Coral growth rate: Variation with depth

Light and temperature are two of the most important physical factors affecting rates of growth of reef corals. The effect of light has been determined by X-radiographic measurement of long-term growth rates for 89 colonies of the coral Montastrea annularis collected over a 27.5?m depth range from St. Croix, U.S. Virgin Islands. These measurements, in conjunction with measurements of skeletal density, have established that M. annularis calcifies most rapidly at intermediate depths, and they have confirmed the identification of two distinct populations within this important frame-building species.     

The natural radiochemical and growth records in contemporary hermatypic corals from the Atlantic and Caribbean

The skeletal banding observed in vertical cross-sections of two species of coral,Montastrea annularis from Jamaica andDiploria labrynthiformis from Bermuda, has been confirmed to be annual by ingrowth of²²⁸Th towards radioactive equilibrium with²²⁸Ra taken up from seawater. In addition the Bermuda coral is shown to have incorporated²¹⁰Pb at essentially constant specific activity over at least the last thirty years.The individual annual patterns of growth banding in a suite of specimens ofD. Labrynthiformis from Bermuda are shown to be correlative. The mass of CaCO₃ accumulated each year is positively correlated with the band width for the corresponding year.     

Sublethal and lethal effects of sediments applied to common Caribbean Reef corals in the field

Experiments to measure natural rates of sedimentation and to assess the tolerance of coral species to increased sedimentation were conducted at San Cristobal Reef, Puerto Rico. Sedimentation rates were measured over an 18 month period. Calcareous sediments were applied to colonies of Montastraea annularis, Diploria strigosa, D. clivosa, Acropora palmata and A. cervicornis in different frequencies and in different doses.Mean sedimentation rates from sediment traps were 9.6±2.4 (S.E.) mg cm^?2 · day^?1 at 10 cm above the bottom and 2.5±0.9 (S.E.) and 2.6±1.2 (S.E.) mg cm^?2 · day^?1 for two sets of traps at 50 cm above the bottom. Sediment application experiments indicated A. palmata was the least tolerant of the species tested. Although A. cervicornis and D. strigosa colonies were not significantly affected, single applications of 800 mg cm^?2 to M. annularis colonies and of 200 mg cm^?2 to A. palmata colonies caused death of underlying coral tissue. Algae colonized the smothered portions of these corals.     

Effects of chronic oil pollution on a Caribbean coral reef

Sublethal effects of oil pollution on coral reefs may not become manifest except over very long periods of time. Uniform reefs with an Acropora palmata belt (2 m depth) and a Montastrea annularis community (4 m depth) were originally present along the coast near an oil refinery that has been in operation for more than 60 years in Aruba. Quantitative surveys of reef structure, coral cover, and numbers of juvenile corals along 15 km of the coast showed these reef characteristics to vary significantly in relation to the location of the refinery and the very persistent local current direction. The spatial structure of the reef has deteriorated, living coral cover is low, and less juveniles are present in front and downcurrent of the refinery. Some coral species, such as A. palmata and M. annularis, show a large gap in their distribution along the coast but a species such as Diploria strigosa is relatively abundant in the polluted area. The results of chronic oil pollution (such as spills, clean-ups, etc.) are, after 60 years, clearly discernible over a distance of 10 to 15 km along the reef.     

Expansion of an invasive coral species over Abrolhos Bank,Southwestern Atlantic

Invasive coral species of the genus Tubastraea have been increasingly recorded in Southwestern Atlantic waters since the 1980s. Their invasion and infestation are mainly related to port and oil exploration activities. For the first time the presence of Tubastraea tagusensis colonies is reported in Espírito Santo State, colonizing a port shore area, and incrusting oil/gas platform structures situated in the southern Abrolhos Bank, which is part of the most important coral reef system of the South Atlantic Ocean. Tubastraea colonies exhibit fast growth and high recruitment rates, and colonized 40% of the analyzed structures in just four years. The projection of port and oil/gas industry growth for the Espírito Santo State (more than 300%) highlights an alert to the dispersal of this alien species to natural areas.     

