Surface Water Transport Research Articles

Analysis of discontinuities across thin inhomogeneities, groundwater/surface water interactions in river networks, and circulation about slender bodies using slit elements in the Analytic Element Method

AbstractGroundwater and surface water contain interfaces across which hydrologic functions are discontinuous. Thin elements with high hydraulic conductivity in a porous media focus groundwater, which flows through such inhomogeneities and causes an abrupt change in stream function across their interfaces, and elements with low conductivity retard flow with discontinuous head. Base flow interactions at the interface between groundwater and surface water transport water between these stores and generate a discontinuous normal component of flow. Thin objects in surface water with Kutta condition generate circulation by the discontinuous tangential component of flow across their interface. These discontinuities across hydrologic interfaces are quantified and visualized using the Analytic Element Method, where slit elements are formulated using the Joukowsky transformation with Laurent series and new influence functions to represent sinks and circulation, and methods are developed for these applications expressing discontinuities as Fourier series. The specific geometries illustrate solutions for a randomly generated heterogeneous porous media with nonintersecting inhomogeneities, for groundwater/surface water interaction in a synthetic river network, and for a slender body with geometry similar to the wings of the Wright Brothers. The mathematical details are reduced to series solutions and matrix multiplications, which are easily extensible to other geometries and applications.

On the limits of heat as a tracer to estimate reach-scale river-aquifer exchange flux

For the past few decades, heat has been used to estimate river-aquifer exchange flux at discrete locations by comparison of river and groundwater temperature. In recent years, heat has also been employed to estimate reach-scale river-aquifer exchange flux based only on river temperature. However, there are many more parameters that govern heat exchange and transport in surface water than in groundwater. In this study, we analyzed the sensitivities of surface water temperature to various parameters and assessed the accuracy of temperature-based estimates of exchange flux in two synthetic rivers and in a field setting. For the large synthetic river with a flow rate of 63 m3 s−1 (i.e., 5.44 × 106 m3 d−1), the upper and lower bounds of the groundwater inflow rate can be determined when the actual groundwater inflow is around 100 m2 d−1. For higher and lower fluxes, only minimum and maximum bounds respectively can be determined. For the small synthetic river with the flow rate of 0.63 m3 s−1 (i.e., 5.44 × 104 m3 d−1), the bounds of the groundwater inflow rate can only be estimated when the actual groundwater inflow rate is near 10 m2 d−1. In the field setting, results show that the inflow rate must be less than 100 m2 d−1, but a lower bound for groundwater inflow cannot be determined. The large ranges of estimated groundwater inflow rates in both theoretical and field settings indicate the need to reduce parameter errors and combine heat measurements with other isotopic and/or chemical methods. This article is protected by copyright. All rights reserved.

An experimental investigation on the surface water transport process over an airfoil by using a digital image projection technique

In the present study, an experimental investigation was conducted to characterize the transient behavior of the surface water film and rivulet flows driven by boundary layer airflows over a NACA0012 airfoil in order to elucidate underlying physics of the important micro-physical processes pertinent to aircraft icing phenomena. A digital image projection (DIP) technique was developed to quantitatively measure the film thickness distribution of the surface water film/rivulet flows over the airfoil at different test conditions. The time-resolved DIP measurements reveal that micro-sized water droplets carried by the oncoming airflow impinged onto the airfoil surface, mainly in the region near the airfoil leading edge. After impingement, the water droplets formed thin water film that runs back over the airfoil surface, driven by the boundary layer airflow. As the water film advanced downstream, the contact line was found to bugle locally and developed into isolated water rivulets further downstream. The front lobes of the rivulets quickly advanced along the airfoil and then shed from the airfoil trailing edge, resulting in isolated water transport channels over the airfoil surface. The water channels were responsible for transporting the water mass impinging at the airfoil leading edge. Additionally, the transition location of the surface water transport process from film flows to rivulet flows was found to occur further upstream with increasing velocity of the oncoming airflow. The thickness of the water film/rivulet flows was found to increase monotonically with the increasing distance away from the airfoil leading edge. The runback velocity of the water rivulets was found to increase rapidly with the increasing airflow velocity, while the rivulet width and the gap between the neighboring rivulets decreased as the airflow velocity increased.

