Liquid Freshwater Research Articles

Four scenarios of environmental risk of diclofenac in European groundwater ecosystems

Groundwater is the largest source of liquid freshwater on Earth. Groundwater ecosystems harbor a rich biodiversity, mainly consisting of microbes and invertebrates that provide substantial ecological services. Despite its importance, groundwater is affected by several anthropic pressures, including pollution from pharmaceutical compounds. Diclofenac is the non-steroidal drug most widely detected in freshwaters, both in surface waters (e.g., rivers, streams, lakes etc.) and groundwaters. Unlike surface waters, the environmental risk of diclofenac in European groundwaters has not yet been assessed by the competent Authorities. The environmental risk assessment refers to the analysis of the potential risk that a chemical compound poses to a given environment by comparing its measured environmental concentrations to its predicted no-effect concentration. In this study, we explored four environmental risk scenarios in European groundwaters using different methodologies. We obtained diverse risk expectations, some indicative of a moderately diffuse environmental risk for concentrations of diclofenac ≥42 ng/L and others indicative of a widespread environmental risk for concentrations ≥5 ng/L. The difference among the four scenarios mainly related to the methods of calculating the predicted no-effect concentration of diclofenac. We discussed the four scenarios in order to identify the most realistic risk expectations posed by diclofenac to European groundwater ecosystems.

Arctic Ocean Freshwater in CMIP6 Ensembles: Declining Sea Ice, Increasing Ocean Storage and Export

AbstractThe Arctic has undergone dramatic changes in sea ice cover and the hydrologic cycle, both of which strongly impact the freshwater storage in, and export from, the Arctic Ocean. Here we analyze Arctic freshwater storage and fluxes in seven climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and assess their performance over the historical period (1980–2000) and in two future emissions scenarios, SSP1‐2.6 and SSP5‐8.5. Similar to CMIP5, substantial differences exist between the models' Arctic mean states and the magnitude of their 21st century storage and flux changes. In the historical simulation, most models disagree with observations over 1980–2000. In both future scenarios, the models show an increase in liquid freshwater storage and a reduction in solid storage and fluxes through the major Arctic gateways (Bering Strait, Fram Strait, Davis Strait, and the Barents Sea Opening) that is typically larger for SSP5‐8.5 than SSP1‐2.6. The liquid fluxes are driven by both volume and salinity changes, with models exhibiting a change in sign (relative to 1980–2000) of the freshwater flux through the Barents Sea Opening by mid‐century, little change in the Bering Strait flux, and increased export from the remaining straits by the end of the 21st century. In the straits west of Greenland (Nares, Barrow, and Davis straits), the models disagree on the behavior of the liquid freshwater export in the early‐to‐mid 21st century due to differences in the magnitude and timing of a simulated decrease in the volume flux.

Stronger Variability in the Arctic Ocean Induced by Sea Ice Decline in a Warming Climate: Freshwater Storage, Dynamic Sea Level and Surface Circulation

AbstractArctic liquid freshwater content (FWC) influences both regional and large‐scale ocean dynamics and climate. In this study the responses of Arctic FWC, sea surface height (SSH) and surface circulation to different atmospheric circulation modes and the impact of sea ice decline on these responses are investigated by using wind perturbation simulations. The responses are intensified by sea ice decline through its resulting enhancement in ocean surface stress, indicating stronger decadal variability in the Arctic liquid FWC, SSH and ocean circulation in a warming climate. The Arctic Oscillation (AO) and Beaufort High (BH) wind forcing can significantly change Arctic regional and total FWC. Compared to the sea ice condition in the 1980s, the amplitudes of the ocean responses to the same AO forcing are much larger under the sea ice condition in the 2010s for both Arctic total FWC (by up to 50%) and regional SSH and velocity (doubled in some places). Sea ice decline intensifies ocean responses to the BH forcing in the Canada Basin with a similar strength. The Arctic Dipole Anomaly (DA) causes opposite changes in FWC between the Eurasian and Amerasian sectors in the cold decade, with the impact through changing sea ice thermodynamics being nonnegligible compared with that through changing ocean surface stress. Sea ice decline makes the ocean response to DA forcing less regular spatially. This study indicates an increasing vulnerability of the Arctic Ocean to winds in a warming world, which implies that extreme marine events may occur more often in the future.

