Upstream Sources Research Articles

A graph-based modeling framework for tracing hydrological pollutant transport in surface waters

Anthropogenic pollution of hydrological systems affects diverse communities and ecosystems around the world. Data analytics and modeling tools play a key role in fighting this challenge, as they can help identify key sources as well as trace transport and quantify impact within complex hydrological systems. Several tools exist for simulating and tracing pollutant transport throughout surface waters using detailed physical models; these tools are powerful, but can be computationally intensive, require significant amounts of data to be developed, and require expert knowledge for their use (ultimately limiting application scope). In this work, we present a graph modeling framework – which we call HydroGraphs – for understanding pollutant transport and fate across waterbodies, rivers, and watersheds. This framework uses a simplified representation of hydrological systems that can be constructed based purely on open-source data (National Hydrography Dataset and Watershed Boundary Dataset). The graph representation provides a flexible intuitive approach for capturing connectivity and for identifying upstream pollutant sources and for tracing downstream impacts within small and large hydrological systems. Moreover, the graph representation can facilitate the use of advanced algorithms and tools of graph theory, topology, optimization, and machine learning to aid data analytics and decision-making. We demonstrate the capabilities of our framework by using case studies in the State of Wisconsin; here, we aim to identify upstream nutrient pollutant sources that arise from agricultural practices and trace downstream impacts to waterbodies, rivers, and streams. Our tool ultimately seeks to help stakeholders design effective pollution prevention/mitigation practices and evaluate how surface waters respond to such practices.

The Bonito Paleochannel in Chaco Canyon, New Mexico: Recent Research and Implications for Causality and Effects

During the late eleventh century AD, a episode of erosion in Chaco Canyon, New Mexico, threatened to destroy portions of the Pueblo Bonito great house and possibly other large buildings. Known as the Bonito Paleochannel, this large arroyo meant the loss of significant amounts of surface water from valley-wide flooding originating in upstream and tributary sources. We believe that erosion was probably the result of an increasing size and frequency of floods. There is no compelling evidence that agriculture was affected by the paleochannel but we hypothesize that great house construction became extremely difficult. Consequently, the impact of the Bonito Paleochannel cycle may have been felt most in the political economy.

Evaluation of sediment phosphorus dynamics in cascade reservoir systems: A case study of Weiyuan River, China

Reservoirs tend to accumulate phosphorus (P) originating from agriculture, industry, and other upstream sources in sediment, with this stored P later released. However, the spatiotemporal dynamics of sediment P release in reservoirs remains unclear. This study investigated the spatiotemporal dynamics in P of the sediment and water of three cascade reservoirs in the Weiyuan River (Tuojiang tributary). The results showed elevated P in sediment [total P (TP): 1208.93 mg kg−1] and water (TP: 0.23 mg L−1) during the low-water season (LWS), which could be attributed to notably higher organic matter content (9.65%), finer particle size (20.95 μm), and extended hydraulic retention time (HRT: 13.13 days) downstream of the cascade reservoirs. Further study employing static in-situ diffusive gradient in thin films (DGT) and dynamic ex-situ adsorption kinetic experiments confirmed that the downstream release of P from sediments [diffusion flux (Fd): 1.67 mg m−2 d−1, equilibrium P concentrations (EPC0): 0.22 ± 0.10 mg L−1] greatly exceeded those upstream (−0.66 ± 0.17 mg m−2 d−1, 0.07 ± 0.001 mg L−1), Fe (II) was a critical factor in regulating sedimentary P release. The combined effects of high P in overlying water and sediment significantly stimulated downstream phytoplankton growth, particularly among cyanobacteria (26.48%) and green algae (8.33%). Further regulatory steps are needed to regulate LWS algal blooms downstream of cascade reservoirs.