High-Speed Imaging to Quantify Transient Ice Accretion Process over an Airfoil

Ice accretion on aircraft wings poses a performance and safety threat as aircraft encounter supercooled droplets suspended in the cloud layer. The details of the ice accretion depend on the atmospheric conditions and the flight parameters. The icing process on the wing consists of a complex interaction of water deposition, surface water transport, and freezing. The aerodynamics affect the water deposition, the heat and mass transport, and ice accumulation; meanwhile, the accumulating ice affects the aerodynamics. Until now, most experimental measurements of aircraft icing have focused on the final ice shapes formed after exposure for a set duration to icing conditions. This approach fails to capture the transient processes that form the final ice formations. Here, we present experiments conducted in the Iowa State Icing Research Tunnel on a NACA 0012 airfoil to study the transient ice accretion process under varying icing conditions. High-speed video of the icing process was acquired under controlled environmental conditions to quantitatively measure the transient water film runback, rivulet formation, and accumulated ice growth. Image processing techniques were developed to extract physical information from the acquired image sequences of the icing events. The experiments demonstrate how varying the environmental conditions modifies the ice accretion process. It was found that the leading-edge ice growth rate is proportional to water deposition rate and the rivulet spacing and rivulet area coverage decrease with increasing wind speed. The water rivulet runback speed over the airfoil surface was found to increase rapidly with increasing wind speed.

The mechanisms of North Atlantic CO<sub>2</sub> uptake in a large Earth System Model ensemble

Abstract. The oceans currently take up around a quarter of the carbon dioxide (CO2) emitted by human activity. While stored in the ocean, this CO2 is not influencing Earth's radiation budget; the ocean CO2 sink therefore plays an important role in mitigating global warming. CO2 uptake by the oceans is heterogeneous, with the subpolar North Atlantic being the strongest CO2 sink region. Observations over the last 2 decades have indicated that CO2 uptake by the subpolar North Atlantic sink can vary rapidly. Given the importance of this sink and its apparent variability, it is critical that we understand the mechanisms behind its operation. Here we explore the combined natural and anthropogenic subpolar North Atlantic CO2 uptake across a large ensemble of Earth System Model simulations, and find that models show a peak in sink strength around the middle of the century after which CO2 uptake begins to decline. We identify different drivers of change on interannual and multidecadal timescales. Short-term variability appears to be driven by fluctuations in regional seawater temperature and alkalinity, whereas the longer-term evolution throughout the coming century is largely occurring through a counterintuitive response to rising atmospheric CO2 concentrations. At high atmospheric CO2 concentrations the contrasting Revelle factors between the low latitude water and the subpolar gyre, combined with the transport of surface waters from the low latitudes to the subpolar gyre, means that the subpolar CO2 uptake capacity is largely satisfied from its southern boundary rather than through air–sea CO2 flux. Our findings indicate that: (i) we can explain the mechanisms of subpolar North Atlantic CO2 uptake variability across a broad range of Earth System Models; (ii) a focus on understanding the mechanisms behind contemporary variability may not directly tell us about how the sink will change in the future; (iii) to identify long-term change in the North Atlantic CO2 sink we should focus observational resources on monitoring lower latitude as well as the subpolar seawater CO2; (iv) recent observations of a weakening subpolar North Atlantic CO2 sink may suggest that the sink strength has peaked and is in long-term decline.

