Circulation Regimes Research Articles

Submarine erosional troughs in the northern South China Sea: Evidence for Early Miocene deepwater circulation and paleoceanographic change

The paleoceanography of the South China Sea (SCS) is poorly understood, although recent cruises and an ODP expedition (Leg 184) have provided a useful general framework. Here we report previously unrecognized multi-km scale sedimentary structures consisting of coupled ridges and troughs within the Early Miocene strata, using high-resolution 3D seismic data from the northern SCS margin. The troughs are interpreted as linear and/or arcuate erosional features which truncate the underlying strata. They range in orientation from E-W in the southern part of the study area to nearly NE-SW in the northwestern part of the study area. The spacing of erosional troughs varies from less than 0.1 km in the southern part to more than 3 km in the northern part, and they are about 50–1500 m in width, with a relief of 10–90 m. The erosional troughs are parallel to the regional strike of the Early Miocene slope of the northern SCS. From their internal geometry, context, regional distribution and most importantly their orientation relative to the paleo-slope gradient at the time of their formation, it is argued that they formed due to the action of bottom currents linked to the broader paleo-circulation regime in the basin. We infer that the paleo-bottom currents intruding from the Pacific flowed along the northern SCS slope, resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography. This study provides new insights into the Early Miocene paleoceanography of the SCS and demonstrates the utility of 3D seismic data to enhance our understanding of paleo-bottom current circulation regimes.

Spring bloom dynamics in a subarctic fjord influenced by tidewater outlet glaciers (Godthåbsfjord, SW Greenland)

AbstractIn high‐latitude fjord ecosystems, the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web. However, the environmental factors that control the timing and intensity of these spring blooms remain uncertain. In 2013, we studied the spring bloom dynamics in Godthåbsfjord, a large fjord system adjacent to the Greenland Ice Sheet. Our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers. A combination of out‐fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring (April–May), which supplied nutrient‐rich water to the surface layer. This surface water was subsequently transported out‐fjord, and due to this circulation regime, the biomass accumulation of phytoplankton was displaced away from the glaciers. In late May, the upwelling weakened and the dominant wind direction changed, thus reversing the direction of the surface water transport. Warmer water was now transported toward the inner fjord, and a bloom was observed close to the glacier terminus. Overall, our findings imply that the timing, intensity, and location of the spring blooms in Godthåbsfjord are controlled by a combination of upwelling strength and wind forcing. Together with sea ice cover, the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem.

On the link between Barents‐Kara sea ice variability and European blocking

AbstractThis study examines the connection between the variability of sea ice concentration in the Barents and Kara (B‐K) seas and winter European weather on an intraseasonal time scale. Low sea ice regimes in autumn and early winter over the B‐K seas are shown to affect the strength and position of the polar vortex, and increase the frequency of blocking regimes over the Euro‐Atlantic sector in late winter. A hypothesis is presented on the mechanism that links sea ice over the B‐K seas and circulation regimes in the North Atlantic, and is investigated considering 34 years of European Centre for Medium‐Range Weather Forecasts reanalysis data. Four key steps have been identified, starting from a local response of the near‐surface fluxes and modification of the upper tropospheric wave pattern, to the stratospheric adjustment and the tropospheric response in the North Atlantic. The proposed mechanism explains the delayed, late winter response of the North Atlantic Oscillation to the late autumn sea ice reduction, which has been found both in observations and model experiments. It also provides valuable insights on how the reduction of Arctic sea ice can influence the position of the tropospheric jet in the Euro‐Atlantic sector.

How do green roofs mitigate urban thermal stress under heat waves?