‘Growth rings’ in crustose lichens: Comparison with directly measured growth rates and implications for lichenometry

Some species of crustose lichens, such as Ochrolechia parella (L.) Massal., exhibit concentric marginal rings, which may represent an alternative technique of measuring growth rates and potentially, a new lichenometric dating method. To examine this hypothesis, the agreement and correlation between ring widths and directly measured annual radial growth rates (RaGR, mm a⁻¹) were studied in 24 thalli of O. parella in north Wales, UK, using digital photography and image analysis. Variation in ring width was observed at different locations around a thallus, between thalli, and from year to year. The best agreement and correlation between ring width and lichen growth rates was between mean width of the outer two rings (measured in 2011) and mean RaGR (in 2009/10). The O. parella data suggest that mean width of the youngest two growth rings, averaged over a sample of thalli, is a predictor of recent growth rates and therefore could be used in lichenometry. Potential applications include as a convenient method of comparing lichen growth rates on surfaces in different environmental settings; and as an alternative method of constructing lichen growth-rate curves, without having to revisit the same lichen thalli over many years. However, care is needed when using growth rings to estimate growth rates as: growth ring widths may not be stable; ring widths exhibit spatial and temporal variation; rings may not represent 1-year's growth in all thalli; and adjacent rings may not always represent successive year's growth.     

Empirical model of Skeletonema costatum photosynthetic rate,with applications in the San Francisco Bay estuary

An empirical model of Skeletonema costatum photosynthetic rate is developed and fit to measurements of photosynthesis selected from the literature. Because the model acknowledges existence of: 1) a light-temperature interaction (by allowing optimum irradiance to vary with temperature), 2) light inhibition, 3) temperature inhibition, and 4) a salinity effect, it accurately estimates photosynthetic rates measured over a wide range of temperature, light intensity, and salinity. Integration of predicted instantaneous rate of photosynthesis with time and depth yields daily net carbon assimilation (pg C cell^?1 day^?1) in a mixed layer of specified depth, when salinity, temperature, daily irradiance and extinction coefficient are known. The assumption of constant carbon quota (pg C cell^?1) allows for prediction of mean specific growth rate (day^?1), which can be used in numerical models of Skeletonema costatum population dynamics.Application of the model to northern San Francisco Bay clearly demonstrates the limitation of growth by low light availability, and suggests that large population densities of S. costatum observed during summer months are not the result of active growth in the central deep channels (where growth rates are consistently predicted to be negative). But predicted growth rates in the lateral shallows are positive during summer and fall, thus offering a testable hypothesis that shoals are the only sites of active population growth by S. costatum (and perhaps other neritic diatoms) in the northern reach of San Francisco Bay.     

The influence of unavoidable saturation averaging on the experimental measurement of dynamic capillary effects: A numerical simulation study

Many studies over the past four decades have observed that capillary pressure–saturation (P_c–S_w) relationships are often different when measured dynamically under rapidly changing pressure inputs. This phenomenon has been referred to as a dynamic capillary effect, and its magnitude is often quantified by the dynamic capillary coefficient, τ. Experimentally-reported values of τ have varied by orders of magnitude, even for seemingly similar experimental systems. The purpose of the present work is to numerically explore the likely impact of fluid properties on the calculation of τ from experimental measurements. Specifically, the emphasis is on understanding how spatial averaging of the saturation profiles resulting from different fluid combinations contributes to the apparent magnitude of τ derived from experimental measurements.Simulations of dynamic drainage in a packed sand column were conducted using the CompSim multiphase flow simulator. Four nonwetting phase fluids with viscosities spanning four orders of magnitude were studied. Comparison between local and spatially-averaged rates of saturation change show significant differences, with the magnitude of the difference increasing with increasing viscosity to interfacial tension ratio and increasing drainage rate. Results show that at averaging scales likely to be experienced during experimental saturation measurements, this effect is likely to produce significant differences in the ultimate magnitude of the calculated τ values for different fluid systems and drainage rates. This result means that conventional flow phenomena may produce an inherent systematic bias in experimental measurements of τ, amplifying measured values for high viscosity or low interfacial tension systems and for experiments where higher drainage rates are used.     