Fate of nitrate in seepage from a restored wetland receiving agricultural tailwater

Constructed and restored wetlands are a common practice to filter agricultural runoff, which often contains high levels of pollutants, including nitrate. Seepage waters from wetlands have potential to contaminate groundwater. This study used soil and water monitoring and hydrologic and nitrogen mass balances to document the fate and transport of nitrate in seepage and surface waters from a restored flow-through wetland adjacent to the San Joaquin River, California. A 39% reduction in NO3-N concentration was observed between wetland surface water inflows (12.87±6.43mgL−1; mean±SD) and outflows (7.87±4.69mgL−1). Redox potentials were consistently below the nitrate reduction threshold (∼250mV) at most sites throughout the irrigation season. In the upper 10cm of the main flowpath, denitrification potential (DNP) for soil incubations significantly increased from 151 to 2437mgNO3-Nm−2d−1 when nitrate was added, but showed no response to carbon additions indicating that denitrification was primarily limited by nitrate. Approximately 72% of the water entering the wetland became deep seepage, water that percolated beyond 1-m depth. The wetland was highly effective at removing nitrate (3866kgNO3-N) with an estimated 75% NO3-N removal efficiency calculated from a combined water and nitrate mass balance. The mass balance results were consistent with estimates of NO3-N removed (5085kgNO3-N) via denitrification potential. Results indicate that allowing seepage from wetlands does not necessarily pose an appreciable risk for groundwater nitrate contamination and seepage can facilitate greater nitrate removal via denitrification in soil compared to surface water transport alone.

Spatiotemporal decomposition of solute dispersion in watersheds

AbstractInformation about the effect of different dispersion mechanisms on the solute response in watersheds is crucial for understanding the temporal dynamics of many water quality problems. However, to quantify these processes from stream water quality time series may be difficult because the governing mechanisms responsible for the concentration fluctuations span a wide range of temporal and spatial scales. In an attempt to address the quantification problem, we propose a novel methodology that includes a spectral decomposition of the watershed solute response using a distributed solute transport model for the network of transport pathways in surface and subsurface water. Closed form solutions of the transport problem in both the Laplace and Fourier domains are used to derive formal expressions of (i) the central temporal moments of a solute pulse response and (ii) the power spectral response of a solute concentration time series. By evaluating high‐frequency hydrochemical data from the Upper Hafren Watershed, Wales, we linked the watershed dispersion mechanisms to the damping of the concentration fluctuations in different frequency intervals reflecting various environments responsible for the damping. The evaluation of the frequency‐dependent model parameters indicate that the contribution of the different environments to the concentration fluctuations at the watershed effluent varies with period. For the longest periods (predominantly groundwater transport pathways) we found that the frequency typical transport time of chloride was 100 times longer and that sodium had a 2.5 times greater retardation factor compared with the shortest periods (predominantly shallow groundwater and surface water transport pathways).

Asymmetric flow field-flow fractionation of manufactured silver nanoparticles spiked into soil solution

Manufactured metallic silver nanoparticles (AgNP) are intensively utilized in consumer products and this will inevitably lead to their release to soils. To assess the environmental risks of AgNP in soils, quantification of both their concentration and size in soil solution is essential. We developed a methodology consisting of asymmetric flow field-flow fractionation (AF4) in combination with on-line detection by UV–vis spectroscopy and off-line HR-ICP-MS measurements to quantify the concentration and size of AgNP, coated with either citrate or polyvinylpyrrolidone (PVP), in water extracts of three different soils. The type of mobile phase was a critical factor in the fractionation of AgNP by AF4. In synthetic systems, fractionation of a series of virgin citrate- and PVP-coated AgNP (10–90nm) with reasonably high recoveries could only be achieved with ultrahigh purity water as a mobile phase. For the soil water extracts, 0.01% (w:v) sodium dodecyl sulfate (SDS) at pH 8 was the key to a successful fractionation of the AgNP. With SDS, the primary size of AgNP in all soil water extracts could be determined by AF4, except for PVP-coated AgNP when clay colloids were present. The PVP-coated AgNP interacted with colloidal clay minerals, leading to an overestimation of their primary size. Similar interactions between PVP-coated AgNP and clay colloids can take place in the environment and facilitate their transport in soils, aquifers, and surface waters. In conclusion, AF4 in combination with UV–vis spectroscopy and HR-ICP-MS measurements is a powerful tool to characterize AgNP in soil solution if the appropriate mobile phase is used.