AbstractAs the climate warms, heat waves (HWs) are projected to be more intense and to last longer, with serious implications for public health. Urban residents face higher health risks because urban heat islands exacerbate HW conditions. One strategy to mitigate negative impacts of urban thermal stress is the installation of green roofs (GRs) given their evaporative cooling effect. However, the effectiveness of GRs and the mechanisms by which they have an effect at the scale of entire cities are still largely unknown. The Greater Beijing Region is modeled for a HW scenario with the Weather Research and Forecasting model coupled with a state‐of‐the‐art urban canopy model (Princeton Urban Canopy Model) to examine the effectiveness of GRs. The results suggest that GR would decrease near‐surface air temperature (ΔT2max = 2.5 K) and wind speed (ΔUV10max = 1.0 m s−1) but increase atmospheric humidity (ΔQ2max = 1.3 g kg−1). GRs are simulated to lessen the overall thermal stress as indicated by apparent temperature (ΔAT2max = 1.7°C). The modifications by GRs scale almost linearly with the fraction of the surface they cover. Investigation of the surface‐atmosphere interactions indicates that GRs with plentiful soil moisture dissipate more of the surface energy as latent heat flux and subsequently inhibit the development of the daytime planetary boundary layer (PBL). This causes the atmospheric heating through entrainment at the PBL top to be decreased. Additionally, urban GRs modify regional circulation regimes leading to decreased advective heating under HW.

Atmospheric drivers of Greenland surface melt revealed by self‐organizing maps

AbstractRecent acceleration in surface melt on the Greenland ice sheet (GrIS) has occurred concurrently with a rapidly warming Arctic and has been connected to persistent, anomalous atmospheric circulation patterns over Greenland. To identify synoptic setups favoring enhanced GrIS surface melt and their decadal changes, we develop a summer Arctic synoptic climatology by employing self‐organizing maps. These are applied to daily 500 hPa geopotential height fields obtained from the Modern Era Retrospective Analysis for Research and Applications reanalysis, 1979–2014. Particular circulation regimes are related to meteorological conditions and GrIS surface melt estimated with outputs from the Modèle Atmosphérique Régional. Our results demonstrate that the largest positive melt anomalies occur in concert with positive height anomalies near Greenland associated with wind, temperature, and humidity patterns indicative of strong meridional transport of heat and moisture. We find an increased frequency in a 500 hPa ridge over Greenland coinciding with a 63% increase in GrIS melt between the 1979–1988 and 2005–2014 periods, with 75.0% of surface melt changes attributed to thermodynamics, 17% to dynamics, and 8.0% to a combination. We also confirm that the 2007–2012 time period has the largest dynamic forcing relative of any period but also demonstrate that increased surface energy fluxes, temperature, and moisture separate from dynamic changes contributed more to melt even during this period. This implies that GrIS surface melt is likely to continue to increase in response to an ever warmer future Arctic, regardless of future atmospheric circulation patterns.

Analysis of surface circulation structures along a frequently repeated XBT transect crossing the Ligurian and Tyrrhenian Seas

A dataset of XBT (eXpendable BathyThermograph) temperature profiles collected by ships of opportunity along the Genova–Palermo route, since September 1999, is analyzed, together with altimetric observations and model results, with the purpose of identifying and characterizing robust circulation features along the track and investigating their variability. An anticyclone is found in the Ligurian Sea, just north of the Corsica Channel, not present in previous descriptions of the Mediterranean Sea circulation. It appears to be a recurrent feature, better defined and stronger in summer and in the beginning of autumn. In the northern part of the Tyrrhenian Sea, the well-known Bonifacio dipole shows a similar seasonality, in agreement with previous observations. However, the Bonifacio anticyclone also displays a strong interannual variability, not previously recorded, with significant variations in position and shape. In fact, the data suggest the existence of two distinct summer circulation regimes related to the position and shape of the Ligurian anticyclone. When the latter is wider, filling the entire region north of the Corsica Channel, the circulation in the northern Tyrrhenian Sea is isolated from that in the Ligurian Sea, in agreement with the common picture. However, the altimeter maps show that there are several cases in the last two decades in which the Ligurian anticyclone is small and displaced to the west, allowing an inflow through the Corsica Channel into the Tyrrhenian Sea. The two regimes appear to result from a delicate balance between the forcings acting in the two sub-basins and the topographic constraints.

