Reef and their connectivity. We divide our scientific review into four sections as follows: (1) ecological characterization of transient multi-species reef fish spawning aggregations, (2) oceanographic and biophysical modeling approaches for understanding connectivity, and (3) validation of models with observations. We conclude that the science behind connectivity is advancing rapidly on many fronts, but there are still large gaps, and it is still largely impossible for managers to apply the results of these studies in specific cases. We further recognize that human and political connectivity may be as important for management as the science behind it. Managers, scientists, fishermen, and politicians can and should embrace connectivity as an important factor in regional fisheries and marine biodiversity management. The collaborative design and implementation of networks of marine reserves that include multi-species spawning aggregation sites, critical nursery habitat, and their connectivity, are likely to provide an important contribution to reversing the decline in fisheries throughout the Gulf of Mexico and Caribbean Region

Staying Local: A Multiple Case Study of Employees Moving From Expatriates to Local Contracts in Multinational Organizations in Sweden and the United States

Localization of expatriate employees is a new trend of employment increasingly adopted by global corporations during the past decade. In recent years, different types of international contracts have been introduced, in substitution of traditional long-term expatriate contracts, including the transfer of expatriate employees to local contracts at host organizations. In spite of its growing popularity, there is a significant lack of research on the impact of this change of contracts to expatriate employees and their families. The purpose of this study is to explore the emerging international HR trend –localization of expatriates, with special focus on investigating the experiences of expatriates in becoming local employees at multinational organizations located in Sweden and the United States. A qualitative multiple case study approach is adopted to capture the nuanced multiple realities as experienced by expatriates during the process of localization. Eight individual case studies, four in Sweden and four in the United States, are part of this study. Themes that emerged described the experience of localization as an unanticipated career transition, significantly different from any other career transition experienced by employees, characterized by much uncertainty, isolation, and lack of a common repertoire of knowledge. This study concluded that localization is often an ill-planned, haphazard event that leaves employees without much support from their employers, mentors, and local colleagues. Implications for practice and research are presented in this study

Hindcasting of hurricane characteristics and observed storm damage on a fringing reef, Jamaica, West Indies

Hurricane Allen is one of the most severe hurricanes on record and caused extensive damage throughout the Caribbean in early August 1980. Coral reefs along the north coast of Jamaica were devastated by the hurricane-induced waves. As in the case of most hurricanes, no wave measurements were made. We have computed the wind field and hindcast the deep water wave characteristics as the storm impacted the fringing reef at Discovery Bay on the north central coast of Jamaica. The deep water waves propagated into shallow water on the forereef and transformed as a result of shoaling and refraction. We found that significant wave height at a given time varied by a factor of 2.6 and that incident wave power for the duration of the storm varied by a factor of 7 along a 3 km section of the Discovery Bay forereef due to variations in local bathymetry. Maximum hindcast breakers reached a height of 11.5 m with a significant wave period of 10.5 s. Observations of the most intense reef damage coincided with areas on the eastern forereef experiencing the highest breakers. We speculate that the degree of reef damage is a function of how much time has elapsed since the previous storm rather than frequency of hurricanes at a locality

Hydrodynamic Variability in a Microtidal Coastal Bay Geographically Susceptible to North East Trade Winds

The ecological integrity and overall health conditions of natural coastal systems are largely based upon the balance among physical processes. The objective of this study was to assess the effects of tides and winds on the water level variability, circulation patterns, and turnover time in Bahia de la Ascension (BA), a shallow, tropical coastal bay in the Mexican Caribbean prone to the influence of Trade winds due to its geographical location. The analysis of the hydrodynamics of BA using a 2D numerical model indicates that the tidal flow in the inlets and central basin of the bay vary by tidal phase. An averaged seawater inflow through the south inlet and outflow through the north inlet is observed for every simulated case, while peak instantaneous current velocities are evident in the northern entrance. Winds play a dominant role in the water turnover from the system’s interior to the main bay. The model shows an average turnover time of 45 days for the whole bay, with shorter turnover when Trade winds impart stress along the main northeast–southwest axis in the bay. Since the tidal signal is attenuated in the southwest endpoint of the bay, the relevance of winds in the transport phenomena was considered fundamental to preserve the ecological heterogeneity of BA

Modeling approach to regime shifts of primary production in shallow coastal ecosystems

Pristine coastal shallow systems are usually dominated by extensive meadows of seagrass species, which are assumed to take advantage of nutrient supply from sediment. An increasing nutrient input is thought to favour phytoplankton, epiphytic microalgae, as well as opportunistic ephemeral macroalgae that coexist with seagrasses. The primary cause of shifts and succession in the macrophyte community is the increase of nutrient load to water; however temperature plays also an important role. A competition model between rooted seagrass (Zostera marina), macroalgae (Ulva sp), and phytoplankton has been developed to analyse the succession of primary producer communities in these systems. Successions of dominance states, with different resilience characteristics, are found when modifying the input of nutrients and the seasonal temperature and light intensity forcing.Comment: 33 pages, including 10 figures. To appear in Ecological Complexit

Estimating coastal lagoon tidal flooding and repletion with multidate ASTER thermal imagery

Coastal lagoons mix inflowing freshwater and tidal marine waters in complex spatial patterns. This project sought to detect and measure temperature and spatial variability of flood tides for a constricted coastal lagoon using multitemporal remote sensing. Advanced Spaceborne Thermal Emission Radiometer (ASTER) thermal infrared data provided estimates of surface temperature for delineation of repletion zones in portions of Chincoteague Bay, Virginia. ASTER high spatial resolution sea-surface temperature imagery in conjunction with in situ observations and tidal predictions helped determine the optimal seasonal data for analyses. The selected time series ASTER satellite data sets were analyzed at different tidal phases and seasons in 2004–2006. Skin surface temperatures of ocean and estuarine waters were differentiated by flood tidal penetration and ebb flows. Spatially variable tidal flood penetration was evaluated using discrete seed-pixel area analysis and time series Principal Components Analysis. Results from these techniques provide spatial extent and variability dynamics of tidal repletion, flushing, and mixing, important factors in eutrophication assessment, water quality and resource monitoring, and application of hydrodynamic modeling for coastal estuary science and management