Groundwater discharges in the Baltic Sea: survey and quantification using a schlieren technique application

Groundwater seeps are known to occur in Eckernförde Bay, Baltic Sea. Their discharge rate and dispersion were investigated with a new schlieren technique application, which is able to visualize heterogeneous water parcels with density anomalies down to Δσ_t = 0.049 on the scale of millimeters. With the use of an inverted funnel, discharged fluids can be captured and the outflow velocity can be determined. Overall, 46 stations could be categorized by three different cases: active vent sites, seep‐influenced sites, and non‐seep sites. New seep locations were discovered, even at shallow near‐shore sites, lacking prominent sediment depression, which indicate submarine springs. The detection of numerous seeps was possible and the groundwater‐influenced area was defined to be approximately 6.3 km². Flow rates of between 0.05 and 0.71 l m^?2 min^?1 were measured. A single focused fluid plume, which was not disturbed by the funnel was recorded and revealed a flux of 59.6 ± 20 ml cm^?2 min^?1 and it was calculated that this single focused plume would be strong enough to produce a flow rate through the funnel of 1.32 ± 0.44 l m^?2 min^?1. The effect of different seep‐meter funnel sizes is discussed.     

The significance of pockmarks to understanding fluid flow processes and geohazards

Underwater gas and liquid escape from the seafloor has long been treated as a mere curiosity. It was only after the advent of the side‐scan sonar and the subsequent discovery of pockmarks that the scale of fluid escape and the moon‐like terrain on parts of the ocean floor became generally known. Today, pockmarks ranging in size from the ‘unit pockmark’ (1–10 m wide, < 0.6 m deep) to the normal pockmark (10–700 m wide, up to 45 m deep) are known to occur in most seas, oceans, lakes and in many diverse geological settings. In addition to indicating areas of the seabed that are ‘hydraulically active’, pockmarks are known to occur on continental slopes with gas hydrates and in association with slides and slumps. However, possibly their potentially greatest significance is as an indicator of deep fluid pressure build‐up prior to earthquakes. Whereas only a few locations containing active (bubbling) pockmarks are known, those that become active a few days prior to major earthquakes may be important precursors that have been overlooked. Pockmark fields and individual pockmarks need to be instrumented with temperature and pressure sensors, and monitoring should continue over years. The scale of such research calls for a multinational project in several pockmark fields in various geological settings.     

Sampling and analysis of geothermal fluids

Sampling of geothermal fluids presents some problems not encountered when sampling surface and nonthermal ground waters. Specific collection techniques are required to obtain representative samples because of the elevated temperature and boiling of these fluids, the effect of exposing them to the atmosphere and cooling of the samples. Sample treatment during collection depends on the analytical method to be used. When sampling wet‐steam wells, both the liquid and the vapour fractions should be collected at the same fluid separation pressure. When sampling fumarole steam, maximum information is obtained if the total discharge is collected into a single container without separating the gas and the steam condensate fractions. Silica polymerization affects the solution pH. The only way to obtain reliable pH measurement of a water sample supersaturated with respect to amorphous silica is to measure it on site, before the onset of polymerization. This paper provides an outline of the geothermal sampling techniques and analytical methods currently in use in Iceland. Sampling of hot‐water and wet‐steam wells is described, as is sampling of hot springs, fumaroles and gas bubbling through hot‐spring waters. Detailed procedures are given for the analysis of total carbonate carbon and total sulphide sulphur in geothermal water and steam condensate samples.     

Thermal springs and heat flow in North America

Thermal springs are commonly thought to be an indicator of geothermal resource potential. However, there have been few analyses of the relationship between thermal springs and the underlying thermal regime. An examination of temperature and discharge rates for a large database of thermal springs in North America demonstrates that there is not a simple relationship between these measurements made at the surface and subsurface heat flow. Hydrogeological factors appear to exert strong controls on the temperature and discharge at these springs and should be carefully considered in geothermal resource assessments.     

H. L. Hunley Revealed: documentation,deconcretion, and recent developments in the investigation of an American Civil War submarine from 1864

Since 2014, the conservation staff at Clemson University's Warren Lasch Conservation Center in Charleston, South Carolina have been removing the concretion from the hull of H. L. Hunley, an American Civil War submarine lost 1864. In parallel, the archaeological team has been documenting the condition of the hull, the concretion layers, and the hull features revealed by the deconcretion process. This involved photography, direct measurements, and 3D scanning. This article will discuss the strategy for recording the concretion, the techniques used to document the newly revealed hull and its unique features, and the preliminary analysis of their archaeological significance.     

Obscure oases: natural,cultural and historical geography of western Queensland's Tertiary sandstone springs

The distribution of surface water dictates human and animal activity in arid zones. Although typically small, hidden, and inaccessible, springs and wells fed by local aquifers were the only sources of reliable water across vast areas of inland Australia until the last century. Compared to larger, more accessible water sources such as riverine waterholes and Great Artesian Basin discharge springs, their history is sketchy and poorly documented, although rich in intrigue and mythology. Since the expansion of artificial waters and motorised transport, many of these small oases have been forgotten, and their location and permanence are now less well‐known than for thousands of years. We examine the distribution, hydrogeology, cultural history, and biological values of Tertiary sandstone springs in western Queensland based on a review of historical literature, interviews with long‐term residents, and extensive field surveys. One hundred and sixty springs were documented, and nearly 40% of these have declined in flow or become inactive since pastoral settlement for reasons that are not well understood. While their decline in some areas seems related to shallow bores sunk into their local aquifers, it is possible that some smaller springs owed their existence to regular human maintenance. Others are probably naturally dynamic over decadal time scales. This study documents an almost‐forgotten aspect of Queensland's natural and cultural history.     