Assessment of the variability of atmospheric pollution in National Parks of mainland Spain

Air quality in nine National Parks in mainland Spain was assessed analysing SO2, NOx, O3, PM10 and PM2.5 data from background stations. As emissions in and around parks are limited, the levels of primary pollutants are low. Concentrations of secondary pollutants are high especially in summer due to photochemical production. The geographical variability of pollutants responds to regional emission patterns and the dominant circulation regimes in different regions resulting in west-east gradients for O3 and PM. Seasonal variability of pollutants was also interpreted in virtue of transport scenarios, changes in photochemical activity and emissions variability. NOx and SO2, maximize in winter due to higher emissions while O3 and PM do it in summer due to photochemical production, lower precipitation and, in the case of PM, the occurrence of African dust outbreaks. The diurnal evolution was interpreted in virtue of variability in emissions and changes in the Planetary Boundar Layer height.

Controls of picophytoplankton abundance and composition in a highly dynamic marine system, the Northern Alboran Sea (Western Mediterranean)

The Alboran Sea is a highly dynamic basin which exhibits a high spatio-temporal variability of hydrographic structures (e.g. fronts, gyres, coastal upwellings). This work compares the abundance and composition of picophytoplankton observed across the northern Alboran Sea among eleven cruises between 2008 and 2012 using flow cytometry. We evaluate the seasonal and longitudinal variability of picophytoplankton on the basis of the circulation regimes at a regional scale and explore the presence of cyanobacteria ecotypes in the basin. The maximal abundances obtained for Prochlorococcus, Synechococcus and picoeukaryotes (12.7×104, 13.9×104 and 8.6×104cellsmL−1 respectively) were consistent with those reported for other adjacent marine areas. Seasonal changes in the abundance of the three picophytoplankton groups were highly significant although they did not match the patterns described for other coastal waters. Higher abundances of Prochlorococcus were obtained in autumn-winter while Synechococcus and picoeukaryotes exhibited a different seasonal abundance pattern depending on the sector (e.g. Synechococcus showed higher abundance in summer in the west sector and during winter in the eastern study area). Additionally, conspicuous longitudinal gradients were observed for Prochlorococcus and Synechococcus, with Prochlorococcus decreasing from west to east and Synechococcus following the opposite pattern. The analysis of environmental variables (i.e. temperature, salinity and inorganic nutrients) and cell abundances indicates that Prochlorococcus preferred high salinity and nitrate to phosphate ratio. On the contrary, temperature did not seem to play a role in Prochlorococcus distribution as it was numerically important during the whole seasonal cycle. Variability in Synechococcus abundance could not be explained by changes in any environmental variable suggesting that different ecotypes were sampled during the surveys. In particular, our data would indicate the presence of at least two ecotypes of Synechococcus: a summer ecotype widely distributed in the whole Alboran Sea and a winter ecotype adapted to lower temperature and higher nutrient concentration whose growth is favoured in the eastern sector.

Climate change and response in bottom water circulation and sediment provenance in the Central Arctic Ocean since the Last Glacial