Spatiotemporal patterns of multiple pesticide residues in central Argentina streams

Pollution of surface waters is a global threat, with particular concern about pesticides due to their severe negative effects on ecosystem functioning and human health. The aims of this study were to identify the spatiotemporal patterns of water and sediment quality, and the key variables related to the variation in pesticide pollution (122 compounds), in headwater streams (surrounding land uses: crop or mixed crop-livestock systems) and floodplain streams (surrounding land uses: urban development or natural wetland) of the Paraná River basin in the central area of Argentina. We found significant differences in water and sediment quality related to local land uses among headwater streams, but not among floodplain streams. These differences were more noticeable during spring than during autumn. Pesticides were widespread in all the streams, independently of the surrounding land use, reflecting the combination of local inputs and the role of floodplain hydrological connectivity in transporting pollutants from upstream sources. The most frequently detected compound was atrazine (75 %), whereas the highest concentration of an individual compound was observed for the glyphosate metabolite aminomethylphosphonic acid (AMPA, up to 4 μg L−1). The significant explanatory variables for pesticide pollution were turbidity, chromophoric dissolved organic matter (CDOM), sub-basin area, side slope of streams (positive relations), wetland cover, and precipitations (negative relations). Our results can be useful for the design of monitoring programs that capture the spatial and temporal variability of pesticide pollution.

Spatiotemporal variations and risk characteristics of potential non-point source pollution driven by LUCC in the Loess Plateau Region, China

With increasing human activities, regional substrate conditions have undergone significant changes. These changes have resulted in temporal and spatial variations of non-point source pollution sources, which has a significant impact on the quality of the regional soil, surface water, and groundwater environments. This study focused on the human-disturbed Loess Plateau region and used an enhanced potential non-point-source pollution index (PNPI) model to explore the dynamic changes of regional potential non-point-source pollution (PNP) and the associated risk due to land use and land cover change (LUCC) over the past 31 years. The Loess Plateau region is mainly composed of cultivated land, grassland and forest, which together account for 93.5% of the watershed area. From 1990 to 2020, extensive soil and water conservation measures were implemented throughout the Loess Plateau region, resulting in a significant reduction in the non-point source pollution risk. Using the quantile classification method, the study area’s PNP risk values were categorized into five distinct levels. The results revealed a polarization phenomenon of PNP risk in the region, with an increase in non-point source pollution risk in the human-influenced areas and a rapid expansion of the very high-risk area. However, the non-point source pollution risk in the upstream water source area of the watershed reduced over the study period. In recent years, the rapid urbanization of the Loess Plateau region has been the primary reason for the rapid expansion of the very high PNP risk area throughout the watershed. This study highlights the significant impact of LUCC on the dynamic changes in PNP risk within the Loess Plateau region, providing crucial insights into future conservation and urban planning policies aimed at enhancing the ecological health and environmental quality of the region.

Detailed analysis of banded chorus gap formation by an electron shell distribution

In a recent paper [K. Min, Phys. Plasmas 30, 012904 (2023)], the formation of the banded chorus with a gap in intensity at half the electron cyclotron frequency (Ωe/2) is demonstrated by particle-in-cell simulations including an isotropic shell distribution at an intermediate energy. This follow-up study focuses on the phase space density (PSD) hill formation process and its role in the chorus wave damping at the gap. We first show that phase-trapped particles closely follow single wave characteristics in momentum space. This means that the formation of either PSD hole or hill is primarily determined by the temperature anisotropy, T⊥/T‖, of an initial distribution function. The critical value of T⊥/T‖ increases (decreases) for a higher (lower) resonant frequency. We then revisit the recent banded chorus simulations to investigate how the presence of an isotropic shell distribution self-consistently affects chorus wave evolution at the gap. Initially, with an increasing wave frequency, more and more shell electrons get trapped and a PSD hill is formed. The enhanced PSD hill counteracts wave growth driven by phase-trapped anisotropic electrons and subsequently reduces wave amplitude. The weakened wave self-consistently feeds back to the particle trapping, ultimately suppressing both the PSD hole and hill. By the time the wave frequency reaches about 0.45Ωe, the gyro-phase structure of the electron distribution becomes much less organized. In some cases, however, the wave growth at the upstream source region can be strong enough that waves still manage to go through the gap frequency, suggesting that additional process(es) should likely be accompanied.