Labrador Sea freshening linked to Beaufort Gyre freshwater release

The Beaufort Gyre (BG), the largest Arctic Ocean freshwater reservoir, has drastically increased its liquid freshwater content by 40% in the past two decades. If released within a short period, the excess freshwater could potentially impact the large-scale ocean circulation by freshening the upper subpolar North Atlantic. Here, we track BG-sourced freshwater using passive tracers in a global ocean sea-ice model and show that this freshwater exited the Arctic mostly through the Canadian Arctic Archipelago, rather than Fram Strait, during an historical release event in 1983–1995. The Labrador Sea is the most affected region in the subpolar North Atlantic, with a freshening of 0.2 psu on the western shelves and 0.4 psu in the Labrador Current. Given that the present BG freshwater content anomaly is twice the historical analog studied here, the impact of a future rapid release on Labrador Sea salinity could be significant, easily exceeding similar fluxes from Greenland meltwater.

Ensemble-based estimation of sea-ice volume variations in the Baffin Bay

Abstract. Sea ice in the Baffin Bay plays an important role in deep water formation in the Labrador Sea and contributes to the variation of the Atlantic meridional overturning circulation (AMOC) on larger scales. Sea-ice data from locally merged satellite observations (Sat-merged SIT) in the eastern Canadian Arctic and three state-of-the-art sea ice–ocean models are used to quantify sea-ice volume variations from 2011 to 2016. Ensemble-based sea-ice volume (SIV) fluxes and the related standard deviations in the Baffin Bay are generated from four different estimates of SIV fluxes that were derived from Sat-merged SIT, three modeled SITs and satellite-based ice-drift data. Results show that the net increase in the SIV in Baffin Bay occurs from October to early April with the largest SIV increase in December (113 ± 17 km3 month−1) followed by a reduction from May to September with the largest SIV decline in July (−160 ± 32 km3 month−1). The maximum SIV inflow occurs in winter with the amount of 236 (±38) km3 while ice outflow reaches the maximum in spring with a mean value of 168 (±46) km3. The ensemble mean SIV inflow reaches its maximum (294 ± 59 km3) in winter 2013 caused by high ice velocity along the north gate while the largest SIV outflow (229 ± 67 km3) occurs in spring of 2014 due to the high ice velocity and thick ice along the south gate. The long-term annual mean ice volume inflow and outflow are 411 (±74) km3 yr−1 and 312 (±80) km3 yr−1, respectively. Our analysis also reveals that, on average, sea ice in the Baffin Bay melts from May to September with a net reduction of 335 km3 in volume while it freezes from October to April with a net increase of 218 km3. In the melting season, there is about 268 km3 freshwater produced by local melting of sea ice in the Baffin Bay. In the annual mean, the mean freshwater converted from SIV outflow that enters the Labrador Sea is about 250 km3 yr−1 (i.e., 8 mSv), while it is only about 9 % of the net liquid freshwater flux through the Davis Strait. The maximum freshwater flux derived from SIV outflow peaks in March is 65 km3 (i.e., 25 mSv).

Dissolved organic matter in large lakes: a key but understudied component of the carbon cycle

The world’s largest five freshwater lakes include tropical meromictic, temperate weakly stratified, and temperate holomictic lakes ranging in age from twenty-five million to ~ 10,000 years old. They contain > 50% of Earth’s surface liquid freshwater and 15% of Earth’s lake-water dissolved organic carbon. Large lakes, however, are understudied in terms of carbon cycling, including the roles of dissolved organic matter (DOM) as dissolved organic carbon (DOC), as chromophoric dissolved organic matter (CDOM), and at the compound class or molecular level. Existing data show that the five largest lakes have lower DOC and CDOM concentrations and clearer water than the global lake median. In Baikal, Superior, and Michigan, however, CDOM is the main non-water absorber of visible light. DOM in these three lakes contain a large proportion of reworked, terrestrially-derived organic matter. Isotopic data for Lake Superior show that its DOM consists of carbon converted into organic matter in the previous decade, though it is difficult to resolve if this organic matter is terrestrial or autochthonous material. No DOC or CDOM characterization or reactivity data exist for the tropical large lakes. Large lakes seem to fall on a continuum with smaller lakes and ocean water, in which water residence time (WRT) and DOC age are linearly related and DOC concentration is negatively correlated with log(WRT). However, existing data are sparse and the mechanisms behind these trends remain to be determined.

