Freshwater hydraulic head and streamlines in the low Malm permeability scenario with the sole hydraulic effect of the Inn Glacier (i.e. model run A introduced in Fig. 3) a at the Last Glacial Maximum 26.3 ka ago (time = 1.037E5 a), and b at present (time = 1.3E5 a). By comparison, freshwater hydraulic head and streamlines in the high Malm permeability scenario with the sole hydraulic effect of the Inn Glacier (i.e. model run B) c at the Last Glacial Maximum 26.3 ka ago (time = 1.037E5 a), and d at present (time = 1.3E5 a). Streamlines indicate Darcy's velocity field resulting from model properties and a constant surface temperature. White lines are isopotential levels at 50 m intervals. Vertical exaggeration equals five

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... runs A and B: hydraulic head and groundwater flow Figure 7 shows the hydraulic head, here the freshwater hydraulic head, which develops at different times in the low Malm k scenario as a result of model run A (Fig. 7a, b) and in the high Malm k scenario as a result of model run B (Fig. 7c, d). In particular, Fig. 7a, c visualizes the freshwater hydraulic head which develops in presence of the Inn Glacier. ...

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... runs A and B: hydraulic head and groundwater flow Figure 7 shows the hydraulic head, here the freshwater hydraulic head, which develops at different times in the low Malm k scenario as a result of model run A (Fig. 7a, b) and in the high Malm k scenario as a result of model run B (Fig. 7c, d). In particular, Fig. 7a, c visualizes the freshwater hydraulic head which develops in presence of the Inn Glacier. However, at first, we study only the hydraulic effect of the Inn Glacier, i.e. without applying paleoclimatic conditions. The point in time of 26.3 ...

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... runs A and B: hydraulic head and groundwater flow Figure 7 shows the hydraulic head, here the freshwater hydraulic head, which develops at different times in the low Malm k scenario as a result of model run A (Fig. 7a, b) and in the high Malm k scenario as a result of model run B (Fig. 7c, d). In particular, Fig. 7a, c visualizes the freshwater hydraulic head which develops in presence of the Inn Glacier. However, at first, we study only the hydraulic effect of the Inn Glacier, i.e. without applying paleoclimatic conditions. The point in time of 26.3 ka (i.e. model . Streamlines indicate Darcy's velocity field resulting ...

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... runs A and B: hydraulic head and groundwater flow Figure 7 shows the hydraulic head, here the freshwater hydraulic head, which develops at different times in the low Malm k scenario as a result of model run A (Fig. 7a, b) and in the high Malm k scenario as a result of model run B (Fig. 7c, d). In particular, Fig. 7a, c visualizes the freshwater hydraulic head which develops in presence of the Inn Glacier. However, at first, we study only the hydraulic effect of the Inn Glacier, i.e. without applying paleoclimatic conditions. The point in time of 26.3 ka (i.e. model . Streamlines indicate Darcy's velocity field resulting from model properties and a ...

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... m intervals. Vertical exaggeration equals five time of 103.7 ka) is shown because it corresponds to the maximum height of the Inn Glacier in Fig. 6. At the upper model boundary corresponding to the surface of the Molasse, the freshwater hydraulic head adequately replicates the topography, including the fluctuation height of the Inn Glacier. When Fig. 7a and c, respectively, Fig. 7b and d are compared, the freshwater hydraulic head decrease directly beneath the surface is stronger in the high Malm k scenario. The low Malm k induces a groundwater flow that is essentially limited to the Molasse. Only a minor fraction of groundwater flows towards the Malm aquifer (Fig. 7a, b). By ...

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... equals five time of 103.7 ka) is shown because it corresponds to the maximum height of the Inn Glacier in Fig. 6. At the upper model boundary corresponding to the surface of the Molasse, the freshwater hydraulic head adequately replicates the topography, including the fluctuation height of the Inn Glacier. When Fig. 7a and c, respectively, Fig. 7b and d are compared, the freshwater hydraulic head decrease directly beneath the surface is stronger in the high Malm k scenario. The low Malm k induces a groundwater flow that is essentially limited to the Molasse. Only a minor fraction of groundwater flows towards the Malm aquifer (Fig. 7a, b). By contrast, the high Malm k induces a ...

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... of the Inn Glacier. When Fig. 7a and c, respectively, Fig. 7b and d are compared, the freshwater hydraulic head decrease directly beneath the surface is stronger in the high Malm k scenario. The low Malm k induces a groundwater flow that is essentially limited to the Molasse. Only a minor fraction of groundwater flows towards the Malm aquifer (Fig. 7a, b). By contrast, the high Malm k induces a groundwater flow that is no longer restricted to the Molasse but descends into the Malm aquifer (Fig. 7c, d). A major difference between the LGM, here represented by the hydraulic effect of the Inn Glacier, and the present situation in both low and high Malm k scenarios consists in the ...