Why the term “operational discipline” is not helpful, and better options for instilling positive process safety culture

AbstractLanguage matters for effective leadership and culture. And the language embedded in the term “operational discipline” is not helpful. This term is inconsistent with decades of learning on cause analysis, systems thinking, and human performance. Humans typically do not fail because they are not disciplined enough. Failures occur for other reasons that stem from the systems within which the humans are working. For many people, the term “discipline” has a negative or punitive connotation. And the term “operational” focuses the spotlight on operations. The two terms taken together may imply to some people that willful operator deviations are the root cause of some incidents. Failures typically involve a range of management processes and functional groups. Thorough failure analysis can identify systemic causes, and follow‐up corrective actions may be targeted at the upstream sources. Healthy culture requires a positive, inclusive, and curious environment that seeks to continuously learn and improve without casting blame. Even if the term “operational discipline” is not intended to place blame, the choice of words defeats that aspiration. When seeking to improve process safety culture, choose language that supports a positive learning environment of ownership and empowerment by the workforce. And support those words through management actions.

KG-Hub-building and exchanging biological knowledge graphs.

Knowledge graphs (KGs) are a powerful approach for integrating heterogeneous data and making inferences in biology and many other domains, but a coherent solution for constructing, exchanging, and facilitating the downstream use of KGs is lacking. Here we present KG-Hub, a platform that enables standardized construction, exchange, and reuse of KGs. Features include a simple, modular extract-transform-load pattern for producing graphs compliant with Biolink Model (a high-level data model for standardizing biological data), easy integration of any OBO (Open Biological and Biomedical Ontologies) ontology, cached downloads of upstream data sources, versioned and automatically updated builds with stable URLs, web-browsable storage of KG artifacts on cloud infrastructure, and easy reuse of transformed subgraphs across projects. Current KG-Hub projects span use cases including COVID-19 research, drug repurposing, microbial-environmental interactions, and rare disease research. KG-Hub is equipped with tooling to easily analyze and manipulate KGs. KG-Hub is also tightly integrated with graph machine learning (ML) tools which allow automated graph ML, including node embeddings and training of models for link prediction and node classification. https://kghub.org.

Tap-Water Security and Policy Implications in Hanoi, Vietnam

This paper investigates tap-water securities using the management of non-traditional security (MNS) framework. The study found that tap-water in Hanoi is insecure due to uncertain upstream water sources, weak water quality monitoring, and poor wastewater drainage. Main challenges to tap-water security in Hanoi are ineffective management capacity of the local authorities as well as aging pipeline systems. Improvement in tap-water governance and collaborative co-governing is necessary. Privatization of tap-water utilities is not always effective to ensure tap water accessibilities to all residents. Finally, advanced water technologies are essential to achieving tap-water security in Hanoi.

Delta lobe development in response to changing fluvial sediment supply by the second largest river in Vietnam

While the importance of sediment supply to river delta evolution is well recognized, the extent to which sediment from upstream sources contributes to the subaerial and subaqueous components of its delta is not yet fully comprehended. To investigate this issue, the present study analyzed satellite images (Landsat) spanning from 1975 to present and nautical charts in different periods to examine the morphological evolution and its relationship with changes in river sediment loads of the Ba Lat delta lobe, located on the central coast of the second largest river system (Red) in Vietnam. We proposed a hybrid approach to estimate suspended sediment entering the sea via the Ba Lat mouth, based on a combination of one-line theory and long-term observation from a gauging station. The results show a significant reduction (∼91.5 %) in annual sediment load over the entire 64-year estimation period (1958–2021), which is associated with the operation of large dam-reservoirs upstream. The evolution of the Ba Lat delta lobe was found to be highly correlated with sediment load, with a huge sediment supply from the Red River causing the delta lobe to move seaward at a rate of more than 100 m/yr and the deltaic land area to accrete at a rate of 117 ha/yr between 1975 and 1990. However, since the early 1990s, the annual sediment flux has reduced of 57 %, resulting in more than 50 % of the delta lobe's shoreline experiencing severe erosion. The current amount of sediment load delivered to the sea (1.4 × 106 m3/yr) is insufficient to prograde the delta lobe, which could lead to continued land loss in the future. We attribute these erosions mainly to the reduced river sediment supply, generated by the large dam-reservoirs located upstream of the delta. The study suggests that these results and methods can inform coastal management and enhance understanding of delta lobe evolution by providing insights into changes in shoreline position, land area, and subaqueous component.