New viral biogeochemical roles revealed through metagenomic analysis of Lake Baikal

BackgroundLake Baikal is the largest body of liquid freshwater on Earth. Previous studies have described the microbial composition of this habitat, but the viral communities from this ecosystem have not been characterized in detail.ResultsHere, we describe the viral diversity of this habitat across depth and seasonal gradients. We discovered 19,475 bona fide viral sequences, which are derived from viruses predicted to infect abundant and ecologically important taxa that reside in Lake Baikal, such as Nitrospirota, Methylophilaceae, and Crenarchaeota. Diversity analysis revealed significant changes in viral community composition between epipelagic and bathypelagic zones. Analysis of the gene content of individual viral populations allowed us to describe one of the first bacteriophages that infect Nitrospirota, and their extensive repertoire of auxiliary metabolic genes that might enhance carbon fixation through the reductive TCA cycle. We also described bacteriophages of methylotrophic bacteria with the potential to enhance methanol oxidation and the S-adenosyl-L-methionine cycle.ConclusionsThese findings unraveled new ways by which viruses influence the carbon cycle in freshwater ecosystems, namely, by using auxiliary metabolic genes that act upon metabolisms of dark carbon fixation and methylotrophy. Therefore, our results shed light on the processes through which viruses can impact biogeochemical cycles of major ecological relevance.B3i_F4qvBy9xmcnWBwjShqVideo

Rapid Reconfiguration of the Greenland Ice Sheet Coastal Margin

AbstractThe Greenland Ice Sheet has lost mass at an accelerating rate over the last two decades, but limits of early remote sensing restricted examination of localized change at an ice‐sheet‐wide scale. We use satellite‐derived ice sheet surface velocities, glacier terminus advance/retreat, and surface elevation change data spanning ~1985–2015 to explore local characteristics of what is now a rapid reconfiguration of the ice sheet coastal margin. Widespread glacier terminus retreat is a more consistent climate response indicator than surface velocities, though local velocity patterns provide indicators of ice flow reconfiguration, including narrowing zones of fast‐flow, ice flow rerouting, and outlet abandonment. The implications of this observed rapid reconfiguration are wide ranging and likely include alteration of subglacial hydrology, iceberg discharge, liquid freshwater flux, potential nutrient and sediment flux, and mass flux. Without detailed observations of earlier deglaciations and with present limits on ice sheet model capabilities, these observational records provide an important analogue for past deglaciation and for projecting future ice loss.

Proteomics reveals sex-specific heat shock response of Baikal amphipod Eulimnogammarus cyaneus

The ancient Lake Baikal is the largest source of liquid freshwater on Earth and home to a unique fauna. Several hundred mostly cold-adapted endemic amphipod species inhabit Baikal, an ecosystem that is already being influenced by global change. In this study, we characterized the core proteome and heat stress-induced changes in a temperature-tolerant endemic amphipod, Eulimnogammarus cyaneus, using a proteogenomic approach (PRIDE dataset PXD013237) to unravel the molecular mechanisms of the observed adverse effects. As males were previously found to be much more tolerant to thermal stress, we placed special emphasis on differences between the sexes. For both sexes, we observed adaption of energy metabolism, cytoskeleton, lipid, and carbohydrate metabolism upon heat stress. In contrast, significant differences were determined in the molecular chaperone response. Females from the control conditions possessed significantly higher levels of heat shock proteins (HSP70, HSPb1, Hsc70-3), which, in contrast to males, were not further increased in response to heat stress. The inability of females to further increase heat shock protein synthesis in response to temperature stress may be due to sex-specific processes, such as egg production, requiring a large proportion of the available energy. As ovigerous females synthesize generally higher amounts of protein, they also need higher levels of molecular chaperones for the folding of these new proteins. Thus, the higher sensitivity of females to heat shock may be due to the lack of molecular chaperone molecules to counteract the heat-induced protein denaturation.

Groundwater Microbial Communities in Times of Climate Change.

