Subsurface Circulation Research Articles

Similar sources but distinct δ13C signatures in adjacent low-temperature travertines from Laguna Amarga (Southern Patagonian Andes)

Similar sources but distinct δ13C signatures in adjacent low-temperature travertines from Laguna Amarga (Southern Patagonian Andes)

Influence of tropical cyclone Jawad on the surface and sub-surface circulation in the Bay of Bengal: ocean–atmosphere feedback

Influence of tropical cyclone Jawad on the surface and sub-surface circulation in the Bay of Bengal: ocean–atmosphere feedback

Interannual changes of the summer circulation and hydrology in the East China Sea: A modeling study from 1981 to 2015

Interannual changes of the summer circulation and hydrology in the East China Sea: A modeling study from 1981 to 2015

Orbital-scale thermocline temperature variability in the western equatorial Pacific during the last 370 kyr

Tropical subsurface circulation plays a key role in regulating heat and salt transport between the hemispheres, and in ocean–atmosphere interactions (e.g., El Niño-Southern Oscillation; ENSO). Therefore, understanding the past behavior of tropical thermoclines is important for predicting long-term global climate change. Here, we provide an orbital-scale thermocline temperature (TT) record based on Mg/Ca measurements of planktonic foraminifer Pulleniatina obliquiloculata in sediment cores obtained from the western equatorial Pacific (WEP) for the last 370 kyr. The vertical temperature gradient between sea surface temperature (SST) and TT in WEP showed weak positive correlations with the tropical Pacific zonal SST gradient in long-term trend and obliquity signal. The relationship of the two gradients does not coincide with modern ENSO variability, suggesting that the long-term TT variation depend primarily on another mechanism. Spectral analysis indicated that TT variability has strong signals in both the obliquity and precession bands. Since the obliquity signal is very weak in local insolation, the significant obliquity in TT variability implies an extratropical influence on tropical thermocline circulation. Therefore, our findings suggest that the subsurface circulation connecting the tropics and extratropics plays an essential role in orbital-scale tropical thermocline variability. • Thermocline temperature and seawater d18O variations are reconstructed using Mg/Ca-thermometry for the last 370 kyr. • Zonal SST and vertical temperature gradients exhibit a weak positive correlation. • Orbital-scale thermocline temperature change was strongly influenced by mid-latitude via subsurface circulation.

A Comparative Study of Vertical Mixing Schemes in Modeling the Bay of Bengal Dynamics

AbstractThe choice of vertical mixing scheme in ocean models plays an important role in modeling the surface and subsurface circulation and the vertical structure. This work performs a comparative study between K‐profile parametrization (KPP) and k‐ϵ mixing schemes for a regional domain in the Bay of Bengal (BoB) using the Modular Ocean Model version 5 (MOM5). It is observed that sea surface temperature (SST) and the mixed layer depth (MLD) show significant improvement with the k‐ϵ mixing scheme. Energetic analysis shows that changes in the viscous dissipation and turbulent buoyancy flux are the primary reason for improvement with k‐ϵ. The overestimation of viscous dissipation in the KPP scheme is corrected by k‐ϵ, resulting in a deeper mixed layer closer to observations. The tendency of buoyancy flux to retain stability in the water column also results in a better representation of SST in k‐ϵ. Overall, we conclude that the k‐ϵ mixing scheme works better for the BoB region.