Eddy‐mediated transport of warm Circumpolar Deep Water across the Antarctic Shelf Break

AbstractThe Antarctic Slope Front (ASF) modulates ventilation of the abyssal ocean via the export of dense Antarctic Bottom Water (AABW) and constrains shoreward transport of warm Circumpolar Deep Water (CDW) toward marine‐terminating glaciers. Along certain stretches of the continental shelf, particularly where AABW is exported, density surfaces connect the shelf waters to the middepth Circumpolar Deep Water offshore, offering a pathway for mesoscale eddies to transport CDW directly onto the continental shelf. Using an eddy‐resolving process model of the ASF, the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break. The shoreward transport of surface waters is purely wind driven, while the shoreward CDW transport is entirely due to mesoscale eddy transfer. The CDW flux is sensitive to all aspects of the model's surface forcing and geometry, suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope.

Quantification of transient behavior of wind-driven surface droplet/rivulet flows using a digital fringe projection technique

A digital fringe projection (DFP) system is developed to achieve non-intrusive thickness measurements of wind-driven water droplet/rivulet flows over a test plate to quantify the unsteady surface water transport process pertinent to various atmospheric icing phenomena. The DFP technique is based on the principle of structured light triangulation in a similar manner as a stereo vision system but replacing one of the cameras for stereo imaging with a digital projector. The digital projector projects line patterns of known characteristics onto the test specimen (i.e., a water droplet/rivulet on a test plate for the present study). The pattern of the lines is modulated from the surface of the test object. By comparing the modulated pattern and a reference image, the 3D profile of the test object with respect to the reference plane (i.e., the thickness distribution of the water droplet/rivulet flow) can be retrieved quantitatively and instantaneously. The feasibility and implementation of the DFP system is first demonstrated by measuring the thickness distribution of a small flat-top pyramid over a test plate to evaluate the measurement accuracy level of the DFP system. After carefully calibrated and validated, the DFP system is applied to achieve time-resolved thickness distribution measurements of a water droplet/rivulet to quantify the transient behavior of a water droplet/rivulet flow driven by a boundary layer air flow over a test plate. The dynamic shape changes and stumbling runback motion of the wind-driven water droplet/rivulet flow were measured in real time in terms of film thickness distribution, contact line moving velocity, wet surface area and droplet evaporation rate.

Exceptional Agulhas leakage prolonged interglacial warmth during MIS 11c in Europe

AbstractThe transport of warm and saline surface water from the Indo‐Pacific Ocean into the South Atlantic (“Agulhas leakage”) influences the Atlantic Meridional Overturning Circulation (AMOC), which in turn exerts control on European climate. Paleoceanographic data document a remarkably strong Agulhas leakage at the end of marine isotope stage (MIS) 11c interglacial (~400 ka B.P.), which is one of the best orbital analogues for the Holocene. Here we assess the potential influence of this exceptional Agulhas leakage on North Atlantic climate based on a compilation of marine and terrestrial proxy records from the Iberian margin and continental Europe. We show that a ~5 ka long warm period persisted across Europe beyond the MIS 11c climatic optimum. This warm period is testified by increases in foraminifer‐derived sea surface temperatures on the Iberian margin, a spread of temperate trees on Iberia, and the expansion both of evergreen trees and thermophilous diatom taxa in Central European lowlands. Paradoxically, this warming coincides with an insolation minimum, implying that orbital forcing can be excluded as the underlying cause. We conclude that persistent warmth during weak insolation at the end of MIS 11c in Europe may have been triggered by strengthened Agulhas leakage, which stimulated a vigorous AMOC and increased the northward transport of warm surface waters to higher latitudes via the North Atlantic Current. The close analogy of the present and MIS 11c orbital forcing underlines the possibility that the present‐day increase of the Agulhas leakage, although driven by different forcing than MIS 11c, may considerably affect future climates across Europe.