Modelling the effects of Zostera noltei meadows on sediment dynamics: application to the Arcachon lagoon

A three-dimensional model has been modified to describe the complex interactions between hydrodynamics, sediment dynamics and biological parameters in the presence of Zostera noltei. The model treats seagrass leafs as flexible blades that bend under hydrodynamic forcing and alter the local momentum and turbulence fluxes and, therefore, the benthic shear conditions; these changes cause related changes to the mass balance at the boundary of the bed, in turn affecting the suspended matter in the column and ultimately primary productivity and the growth of the dwarf-grass. Modelling parameters related to the impact of Z. noltei to the local flow and to erosion and deposition rates were calibrated using flume experimental measurements; results from the calibration of the model are presented and discussed. The coupled model is applied in the Arcachon Bay, an area with high environmental significance and large abundance of dwarf-grass meadows. In the present paper, results from preliminary applications of the model are presented and discussed; the effectiveness of the coupled model is assessed comparing modelling results with available field measurements of suspended sediment concentrations and seagrass growth parameters. The model generally reproduces sediment dynamics and dwarf-grass seasonal growth in the domain efficiently. Investigations regarding the effects of the vegetation to the near-bed hydrodynamics and to the sediment suspension in the domain show that dwarf-grass meadows play an important part to velocity attenuation and to sediment stabilisation, with flow and suspended sediment concentrations damping, compared to an unvegetated state, to reach 35–50 and 65 %, respectively, at peak seagrass growth.     

Growth of Mytilus edulis in net bags transferred to different localities in a eutrophicated Danish fjord

The growth rate has been measured in Mytilus edulis transferred in net bags to seven localities in the brackish Danish fjord, Limfjorden, in which certain areas are heavily eutrophicated. The increase in shell length, shell weight and flesh body weight was measured after growth periods of 14–18 days. The increase in, e.g., flesh dry weight ranged from twice the start weight to a four-fold increase of the start weight. The net growth efficiencies were estimated to be between 54 and 73%. Algal concentration was in no case the limiting growth factor, but low growth rates were observed in areas with seasonal oxygen depletion and release of toxic H₂S from the sediments. It is suggested that measurements of actual growth in M. edulis can be a useful technique in the study of biological effects in marine recipients.     

Implications of a concentration-dependent growth rate on the boundary layer crystal-melt model

The influence of a melt boundary layer on crystal growth is analyzed. The treatment extends the results of Burton, Prim and Slichter (1953) and incorporates composition-dependent growth rates. It is shown that in these general cases the growth rate cannot be arbitrarily fixed but must satisfy a self-consistent equation. Self-consistency problems arise because the growth rate determines the composition profile in the melt and, in turn, the composition profile determines the growth rate. The self-consistent growth rate is shown to vary markedly with the ratio δ/D, where δ is the thickness of the boundary layer and D is the appropriate diffusion coefficient in the melt. This self-consistency can be very important in the analysis of both field and laboratory growth rates as well as in trace element partition kinetic models.     

Turbulent mixing in fine-scale phytoplankton layers: Observations and inferences of layer dynamics

Turbulence measurements in fine-scale phytoplankton layers (∼1 to ∼10 m) in the Gulf of Aqaba (Red Sea) were used to evaluate mechanisms of layer formation, maintenance, and breakdown. Simultaneous profiles of chlorophyll a (Chl a) fluorescence and temperature microstructure were measured in the upper 40 m of a 430 m water column over a 16-d period, using a Self Contained Autonomous MicroProfiler (SCAMP). Layers of concentrated phytoplankton were identified in 95 of the 456 profiles. The layers were situated in density stratified regions between 15 and 38 m depth and were characterized by intensities of 0.1 to 0.35 μg Chl a L⁻¹ (as much as two times background concentrations) and an average thickness of 10 m. We show that turbulent mixing and isopycnal displacements associated with internal waves modulated the thickness of the layers. Variations in mixing rates within layers were connected to the vertical structure of the stratified turbulence and the stage of layer development. The breakdown of a persistent phytoplankton layer was tied to strong turbulent mixing at the base of the surface mixed layer, which encroached on the layer from above. Hydrographic observations and scaling analysis suggest that the layers most likely formed in horizontal intrusions from the adjacent coastal region. The cross-shore propagation of phytoplankton-rich intrusions may have important implications for the trophic state of offshore planktonic communities.     

