A multi‐method investigation of temperature,moisture and salt dynamics in tafoni (Tafraoute,Morocco)

Despite numerous investigations and theoretical models, tafoni weathering is still not fully understood largely because of limited data available on temperature, moisture and salt regimes. We investigated tafoni developed in granite in the Tafraoute region, Morocco, through an exploratory, two‐week multi‐method field campaign. Temperatures were measured with iButtons and by means of infrared thermography; moisture distribution and progress were captured with handheld moisture sensors and with drilled‐in iButtons. Salts were analysed in drill dust samples from different positions and rock depths. The results derived from very different techniques mutually support one another. Salts and moisture are concentrated near the base of the investigated tafoni, probably due to a saturated pore water body around the base of rock tors. Salts are accumulated close to the rock surface in tafoni, but not on the surrounding rock surfaces. A clear correlation was found between moisture and salt contents. Within a tafone, areas of higher humidity also display increased salt concentration near the surface. The temperature/humidity records allied with ionic analyses suggest that sodium sulfate dominates and is likely to undergo frequent phase changes from thenardite to mirabilite and vice versa. Two pathways of salt transport in and around tafoni are assumed based on the data: infiltration with rainfall on the top and around tors and boulders, and capillary rise from saturated pore water bodies to the surface. Copyright © 2015 John Wiley & Sons, Ltd.     

In situ evaluation of nearshore marine and fresh pore water transport into Flamengo Bay,Brazil

Transport between pore waters and overlying surface waters of Flamengo Bay near Ubatuba, Brazil, was quantified using natural and artificial geochemical tracers, ²²²Rn, Cl⁻, and SF₆, collected from multi-level piezometers installed along a transect perpendicular to the shore. Eight sampling ports positioned along the length of the piezometers allowed sampling of pore waters at discrete depth intervals from 10 to 230 cmbsf (centimeters below seafloor). Small volume samples were collected from the piezometers using a peristaltic pump to obtain pore water depth profiles. Pore water ²²²Rn is deficient in shallow sediments, allowing application of a diffusion-corrected ²²²Rn exchange rate. This model estimates the magnitude of pore water exchange rates to be about 130–419 cm/day. An SF₆-saturated fluorescein dye tracer was gently pumped into deep pore waters and exchange rates estimated from this method range from 29 to 185 cm/day. While absolute rates are higher using ²²²Rn than SF₆, rates are of similar magnitudes and the trends with distance from shore are the same – flow is greatest 6 m from shore and decreases by more than 50% further offshore. A Cl⁻ mass balance indicates the greatest fraction of fresh SGD occurs along an apparent preferential flow path in sediments within 5–7 m of the shoreline (87%). Recirculating bay waters through sediments dominate pore water advection at 10 m offshore where only 4% of the flow can be attributed to a freshwater source. Both fresh and marine sources combine to make up submarine groundwater discharge to coastal water bodies. The magnitude of fresh aquifer discharge is often a spatially variable and minor component of the total discharge.     

Submarine groundwater discharge is an important net source of light and middle REEs to coastal waters of the Indian River Lagoon, Florida, USA

Porewater (i.e., groundwater) samples were collected from multi-level piezometers across the freshwater-saltwater seepage face within the Indian River Lagoon subterranean estuary along Florida’s (USA) Atlantic coast for analysis of the rare earth elements (REE). Surface water samples for REE analysis were also collected from the water column of the Indian River Lagoon as well as two local rivers (Eau Gallie River, Crane Creek) that flow into the lagoon within the study area. Concentrations of REEs in porewaters from the subterranean estuary are 10-100 times higher than typical seawater values (e.g., Nd ranges from 217 to 2409 pmol kg⁻¹), with submarine groundwater discharge (SGD) at the freshwater-saltwater seepage face exhibiting the highest REE concentrations. The elevated REE concentrations for SGD at the seepage face are too high to be the result of simple, binary mixing between a seawater end-member and local terrestrial SGD. Instead, the high REE concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the REE cycle. A simple mass balance model is used to investigate the cycling of REEs in the Indian River Lagoon and its underlying subterranean estuary. Mass balance modeling reveals that the Indian River Lagoon is approximately at steady-state with respect to the REE fluxes into and out of the lagoon. However, the subterranean estuary is not at steady-state with respect to the REE fluxes. Specifically, the model suggests that the SGD Nd flux, for example, exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial SGD and recirculating marine SGD by, on average, ∼100 mmol day⁻¹. The mass balance model also reveals that the subterranean estuary is a net source of light REEs (LREE) and middle REEs (MREE) to the overlying lagoon waters, but acts as a sink for the heavy REEs (HREE). Geochemical modeling and statistical analysis further suggests that this fractionation occurs, in part, due to the coupling between REE cycling and iron redox cycling within the Indian River Lagoon subterranean estuary. The net SGD flux of Nd to the Indian River Lagoon is ∼7-fold larger than the local effective river flux to these coastal waters. This previously unrecognized source of Nd to the coastal ocean could conceivably be important to the global oceanic Nd budget, and help to resolve the oceanic “Nd paradox” by accounting for a substantial fraction of the hypothesized missing Nd flux to the ocean.     