Transfer and degradation of polyacrylamide-based flocculants in hydrosystems: a review.

The aim of this review was to summarize information and scientific data from the literature dedicated to the fate of polyacrylamide (PAM)-based flocculants in hydrosystems. Flocculants, usually composed of PAMs, are widely used in several industrial fields, particularly in minerals extraction, to enhance solid/liquid separation in water containing suspended matter. These polymers can contain residual monomer of acrylamide (AMD), which is known to be a toxic compound. This review focuses on the mechanisms of transfer and degradation, which can affect both PAM and residual AMD, with a special attention given to the potential release of AMD during PAM degradation. Due to the ability of PAM to adsorb onto mineral particles, its transport in surface water, groundwater, and soils is rather limited and restricted to specific conditions. PAM can also be a subject of biodegradation, photodegradation, and mechanical degradation, but most of the studies report slow degradation rates without AMD release. On the contrary, the adsorption of AMD onto particles is very low, which could favor its transfer in surface waters and groundwater. However, AMD transfer is likely to be limited by quick microbial degradation.

The Atlantic Overturning Circulation: More Evidence of Variability and Links to Climate

A unique feature of the Atlantic Ocean is the presence of regions in the Labrador Sea and Nordic Seas where surface water can convect and sink to deep levels. This process of deep water formation and the related northward transport of warm surface water are components of the Atlantic meridional overturning circulation (AMOC), which annually transports in excess of 1 PW of heat northward through the northern subtropics. Between 26°N and Greenland much of this heat flux enters the atmosphere where it is then transported eastward by the atmospheric circulation and is responsible for the mild U.K. and European climate. Coupled models suggest that one of the consequences of anthropogenic climate change will be a slowing of the AMOC and an alteration of the ocean's role in climate (e.g., Cheng et al. 2013). Observing, quantifying, and understanding the detailed mechanisms controlling AMOC variability, its present circulation, and past behaviors, and the extent to which changes in the AMOC are predictable all remain preeminent scientific challenges for the twenty-first century.

Incorporation of Pb at the calcite (104)-water interface.

Lead (Pb) is a common environmental pollutant, and its transport in surface waters and groundwater is controlled in part by sorption and precipitation reactions at mineral surfaces. Using in situ specular and resonant anomalous X-ray reflectivity measurements, we investigated the interaction of the calcite (104) surface with a dilute Pb- and EDTA-bearing solution that is slightly undersaturated with respect to calcite. The X-ray results reveal Pb coherently substituting for Ca in the near-surface layers of strained calcite with Pb/(Pb + Ca) atom fractions as high as 0.28 in the outermost layer. The larger ionic radius of Pb(2+) relative to Ca(2+) is accommodated in calcite by vertical displacements of Pb relative to the Ca site. In situ atomic force microscopy images obtained during the reaction suggest that Pb incorporation below the surface occurs after initial dissolution followed by regrowth of a strained epitaxial Pb-rich calcite solid-solution at the calcite (104)-water interface. This process could produce a widespread host phase for Pb in groundwater aquifers and soil pore fluids.