Quantifying the contribution of local drivers to observed weakening of spring dust storm frequency over northern China (1982–2017)

Recent studies have suggested that spring dust storm (SDS) events in northern China (NC) have exhibited substantial decline over the past 30 years. However, it is unclear which local factors are most responsible for the decline in SDS events, and the contribution of each dominant factor remains to be determined. This study utilized high-density DS records and collocated homogenized surface meteorological observations from 1982 to 2017, in conjunction with land surface products, to examine the local drivers that influence the long-term variation in SDS frequency (SDSF) over the entire NC area and its three dust-source areas: northwestern China (NWC), north-central China (NCC), and northeastern China (NEC). Results indicated that the observed SDSF averaged over NC, NWC, NCC, and NEC has decreased by 144.4 %, 109.3 %, 166.4 %, and 92.2 %, respectively, during 1982–2017. The variation in SDSF is largely explained by variation in wind speed (WS), precipitation, volumetric soil moisture, and surface bareness. A multivariable linear regression model incorporating these local drivers accounted for 81.0 %, 74.0 %, and 46.9 % of the variance in SDSF in NWC, NCC, and NEC, respectively. Statistical analyses on the local drivers suggested that weakening of WS was the dominant factor in the reduction in SDSF over recent decades, contributing 76.9 %, 54.7 %, and 33.6 % of the variation in NWC, NCC, and NEC, respectively. More importantly, we revealed that the interannual variation in regional SDSF was not only controlled by local drivers, but also influenced by cross-regional transport of dust aerosols emitted from upstream source areas.

Optimization Techniques in the Control of Fluid Flow Dynamics

This paper explores the application of optimization techniques in fluid dynamics, focusing on mathematical modeling, numerical simulations, and practical case studies. We begin by providing a comprehensive overview of optimization methods in fluid dynamics, covering gradient-based optimization, adjoint methods, control theory approaches, and machine learning techniques. Subsequently, we delve into three key application areas: aerodynamic shape optimization, flow control in pipelines, and environmental fluid dynamics. Through detailed case studies, we demonstrate the effectiveness of optimization algorithms in improving system performance and efficiency. In aerodynamic shape optimization, we minimize drag while maintaining lift, showcasing the power of gradient-based optimization and adjoint methods. In flow control, we optimize inlet velocity profiles to minimize energy loss and ensure specified flow rates, employing linear quadratic regulator (LQR) techniques. Finally, in environmental fluid dynamics, we address pollutant dispersion in rivers by optimizing flow rates from upstream sources to minimize downstream pollution concentration, using model predictive control (MPC) methods. Our study contributes practical insights into the integration of optimization techniques with fluid dynamics, offering guidance for researchers and practitioners in tackling real-world engineering challenges.