Hg in the hydrothermal fluids and gases in Baia di Levante, Vulcano, Italy

The importance of fluid and gaseous mercury (Hg) emissions from hydrothermal systems in the shallow, coastal ocean is poorly constrained. However, there are indicators that they could be a significant natural Hg source. We evaluated the hydrothermal Hg emissions around Vulcano Island, Aeolian Arc, Italy, which is host to a marine shallow-water hydrothermal system (MSWHS) in Baia di Levante. Fluids were collected with porewater probes, and gases were collected into Tedlar© bags. Total Hg (THg) concentrations in the hydrothermal fluids ranged from 2.9 to 2888 pM. The concentrations of volatile Hg were below 8 pM and trended positively with increasing temperature. Monomethyl Hg (MMHg) was not detected. Total Hg in the gases ranged from 0.03 to 1.82 μmol/m 3 . High concentrations of THg were associated with low Cl-concentrations, low pH-values, and high K/Cl and Mg/Cl ratios. Concentrations of THg in the hydrothermal fluids resulted from mixing between meteoric water , seawater , condensed fumarolic vapor, and a deep hydrothermal fluid. However, not all low-Cl fluids were high THg samples. Samples taken along the coast of the La Fossa crater contained substantially less THg (2.9 to 29.4 pM), despite similar hydrothermal indicators as those in the Baia di Levante samples. These data support subsurface circulation models, which discuss the downslope flow of condensed La Fossa crater gases to the coast. In the hydrothermally active area of Baia di Levante, concentrations of THg were elevated relative to background surface seawater, ranging from 40 to 5110 pM. In comparison, the remainder of the bay ranged from 0.8 to 2.4 pM. The flux of Hg to the atmosphere from surface waters was calculated through dissolved Hg concentrations. The flux at each sampled site ranged from 0 to 19.6 pmol/m 2/ hr. The highest flux rates were determined for those areas with visible hydrothermal activity , particularly those with high gaseous emission rates. Surface water concentrations declined rapidly away from point sources, indicating atmospheric emission , dilution through mixing, or scavenging and sedimentation. In hydrothermally active areas, Baia di Levante sediments contained THg concentrations of 2.42 nmol/g and 49.52 nmol/g, which were significantly above background (0.03 nmol/g). The largest gaseous point source, Bambino, released >2 L of gas per second. Although, Hg concentrations in the gas were low (113 to 122 nmol/m 3 ) relative to other measured point sources near the beach (1768 to 1817 nmol/m 3 ), due to the volume of discharge, surface water concentrations were elevated (131 pM). The Hg present in the hydrothermal system of Vulcano contributes Hg to the atmosphere and local seawater as a natural source. • Concentrations of THg within hydrothermal fluids exceeded background concentrations up to 1500 times. • Concentrations of THg within hydrothermal gases were spatially variable. • Surface waters of Baia di Levante were enriched in THg due to hydrothermal sources. • Flux of Hg from surface waters to the atmosphere was estimated up to 19.6 pmol/m 2 /h. • Shallow point sources with high rates of gas emission directly contributed Hg to the atmosphere.

Characteristics and Formation of the Luzon Undercurrent in the Western North Pacific: Observational Study

AbstractThe subsurface circulation system in the western North Pacific is dominated by the convergence of the Luzon Undercurrent (LUC) and the Mindanao Undercurrent, which forms the basin‐scale eastward North Equatorial Undercurrent jets. The southward LUC, situated to the east of Luzon Island, plays a significant role in transporting subsurface waters equatorward in the western boundary of the subtropical North Pacific. Despite its crucial contributions to the water, heat, and energy distributions in the subsurface layer, its characteristics and formation mechanism remain unclear. In this study, we utilize monthly climatological temperature and salinity data and the derived geostrophic velocity to investigate the spatiotemporal variability of the LUC and its formation dynamics. The LUC transport exhibits weak seasonality and strong intra‐seasonal variation, peaking in May/June and October. The origin of the LUC is closely connected with the southward veering of the Deep North Equatorial Current (DNEC) off the Ryukyu Islands and the Luzon Strait middle‐layer outflow (LSMO). The DNEC dominates transport in the LUC, and the LSMO of the South China Sea (SCS) Intermediate Water contributes to the water mixing in the LUC. Locally, the appearance of the LUC is dynamically linked with the barotropic effect associated with the sea surface height gradient and the baroclinic effect raised from the downward tilting of the zonal isopycnal off the Philippine coast. Spatially, the core of the LUC shifts from in‐shore to off‐shore waters from May/June to October. This study reveals the spatiotemporal characteristics of the LUC and identifies its separate origins from the interior North Pacific and the SCS middle layer.

