28 research outputs found
The impact of the last glaciation on groundwater flow in the northern baltic artesian basin (BAB): a numerical study
Subglacial recharge model, stable isotope, noble gases, 14C dating
Using 81Kr and Noble Gases to Characterize and Date Groundwater and Brines in the Baltic Artesian Basin on the One-Million-Year Timescale
Analyses for Kr and noble gases on groundwater from the deepest
aquifer system of the Baltic Artesian Basin (BAB) were performed to determine
groundwater ages and uncover the flow dynamics of the system on a timescale of
several hundred thousand years. We find that the system is controlled by mixing
of three distinct water masses: Interglacial or recent meteoric water
(\delta^{18}\text{O} \approx -10.4\unicode{x2030}) with a poorly evolved
chemical and noble gas signature, glacial meltwater (\delta^{18}\text{O} \leq
-18\unicode{x2030}) with elevated noble gas concentrations, and an old,
high-salinity brine component (\delta^{18}\text{O} \geq -4.5\unicode{x2030},
\geq 90 \text{g Cl}^{-}/\text{L}) with strongly depleted atmospheric noble gas
concentrations. The Kr measurements are interpreted within this mixing
framework to estimate the age of the end-members. Deconvoluted Kr ages
range from 300 ka to 1.3 Ma for interglacial or recent meteoric water and
glacial meltwater. For the brine component, ages exceed the dating range of the
ATTA 3 instrument of 1.3 Ma. The radiogenic noble gas components He* and
Ar* are less conclusive but also support an age of > 1 Ma for the brine.
Based on the chemical and noble gas concentrations and the dating results, we
conclude that the brine originates from evaporated seawater that has been
modified by later water-rock interaction. As the obtained tracer ages cover
several glacial cycles, we discuss the impact of the glacial cycles on flow
patterns in the studied aquifer system.Comment: Accepted for publication in Geochimica et Cosmochimica Act
Two ice-core delta O-18 records from Svalbard illustrating climate and sea-ice variability over the last 400 years
Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited in climatic studies owing to uncertainties about the effect of meltwater percolation. However, results from two new Svalbard ice cores, at Lomonosovfonna and Austfonna, have shown that with careful site selection, high-resolution sampling and multiple chemical analyses it is possible to recover ice cores from which part of the annual signals are preserved, despite the considerable meltwater percolation. The new Svalbard ice cores are positioned in different parts of Svalbard and cover the past 800 years. In this paper we focus on the last 400 years. The delta(18)O signals from the cores are qualitatively similar over most of the twentieth century, suggesting that they record the same atmospheric signal. Prior to AD 1920, the Austfonna ice core exhibits more negative delta(18)O values than Lomonosovfonna, although there are intermittent decadal-scale periods throughout the record with similar values. We suggest that the differences reflect the effect of the inversion layer during the winter. The pattern in the delta(18)O records is similar to the Longyearbyen air-temperature record, but on an annual level the correlation is low. The Austforma record correlates well with the temperature record from the more distant and southwesterly located Jan Mayen. A comparison of the ice-core and sea-ice records from this period suggests that sea-ice extent and Austforma delta(18)O are related over the past 400 years. This may reflect the position of the storm tracks and their direct influence on the relatively low-altitude Austfonna. Lomonosovfonna may be less sensitive to such changes and primarily record free atmospheric changes instead of variations in sea-ice extent, the latter is probably a result of its higher elevation
Two ice-core d18O records from Svalbard illustrating climate and sea-ice variability over the last 400 years
Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited in climatic studies owing to uncertainties about the effect of meltwater percolation. However, results from two new Svalbard ice cores, at Lomonosovfonna and Austfonna, have shown that with careful site selection, high-resolution sampling and multiple chemical analyses it is possible to recover ice cores from which part of the annual signals are preserved, despite the considerable meltwater percolation. The new Svalbard ice cores are positioned in different parts of Svalbard and cover the past 800 years. In this paper we focus on the last 400 years. The delta(18)O signals from the cores are qualitatively similar over most of the twentieth century, suggesting that they record the same atmospheric signal. Prior to AD 1920, the Austfonna ice core exhibits more negative delta(18)O values than Lomonosovfonna, although there are intermittent decadal-scale periods throughout the record with similar values. We suggest that the differences reflect the effect of the inversion layer during the winter. The pattern in the delta(18)O records is similar to the Longyearbyen air-temperature record, but on an annual level the correlation is low. The Austforma record correlates well with the temperature record from the more distant and southwesterly located Jan Mayen. A comparison of the ice-core and sea-ice records from this period suggests that sea-ice extent and Austforma delta(18)O are related over the past 400 years. This may reflect the position of the storm tracks and their direct influence on the relatively low-altitude Austfonna. Lomonosovfonna may be less sensitive to such changes and primarily record free atmospheric changes instead of variations in sea-ice extent, the latter is probably a result of its higher elevation
Assessment of paleo-recharge under the Fennoscandian Ice Sheet and its impact on regional groundwater flow in the northern Baltic Artesian Basin using a numerical model
The study investigates the mechanism of glacial meltwater recharge under the Fennosciandian Ice Sheet during the last glacial
maximum (LGM) and its impact on regional groundwater flow in the northern Baltic Artesian Basin (BAB) in Estonia and
Latvia. The current hypothesis is that a flow reversal occurred in the BAB due to subglacial recharge during the LGM. This
hypothesis is supported by an extensive dataset of geochemical and isotopic measurements in the groundwater of northern
Estonia, exhibiting significant depletion in δ18O with respect to modern precipitation. To verify the consistency of this hypothesis
and better understand groundwater flow dynamics during the LGM period, a numerical model is developed for this area. Two
cross-sectional models have been created across the northern BAB, in which groundwater flow and the transport of δ18O have
been simulated from the beginning of the LGM to present-day. Several simulations were performed with different subglacial
boundary conditions, to investigate the uncertainty related to subglacial recharge of meltwater during the LGM and the subsequent flow reversal in the northern BAB. Several simulations provide a satisfying fit between computed and observed values of
δ18O, which means that the hypothesis of subglacial recharge of meltwater is consistent with δ18O distribution. The numerical
model suggests that preservation of meltwater in northern Estonia is controlled by confining layers and the proximity to the
outcrop area of aquifers, located in the Gulf of Finland. The results also suggest that glacial meltwater has been preserved under
the Baltic Sea in the Gulf of Riga
Representing glaciations and subglacial processes in hydrogeological models : a numerical investigation
The specific impact of glacial processes on groundwater flow and solute transport under ice-sheets was determined by means of numerical simulations. Groundwater flow and the transport of δ18O, TDS, and groundwater age were simulated in a generic sedimentary basin during a single glacial event followed by a postglacial period. Results show that simulating subglacial recharge with a fixed flux boundary condition is relevant only for small fluxes, which could be the case under partially wet-based ice-sheets. Glacial loading decreases overpressures, which appear only in thick and low hydraulic diffusivity layers. If subglacial recharge is low, glacial loading can lead to underpressures after the retreat of the ice-sheet. Isostasy reduces considerably the infiltration of meltwater and the groundwater flow rates. Below permafrost, groundwater flow is reduced under the ice-sheet but is enhanced beyond the ice-sheet front. Accounting for salinity-dependent density reduces the infiltration of meltwater at depth. This study shows that each glacial process is potentially relevant in models of subglacial groundwater flow and solute transport. It provides a good basis for building and interpreting such models in the future