Hydrodynamic response of the Breton Sound estuary to pulsed Mississippi River inputs

Pulsed re-introduction of Mississippi River water into the deltaic plain has been proposed as a wetland restoration strategy for coastal Louisiana. In this study, the hydrodynamic response of the Breton Sound estuary to a two-week pulse of Mississippi River water via the Caernarvon river diversion structure was investigated using a barotropic, three-dimensional, Finite-Volume Coastal Ocean Model (FVCOM). The numerical model was driven by tidal and subtidal forcing at the open Gulf boundary, freshwater discharge from the Caernarvon river diversion structure, as well as wind stress at the water surface. After successfully validating the model with field observations, three numerical experiments were run to assess the response of current, water level, and marsh flooding to different diversion discharge scenarios. The three scenarios considered were: a pulsed scenario of ∼200 m³ s⁻¹ corresponding to the actual diversion discharge in March 2001, a constant discharge scenario of 40 m³ s⁻¹ corresponding to the annually averaged discharge of 2001, and a scenario with no discharge. Numerical simulation results indicated that constant 40 m³ s⁻¹ discharge caused little change in wetland inundation comparing to the no discharge case and, thus, inter-exchange between deep channels and the wetlands was not improved by this rate of diversion discharge. In contrast, the two-week ∼200 m³ s⁻¹ discharge caused enhanced water exchange between wetlands and adjacent water bodies, substantially increasing water velocity in the bayous and channels of the upper estuary. These effects occurred in the estuary to about 20–25 km from the diversion structure, and caused a noticeable increase in down-estuary residual current with a significant reduction of local estuarine residence times for the whole estuary. Beyond 30 km from the diversion structure, the impact of high water discharge was small and the hydrodynamics was mostly controlled by tides and wind.     

Palaeogeographic Changes at Lake Chokrak on the Kerch Peninsula,Ukraine, during the Mid‐ and Late‐Holocene

This project has reconstructed the palaeogeographic and environmental evolution of Lake Chokrak on the Kerch Peninsula, Ukraine, during the mid‐ and late‐Holocene. This record has been evaluated in association with a regional archaeological data set to explore human–environment interactions over this period. The results show major changes in the palaeogeographic setting of Lake Chokrak since the 3rd millennium B.C., when the postglacial marine transgression had started to fill the study area. Microfaunal analyses reveal the long persistence of an open marine embayment that only became separated from the Sea of Azov when a sand barrier developed during the late 2nd millennium B.C. When colonizing the Black Sea region after the 8th century B.C., the Greek settlers erected a fortification with a small settlement on a promontory that was by then a peninsula‐like headland extending into the lake. The colonists abandoned their settlement at the end of the 1st millennium B.C. when the depth of the surrounding lake decreased from 1.5 m to less than 1 m. Today, Lake Chokrak dries up completely during summer. A detailed relative sea level (RSL) curve for the northern coast of Kerch has been established. Sea level reached its highest position at the present day. Since the 3rd millennium B.C., sea level continuously rose, without any of the previously postulated regression/transgression cycles. The RSL curve indicates differential subsidence rates within short distances in relatively stable areas, exceeding 40 cm per 1000 years. © 2012 Wiley Periodicals, Inc.     

Measurement of sound transmission and signal gain in the complex Strait of Korea

The experiment, The Acoustic Characterization Test III, was conducted in the oceanographically complex Strait of Korea to accurately measure the sound transmission under known environmental conditions. Geoacoustic profiles derived from geophysical measurements, measured bathymetry, and sound-speed profiles were the basis for range dependent parabolic equation (PE) calculations. Agreement between measured and calculated transmission loss was obtained with an attenuation profile in the near water-sediment interface layer with a dependence on frequency to the 1.8 power consistent with measurements in other sand-silt areas. Since the environment was oceanographically complex and the shipping noise levels were high, the coherency of the sound transmission was estimated using relative signal gain (RSG). RSG was taken as the difference between the gain calculated with PE and measured with the array and at longer ranges and higher frequencies was found to be approximately -2 dB with a signal gain coefficient of variation of 5%. This RSG degradation, attributed to the random signal phase fluctuations resulting from scattering from the surfaces and volume of the waveguide, yielded using a Gaussian coherence function a spatial coherence length of 30/spl lambda/ @ 400 Hz-40 km. In addition, high resolution imaging of five targets with two bottom mounted arrays illustrate the achievable performance of low-to-mid frequency active sonar in this environment.     

Application Procedures for the Electromagnetic Borehole Flowmeter in Shallow Unconfined Aquifers

It is increasingly common for the electromagnetic borehole flowmeter (EBF) to he used to measure hydraulic conductivity (K) distributions in subsurface flow systems. Past applications involving the EBF have been made mostly in confined aquifers (Kabala 1994; Boman et al. 1997; Podgorney and Ritzi 1997; Ruud and Kabala 1997a, 1997b; Flach et al. 2000), and it has been common to set up a flow field around a test well using a small pump that is located near the top of the well screen (Mob, and Young 1993). In thin, unconfined aquifers that exhibit ground water tables near the ground surface and that undergo drawdown during pumping, such a configuration can be problematical because pumping and associated drawdown may effectively isolate the upper portion of the aquifer from the flowmeter. In these instances, a steady-state flow field in the vicinity of the test well may be created using injection rather than pumping, allowing for testing in the otherwise isolated upper portion of the aquifer located near the initial water table position. Using procedures developed by Molz and Young (1993), which were modified for an injection mode application, testing was conducted to determine whether or not the injection mode would provide useful information in a shallow, unconfined aquifer that required the collection of data near the initial water table position. Results indicated that the injection mode for the EBF was well suited for this objective.     

Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.