Modeling the seasonal circulation and connectivity in the North Patagonian Gulfs, Argentina

The coastal region surrounding the North Patagonian Gulfs is considered one of the most productive areas of the Patagonian Shelf ecosystem. Despite its ecological and economical importance the physical processes that contribute to their fertilization are poorly understood. Here we expand previous studies performing a detailed analysis of the Nuevo (NG) and San José (SJG) gulfs seasonal circulation using a high-resolution numerical model. The circulation patterns in NG are characterized by two distinct modes corresponding to the summer and winter seasons. During summer, stratification decouples the upper and deeper layers of the NG, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. Differential tidal mixing in coastal and deep areas induces the subsurface circulation. As stratification weakens during fall and winter, the circulation patterns are replaced by a large wind-driven anticyclonic gyre in the south and a small cyclonic loop in the north. The western sector of SJG is dominated by two counterrotating gyres generated by tidal rectification while the eastern portion shows sluggish circulation patterns. Consequently, a meridional thermal front develops in summer and winter. Particle tracking experiments indicate that the inner portion of the southern Patagonian shelf replenish the surface layers of the NG and SJG. The deeper layer in NG is mostly renovated by local winter convection. Residence times are very different for NG and SJG; while NG is highly retentive, SJG exchanges with the San Matías Gulf are very effective. There is more connectivity between NG and the coastal region of Valdés Peninsula and the Valdés Front in summer than in winter and a weak seasonal connection between NG and SJG. The connectivity of particles released in SJG with coastal regions of San Matías Gulf are quite important in summer but declines substantially in winter.

Mineralogical and hydrogeological study of "pouhons" in the lower Palaeozoic formations of the Stavelot-Venn Massif, Belgium

Numerous naturally CO2-rich mineral water springs, locally called pouhons, occur in the Stavelot-Venn Massif. These water springs show a particular composition with a high content of iron, manganese and lithium, and are characterised by a red-orange colour resulting from iron hydroxide precipitation near the land surface. Radon measurements have shown that these ferruginous deposits are weakly radioactive. The Upper Cambrian black shales of the La Gleize Formation are also known to display radioactive anomalies. These rocks show enrichment in HFSE (Pb, U, Y, Ce, Zr, Ti, Nb) and are depleted in transition metals (Co, Ni, Cu, Zn). Specific minerals such as florencite-(Ce), monazite-(Ce), xenotime-(Y) and zircon have been identified and are probably at the origin of the radioactive anomalies. Uranium was gradually leached from these minerals, transported in solution, and finally concentrated in ferruginous muds. These muds are mainly composed of goethite (most often amorphous), residual quartz and calcite in some samples. The most probable hypothesis is that uranium is adsorbed in small concentrations on the goethite surface. On the other hand, the Ottré Formation (Ordovician) appears to be the main source of lithium, iron and manganese. Pouhon waters have therefore probably leached rocks of various mineralogy and chemical composition during their sub-surface circulation.

A geochemical comparison between volcanic and non-volcanic hot springs from East Malaysia: Implications for their origin and geothermometry

• Non-volcanic hot springs are K-Na-bicarbonate rich waters with low SO 4 contents. • Volcanic hot springs are neutral chloride waters with high SO 4 contents. • Radioactivity of granites is the main heat source for non-volcanic hot springs. • Volcanic activity is the main heat source for volcanic hot springs. • Hot springs show intermediate to high enthalpy with potential energy generation. Sources of volcanic and non-volcanic thermal sources have been studied in East Malaysia to differentiate their geothermal reservoir temperatures and first-ever reports on its geochemical processes that affect the evolution of the constituents of thermal groundwater subsurface circulation. The study of geothermal potentials includes indices of geochemistry, geothermometry, and mineral saturation. The surface temperatures of thermal springs range from 27 to 56 °C, and the pH values range from 5.6 to 9.0. The geochemical characteristic distinguishes non-volcanic thermal sources as K-Na-HCO 3 , while volcanic thermal sources present the Cl-HCO 3 -SO 4 -Na type. The quartz geothermometer showed that the reservoir temperatures of non-volcanic hot springs range between 61 and 135 °C. In comparison, the volcanic thermal sources range from 55 to 185 °C requiring 257 to 565 kJ/kg and energy from 231 to 786 respectively to heat water. Subsequently, it is defined as intermediate to slightly high enthalpy for most thermal springs, especially volcanic springs. The mixing of hot water with sources close to the surface can be seen by the disagreement between the silica and cation geothermometers and the disequilibrium with their associated host rocks as indicated from the plot of studied hot springs in the Na-K-Mg ternary diagram and saturation indices calculations. Radiogenic granitic host rock represents the main heat source for non-volcanic hot springs govern by meteoric water generated in deep-seated fault systems. Meanwhile, in volcanic areas with high secondary permeability caused by faults, fractures and fractures, meteorological waters can descend to a considerable depth and heat up. In a favourable situation, thermal waters return to the surface by faults and fracture zones.