Biological enhancement of solute exchange between sediments and bottom water on the Washington continental shelf

Solute exchange between the interstitial waters and overlying waters on the Washington continental shelf was investigated based on measurements of the pore-water sulfate distribution and sulfate reduction rates as well as through models describing the distribution of sulfate in anaerobic pore waters. The depth-integrated sulfate reduction rate greatly exceeded the influx of sulfate attributable to molecular diffusion and sediment accumulation acting on the measured vertical sulfate gradients, and indicated that additional transport mechanisms must have been operating. Sediment mixing was probably not the primary mechanism since high eddy diffusivities would be required to depths of 30 cm to maintain the observed sulfate distribution, whereas previously measured²¹⁰Pb distributions indicated sediment mixing is primarily restricted to depths <7 cm. Irrigation of bottom water through animal burrows was the most likely mechanism. To describe this process, a general diffusive irrigation coefficient, B, was formulated. Vertical profiles of B showed the main irrigation zone occurred between 2 and 10 cm with reduced irrigation rates occurring below this. These coefficients calculated from the sulfate distribution were similar to ones calculated from previously published radon measurements at the same stations, indicating that this formulation of irrigation exchange may be useful in modelling the exchange of dissolved solutes between the pore water and the bottom water.     

Solar flare effect on the geomagnetic field and ionosphere

This paper studies the ionospheric and geomagnetic response to an X6.2 solar flare recorded at 14:30 UT on December 13, 2001, in quiet geomagnetic conditions which allow the variations in the geomagnetic field and ionosphere measurements to be easily related to the solar flare radiation.By using measurements from the global positioning system (GPS) and geomagnetic observatories, the temporal evolution of ionospheric total electron content variation, vTEC_V, and geomagnetic field variations, δB, as well as their rates of variation, were obtained around the subsolar point at different solar zenith angles. The enhancement of both parameters was recorded one to three minutes later than the Geostationary Operational Environmental Satellite (GOES) programme recording; such delay tends to depend on the latitude, longitude, and solar zenith angle of the observatory's observations.The vTEC_V is related to the local time and the δB to the intensity and position of the ionospheric currents.The vTEC_V′s maximum value is always recorded later than the maximum values reached by δB and the X-ray intensity. The maximum δB is larger in the local morning than in the afternoon.The rates of vTEC_V and δB have two maximum values at the same time as the maximum values recorded by Hα (for each ribbon).This work shows the quantitative and qualitative relations between a solar flare and the ionospheric and geomagnetic variations that it produces.     

On the sensitivity of total electron content (TEC) to upper atmospheric/ionospheric parameters

The total electron content (TEC) is a key ionospheric parameter for various space weather applications. Over the last decade an extensive database of TEC measurements has become available from both space- and ground-based observations, and these measurements have established the general morphology of the global TEC distributions. In particular, the TOPEX TEC measurements have shown strong longitudinal variations of TEC in addition to the observed day-to-day variabilities. To better understand the observed TEC variations and to better guide its modeling, we have studied the sensitivity of quiet-time TEC to the following key atmospheric and ionospheric parameters: neutral density, neutral wind, plasma temperatures, plasmaspheric flux, and the O⁺–O collision frequency. These parameters are often only roughly known and can cause large uncertainties in model results. For this study, we have developed a numerical mid-latitude ionospheric model, which solves the momentum and continuity equations for the O⁺ density and a simplified set of equations for the H⁺ density. To obtain TEC, the calculated ion densities have been integrated from the bottom altitude (100 km) to the altitude of the TOPEX satellite (1336 km). Our study shows that during the day the neutral wind and the neutral composition have the most important effect on TEC. In particular, the zonal component of the neutral wind can have a large effect on TEC in the southern hemisphere where the magnetic declination angle is large. During the night, most of the above-mentioned parameters can play a significant role in the TEC morphology, except for the plasma temperature, which has only a small effect on TEC. Finally, the TEC varies roughly linearly with respect to all of the parameters except for the neutral wind.     