Climate change has a massive impact on the global water cycle. Subsurface ecosystems, the earth largest reservoir of liquid freshwater, currently experience a significant increase in temperature and serious consequences from extreme hydrological events. Extended droughts as well as heavy rains and floods have measurable impacts on groundwater quality and availability. In addition, the growing water demand puts increasing pressure on the already vulnerable groundwater ecosystems. Global change induces undesired dynamics in the typically nutrient and energy poor aquifers that are home to a diverse and specialized microbiome and fauna. Current and future changes in subsurface environmental conditions, without doubt, alter the composition of communities, as well as important ecosystem functions, for instance the cycling of elements such as carbon and nitrogen. A key role is played by the microbes. Understanding the interplay of biotic and abiotic drivers in subterranean ecosystems is required to anticipate future effects of climate change on groundwater resources and habitats. This review summarizes potential threats to groundwater ecosystems with emphasis on climate change and the microbial world down below our feet in the water saturated subsurface.

Glochids microstructure and dew harvesting ability in Opuntia stricta (Cactaceae)

Liquid fresh water is scarce in arid and semi-arid regions. Some organisms in these stressful habitats are well adapted to the environmental conditions and obtain fresh water directly from the atmosphere. This ability of “moisture harvesting” relies on specific microstructural features organisms exhibit at their external surfaces. In this respect, the dew harvesting ability of the arid plant species Opuntia stricta (Cactaceae) has been investigated. Its tiny stem spines, known as glochids, have a unique microstructure, ordered in hierarchical manner with an anisotropic surface. The glochids are covered with cone-shaped barbs and have dense mats of hygroscopic trichomes at the base. Dew harvesting ability in O. stricta seems to be controlled by three driving forces, namely: Laplace pressure difference, Wenzel relation and differences in wettability. The formation of special external microstructural features supporting this ability represents an adaptive trait in O. stricta to dry arid environments. Studying such structures in detail will give insights on how biomimetic inspired devices may contribute to optimize moisture harvesting in dry regions.

Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century

AbstractArctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multidecadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state‐of‐the‐art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first flux to show emergence outside the range of background variability, with this change potentially already occurring. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability.

Embedded processor based automated assessment of quality of the water in an IoT background

For the life of human beings, water is necessary. While nearly 70% of the earth is drained, just 3% are known to be fresh water. Moreover, approximately 2.6% of the cooling water is not accessible to people. They are either trapped in glaciers and polar ice caps, contained in the soil or water, heavily poisoned, or unnecessarily drained below the Earth's surface. So only 0.4% of the drinkable water in the world is shared by the 7 billion inhabitants. Fresh water is therefore a valuable resource to be regulated and properly maintained. Only 80% of liquid fresh water should not be available to the public in many developing countries. By exponentially increasing the population of India, Fresh Water management in the farming, manufacturing and other fields is much more critical because of water requirements. “Physical, biological and chemical” parameters can be analyzed in determining the Fresh Water Quality. The scientists will manually carry out traditional water quality sampling. Nonetheless, this method takes a little bit of time and is cost-effective. Now, the IoT technology is used to track, capture and analyze the data in various fields of research. In this paper, we design a low-cost system to achieve water value in an IOT environment. The system consists of several sensors used for the calculation of chemical and physical water parameters. The machine learning algorithm has also been used to forecast water quality based on its data set, which were learned from a number of water samples. This system was modeled by using the U D00* 86 Ultra and Teensy++2.0 data processors at low budgets.

Sensitivity of the Arctic freshwater content and transport to model resolution

We compare the representation of the Arctic liquid and solid freshwater volumes, and their transports to/from the Arctic, using simulations with different ocean and atmosphere model resolutions from models participating in the EU H2020 PRIMAVERA project. Regarding ocean resolution, we find less liquid freshwater in the central Arctic Ocean and more in the Kara and Laptev seas in the model simulations at higher resolution compared with the model simulations at lower resolution. The mean sea ice thickness does not show a systematic behaviour across models regarding model resolution increase. In terms of atmospheric resolution, we find that both liquid freshwater and mean sea ice thickness decrease when the resolution of the atmospheric model increases. We also analyze differences of Arctic liquid freshwater volume and mean sea ice thickness caused by pre-industrial and historical atmospheric forcings. Pre-industrial simulations show less freshwater volume and increased mean sea ice thickness and export from the Arctic compared with present day simulations. Finally, we find an increasing impact of Arctic freshwater export on North Atlantic convection with increased atmospheric resolution.