Stable isotope and anthropogenic tracer signature of waters in an Andean geothermal system

In the present study, we combined stable isotopes and anthropogenic tracers to investigate the origin, residence times, and evolution of thermal waters in the Lonquimay-Tolhuaca Volcanic Complex (LTVC) of the southern Chilean Andes. A total of 20 water samples from springs discharging at a broad range of temperatures (8–96 °C) were collected and analyzed for major ion geochemistry, stable isotope ratios (δ 2 H, δ 18 O, δ 13 C TDIC ), dissolved chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF 6 ). In addition, we compiled all available data on the isotopic composition of precipitation in the region to derive the local meteoric water line. Coupled with a Rayleigh-fractionation model of precipitation, we provide constraints on the elevation at which infiltration and recharge to the system is produced. δ 13 C TDIC values are consistent with the bulk of dissolved inorganic carbon being derived from the addition of soil CO 2 to an atmospheric source, while magma degassing and boiling processes are evidenced in samples discharging directly on the flanks of volcanoes. The isotopic composition of thermal water, once heated at depth, is further modified by CO 2 degassing and carbonate precipitation during ascent. All geothermal samples contain low but detectable concentrations of CFC-11, CFC-12, CFC-113, and SF 6 , suggesting the addition of only a small fraction (2–22%) of modern meteoric water. The discharge temperature of naturally outflowing springs in the LTVC correlates directly with the age distribution of the water samples. This difference in residence times is attributed to the distinct subsurface circulation pathways of each water type—i.e., the shallow, diffuse flow of cold groundwater vs. the deep, focused circulation of thermal water along fault zones. Conduit flow along high vertical permeability networks allows hydrothermal fluid to remain relatively unmixed with shallow meteoric water during ascent. Data from this study confirm that fault-fracture meshes with different orientations exert a first order control on the residence times, ascent, and mixing rates of thermal waters in this segment of the Andean Cordillera, thus modulating their chemical and isotopic signature. Additionally, our results show that the combined use of conventional hydrogeochemical and isotopic data with environmental tracers, including anthropogenic CFCs and SF 6 , is a powerful tool to better understand the dynamics of geothermal systems. • Different circulation pathways modulate residence times and chemical signature of fluids. • High vertical permeability fault-fracture networks allow thermal waters to remain undiluted during ascent. • CFCs and SF 6 are powerful tools to understand the dynamics of geothermal systems.

A numerical investigation of bedrock groundwater recharge and exfiltration on soil mantled hillslopes