Leaching and microbial degradation of dissolved organic matter from salt marsh plants and seagrasses

Dissolved organic matter (DOM) is outwelled from highly productive salt marshes, but its sources and fates are unclear. To examine common salt marsh plants as sources of coastal DOM, two dominant salt marsh vascular plants Spartina alterniflora and Juncus roemarianus, and two major coastal seagrasses Syringodium filiforme and Halodule wrightii, were collected from a Florida salt marsh and studied using laboratory incubation experiments. We investigated the leaching dynamics of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and chromophoric dissolved organic matter (CDOM) from these plants, in conjunction with our field investigations of the sources and outwelling of DOM from Florida salt marshes. The leaching of DOM and CDOM from the plants was a rapid process, and leaching rates were 65–288 µM/g dry weight/day for DOC and 3.8–16 µM/g dry weight/day for TDN from different plants in the bacteria-inhibited incubations. DOC was proportional to TDN in the leachates, but the quantity of C and N leached was dependent on the species and growth stage of the plants. At the end of the 25-day experiments, 5.4–23 % and 10–45 % of solid phase C and N were released into DOC and TDN pools, respectively. Bacteria played an important role during the leaching process. The majority of DOC and TDN leached from marsh plants and seagrasses was labile and highly biodegradable with 56–90 % of the leached DOC and 44–72 % of the leached TDN being decomposed at the end of the experiments. The fluorescence measurements of CDOM indicate that organic matter leached from marsh plants and seagrasses contained mainly protein-like DOM which was degraded rapidly by bacteria. Our study suggests that leaching of DOM from salt marsh plants and seagrasses provide not only major sources of DOC, TDN, and CDOM that affect many biogeochemical processes, but also as important food sources to microbial communities in the marsh and adjacent coastal waters.     

40Ar/39Ar dating of cryptomelane from the Baye manganese deposit, SW Yunnan, China: Implications for growth rate of supergene Mn-oxide veins

Supergene Mn-oxide deposits are commonly related to thick weathering profiles and form as a result of intense and prolonged weathering of Mn-bearing precursor rocks, processes facilitated by a combination of multiple factors including warm and wet climate, relatively quiescent tectonic environment, and favorable geomorphic setting. Precise age constraints of supergene Mn-oxides may provide valuable information on the climatic, tectonic, and geomorphic conditions prevailing in the geological past. ⁴⁰Ar/³⁹Ar laser incremental heating analysis of cryptomelane from the Baye manganese deposit, western Yunnan-Guizhou Plateau, SW China, was conducted to provide numerical constraints on the ages of supergene Mn enrichment and growth rates of Mn-oxide veins. In this study, two Mn-oxide veins of 3–6 cm thickness, termed as Vein A and B, respectively, were collected for ⁴⁰Ar/³⁹Ar dating. Vein A is subhorizontal and present in fractures parallel to schistosity of the Proterozoic spessartine schists, whereas Vein B is filled in nearly vertical fractures penetrating the schistosity. A combination of optical microscopy, XRD, SEM, and EMP analyses demonstrate that mineral grains extracted from both veins consist of pure, well-crystallized cryptomlane, which has acicular crystal forms and contains 0.96%–4.70% K₂O. Fourteen cryptomelane subsamples extracted from different growth bands of Vein A yield well-defined plateau ages ranging from 1.35 ± 0.05 to 1.16 ± 0.04 Ma (2σ), whereas seven subsamples obtained from Vein B have plateau ages ranging from 1.23 ± 0.05 to 1.01 ± 0.04 Ma (2σ). The age results permit estimation for the growth rates of both veins at ca. 115–153 and 34–67 mm Ma^?1, respectively. Distinct growth rates between Veins A and B are likely reflective of different fluid pressures during their formation governed by the orientation of the fractures hosting the veins. The growth rates calculated for both veins are 1–2 orders of magnitude higher than the values (<1–10 mm Ma^?1) estimated for Mn-oxide nodules in supergene Mn deposits elsewhere. The high growth rates obtained for the Baye samples are consistent with direct precipitation of tetravalent Mn-oxides from weathering solution in open cavities or fractures, characterized by incremental growth of Mn-oxide bands from the margin to the center of the cavities or fractures. In contrast, Mn-oxide nodules with low growth rates from other deposits formed through self-oxidation and self-catalization, and grow outwards from the nuclei. In addition, prevalence of warm and humid climate and prolonged tectonic uplift in the Yunnan Plateau may have also partly contributed to the rapid growth of Mn-oxides in the Baye deposit.     