Worldwide alteration of lake mixing regimes in response to climate change

Lakes hold much of Earth’s accessible liquid freshwater, support biodiversity and provide key ecosystem services to people around the world. However, they are vulnerable to climate change, for example through shorter durations of ice cover, or through rising lake surface temperatures. Here we use a one-dimensional numerical lake model to assess climate change impacts on mixing regimes in 635 lakes worldwide. We run the lake model with input data from four state-of-the-art model projections of twenty-first-century climate under two emissions scenarios. Under the scenario with higher emissions (Representative Concentration Pathway 6.0), many lakes are projected to have reduced ice cover; about one-quarter of seasonally ice-covered lakes are projected to be permanently ice-free by 2080–2100. Surface waters are projected to warm, with a median warming across lakes of about 2.5 °C, and the most extreme warming about 5.5 °C. Our simulations suggest that around 100 of the studied lakes are projected to undergo changes in their mixing regimes. About one-quarter of these 100 lakes are currently classified as monomictic—undergoing one mixing event in most years— and will become permanently stratified systems. About one-sixth of these are currently dimictic—mixing twice per year—and will become monomictic. We conclude that many lakes will mix less frequently in response to climate change. Many lakes that currently mix once or twice a year may become permanently stratified or mix only once in a warming climate, suggest numerical simulations of lake mixing regimes. Mixing regimes are most affected by ice-cover duration and surface temperatures.

On the Feedback of Ice–Ocean Stress Coupling from Geostrophic Currents in an Anticyclonic Wind Regime over the Beaufort Gyre

AbstractBased on analysis of observational data it has been suggested that a negative feedback of ice–ocean stress coupling may limit freshwater accumulation in the Beaufort Gyre (BG). In this paper we explore how this feedback can significantly contribute to BG stabilization in an anticyclonic wind regime. We use an ice–ocean model and turn on and off the feedback in simulations to elucidate the role of the feedback. When a persistent anticyclonic wind anomaly is applied over the BG, liquid freshwater content (FWC) increases because of enhanced Ekman downwelling. As a consequence, ocean surface geostrophic currents speed up. However, the spinup of sea ice is weaker than the acceleration of surface geostrophic currents during wintertime, because of strong sea ice internal stress when ice concentration is high and ice is thick. This leads to cyclonic anomalies in the ice–ocean relative velocity and stress over the BG. The resultant seasonal Ekman upwelling anomaly reduces freshwater accumulation by about 1/4 as compared to a simulation with the negative feedback turned off in a control experiment, with a reduction range of 1/10–1/3 in all experiments conducted. We show that the feedback is more effective when the model’s mesoscale eddy diffusivity is smaller or when sea ice internal stress is stronger. Finally, we argue that the ice–ocean stress feedback may become less significant as the Arctic warms and sea ice declines.

Recent Sea Ice Decline Did Not Significantly Increase the Total Liquid Freshwater Content of the Arctic Ocean

Abstract The freshwater stored in the Arctic Ocean is an important component of the global climate system. Currently the Arctic liquid freshwater content (FWC) has reached a record high since the beginning of the last century. In this study we use numerical simulations to investigate the impact of sea ice decline on the Arctic liquid FWC and its spatial distribution. The global unstructured-mesh ocean general circulation model Finite Element Sea Ice–Ocean Model (FESOM) with 4.5-km horizontal resolution in the Arctic region is applied. The simulations show that sea ice decline increases the FWC by freshening the ocean through sea ice meltwater and modifies upper ocean circulation at the same time. The two effects together significantly increase the freshwater stored in the Amerasian basin and reduce its amount in the Eurasian basin. The salinification of the upper Eurasian basin is mainly caused by the reduction in the proportion of Pacific Water and the increase in that of Atlantic Water (AW). Consequently, the sea ice decline did not significantly contribute to the observed rapid increase in the Arctic total liquid FWC. However, the changes in the Arctic freshwater spatial distribution indicate that the influence of sea ice decline on the ocean environment is remarkable. Sea ice decline increases the amount of Barents Sea branch AW in the upper Arctic Ocean, thus reducing its supply to the deeper Arctic layers. This study suggests that all the dynamical processes sensitive to sea ice decline should be taken into account when understanding and predicting Arctic changes.