AbstractHere we use Richards Equation models of variably saturated soil and bedrock groundwater flow to investigate first‐order patterns of the coupling between soil and bedrock flow systems. We utilize a Monte Carlo sensitivity analysis to identify important hillslope parameters controlling bedrock recharge and then model the transient response of bedrock and soil flow to seasonal precipitation. Our results suggest that hillslopes can be divided into three conceptual zones of groundwater interaction, (a) the zone of lateral unsaturated soil moisture accumulation (upper portion of hillslope), (b) the zone of soil saturation and bedrock recharge (middle of hillslope) and (c) the zone of saturated‐soil lateral flow and bedrock groundwater exfiltration (bottom of hillslope). Zones of groundwater interaction expand upslope during periods of precipitation and drain downslope during dry periods. The amount of water partitioned to the bedrock groundwater system a can be predicted by the ratio of bedrock to soil saturated hydraulic conductivity across a variety of hillslope configurations. Our modelled processes are qualitatively consistent with observations of shallow subsurface saturation and groundwater fluctuation on hillslopes studied in our two experimental watersheds and support a conceptual model of tightly coupled shallow and deep subsurface circulation where groundwater recharge and discharge continuously stores and releases water from longer residence time storage.

Multi-tracer (δ18O, δD, 3H, CFCs and SF6) investigation of groundwater recharge and apparent age at the Bamenda Highlands along the Cameroon volcanic line

The Bamenda Highlands contains numerous dilute and soda springs of unknown hydrological provenance. These dilute springs are a vital source of drinking water to the inhabitants. As a contribution to water management, this study investigated the spring water recharge, residence time and sub-surface circulation using δ18O, δD, 3H, CFCs, SF6 and TDS. A plot of both water types along the local meteoric water line indicated the meteoric origin and rapid recharge following precipitation. Dilute springs with a δ18O altitude effect of 0.27/100 m suggested recharge at different elevations. The CFC-12, CFC-11 and CFC-113 dating (complemented by 3H) showed reasonable young apparent ages of dilute springs ranging from 21 to > 52 (mean/median of 25) years and old soda springs (> 52 years). SF6 concentrations in dilute springs revealed exceptionally young ages relative to CFCs modelled ages suggesting a terrigenous enrichment of the former. Thus, groundwater dating with SF6 is unreliable in the area. Besides the old apparent ages of soda springs, their highly depleted δ18O and high TDS (mean of 1396 mg/l) indicated palaeo-recharge and high water–rock interaction, respectively. In contrast, the low TDS of dilute springs (< 140 mg/l) indicated low-water interaction. Most dilute springs showed exponential mixing models indicating heterogeneous recharge under unconfined aquifer conditions. Conversely, the old soda springs displayed piston flow and binary mixing models. The meteoric recharge and similar residence time of the shallow dilute springs suggested natural resilience to short-term changes in climatic conditions. Thus, low shallow groundwater abstraction is sustainable at the Bamenda Highlands.

Dynamical analysis of the oceanic circulation in the Gulf of San Jorge, Argentina

Abstract This study identifies the dynamical mechanisms driving seasonal variations in oceanic circulation and water mass characteristics of the Gulf of San Jorge (GSJ) and its exchanges with the Patagonian Shelf (PS). A suite of process-oriented numerical experiments indicates that GSJ circulation is mainly driven by tidal forcing and modulated by wind forcing and intrusions from the PS. During late spring and summer, stratification decouples the upper and deeper layers of the gulf, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. The subsurface circulation is induced by differential tidal mixing in coastal and deep areas and its intensity is strongly affected by the temporal variability of the atmospheric heat flux, which increases from spring to summer and fades from fall to winter. As stratification weakens, circulation patterns are replaced by wind-driven anticyclonic gyres in the south and an open cyclonic loop in the north. Passive tracer diagnostics show that in summer, surface and subsurface waters from the GSJ northern coast are exported and replaced by waters from the coastal portion of PS currents. The renewal of bottom waters is slower: A small portion upwells in the southwestern coast but most are ventilated by winter convection in the southern region and by intrusions of PS waters in the northern region.

Seasonal variability and long-term trends of the surface and subsurface circulation features in the Equatorial Indian Ocean.