In this study, Arctic Ocean patterns of deep water circulation and sediment provenance during the Last Glacial (LG) were compared with the recent situation by investigating the Nd and Sr isotopic composition (143Nd/144Nd, expressed as εNd, 87Sr/86Sr) of the leachable and lithogenic sediment fractions as well as the elemental composition (Mn, Ca, Mg, total inorganic carbon (TIC)) on a spatially extended scale encompassing 11 sediment cores from several Arctic Ocean basins and ridges.The leachable, authigenic signature of the surface sediments implies a North Atlantic deep water source and a late Holocene circulation regime that leads to well-mixed, mostly uniform, εNd values of −10.9 to −10.3. Sediments from the LG have overall more variable authigenic εNd values (−13.9 to −7.4). Lower values specifically occur in the Amerasian and Amundsen Basins, documenting an enhanced flow of deep waters from the Makarov Basin to the Amundsen Basin probably via the Lomonosov Ridge intra-basin.In terms of detrital provenance areas, the lithogenic material deposited at the core locations cannot be unambiguously assigned to distinct source areas based on its radiogenic isotope composition, but represents a diverse mixture. Nevertheless, the Nd and Sr isotope signatures of surface sediments from the Amerasian Basin are dominated by western Arctic sources (εNd=−12.8 to −11.0; 87Sr/86Sr=0.7214 to 0.7251), while Eurasian Basin surface sediments are dominated by Eurasian sources (εNd=−10.9 to −9.7, 87Sr/86Sr=0.7178 to 0.7299), which is in agreement with previous studies. Bulk element patterns (Ca, Mg, TIC) of the studied sediments support these differences in provenance. The LG samples show the same trends with low εNd (−16.1 to −13.7) and high 87Sr/86Sr (0.7294) in the Canada Basin, and higher εNd (−12.6 to −8.8) and lower 87Sr/86Sr (0.7154 to 0.7249) in the Eurasian Basin sediments. However, LG samples have mostly lower and more heterogenous εNd and 87Sr/86Sr values than the surface samples.Our geochemical study shows that the overall circulation pattern of the deep water masses during the LG was locally influenced by brine formation but was generally similar to today. The isotopic composition of the lithogenic material from the LG is different from modern times, presumably due to shorter transport pathways of lithogenic material to the Arctic Ocean because of a lower sea level and exposed shelves during the LG. Nevertheless, the lithogenic fraction still represents a mixture from several sources.

Preliminary thermal-hydraulic sub-channel analysis of 61 wire-wrapped bundle cooled by lead bismuth eutectic

Lead bismuth eutectic (LBE) is one of the most promising materials for coolant and spallation target for Accelerator Driven Systems (ADS). The thermal-hydraulic features in fuel assembly are one of the most important issues for development of this system. Aiming to get a deeper understanding on heat transfer behavior of wire-wrapped bundle cooled by LBE and to support the design of ADS systems, a fuel bundle simulator with 61 electrical rods spaced by helical wire was developed in KYLIN-II facility. In this paper, the preliminary heat transfer experiments with 70kW under forced and natural circulation regimes were performed. The thermal-hydraulic behaviors including thermal entrance characteristics, heat transfer coefficients, and temperature distribution at the cross section were investigated under both regimes. The experiments depict reasonable results, and the Nu based on center sub-channel shows an agreement with empirical correlations. Besides, a special sub-channel code named SACOS-PB was employed to support the sub-channel analysis; and similar results to each other were obtained. It can be concluded that the SACOS-PB is a reliable tool for LBE system sub-channel analysis. Based on the present work the comprehensive thermal-hydraulic analysis with a detailed test matrix in terms of different flow rates and heating powers will be conducted in near future.

Characterizing the circulation off the Kenyan‐Tanzanian coast using an ocean model

AbstractThe Kenyan‐Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan‐Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite‐derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan‐Tanzanian coastal region based on a climatology of 8 years (2000–2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December–March, there are relatively sluggish shelf flows and (2) during April–November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.

Windiness spells in SW Europe since the last glacial maximum

Dunefields have a great potential to unravel past regimes of atmospheric circulation as they record direct traces of this component of the climate system. Along the Portuguese coast, transgressive dunefields represent relict features originated by intense and frequent westerly winds that largely contrast with present conditions, clearly dominated by weaker northwesterly winds. Optical dating and subsurface stratigraphy document three age clusters indicating main episodes of dune mobilization during: the last termination (20–11.6 ka), Middle Holocene (5.6 ka), and Late Holocene (1.2–0.98 and 0.4–0.15 ka).We find reconstructed windfields to be analogous during all episodes and dominated by strong westerlies. Yet, larger grain size diameters and dune volumes documented for the last termination support amplified patterns compatible with a southward shift and intensification of the North Atlantic westerlies during winters. Conversely, dunes deposited after the Middle Holocene are compatible with more variable windfields and weakened patterns controlled by interannual shifts towards low values of the North Atlantic Oscillation (NAO).This work demonstrates that present windfield regimes in southern Europe are not compatible with past aeolian activity. Indeed, present day analogs indicate that wind intensities compatible with past aeolian activity are rare at present (sediment transport potentials below estimates in the aeolian record), but can occur if the jet stream is diverted to the south (i.e. 30°N with negative NAO index) or if very deep cyclones anchor around 50°N, extending their influence to the western Portuguese coast (relatively low NAO index). However, these conditions represent temporary patterns lasting around one day, while we suggest that the identified episodes of aeolian activity may represent semi-permanent conditions.