Potential bioactivity and association of 17β-estradiol with the dissolved and colloidal fractions of manure and soil

The dissolved (DF) and colloidal fractions (CF) of soil and manure play an important role in the environmental fate and transport of steroidal estrogens. The first objective of this study was to quantify the association of 17β-estradiol (E2) with the DF and CF isolated from (i) liquid swine manure (LSM), (ii) a soil:water mixture (soil), and (iii) a LSM:soil:water mixture (Soil+LSM). The appropriate CF and DF size fractions of the Soil, Soil+LSM, and LSM media were obtained by first filtering through a 0.45μm filter, which provided the combined DF and CF (DF/CF). The DF/CF from the three media was spiked with carbon-14 ([14C]) radiolabeled E2 ([14C]-E2), and then ultrafiltered to isolate the CF (<0.45μm and >1kDa) from the DF (<1kDa). The average recoveries of the [14C] associated with the DF were 67%–72%, 67%–79%, and 76%–78% for the Soil, Soil+LSM and LSM, respectively. For the CF that was retained on the 1kDa filter, organic carbon and [14C]-E2 were dislodged with subsequent water rinses the Soil+LSM and LSM, but not the Soil. The second objective was to evaluate whether the E2 associated with the various fractions of the different media could still bind the estrogen receptor using an E2 receptor (17β-ER) competitor assay, which allowed E2 equivalent concentrations to be determined. The estrogen receptor assay results indicated that E2 present in the DF of the Soil and Soil+LSM solutions could still bind the estrogen receptor. Results from this study indicated that E2 preferentially associated with the DF of soil and manure, which may enhance its dissolved advective transport in surface and subsurface water. Furthermore, this study indicated that E2 associated with DF solutions in the environment could potentially induce endocrine responses through its interactions with estrogen receptor.

A linear systems approach to watershed transport simulation

AbstractModels that simulate loadings of pollutants from agricultural landscapes to surface waters often operate at time scales that are relatively coarse (e.g. daily) compared with how fast water moves in streams, suggesting a commensurate physical scale that is substantially larger than typical agricultural fields. In general, as pollutants enter water and move downstream, longitudinal dispersive effects and travel time de‐synchronization tend to cause flattening and broadening of concentration peaks—an effect with implications for potential impacts on ecological and human health, and for which adequate representation is thus important for risk assessment. In‐stream transport is often approximated in practice using numerical implementation of the one‐dimensional advection–dispersion equation (ADE), with streams discretized into linked homogeneous segments. However, when a daily time step is employed, limitations inherent in the finite difference methodology may constrain simulated dispersion in lotic waters to unrepresentative or unrealistic magnitudes. In this paper, a convolution‐based approach to surface water transport is suggested as an alternative to the ADE, for use in combination with daily input loading models. This approach offers the advantage of greater flexibility in representing longitudinal mixing by using impulse response functions (IRF) to represent inter‐segment transport. Networks of stream segments are represented using nested convolutions, implemented using forward and inverse discrete Fourier transform to simplify calculations. Enhanced representational flexibility arises from the freedom afforded the modeller in selecting each segment's IRF, which may be chosen to represent dispersive regimes ranging from pure advection (plug flow) to compete mixing, and beyond to the sort of long‐tailed mixing characterized by fractal inverse frequency power‐law scaling. The approach is explored in proof‐of‐concept exercises that make use of atrazine monitoring data sets collected over common time periods from upstream and downstream locations within the same watersheds. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Differences in nitrous oxide distribution patterns between the Bering Sea basin and Indian Sector of the Southern Ocean

Nitrous oxide (N2O) distribution patterns in the Bering Sea basin (BSB) and Indian Sector of the Southern Ocean (ISSO) were described and compared. In both sites, the waters were divided into four layers: surface layer, subsurface layer, N2O maximum layer, and deep water. Simulations were made to find out the most important factors that regulate the N2O distribution patterns in different layers of both sites. The results showed that in the surface water, N2O was more understaturated in the ISSO than the BSB. This phenomenon in the surface water of ISSO may result from ice melt water intrusion and northeastward transport of the Antarctic surface water. Results of the rough estimation of air-sea fluxes during the expedition were (−0.34±0.07)–(−0.64±0.13) μmol/(m2·d) and (−1.47±0.42)–(−1.77±0.51) μmol/(m2·d) for the BSB and the ISSO, respectively. Strongly stratified surface layer and temperature minimum layer restricted exchange across the thermocline. The N2O maximum existed in higher concentration and deeper in the BSB than the ISSO, but their contribution to the upper layer by eddy diffusions was negligible. In deep waters, a concentration difference of 5 nmol/L N2O between these two sites was found, which suggested that N2O production occurred during thermohaline circulation. N2O may be a useful tracer to study important large-scale hydrographic processes.

Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach

The Crozet Archipelago, in the Indian sector of the Southern Ocean, constitutes one of the few physical barriers to the Antarctic Circumpolar Current. Interaction of the currents with the sediments deposited on the margins of these islands contributes to the supply of chemical elements--including iron and other micro-nutrients--to offshore high-nutrient, low-chlorophyll (HNLC) waters. This natural fertilization sustains a phytoplankton bloom that was studied in the framework of the KEOPS-2 project. In this work, we investigated the time scales of the surface water transport between the Crozet Island shelves and the offshore waters, a transport that contributes iron to the phytoplankton bloom. We report shelf-water contact ages determined using geochemical tracers (radium isotopes) and physical data based on in situ drifter data and outputs of a model based on altimetric Lagrangian surface currents. The apparent ages of surface waters determined using the three independent methods are in relatively good agreement with each other. Our results provide constraints on the time scales of the transport between the shelf and offshore waters near the Crozet Islands and highlight the key role played by horizontal transport in natural iron fertilization and in defining the extension of the chlorophyll plume in this HNLC region of the Southern Ocean.

PERSiST: a flexible rainfall-runoff modelling toolkit for use with the INCA family of models

Abstract. Runoff generation processes and pathways vary widely between catchments. Credible simulations of solute and pollutant transport in surface waters are dependent on models which facilitate appropriate, catchment-specific representations of perceptual models of the runoff generation process. Here, we present a flexible, semi-distributed landscape-scale rainfall-runoff modelling toolkit suitable for simulating a broad range of user-specified perceptual models of runoff generation and stream flow occurring in different climatic regions and landscape types. PERSiST (the Precipitation, Evapotranspiration and Runoff Simulator for Solute Transport) is designed for simulating present-day hydrology; projecting possible future effects of climate or land use change on runoff and catchment water storage; and generating hydrologic inputs for the Integrated Catchments (INCA) family of models. PERSiST has limited data requirements and is calibrated using observed time series of precipitation, air temperature and runoff at one or more points in a river network. Here, we apply PERSiST to the river Thames in the UK and describe a Monte Carlo tool for model calibration, sensitivity and uncertainty analysis.

North Atlantic marine radiocarbon reservoir ages through Heinrich event H4: a new method for marine age model construction

Abstract Cooling and sinking of dense saline water in the Norwegian–Greenland Sea is essential for the formation of North Atlantic Deep Water. The convection in the Norwegian–Greenland Sea allows for a northward flow of warm surface water and southward transport of cold saline water. This circulation system is highly sensitive to climate change and has been shown to operate in different modes. In ice cores the last glacial period is characterized by millennial-scale Dansgaard–Oeschger (D–O) events of warm interstadials and cold stadials. Similar millennial-scale variability (linked to D–O events) is evident from oceanic cores, suggesting a strong coupling of the atmospheric and oceanic circulations system. Particularly long-lasting cold stadials correlate with North Atlantic Heinrich events, where icebergs released from the continents caused a spread of meltwater over the northern North Atlantic and Nordic seas. The meltwater layer is believed to have caused a stop or near-stop in the deep convection, leading to cold climate. The spreading of meltwater and changes in oceanic circulation have a large influence on the carbon exchange between atmosphere and the deep ocean and lead to profound changes in the 14 C activity of the surface ocean. Here we demonstrate marine 14 C reservoir ages ( R ) of up to c. 2000 years for Heinrich event H4. Our R estimates are based on a new method for age model construction using identified tephra layers and tie-points based on abrupt interstadial warmings.