Herein, we have examined the seasonal variability and long-term trends in the recent 35 years (1980-2014) of the wind stresses and circulation features in the Equatorial Indian Ocean (EIO) using reanalysis and observed data. Annual mean flow of the EIO is eastward along the equator, with the strong current in the upper 80 m and weak below that. The prominent surface currents in the EIO are the eastward Wyrtki Jets (WJs) occurring during spring (April-May) and fall (October-November), with active flows within 2° of the equator between 60° E and 90° E. The fall WJs are stronger than the spring WJs. The Equatorial Undercurrent (EUC), the prominent subsurface eastward flow with core within 70-150 m, occurs twice annually-February-April and August-October-with the well-developed flow in March-April. Long-term trends reveal that during 1980-2014, the annual mean eastward surface current in the upper 75 m has increased, primarily due to the rise of WJs forced by the westerly wind stresses during November-December. But the subsurface eastward current (below 75 m) has decreased due to the weakening of winter North Equatorial Current (NEC) and EUC during February-April. Consolidation of the westerly wind stresses during November-April results in the strengthening of the wind-driven surface WJs and weakening of the pressure-driven EUCs during 1980-2014. Intensification of WJs are the direct effects of wind forcing. However, strengthening of westerly stresses also results in weakening of the surface westward NEC and thereby restricts the strong eastward gradient of SSH which is required to build up the essential eastward pressure gradient for the EUC. Since WJs and EUCs modulate the hydrographic structure of the eastern part of the EIO, any change in the strength of these flows, in turn, will influence mostly this oceanic region and thereby the local as well as global climate.

Circulação Oceânica a 1000 Metros na Região da Cadeia Vitória - Trindade

A circulacao oceânica de subsuperficie desempenha um papel crucial nos transportes oceânicos de calor e massa e consequentemente no sistema climatico terrestre. Algumas regioes oceânicas ate os dias atuais ainda apresentam poucos estudos que busquem caracterizar aspectos basicos relativos a dinâmica oceânica existente em niveis intermediarios e profundos, como e o caso de parte significativa da regiao oceânica adjacente a costa leste brasileira. Este trabalho tem como objetivo a caracterizacao da circulacao oceânica a 1000 metros e a estrutura termohalina na regiao da Cadeia Vitoria – Trindade (CVT) a partir de perfiladores lagrangeanos Argo. Os resultados indicam que a profundidade de 1000 metros e uma regiao de transicao na coluna d’agua entre a circulacao intermediaria e a profunda, sobretudo sob o ponto de vista da analise da trajetoria. Ao norte da cadeia, o fluxo e dominado por uma corrente de norte para sul, atribuido a Corrente de Contorno Profunda (CCP). Enquanto no sul da cadeia, um fluxo zonal de leste para oeste domina a regiao oceânica e a Corrente de Contorno Intermediaria (CCI) aparece junto ao talude indo para norte, enquanto um fluxo contrario para sul ocorre mais afastado da costa. Na analise termohalina da regiao, as caracteristicas termohalinas da Agua Intermediaria Antartica (AIA) dominam o nivel de 1000 metros, o que sugere que ao norte da cadeia a CCP influencie no transporte da AIA para sul.

Geothermometry and Circulation Behavior of the Hot Springs in Yunlong County of Yunnan in Southwest China

Travertine and nontravertine thermal springs have been studied in Yunlong County in southwest China to determine the geothermal reservoir temperatures and to find the geochemical processes that affect the evolution of thermal groundwater constituents during subsurface circulation. Hydrochemical characteristics distinguish travertine from nontravertine types. Travertine springs show HCO3·Cl-Na and SO4·HCO3-Ca·Na type, and a nontravertine spring presents Cl·HCO3·SO4-Na type. Log(Q/K) versus T diagrams show that reservoir temperatures can be expressed as intervals based on the equilibrium mineral assemblages coexisting in equilibrium and multiminerals in equilibrium with the aid of the PHREEQC and WATCH programs. The spring water mixing ratio with shallow water is between 59% and 82% with steam loss ranging from 12.1% to 27.8%. The Dalang Spring mixes with the highest proportion of cold water (76% to 82%) among the four hot springs and has the highest geothermal reservoir temperature (132°C to 176.9°C). The water-rock interaction during recharge from precipitation demonstrates that the minerals halite, kaolinite, chalcedony, plagioclase, and CO2(g) play an important part in the evolution of the thermal groundwater. Four inverse modeling simulation paths between precipitation and spring discharge were established to calculate the mass flux of minerals by the PHREEQC program. Halite, kaolinite, chalcedony, plagioclase, and CO2(g) participate in dissolution reactions in the thermal groundwater circulation, while gypsum, calcite, dolomite, biotite, and fluorite keep the geochemical processes in equilibrium.