Earthquake‐related temperature changes in two neighboring hot springs at Xiangcheng,China

Pre‐earthquake and postearthquake temperature changes were documented in two hot springs at Xiangcheng. Pre‐earthquake changes were documented in spring I, 13 days before and 106 km away from the M_s 5.8 Zhongdian earthquake. The 11‐year cutoff spring spouted again, and the spouted water was 24°C hotter than the former escaping gas. Postearthquake changes were documented in spring II following the 2008 M_w 7.9 Wenchuan earthquake, approximately 425 km away from the epicenter. Temperature in spring II showed a step‐like increase with a magnitude of 4°C induced by the earthquake. Spring I which is 0.3 m apart from spring II did not show a sudden change following the earthquake. However, temperatures in the two springs were identical after the Wenchuan earthquake. It indicates that the earthquake generated new hydraulic connectivity between springs I and II, and the heat transport between the two springs accounts for the postearthquake temperature changes.     

Surveying for Mars Analogue Research Sites in the Central Australian Deserts

In anticipation of a future crewed mission to Mars, the international non‐profit organisation known as the Mars Society is currently establishing four mockup bases at which planetary surface operations simulations, equipment testing and personnel training exercises will be conducted over the next decade. These should provide valuable design data for, and raise public awareness about, plans to explore the red planet. One of these bases, which are organised around a habitat of the kind that is likely to serve as shelter for surface‐dwelling astronauts, is to be sited in central Australia under the name MARS‐OZ. To find a suitable location, the Mars Society Australia has conducted a ground‐truth survey of 15 potential sites as practical scientific analogues of the Martian surface, recording these in a specialised database. Each site was assessed on a set of geomorphic, science/engineering, logistic and visual analogue criteria. Six circular exploration zones 200 km in diameter were identified as clusters of the most significant, observed, comparative planetological features. These zones were then ranked to recommend a series of ‘landing sites’, at which future field seasons of exploratory science may be conducted.     

Barite–pyrite mineralization of the Wiesbaden thermal spring system, Germany: a 500-kyr record of geochemical evolution

Barite–(pyrite) mineralizations from the thermal springs of Wiesbaden, Rhenish Massif, Germany, have been studied to place constraints on the geochemical evolution of the hydrothermal system in space and time. The thermal springs, characterized by high total dissolved solids (TDS) contents and predominance of NaCl, ascend from aquifers at 3–4 km depth and discharge at a temperature of 65–70°C. The barite–(pyrite) mineralization is found in upflow and discharge zones of the present‐day thermal springs as well as at elevations up to 50 m above the current water table. Hence, this mineralization style constitutes a continuous record of the hydrothermal activity, linking the past evolution with the present state of this geothermal system. The sulphur isotope signatures of the mineralization indicate a continuous decrease of the δ³⁴S of sulphate from +16.9‰ in the oldest barite to +10.1‰ in the present‐day thermal water. The δ³⁴S values of barite closely resemble various recently active thermal springs along the southern margin of the Rhenish Massif and contrast strongly with different regional ground and mineral waters. The mineralogical and isotopic signatures, combined with calculations based on uplift rates and the regional geological history, indicate a minimum activity of the thermal spring system at Wiesbaden of about 500 000 years. This timeframe is considerably larger than conservative models, which estimate the duration of thermal spring systems in continental intraplate settings to last for several 10 000 years. The calculated equilibrium sulphur isotope temperatures of coexisting barite and pyrite range between 65 and 80°C, close to the discharge temperature of the springs, which would indicate apparent equilibrium precipitation. Kinetic modelling of the re‐equilibration of the sulphate–sulphide pair during water ascent shows that this process would require 220 Myr. Therefore, we conclude that pyrite is formed from precursor Fe monosulphide phases, which rapidly precipitate in the near‐surface environment, preserving the isotope fractionation between dissolved sulphate and sulphide established in the deep aquifer. Equilibrium modelling of water–mineral reactions shows slight supersaturation of barite at the discharge temperature. Pyrite is already strongly supersaturated at the temperatures estimated for the aquifer (110°C) and processes in the near‐surface environment are most probably related to contact of the thermal water with atmospheric oxygen, resulting in formation of oxidized intermediate sulphur species and precipitation of Fe monosulphide phases, which subsequently recrystallize to pyrite.     

The influence of poorly interconnected fault zone flow paths on spring geochemistry

Thermal springs commonly occur along faults because of the enhanced vertical permeability afforded by fracture zones. Field and laboratory studies of fault zone materials document substantial heterogeneities in fracture permeabilities. Modeling and field studies of springs suggest that spatial variations in permeability strongly influence spring locations, discharge rates and temperatures. The impact of heterogeneous permeability on spring geochemistry, however, is poorly documented. We present stable isotope and water chemistry data from a series of closely spaced thermal springs associated with the Hayward Fault, California. We suggest that substantial spatial variations observed in δ¹⁸O and chloride values reflect subsurface fluid transport through a poorly connected fracture network in which mixing of subsurface waters remains limited. Our measurements provide insight into the effect of fracture zone heterogeneities on spring geochemistry, offer an additional tool to intuit the nature of tectonically induced changes in fault zone plumbing, and highlight the need to consider local variations when characterizing fracture zone fluid geochemistry from spring systems with multiple discharge sites.