Generation of baroclinic topographic waves by a tropical cyclone impacting a low-latitude continental shelf

Numerical model experiments have been performed to analyze the low-latitude baroclinic continental shelf response to a tropical cyclone. The theory of coastally trapped waves suggests that, provided appropriate slope, latitude, stratification and wind stress, bottom-intensified topographic Rossby waves can be generated by the storm. Based on a scale analysis, the Nicaragua Shelf is chosen to study propagating topographic waves excited by a storm, and a model domain is configured with simplified but similar geometry. The model is forced with wind stress representative of a hurricane translating slowly over the region at 6 km h⁻¹. Scale analysis leads to the assumption that baroclinic Kelvin wave modes have minimal effect on the low-frequency wave motions along the slope, and coastal-trapped waves are restricted to topographic Rossby waves. Analysis of the simulated motions suggests that the shallow part of the continental slope is under the influence of barotropic topographic wave motions and at the deeper part of the slope baroclinic topographic Rossby waves dominate the low-frequency motions. Numerical solutions are in a good agreement with theoretical scale analysis. Characteristics of the simulated baroclinic waves are calculated based on linear theory of bottom-intensified topographic Rossby waves. Simulated waves have periods ranging from 153 to 203 h. The length scale of the waves is from 59 to 87 km. Analysis of energy fluxes for a fixed volume on the slope reveals predominantly along-isobath energy propagation in the direction of the group velocity of a topographic Rossby wave. Another model experiment forced with a faster translating hurricane demonstrates that fast moving tropical cyclones do not excite energetic baroclinic topographic Rossby waves. Instead, robust inertial oscillations are identified over the slope.     

Subduction-related P–T path for eclogites and garnet glaucophanites from the Samaná Peninsula basement complex, northern Hispaniola

Eclogite and garnet glaucophanite lenses from the Punta Balandra unit of the Samaná basement complex (northern Hispaniola) preserve information of the early metamorphic and tectonic history of subduction in the Caribbean island-arc and its collision with the North America plate. For this reason, P–T paths were reconstructed from the interpretation of meso- and microfabrics, mineral assemblages and chemistry, with the aid of equilibrium phase diagrams calculated for specific bulk compositions in the CKNFMASH system and isopleths for selected solution end-members. The obtained results suggest that the subduction-related prograde path evolved from garnet-free and garnet-bearing lawsonite-blueschist facies, to phengite eclogite facies conditions at P=22–24 kbar and T=610–625°C, with a probable intermediate stage of low-P lawsonite eclogite facies. The subsequent retrograde P–T path entered the epidote-blueschist (garnet-free) facies and ended within the greenschist facies field, similar to the prograde evolution at low-P. Eclogites and garnet glaucophanites formed in a subduction zone in which oceanic lithosphere was subducted WSW/W beneath the Caribbean plate.     

Ecohydrology and water resources management: a pilot study in Trinidad

Abstract

An area of rainforest in Trinidad (10°N, 61°W) is remarkably rich in biodiversity, and receives the highest amount of rainfall in the island due to its orography and the dominant northeast trade winds. However, a year-round transfer of water from its pristine rivers is likely in the future, with ecological consequences. The results of a pilot study are presented, based on a simple, and graphical, segment-scale multi-objective methodology for the estimation of the optimal instream flow of the 13 rivers in this area. This methodology is based on a dimensionless ecohydrological factor, Δ, which enables the required hydraulic mean depth at a river cross-section to be expressed in terms of the average species length at maturity for a target group of amphibians, birds, fish, mammals and reptiles. Moreover, the methodology considers the socio-economic cost of ecological degradation brought about by streamflow abstraction, as well as the economic benefit of the same. An example illustrates the estimation of optimal instream flow for a value of Δ and, thereby, the corresponding optimal river intake operating rule, based on the hydraulic characteristics of a 0.1 km segment of one of the rivers, for the 20-year average dry (January—May) and wet (June–December) seasons. The limitations of the pilot study, and areas for further research, are also highlighted with a hope that it will ultimately evolve into a decision-making tool for water resources management.     

Fruit of the cyclone: Undoing geopolitics through geopoetics

How can a geopolitical worldview be undone? Can it be undone? These questions have played a central role in critical geopolitics, particularly with feminist and postcolonial authors who seek to show how geopolitics are constituted through everyday processes. This article puts this work into dialogue with a relatively recent strand of geopolitics that attempts to re-examine its environmental foundations. What role might geophysical forces play in challenging hegemonic geopolitical worldviews? The role of materiality in geopolitics will be examined through the work of Guadeloupian author Daniel Maximin. In his book Les Fruits du Cyclone: Une Géopoétique de la Caraïbe, Maximin argues for the unique position of a Caribbean geopoetics, channelled into the figure of humanity as the ‘fruit of the cyclone’, to challenge contemporary geopolitics. In turning to both the natural and the political disasters that visit the Caribbean, he illustrates how impoverished understandings of the geophysical lead to a continuation of colonial patterns. Against this background, Maximin calls for a decolonisation of the coloniser through unsettling their geographical imagination. This decolonisation utilises the geophysical not as a model for human or human–world relations, but as a tool for re-situating oneself and for reimagining global divisions.     