Unknown Widespread Iron- and Sulfur-Oxidizing Bacteria beneath the East Antarctic Ice Sheet

Comparative analysis of the Vostok ice core (Central East Antarctica; one horizon, three boreholes) and D10 ice core (shoreline nearby the French Dumont d’Urville station) has reliably revealed three phylotypes (species) of aerobic iron-oxidizing betaproteobacteria of the family Gallionellaceae (closely related at the genus level to Sideroxydans lithotrophicus and Ferriphaselus amnicola), one of which has been detected from both the Vostok (borehole 5G-3) and D10 cores. In addition, the phylotype related to sulfur-oxidizing bacteria Tumebacillus sp. has been detected from both the Vostok (borehole 5G-2) and D10 cores. The both ice cores are almost equal in age, about 20 000 years; however, they differ in origin: the ice from Dumont d’Urville is atmospheric, while that from Vostok is a lake ice. The ice samples greatly vary in the storage time before treatment in the laboratory (from 0.5 to 40 years) and in intervals between treatments (from 1 to 5 years). The drilling sites are more than 1000 km apart. No evident hydrological links (the transfer of water beneath the ice sheet) between the Lake Vostok and Dumont D’Urville station have been found. This coincidence can be explained by the fact that minerals from the bedrock under the glacier, containing ferrous iron and reduced sulfur compounds, as well as physical and chemical conditions in both sites, liquid fresh water at a temperature near the freezing point, are similar. These and other assumptions are considered in the present article.

Arctic Sea Ice Decline Significantly Contributed to the Unprecedented Liquid Freshwater Accumulation in the Beaufort Gyre of the Arctic Ocean

AbstractThe Beaufort Gyre (BG) is the largest liquid freshwater reservoir of the Arctic Ocean. The liquid freshwater content (FWC) significantly increased in the BG in the 2000s during an anticyclonic wind regime and remained at a high level despite a transition to a more cyclonic state in the early 2010s. It is not well understood to what extent the rapid sea ice decline during this period has modified the trend and variability of the BG liquid FWC in the past decade. Our numerical simulations show that about 50% of the liquid freshwater accumulated in the BG in the 2000s can be explained by the sea ice decline caused by the Arctic atmospheric warming. Among this part of the FWC increase, 60% can be attributed to surface freshening associated with the reduction of the net sea ice thermodynamic growth rate, and 40% to changes in ocean circulation, which makes freshwater more accessible to the BG for storage. Thus, the rapid increase of the BG FWC in the 2000s was due to the concurrence of the anticyclonic wind regime and the high freshwater availability. We also find that if the Arctic sea ice had not declined, the liquid FWC in the BG would have shown a stronger decreasing tendency at the beginning of the 2010s owing to the cyclonic wind regime. From our results we argue that changes in sea ice conditions should be adequately taken into account when it comes to understanding and predicting variations of BG liquid FWC in a changing climate.

Subsurface iceberg melt key to Greenland fjord freshwater budget

Liquid freshwater fluxes from the Greenland ice sheet affect ocean water properties and circulation on local, regional and basin-wide scales, with associated biosphere effects. The exact impact, however, depends on the volume, timing and location of freshwater releases, which are poorly known. In particular, the transformation of icebergs, which make up roughly 30–50% of the loss of the ice-sheet mass to liquid freshwater, is not well understood. Here we estimate the spatial and temporal distribution of the freshwater flux for the Helheim–Sermilik glacier–fjord system in southeast Greenland using an iceberg-melt model that resolves the subsurface iceberg melt. By estimating seasonal variations in all the freshwater sources, we confirm quantitatively that iceberg melt is the largest annual freshwater source in this system type. We also show that 68–78% of the iceberg melt is released below a depth of 20 m and, seasonally, about 40–100% of that melt is likely to remain at depth, in contrast with the usual model assumptions. Iceberg melt also peaks two months after all the other freshwater sources peak. Our methods provide a framework to assess individual freshwater sources in any tidewater system, and our results are particularly applicable to coastal regions with a high solid-ice discharge in Greenland. Iceberg melt is the largest annual freshwater source in a south Greenland fjord, with release largely below 20 m depth, according to iceberg-model simulations. Furthermore, iceberg melt peaks later in the year than other sources of freshwater.