Trends in Summer Season Climate for Eastern Europe and Southern Russia in the Early 21st Century

The goal of this research is to evaluate changes in temperature and precipitation in the Central Chernozem Region of southwestern Russia during the summer and relate these to large-scale circulation types and synoptic circulation processes. Some of these circulation regimes result in extreme weather conditions over the region. Using a classification system for Northern Hemisphere large-scale flow regimes and observations of weather within the Central Chernozem Region, the role of individual synoptic patterns in the formation of weather anomalies was identified. Also, comparing the periods 1981–2010 and 1971–2000, the mean summer temperatures increased by 0.6°C regionally. During the most recent decade the increase was 1.3°C. Total precipitation for the summer increased over the 20th century and was characterized by less variability during the second half when compared to the first half. However, in the beginning of the 21st century, precipitation has decreased during the growing season, but variability has increased. The increase in summer temperatures and increased variability in precipitation were then linked to an increase in the occurrence of weather regimes associated with warm anomalies and blocking. Finally, the results of this study can be used to translate larger-scale seasonal or climate forecasts to the regional scale.

The switching between zonal and blocked mid-latitude atmospheric circulation: a dynamical system perspective

Atmospheric mid-latitude circulation is dominated by a zonal, westerly flow. Such a flow is generally symmetric, but it can be occasionally broken up by blocking anticyclones. The subsequent asymmetric flow can persist for several days. In this paper, we apply new mathematical tools based on the computation of an extremal index in order to reexamine the dynamical mechanisms responsible for the transitions between zonal and blocked flows. We discard the claim that mid-latitude circulation features two distinct stable equilibria or chaotic regimes, in favor of a simpler mechanism that is well understood in dynamical systems theory: we identify the blocked flow as an unstable fixed point (or saddle point) of a single basin chaotic attractor, dominated by the westerlies regime. We also analyze the North Atlantic Oscillation and the Arctic Oscillation atmospheric indices, whose behavior is often associated with the transition between the two circulation regimes, and investigate analogies and differences with the bidimensional blocking indices. We find that the Arctic Oscillation index, which can be thought as a proxy for a hemispheric average of the Tibaldi–Molteni blocking index, tracks unstable fixed points. On the other hand, the North Atlantic Oscillation, representative only for local properties of the North Atlantic blocking dynamics, does not show any trace of the presence of unstable fixed points of the dynamics.

Global circulation of the Earth’s atmosphere at altitudes from 0 to 135 Km simulated with the ARM model. Consideration of the solar activity contribution

The results of simulations of the global circulation and temperature regime in the altitude range from the lower tropospheric layers to 135 km are presented. They were obtained with the Atmospheric Research Model (ARM), an advanced modification of a version of the Cologne Middle Atmosphere Model (COMMA). The ARM is characterized by higher spatial resolution and better parameterizations of the radiation sources and heat sinks. At the lower boundary of the model, wavy sources of perturbations, which are caused by internal gravity waves and planetary waves, are specified. The results of the modeling of the global temperature and wind fields for the mean solar activity level are presented, and their changes, which are caused by variations of the UV-radiation fluxes in the solar activity cycle and by solar proton flares, are also considered.

Arctic circulation regimes

Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability.

Collectors, Producers, and Circulators of Tibetan and Chinese Medicines in Sichuan Province.

The act of prescribing pharmaceutical drugs to patients is normally the site of judgements about the drug's efficacy and safety. The success of treatments and the licences for commodities depend on the biochemical identity of the drugs and of their path and transformations inside the body. However, the 'supply chain' outside the body is eschewed by such discourse, and its importance for both pharmaceutical brands and physician-centred historiographies is ignored. As this ethnographic fieldwork on Tibetan and Chinese medicines in Sichuan shows, overlooked social actors ensure reliable knowledge about medicinal things and materials long before patients take their medicine. This paper takes a step back from the final products-clearly defined as 'Tibetan' or 'Chinese'-and introduces those who produce and distribute them. Via observations of particular regimes of circulation and processing, the actions of collecting, manufacturing, transporting, and educating appear as the first and foremost acts of efficacy and safety.