Recruitment of Demosponges (Porifera,Demospongiae) in Rocky and Coral Reef Habitats of Santa Marta,Colombian Caribbean*

Abstract. Recruitment of demosponges (Porifera, Demospongiae) was monitored bimonthly for one year (March 1987 – March 1988) on acrylic plates, and compared to cover of adults, in six rocky and coral reef habitats at Santa Marta, Colombian Caribbean, an area subjected to seasonal, upwelling-outwelling regimes. According to suggestive but not significant trends, recruitment rates are more positively influenced by the total sponge cover near groups of plates than by cover at a larger (habitat) scale; recruit mortality is lower where recruitment is higher. These findings are in agreement with a model of higher settlement (probably due to short-distance dispersal) and lower postsettlement mortality within a few meters of adult sponges. Recruitment varied seasonally, being relatively high from May to November-December during the rainy, outwelling season, when seawater temperature was warmer, water turbidity higher, and benthic algal density lower; it was very low from January to April during the dry, upwelling season.     

The Hispaniola Fluvial System and its Morphostructural Context

This paper presents results of the geomorphological study of river elements for a morphostructural characterization of Hispaniola. The fluvial system and its primary and secondary drainage divides were delimited using a specially developed methodology. More than 120 fluvial basins were studied. The largest rivers are the sixth-order Yaque del Norte and Yaque del Sur. The fluvial density is in the range of 0.08-4.0 km/km², with highest values in the Cordillera Central. There are two large hydrological regions, the Western and the Eastern, with a northeastern transverse diagonal boundary, coinciding with the direction of the Beata Escarpment. Using quantitative data to characterize the morphostructure of the fluvial network in Hispaniola enabled us to make comparisons with a Cuban network. As is shown, the river pattern in Hispaniola is basically tectonic, with a remarkable directional diversity in the main first-order drainage divide. In the Caribbean area, Eastern Cuba is the only other location with this pattern.     

Evaluation of stony coral indicators for coral reef management

Colonies of reef-building stony corals at 57 stations around St. Croix, US Virgin Islands were characterized by species, size and percentage of living tissue. Taxonomic, biological and physical indicators of coral condition were derived from these measurements and assessed for their response to gradients of human disturbance—a requirement for indicators used in regulatory assessments under authority of the Clean Water Act. At the most intensely disturbed location, five of eight primary indicators were highly correlated with distance from the source of disturbance: Coral taxa richness, average colony size, the coefficient of variation of colony size, total topographic coral surface area, and live coral surface area. An additional set of exploratory indicators related to rarity, reproductive and spawning mode and taxonomic identity were also screened. The primary indicators demonstrated sufficient precision to detect levels of change that would be applicable in a regional-scale regulatory program.     

Composition,export and faunal utilization of drift vegetation in the salt river submarine canyon

Submarine canyons may be particularly important in the transport process of drift seagrasses and seaweeds from highly productive shallow lagoon areas to deeper water. We studied the composition, export, and faunal utilization of shallow, nearshore benthic vegetation as it was transported to offshore areas via the Salt River submarine canyon on the island of St Croix, U.S. Virgin Islands. The study was conducted using a saturation diving system (NULS-1: Hydrolab) during two missions in April and August, 1980. Using bottom drifters deployed in Salt River Bay and the submarine canyon, we recorded net benthic current flow up to 2 cm s^?1 moving out of the lagoon and down the canyon to deeper water. Using bottom nets set up at the canyon head and at the 29 m isobar, and from transect surveys and drift clump samples, we determined drift plant export rates and drift clump biomass and species composition. The dominant drift plants were Thalassia testudinum and Syringodium filiforme and algae in the genera Dictyota, Dictyopterus, and Diloplus. During the second mission, the seagrass Halophila decipiens became more abundant, both in the drift and in large patches along the canyon floor. In both missions, more drift was collected in the nets during high wind conditions than during calmer days. Calculated turnover times ranged from 0·01 to 4·4 days for algae in the order Dictyotales and 4·4 to 18 days for Thalassia blades. Total exported biomass of drift vegetation varied between 1·4 to 65·1 kg wet wt day^?1. Samples of drift vegetation contained mostly juvenile forms of both invertebrates and fishes, but in relatively low numbers. Faunal numbers were most strongly related to rate of drift movement.