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... is stronger in the high Malm k scenario. The low Malm k induces a groundwater flow that is essentially limited to the Molasse. Only a minor fraction of groundwater flows towards the Malm aquifer (Fig. 7a, b). By contrast, the high Malm k induces a groundwater flow that is no longer restricted to the Molasse but descends into the Malm aquifer (Fig. 7c, d). A major difference between the LGM, here represented by the hydraulic effect of the Inn Glacier, and the present situation in both low and high Malm k scenarios consists in the contrasting groundwater flow patterns. In our models, this particular situation exists because a region of higher altitude is located between the Danube in ...

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... groundwater flow patterns. In our models, this particular situation exists because a region of higher altitude is located between the Danube in the north and the Inn in the south of the section. Presently, two cells of forced convection exist: a southern one draining towards the Inn River, and a northern one draining towards the Danube River (Fig. 7b, d). In the southernmost part of the model, where the surface falls off towards the Inn valley near Rosenheim, groundwater flow descends from the highest freshwater head at 600 m altitude and ascends near the Inn valley (Fig. 7b, d). This groundwater thus forms a separate convection cell, which is decoupled from the flow heading towards ...

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... convection exist: a southern one draining towards the Inn River, and a northern one draining towards the Danube River (Fig. 7b, d). In the southernmost part of the model, where the surface falls off towards the Inn valley near Rosenheim, groundwater flow descends from the highest freshwater head at 600 m altitude and ascends near the Inn valley (Fig. 7b, d). This groundwater thus forms a separate convection cell, which is decoupled from the flow heading towards the Malm aquifer and to the north. During cold periods, however, each foreland advance of the Inn Glacier onto the MB induces a reorganization of groundwater flow leading to a single cell of forced convection towards the Danube in ...

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... This groundwater thus forms a separate convection cell, which is decoupled from the flow heading towards the Malm aquifer and to the north. During cold periods, however, each foreland advance of the Inn Glacier onto the MB induces a reorganization of groundwater flow leading to a single cell of forced convection towards the Danube in the north (Fig. 7a, c). This reorganization of groundwater flow as a hydraulic effect of the Inn Glacier is practically immediate (at most a few hundred years) even for the short foreland advance of the Inn Glacier 40 ka ago (Fig. ...

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... into the basin barely influences the thermal field, except for a small negative thermal anomaly at the southern model boundary (Fig. 10b). In our models, the southern convection cell induces an upflow of groundwater and heat mostly within the Molasse near the Alpine Front and towards the Inn valley near Rosenheim in the south of the section (Fig. 7b, d). In fact, the hydraulic effect of the Inn Glacier produces the small negative thermal anomaly by temporarily precluding this upflow. Flow reversal and cold-water infiltration causes temperatures at the same depth (0-4 km) to decrease by up to 40 °C. (Fig. 3). By contrast, Fig. 11c and d shows the high Malm k scenario with permafrost ...

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... permeability scenario (i.e. difference between model runs D and F introduced in Fig. 3): a 80 ka ago (time = 50,000 a), b 20 ka ago (time = 1.1E5 a), and c at present (time = 1.3E5 a). Vertical exaggeration equals three groundwater flow is directed from the recharge to the discharge areas and always in the direction of decreasing hydraulic head (Fig. 7). The particular situation along our section, where a topographic high generates two opposite cells of forced convection, actually illustrates a groundwater divide between the Danube and Inn Rivers (Fig. 7b, d). A similar situation exists between the Danube and the Rhine Rivers in the MB near Lake Constance, where the potentiometric ...

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... equals three groundwater flow is directed from the recharge to the discharge areas and always in the direction of decreasing hydraulic head (Fig. 7). The particular situation along our section, where a topographic high generates two opposite cells of forced convection, actually illustrates a groundwater divide between the Danube and Inn Rivers (Fig. 7b, d). A similar situation exists between the Danube and the Rhine Rivers in the MB near Lake Constance, where the potentiometric surface provides evidence that the Rhine drains the Malm aquifer in the western part of the MB ( Bertleff et al. 1993;Stober and Villinger 1997). Figure 7a, b shows that in the low Malm k scenario the present-day ...