Cross–Time Scale Interactions and Rainfall Extreme Events in Southeastern South America for the Austral Summer. Part I: Potential Predictors

Abstract The physical mechanisms and predictability associated with extreme daily rainfall in southeastern South America (SESA) are investigated for the December–February season in a two-part study. Through a k-mean analysis, this first paper identifies a robust set of daily circulation regimes that are used to link the frequency of rainfall extreme events with large-scale potential predictors at subseasonal-to-seasonal scales. This represents a basic set of daily circulation regimes related to the continental and oceanic phases of the South Atlantic convergence zone (SACZ) and wave train patterns superimposed on the Southern Hemisphere polar jet. Some of these recurrent synoptic circulation types are conducive to extreme rainfall events in the region through synoptic control of different mesoscale physical features and, at the same time, are influenced by climate phenomena that could be used as sources of potential predictability. Extremely high rainfall (as measured by the 95th and 99th percentiles) is associated with two of these weather types (WTs), which are characterized by moisture advection intrusions from lower latitudes and the Pacific Ocean; another three WTs, characterized by above-normal moisture advection toward lower latitudes or the Andes, are associated with dry days (days with no rain). The analysis permits the identification of several subseasonal-to-seasonal scale potential predictors that modulate the occurrence of circulation regimes conducive to extreme rainfall events in SESA. It is conjectured that a cross–time scale interaction between the different climate drivers improves the predictive skill of extreme precipitation in the region.

Spatial coherence of extreme precipitation events in the Northwestern United States

ABSTRACTThe complexity of impacts resulting from extreme precipitation events varies with the spatial extent of precipitation extremes. Characteristics of precipitation extremes, defined by the top 5% of 3‐day accumulated precipitation, including their spatial coherence and relationships to two contrasting synoptic phenomena, were examined at stations across the Northwestern United States. The spatial coherence of precipitation extremes generally decayed with distance between stations. However, distinct geographic variability in region‐wide coherence of precipitation extremes was present with overall higher coherence west of the Cascades, and lower coherence in the lee of the Cascades and Northern Rocky Mountains. Illustrative patterns of coherence were also seen with respect to atmospheric circulation regimes; atmospheric rivers favoured broadly coherent extremes occurring primarily west of the Cascades during fall and winter, while closed lows favoured more isolated precipitation extremes in the lee of the Northern Rocky Mountains and Cascades, occurring primarily during spring. Geographic variability in spatial coherence, direction of maximum coherence and seasonality of extremes suggest that extreme precipitation events result from the interaction of atmospheric circulation and complex topography.

Impact of climate changes during the last 5 million years on groundwater in basement aquifers.

Climate change is thought to have major effects on groundwater resources. There is however a limited knowledge of the impacts of past climate changes such as warm or glacial periods on groundwater although marine or glacial fluids may have circulated in basements during these periods. Geochemical investigations of groundwater at shallow depth (80–400 m) in the Armorican basement (western France) revealed three major phases of evolution: (1) Mio-Pliocene transgressions led to marine water introduction in the whole rock porosity through density and then diffusion processes, (2) intensive and rapid recharge after the glacial maximum down to several hundred meters depths, (3) a present-day regime of groundwater circulation limited to shallow depth. This work identifies important constraints regarding the mechanisms responsible for both marine and glacial fluid migrations and their preservation within a basement. It defines the first clear time scales of these processes and thus provides a unique case for understanding the effects of climate changes on hydrogeology in basements. It reveals that glacial water is supplied in significant amounts to deep aquifers even in permafrosted zones. It also emphasizes the vulnerability of modern groundwater hydrosystems to climate change as groundwater active aquifers is restricted to shallow depths.