The tropical-subtropical coupling in the Southeast Atlantic from the perspective of the northern Benguela upwelling system.

In the Benguela upwelling system, the environmental conditions are determined to a large extent by central water masses advected from remote areas onto the shelf. The origin, spreading pathways and fate of those water masses are investigated with a regional ocean model that is analysed using Eulerian passive tracers and on the basis of Lagrangian trajectories. Two major water masses influencing the Benguela upwelling system are identified: tropical South Atlantic Central Water (SACW) and subtropical Eastern South Atlantic Central Water (ESACW). The spreading of tropical waters into the subtropical Benguela upwelling system is mediated by equatorial currents and their continuation in the Southeast Atlantic. This tropical-subtropical connection has been attributed to signal propagation in the equatorial and coastal waveguides. However, there exists an additional spreading path for tropical central water in the open ocean. This mass transport fluctuates on a seasonal scale around an averaged meridional transport in Sverdrup balance. The inter-annual variability of the advection of tropical waters is related to Benguela Niños, as evidenced by the 2010/2011 event. The northern Benguela upwelling system is a transition zone between SACW and ESACW since they encounter each other at about 20°S. Both water masses have seasonal variable shares in the upwelled water there. To summarise the main pathways of central water mass transport, an enhanced scheme for the subsurface circulation in the Southeast Atlantic is presented.

Research on qanats in Spain

Different types of drainage galleries exist in Span: mina de agua, qanat, cimbra or tajea and galleries associated with a groundwater dam (buried in the bed of the channel to stop sub-surface circulation). A qanat is a type of drainage gallery located in the foothills where groundwater is captured. Qanats, also called galerias con lumbreras, minados con espejuelos, viajes de agua, or alcavons in Spain, can be seen as models for sustainable use of water in arid and semi-arid environments. Furthermore, in their local contexts, these hydraulic systems create their own landscapes and hydraulic heritage. As such, the technique is the basis for new ways of thinking about how to generate water in dry environments like the Southeast of Spain. There are several groups of Spanish researchers studying qanats and other types of horizontal wells as systems being able to generate endogenous water resources. Because of their extensive and continuous research over a number of years, the teams from the Universities of Murcia and Valencia stand out.

The subsurface circulation of the Iceland Sea observed with RAFOS floats

Abstract The pathways of dense waters located above the sill depth of Denmark Strait were investigated in the Iceland Sea using 52 acoustically tracked RAFOS floats. These floats were deployed in summer 2013 and 2014, with a target depth of 500 m, resulting in a total of 40.9 float-years of track data covering the Iceland Sea basin. In the interior Iceland Sea basin, the float tracks showed a double gyre circulation, out of which floats eventually escaped towards the Norwegian Sea in the East Icelandic Current, with some appearing to be en route to the Faroe Bank Channel. Four floats exited through Denmark Strait and surfaced in the Labrador and Irminger Seas. Four other floats deployed west of the Kolbeinsey Ridge at 70°N show the connection between the East Greenland Current and the East Icelandic Current. Floats deployed east of the Kolbeinsey Ridge along the Icelandic slope were captured in a region with no clear main flow. Eddy motions, mainly small scale (radii of 0.5–3 km), are seen throughout the Iceland Sea. Several floats were grounded on the Icelandic slope both east and west of the Kolbeinsey Ridge due to upslope currents, which created a rim of cold water along the slope. While this water was indicative of the presence of the North Icelandic Jet, no connection between the eastern Iceland Sea and Denmark Strait sill was found. Our investigation of wind stress curl fields from atmospheric reanalysis data suggests that high wind stress curl conditions may have been unfavorable for a westward connection by the North Icelandic Jet at the time of the float observations.