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Numerical analysis of seawater circulation in carbonate platforms: I. Geothermal convection

Differences in fluid density between cold ocean water and warm ground water can drive the circulation of seawater through carbonate platforms. The circulating water can be the major source of dissolved constituents for diagenetic reactions such as dolomitization. This study was undertaken to investigate the conditions under which such circulation can occur and to determine which factors control both the flux and the patterns of fluid circulation and temperature distribution, given the expected ranges of those factors in nature. Results indicate that the magnitude and distribution of permeability within a carbonate platform are the most important parameters. Depending on the values of horizontal and vertical permeability, heat transport within a platform can occur by one of three mechanisms: conduction, forced convection, or free convection. Depth-dependent relations for porosity and permeability in carbonate platforms suggest circulation may decrease rapidly with depth. The fluid properties of density and viscosity are controlled primarily by their dependency on temperature. The bulk thermal conductivity of the rocks within the platform affects the conductive regime to some extent, especially if evaporite minerals are present within the section. Platform geometry has only a second-order effect on circulation. The relative position of sealevel can create surface conditions that range from exposed (with a fresh-water lens present) to shallow water (with hypersaline conditions created by evaporation in constricted flow conditions) to submerged or drowned (with free surface water circulation), but these boundary conditions and associated ocean temperature profiles have only a second-order effect on fluid circulation. Deep, convective circulation can be caused by horizon tal temperature gradients and can occur even at depths below the ocean bottom. Temperature data from deep holes in the Florida and Bahama platforms suggest that geothermal circulation is actively occurring today to depths as great as several kilometers.

American Journal of Science

Atlantic spotted and bottlenose dolphin sympatric distribution in nearshore waters off Bimini, The Bahamas, 2003–2018

Within nearshore waters off Bimini, The Bahamas, Atlantic spotted ( Stenella frontalis ) and common bottlenose ( Tursiops truncatus ) dolphins are sympatric but separated spatially in different geographic areas and water depth ranges. Afternoon surveys during summer months across a 16-year period showed S. frontalis used the northern part of the nearshore area more, while T. truncatus used the southern area more. Generally, examination of geographic zones and water depth distributions of both species before and after construction of a pier in the study area suggested these dolphins were not impacted, long-term, by this anthropogenic activity. Still some differences in use of the nearshore area were identified. For water depth, S. frontalis varied use between 5–<12 m and 12–<20 m, depending on location along the coast. In contrast, T. truncatus consistently used the 5–<12 m depths. This difference may be related to how each species used the nearshore area, with T. truncatus feeding more and S. frontalis travelling and doing other activities. A small change in the distribution of S. frontalis by water depth off the northern coast of Bimini was found, specifically an increased use of deeper (12–20 m) water post 2014, which is unlikely an effect of pier construction as S. frontalis continued to use the 5–12 m depths as they had before pier construction. How this change might be related to an unprecedented 2013 S. frontalis immigration event, which might have disrupted the social structure, habitat/resource use, and distribution of both species, is discussed.

Bimini

Diet of the invasive Cuban treefrog (Osteopilus septentrionalis) in pine rockland and mangrove habitats in South Florida

Native to Cuba, the Bahamas and the Cayman Islands, the Cuban Treefrog (CTF) is an invasive species in Florida, with the ability to inflict serious ecological damage to invaded habitats. By examining the diet of the CTF, a known predator of native frogs, better predictions may be made of the impacts on native species and ecosystems. From 2002 - 2003, CTF diet was investigated in south Florida at four sites, two each within pine rockland and mangrove habitat. Within each habitat, one site exhibited a low density of CTFs and the other a high density of CTFs. CTFs were captured in PVC pipes attached to trees and stomach contents were examined after euthanasia. Beetles were the most numerous and widely consumed prey item among sites; roaches, orthopterans, spiders, ants, and caterpillars were also major dietary components. There were significant differences in the proportion of taxa consumed by CTFs between low and high density populations within each habitat, with the low density site in every instance having the higher proportion. Across habitats, ants comprised a significantly higher proportion of the diet in mangroves, whereas beetles, orthopterans, and snails comprised a significantly higher proportion of the diet in pine rocklands. Approximately 3.5% of all stomachs examined contained anuran remains. Though not significant, CTFs from low density sites consumed a higher proportion of frogs than those at high density sites. Corroborating previous research, the data show the CTF to be a generalist feeder, consuming a wide variety of invertebrate prey, with anurans playing only a minor role in the overall diet.

Florida