Eidem nerijos (Svalbardo salynas) poveikis vandens apytakai tarp ledyninės lagūnos ir Arkties vandenyno
Šeršenytė, Kamilė |
Eidem nerija (Svalbardo salynas) – besiformuojantis barjeras, atskiriantis Eidembreen ledyno tirpsmo vandeniu pildomą lagūną nuo Arkties vandenyno. Nors lagūna turėtų būti gėlavandenė, ~5 m gylyje aptiktas haloklino sluoksnis (20–25 PSU) rodo druskingo vandens prietaką. Tyrimo tikslas – nustatyti, kaip Eidem nerija veikia vandens apytaką ir kokie galimi druskingo Arkties vandenyno vandens patekimo keliai. Objektas – Eidem nerija. Tyrimas buvo atliktas remiantis 2023 metais Svalbarde Eidem lagūnoje ir nerijoje atliktų mokslinių tyrimų EIDEMBUKTA „Naujos pakrantės lagūnos ekosistemos susidarymas po ledynų atsitraukimo Eidembuktoje Svalbardo Arktyje“ (S-MIP-22- 48) ir surinktų duomenų tokių kaip: nerijos aukštis, 21 nerijos paviršiaus nuogulų ėminių granuliometrinė analizė, lagūnos hidrologiniai parametrai, vaizdinė medžiaga, pagrindu. Tyrime apskaičiuoti filtracijos koeficientai (pagal Slichter ryšį), geofiltracijos greičiai; analizuoti bangų modeliai, Sentinel-2 vaizdai ir kita vazidinė medžiaga bei nustatyti alternatyvūs druskingo vandens patekimo keliai. Nustatytas nerijos aukštis virš vidutinio jūros lygio – 0,2–6,6 m (vidutinis ~3,8 m), plotis skersiniuose profiliuose – nuo 19,5 iki 130 m. Eidem nerijoje vyrauja žvirgždo ir gargždo nuogulos (~66 %); smėlis - ~34 %; molis ir aleuritas sudaro tik 0,16 %. Apskaičiuoti filtracijos koeficientai skersiniuose nerijos profiliuose svyravo nuo 107,24 iki 51093,89 m/parą priklausomai nuo profilio granuliometrinės sudėties. Apskaičiavus geofiltracijos greičius šiltuoju sezonu esant 1, 3 ir 5 m vandens lygių skirtumui, druskingo vandens geofiltracija galėjo įvykti per 2, 3 ir 5 profilius (greitis iki 244,08 m/parą), o esant 3 m – ir per 1 profilį (iki 732,25 m/parą). Esant 5 m skirtumui, filtracija galima visuose profiliuose, išskyrus 6 profilį. Alternatyvūs vandens apytakos keliai apima vandens persiliejimą per nerijos žemiausias vietas audrų metu, bei gėlo lagūnos vandens ištekėjimą per jungiamąjį sąsiaurį. Druskingo vandens prietaka per sąsiaurį nebuvo nustatyta. Eidem nerija vandens apytakos dinamikoje yra pralaidus barjeras, sudarantis galimybę druskingo vandens prietakai į lagūną. Šis tyrimas svarbus arktinių pakrančių hidrodinaminės aplinkos supratimui klimato kaitos sąlygomis.
Eidem Spit, located in the Svalbard archipelago, is a developing gravel barrier separating a glacial lagoon, fed by the Eidembreen glacier meltwater, from the Arctic Ocean. Although the lagoon receives predominantly freshwater inflow, a persistent halocline at ~5 m depth (20–25 PSU) indicates periodic intrusion of saline water. The aim of this study was to assess how the spit influences water exchange between the lagoon and the ocean and to identify water exchange pathways between Eidem lagoon and arctic ocean and also possible pathways for saline water entry. The research object is the Eidem spit. The data used in this study were obtained during a field expedition conducted in August 2023 in the Eidem Lagoon, as part of the research project EIDEMBUKTA, “Formation of a New Coastal Lagoon Ecosystem Following Glacier Retreat in Eidembukta, Svalbard Arctic”, funded by the Research Council of Lithuania. The collected data includes elevation of Eidem spit, salinity and temperature of the lagoon, granulometric analysis of 21 spit surface sediment samples, and visual materials like pictures of the spit and orthophotos. In this research filtration coefficients were calculated using Slichter's equation, and infiltration rates were calculated using different hydraulic gradient scenarios. Wave height model data and Sentinel-2 satellite images of the reserach region were also analyzed to detect alternative water exchange pathways. The morphological measurements revealed that the elevation of the spit ranges from 0,2 to 6,6 m above sea level, with an average of approximately 3,8. Its width varies considerably along its cross profiles— from 19,5 m in profile 1 (adjacent to the tidal inlet) to 130 m in profile 6, the widest and most inland segment. Granulometric analysis showed that coarse materials dominate: gravel and pebbles make up roughly 66% of the sediments, sand 34%, while clay and silt together account for only 0,16%. Sediment composition changes from east to west, with sand dominating the eastern section and coarser material (gravel and pebbles) dominating the central and western profiles. Calculated filtration coefficients during warm season varied widely depending on sediment composition, ranging from 107,24 m/day in sand-dominated profiles to as high as 51093,89 m/day in zones with the coarsest gravel. Simulations of potential saline infiltration under storm surge scenarios, which was hydraulic gradient differences of 1, 3, and 5 meters over a 24-hour period revealed diferences in permeability across the spit. During 1 m gradient, complete saline water infiltration was possible through 2, 3, and 5 profiles, with infiltration rates of 99,84 m/day, 233,43 m/day, and 244,08 m/day, respectively. During 3 m gradient, additional infiltration occurred through profile 1 (732,25 m/day), while at 5 m gradient, all profiles except profile 6 exhibited significant permeability, with maximum rates reaching 1220,42 m/day in profile 5 and 1167,17 m/day in profile 3. The highest infiltration rates were observed where the spit was narrowest and composed predominantly of coarse sediment. Differently, profile 6 remained impermeable even under extreme conditions due to its large width (130 m) and finer spit surface composition. In addition to subsurface infiltration, alternative water exchange pathways were identified. Sentinel-2 satellite imagery, ortophotos and field observations provided evidence of storm overwash events, where wave-driven seawater overtops low-elevation segments of the spit. Washed up tree logs, marine debris, boulders covered with kelp, and sediment displacement further supported the occurrence of overwash. Another possible route for the saltwater inflow is through a narrow tidal inlet on the southeastern edge of the spit. In this specific cases, it might allow a small amount of ocean water to flow back into the lagoon. Still, without more data, this idea remains unconfirmed. Eidem Spit doesn’t act as a complete barrier. It more or less works like a filter. During normal conditions, it limits surface-level seawater from entering. But now and then, especially under storm events or pressure shifts, saline water slips through— either below the surface or across the top. That would explain the halocline formation inside the lagoon. So the spit is doing two things at once – shields the lagoon, but it also lets water through. This research gives a better sense of how these Arctic lagoon systems behave. That’s vital, considering how fast climate is changing in the Artic. As glaciers melt, sea levels rise, and storms become more frequent, it is important to understand how these coastal structures adapt to these changes. Eidem spit is an example of how Arctic coastal landscapes are not passive barriers but act as active regulators of salinity and hydrodynamic processes. Quantifying filtration capacity of such structures is critical to predicting the ecological and physical evolution of glacial lagoons in a warming Arctic.