Effects of suspended particles on the growth of two dominant phytoplankton species of Bohai Bay,China

Suspended particles (SP) are increasing dramatically in Bohai Bay, China and may affect the growth and composition of phytoplankton assembly. To determine the effects of SP on the growth of two dominant phytoplankton species, Phaeodactylum tricornutum Bohlin and Gymnodinium sp., we cultured and tested their growth characteristics under SP concentrations ranging from 0 g L⁻¹ to 0.8 g L⁻¹. Our results show that the increase in the SP concentrations results in significant decrease in the maximum cell densities and the maximum specific growth rates of these two species. The half maximal inhibitory concentration (IC₅₀) of SP to P. tricornutum and Gymnodinium sp. were 1.07 g L⁻¹ and 0.68 g L⁻¹ respectively, indicating the inhibitory effect of SP on Gymnodinium sp. was greater than on P. tricornutum. These results suggest that SP inhibits the growth of the two algal species and P. tricornutum is more tolerant to SP than Gymnodinium sp.     

Defining a chronological framework for the Middle Stone Age in West Africa: Comparison of methods and models for OSL ages at Ounjougou (Mali)

Ounjougou is the name of a large complex of archaeological sites, that were extensively studied between 1997 and 2008 by the international team of the “Human settlement and palaeoenvironment in West Africa” project. This complex is important because well stratified Palaeolithic sites in West Africa are rare, and because it covers a long period of time (most of the Upper Pleistocene and Holocene) and exhibits a wide set of technical cultures. Therefore, for the first time it is possible to propose a chronological framework for the human settlement in this region that can be related to other technical cultures in Africa and to palaeoenvironmental data.The purpose of this paper is to present the OSL dating results obtained from 57 sediment samples that led to this framework. Measurements were first performed between 2004 and 2006 in Oxford (School of Geography), using micro-aliquots (2–10 grains) OSL and ICP-MS for determination of equivalent doses and beta-dose rates, respectively (gamma dose rates being deduced from field gamma spectrometry). More recently, new measurements were done on 28 samples of this former set at the IRAMAT-CRP2A laboratory in Bordeaux, where “true” single quartz grain OSL and high resolution gamma spectrometry measurements were performed. Both sets of results are, for all but two samples, statistically consistent with each other. A consistent chrono-stratigraphic framework can thus be deduced, covering the Upper Pleistocene. It suggests that the region was regularly visited during this time interval and more particularly during Marine Isotope Stage 3, when groups with different technical cultures followed each other relatively rapidly.     

Comparison of models and data at Millstone Hillduring the 5–11 June 1991 storm

We compare measurements of the ionospheric F region at Millstone Hillduring the severe geomagnetic disturbances of 5–11 June 1991 with results from the IZMIRANand FLIP time-dependent mathematical models of the Earths ionosphere and plasmasphere. Somecomparisons are also made with the Millstone Hill semi-empirical model which was previouslyused to model this storm. New rate coefficients from recent laboratory measurements of the O⁺+N₂ and O⁺+O₂ loss rates are included in theIZMIRAN and Millstone Hill models. The laboratory measurements show that vibrationallyexcited N₂ and O₂ (N₂(v) and O₂(v)) are both important at high temperatures such as found in the thermosphere during disturbedconditions at summer solar maximum. Increases in the O⁺+N₂ loss ratedue to N₂(v) result in a factor ∼2 reduction in the daytime F₂ peak electron density. On some days inclusion of N₂(v) improves theagreement between the models and the data, and on other days it worsens it. In the present workwe show for the first time the significant effect that the increase in the O⁺recombination rate due to O₂(v) may have on the calculated NmF₂. There are considerable uncertainties in the model calculations during the unusual,extremely disturbed conditions found during the daytime on 6 June. The results illustratedifficulties involved and the current state of the art in modelling severe disturbances, and thusprovide a benchmark against which future progress can be gauged.