Environmental DNA clarifies impacts of combined sewer overflows on the bacteriology of an urban river and resulting risks to public health

There is no reference of microbiological water quality in the European Union's Water Framework Directive, adapted into English law, and consequently microbial water quality is not routinely monitored in English rivers, except for two recently designated bathing water sites. To address this knowledge gap, we developed an innovative monitoring approach for quantitative assessment of combined sewer overflow (CSO) impacts on the bacteriology of receiving rivers. Our approach combines conventional and environmental DNA (eDNA) based methods to generate multiple lines of evidence for assessing risks to public health. We demonstrated this approach by investigating spatiotemporal variation in the bacteriology of the Ouseburn in northeast England for different weather conditions in the summer and early autumn of the year 2021 across eight sampling locations that comprised rural, urban, and recreational land use settings. We characterized pollution source attributes by collecting sewage from treatment works and CSO discharge at the peak of a storm event. CSO discharge was characterized by log10 values per 100 mL (average ± stdev) of 5.12 ± 0.03 and 4.90 ± 0.03 for faecal coliforms and faecal streptococci, and 6.00 ± 0.11 and 7.78 ± 0.04 for rodA and HF183 genetic markers, for E. coli and human host associated Bacteroides, respectively, indicating about 5 % sewage content. SourceTracker analysis of sequencing data attributed 72–77 % of bacteria in the downstream section of the river during a storm event to CSO discharge sources, versus only 4–6 % to rural upstream sources. Data from sixteen summer sampling events in a public park exceeded various guideline values for recreational water quality. Quantitative microbial risk assessment (QMRA) predicted a median and 95th percentile risk of 0.03 and 0.39, respectively, of contracting a bacterial gastrointestinal disease when wading and splashing around in the Ouseburn. We show clearly why microbial water quality should be monitored where rivers flow through public parks, irrespective of their bathing water designation.

HYBRIDIZATION OF THE NAIVE BAYES CLASSIFICATION METHOD IN THE FRESHWATER FISH SEED SELLER CLASSIFICATION MODEL

Freshwater fish seed sellers play several roles in the supply chain process in the freshwater fish farming business. The role of the seller of freshwater fish seeds in this process is to distribute fish seeds which are one of the upstream sources in the supply chain process. Freshwater fish cultivators must select competent freshwater fish seed sellers so the supply chain process can run well. A large number of freshwater fish seed sellers in the market remind freshwater fish cultivators to choose the quality of the freshwater fish seed seller in terms of seed quality, low prices, shipping that can reach many areas, ergonomic packaging, and others. This study proposes Hybrid Naïve Bayes Classifiers (HNBCs) as a machine learning method for classification. This study aimed to compare the seed seller classification method in which the appropriate pattern of seed seller was identified by hybridization of Naïve Bayes Classifiers (NBCs), and then the researchers conducted performance appraisal and evaluation. The results are beneficial for freshwater fish cultivators and researchers which will enable them to formulate their plans according to the predicted results. The proposed method has produced significant results by achieving a training data accuracy of 82.61% and the testing data accuracy of 73.91%.

A comprehensive environmental assessment of beef production and consumption in the United States

Life cycle assessments of have been completed documenting the environmental sustainability of beef, but these studies have often focused on specific cattle production systems with an emphasis on global warming potential. A need exists for a national-scale full life cycle assessment of beef production through consumption in the United States. Process level simulation of archetypical cattle production systems throughout the nation were combined with information gathered for harvest, processing, retail, and consumption of beef to provide inventory data for a cradle-to-grave life cycle assessment. A set of 18 environmental impact categories were quantified, and important sources of each were identified. In 13 of the categories, the major sources of impact were related to cattle production, and for 10 of these categories, cattle production and related upstream sources contributed more than half of the total impact. These categories were fine particulate matter, global warming, land use, mineral resource scarcity, ozone formation, stratospheric ozone depletion, terrestrial acidification, and water consumption. Categories where most of the impact occurred post farmgate were fossil resource scarcity, freshwater ecotoxicity, freshwater eutrophication, human carcinogenic toxicity, human non-carcinogenic toxicity, ionizing radiation, marine ecotoxicity, and terrestrial ecotoxicity. Mitigation strategies for reducing these environmental impacts are normally specific to the impact category. Because electricity use is an important contributor to many of the potential impacts throughout the full chain, reducing electricity use is an important mitigation strategy. We evaluated the sensitivity associated with greening of the electric grid in which the Northeast US power grid, which has a larger percentage of renewables, was used as the source of electricity for all systems. The impact remained constant or were reduced in 15 of the 18 impact categories including a 6% reduction in global warming and 22% reduction in particulate matter formation. Another major contributor to all impact categories was food loss and waste. A 50% reduction in food waste, primarily by the consumer, resulted in an across-the-board reduction of approximately 11% in each of the impact categories, which makes food waste reduction one of the most important strategies for improving the environmental sustainability of beef. This assessment provides a current baseline for evaluating mitigation strategies and measuring future improvements in sustainability for the U.S. beef industry.