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... similar situation exists between the Danube and the Rhine Rivers in the MB near Lake Constance, where the potentiometric surface provides evidence that the Rhine drains the Malm aquifer in the western part of the MB ( Bertleff et al. 1993;Stober and Villinger 1997). Figure 7a, b shows that in the low Malm k scenario the present-day freshwater hydraulic head corresponds to about 400-500 m altitude within large parts of the Malm aquifer. In Fig. 7c, an explanation for the stronger freshwater hydraulic head decrease in the high Malm k scenario is the faster dissipation of the hydraulic pressure induced by topography and the Inn Glacier. ...

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... 7a, b shows that in the low Malm k scenario the present-day freshwater hydraulic head corresponds to about 400-500 m altitude within large parts of the Malm aquifer. In Fig. 7c, an explanation for the stronger freshwater hydraulic head decrease in the high Malm k scenario is the faster dissipation of the hydraulic pressure induced by topography and the Inn Glacier. When permafrost occurs, notably in model runs C or E, the freshwater hydraulic head also decreases fast beneath the permafrost layer, because it hampers recharge (e.g. ...

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... the high Malm permeability scenario (i.e. difference between model runs E and G introduced in Fig. 3): a 80 ka ago (time = 50,000 a), b 20 ka ago (time = 1.1E5 a), and c at present (time = 1.3E5 a). Vertical exaggeration equals three a water table up to 200 m below terrain level towards the Alpine front. Accordingly, the high Malm k scenario in Fig. 7c and d indicates that the hydraulic head within the Malm aquifer in the central part of the section can theoretically be as low as the Danube in case the k contrast between Malm and Molasse is very high. Frisch and Huber (2000) indicate a relatively low freshwater head of 370 m in the Munich region, reaching southwards as far as the ...

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... very high. Frisch and Huber (2000) indicate a relatively low freshwater head of 370 m in the Munich region, reaching southwards as far as the Starnberger See and being only 40 m higher than the Danube near Regensburg over a distance of more than 100 km. A similar low freshwater head over 80 to 100 km distance results from our high Malm k scenario (Fig. 7d). Therefore, the low hydraulic head values in the Malm aquifer confirm the excellent hydraulic connection with the Danube, which was postulated by Frisch and Huber (2000) and Stober et al. (2014) because of the existence of freshwater with a mineralization below 1 g L −1 in the Malm aquifer in large areas of the MB. Mraz et al. (2019) ...

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... glaciations represent the strongest impacts on groundwater during recent geological time. Figure 7 best shows how the model results recreate the observations of Boulton et al. (1995) and Piotrowski (1997a) by exemplifying the reorganization of the relatively small, topographically controlled groundwater catchments typical of interglacial periods, such as the present, to produce basin-scale integration of groundwater flow when glaciers advance into the foreland. Specifically, the hydraulic effect of the Inn Glacier completely suppresses the convection cell of groundwater ascending towards the Inn River and thereby concentrates groundwater flow towards the Danube River (Fig. 7). ...

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... interglacial periods, such as the present, to produce basin-scale integration of groundwater flow when glaciers advance into the foreland. Specifically, the hydraulic effect of the Inn Glacier completely suppresses the convection cell of groundwater ascending towards the Inn River and thereby concentrates groundwater flow towards the Danube River (Fig. 7). The consequence is significant groundwater flow in deep aquifers (i.e. in the deep Molasse and in the Malm) and the complete replacement of pre-existing groundwater by colder water in shallow aquifers, where permafrost is absent, such as in the Quaternary and the shallow Molasse beneath larger perennial rivers and lakes, and probably ...

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... The Péclet number calculation generally confirms the interpretation by Bertleff et al. (1993) and Bertleff and Watzel (2002) that the southern, deepest part of the Malm is characterized by a relatively stagnant groundwater system dominated by heat conduction. This groundwater can only be renewed by leakage through the Tertiary Molasse (Fig. 7), whereby an ion-exchange water composition formed ( Bertleff et al. 1993;Birner et al. ...

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... et al. 2018) and recurrent, persistent permafrost. Therefore, contrary to Bertleff et al. (1993) who put forward that recharge rates under recent climatic conditions are comparatively low, we suggest that recharge in the MB generally was lower during colder climatic conditions. According to our model results for the high Malm k scenario (Fig. 7c, d), it is possible that cold meltwater from the Inn and Achen glaciers (Van Husen 1987) infiltrated down to the Malm aquifer under an increased hydraulic head in the course of several glaciations. However, meltwater infiltration apparently did not produce an appreciable cold anomaly in the deeper MB (Fig. 10b). Equally, the much larger ...