Study on the Impact of Future Climate Change on Extreme Meteorological and Hydrological Elements in the Upper Reaches of the Minjiang River

Global warming increases global average precipitation and evaporation, causing extreme climate and hydrological events to occur frequently. Future changes in temperature, precipitation, and runoff from 2021 to 2050 in the upper reaches of the Minjiang River were analyzed using a distributed hydrological model, the SWAT (Soil and Water Assessment Tool), under a future climate scenario. Simultaneously, future variation characteristics of extreme climate hydrological elements in the upper reaches of the Minjiang River were analyzed using extreme climate and runoff indicators. The research shows that the frequency and intensity of the extreme temperature warming index will increase, while those of the extreme temperature cooling index will increase and then weaken in the upper reaches of the Minjiang River under a future climate scenario. The duration of precipitation, the intensity of continuous heavy precipitation, and the frequency of heavy precipitation will increase, whereas the intensity of short-term heavy precipitation and the frequency of heavy precipitation will decrease. However, spatial distribution of flood in the upper reaches is different, and thus flood risk in the upstream source area will still tend to increase. Particular attention should be given to the increase in autumn flood risk in the upper reaches of the Minjiang River.

Linking Seasonal Changes in Organic Matter Composition and Nutrients to Shifting Hydraulic Gradients in Coastal Urban Canals

AbstractThe capacity for coastal river networks to transport and transform dissolved organic matter (DOM) is widely accepted. However, climate‐induced shifts in stormwater runoff and tidal extension alter fresh and marine water source contributions, associated DOM, and processing rates of nutrients entering coastal canals. We investigate how time‐variable interactions among coastal water source contributions influence the concentrations of dissolved organic carbon (DOC), nutrients, and DOM composition in urban canals. We quantified the spatiotemporal variability of DOM quality and nutrient concentrations to determine contributions of tidal marine water, rainwater, stormwater runoff, and groundwater to three coastal urban canals of Miami, Florida (USA). We created a Bayesian Monte Carlo mixing model using measurements of fluorescent DOM (fDOM), DOC concentrations, δ18O and δ2H isotopic signatures, and chloride (Cl−). Fractional contributions of groundwater averaged 17% in the dry season and 26% at peak high tide during the subtropical wet season (September–November). The canal‐to‐marine head difference (CMHD) was a primary driver of groundwater contributions to coastal urban canals and monthly patterns of fDOM/DOC. High tide (>1 m) and discharge events were found to connect canals to upstream sources of terrestrial DOM. Loading of terrestrially sourced DOC and DOM is pulsed to urban canals, shunted downstream and supplemented by microbially sourced DOM during the wet season at high tide. Overall, we demonstrate that a combined tracer approach with isotopes and fDOM can help identify groundwater contributions to coastal waterways and that autochthonous fDOM may prime the degradation of carbon or nutrients as the CMHD pushes inland.

DIGITAL PRODUCT INNOVATIONS: THE IMPACT OF INTER-FIRM COLLABORATION AND MANAGERS’ ATTITUDES

Although digital innovation is increasingly important for all types of firms, studies of the drivers of digital innovation rarely cover all sectors. Furthermore, organisational and individual factors are often overlooked. To address these gaps, we use data from a purpose-built cross-industry survey of 1,201 firms in Norway to examine how various types of collaborations and managers attitudes toward them shape firms’ achievement of digital product innovation. We find that collaborations with suppliers, consultants, and universities and research institutes, and the presence of open-minded managers, are positively associated with a firm’s likelihood of digital product innovation. Although much attention has been given to customer relationships, upstream sources of knowledge from suppliers, consultants, and universities and research institutes are also important to strengthen firms’ capacities for digital product innovation. Furthermore, we go beyond examining the existence of partnerships to show that manager’s attitudes towards collaboration also matter.

Inter-Industry Transfer of Intermediate Virtual Water Scarcity Risk: The Case of China

Multiple factors need to be considered when allocating water resources, among which water scarcity risk is often ignored. However, the unmet water demand of upstream sectors with high water dependency will exacerbate water scarcity, and lead to potential economic risk to the industrial chain. To solve it, we propose a method to quantify the intermediate virtual water scarcity risk transfer via the intermediate use matrix and Leontief inverse matrix, and apply it to virtual water trade in China in 2018. Meaningful conclusions are drawn as follows: (i) Although the water-use efficiency of all sectors in China increased steadily from 2007 to 2018, the overall input concentration of virtual water scarcity risk showed a rising trend, reflecting the gradual increase in the vulnerability of the industrial chain to water shortage. (ii) The virtual water scarcity risk in China mainly transferred through the secondary industry. The secondary industry accounted for 51.8% of the output and 71.8% of the input in the intermediate virtual water transfer, while 77.0% and 74.7%, respectively, in intermediate virtual water scarcity risk output and input. (iii) From 2007 to 2018, agriculture, chemical industry, metallurgy, electricity and heat supply always ranked as the top four of intermediate virtual water scarcity risk output sectors. As their downstream sectors, the construction industry, metallurgy, and other services are stable within the top four input sectors. (iv) The virtual water scarcity risk upstream transmitted is significantly dispersed after the intermediate inputs process, indicating that abundant import relationships are conducive to reduce the risk taken in. From the perspective of intermediate input, this paper argues that it is necessary to both ensure the water supply of the upstream source sectors and disperse the downstream import sources. Moreover, enriching industrial structures and closing production linkages between sectors is also beneficial for promoting sustainable economic development.

Formation and pathways of dense water in the Nordic Seas based on a regional inversion

Dense waters formed in the Nordic Seas spill across gaps in the Greenland-Scotland Ridge into the abyss of the North Atlantic to feed the lower limb of the Atlantic Meridional Overturning Circulation. The overflow water transport is well known, but open questions remain regarding where and how the dense overflow waters are formed and transported to the ridge. Here we develop a regional high-resolution version of an inverse method called Total Matrix Intercomparison, which combines hydrographic and geochemical tracer observations between 2000 and 2019 to resolve the pathways that connect the overflows to their origins. Consistent with previous studies we find two main pathways feeding the Denmark Strait Overflow Water (DSOW): the East Greenland Current and the North Icelandic Jet. Most of the water supplied by the North Icelandic Jet originates in the Greenland Sea (82 ± 2%) and flows southward along an outer core of the East Greenland Current, as well as along a previously unknown pathway crossing the Jan Mayen Ridge into the Iceland Sea. In total, 39 ± 2% of the DSOW originates in the Greenland Sea, while the Iceland Sea and the Atlantic Domain of the Nordic Seas account for 20 ± 3% and 19 ± 2%, respectively. The majority of the Faroe Bank Channel Overflow Water originates in the Greenland Sea (46 ± 8%) and the Arctic Ocean (25 ± 9%). These dense waters approach the sill in the Iceland-Faroe Slope Jet and along the eastern side of the Jan Mayen Ridge. The inversion reveals unprecedented details on the upstream sources and pathways of the overflows, which have not previously been obtained using observations.