Relation of surface and underground waters in Chungará and Cotacotani lake districts, northern Chile: an isotopic study.

Lake Chungará and Cotacotani lake districts are surface water bodies located to the northwest of Lauca Basin in the northern Chilean Altiplano. Surface and underground waters show low to moderate saline content and an electrical conductivity in the range of 48.7 to 3090 μS/cm. The lakes are related to a system of aquifers on the nearby volcano flanks and debris avalanche deposits of Parinacota volcano. On the basis of δ18O and δD isotopic composition and its correlation with the chloride content in Chungará and Cotacotani lake, spring, and Chungará river waters it is demonstrated that: a. Lake Chungará's waters show vertical and horizontal homogeneous isotopic composition, which indicates a good mixture of waters in the lake; b. an important part of the Cotacotani lake recharge feeding come from Lake Chungará, that flows laterally as groundwater; c. the groundwater that feeds the springs of the area has its main recharge in the spring-summer (October-March) precipitation. The high content of tritium (3H) measured in spring waters of the area suggested a very recent recharge (last decades) of the aquifer system. The application of lumped parameter models to interpret the water residence time in the aquifer indicates that the piston flow model shows the best fit to the isotopic composition of Chungará-Cotacotani groundwater

Hydrological evidence for a North Atlantic oscillation during the Little Ice Age outside its range observed since 1850.

An annual-resolved precipitation reconstruction for the last 800 yr in Southern Spain has been performed using stable carbon isotope (δ13C) of Pinus nigra tree rings. The reconstruction exhibits high- to low-frequency variability and distinguishes a Little Ice Age (LIA, AD 13501850) characterized by lower averaged rainfall than both in the transition from the Medieval Climate Anomaly to the LIA and in the 20th century. The driest conditions are recorded during the Maunder solar Minimum (mid 17thearly 18th centuries), in good agreement with the Spanish documentary archive. Similar linkage between solar activity (maximum/minimum) and precipitation (increase/decrease) is observed throughout the entire LIA. Additionally, the relationship between the hydrological pattern in the Iberian Peninsula and Morocco during the LIA suggests different spatial distribution of precipitation in the south-eastern sector of the North Atlantic region such as it is known currently. Whereas in the instrumental record the precipitation evolves similarly in both regions and opposite to the North Atlantic oscillation (NAO) index, the coldest periods of the LIA shows a contrasting pattern with drier conditions in the South of Spain and wetter in Northern Africa. We suggest an extreme negative NAO conditions, accompanied by a southward excursion of the winter rainfall band beyond that observed in the last century, can explain this contrast. The sustained NAO conditions could have been triggered by solar minima and higher volcanic activity during the LIA

Diatom and vegetation responses to Late Glacial and Early Holocene climate changes at Lake Estanya (Southern Pyrenees, NE Spain)

We investigate Lake Estanya's diatom and pollen records from the Late Glacial (LG) to the Early Holocene (EH), in order to compare limnological and vegetation responses to common climate forcing. The biotic changes recognized in this study largely agree with the hydrological evolution of the lake described previously for the same period. The diatom record shows high sensitivity to fluctuations in both lake level and salinity concentration as consequence of climate shifts. In addition vegetation results indicate that the area could have played an important role as regional vegetation refuge. Shallow lake conditions during the Last Glacial Maximum (LGM) were punctuated by relatively deeper freshwaters between 19.3 and 18.6 cal kyr BP and at 18.0 cal kyr BP, as recorded by diatom shifts. A subsequent increasing aridity trend, coinciding with the Mystery Interval (MI), affected the diatom accumulation rates, which dropped to its minimum values between 17.2 to 14.7 cal kyr BP. Particularly dry and cold conditions during the LGM and MI are supported by the largest values of steppic pollen taxa of the whole sequence, which account for up to 40%. However, relatively high values of Betula during the Heinrich Event 1 suggest a plausible regional vegetation refuge. Abrupt cooling and warming episodes within the LG triggered remarkable ecological threshold crossings in the diatom communities, especially during the stadial/interstadial episodes. At this point, the vegetation reflect the onset of warm conditions during the Bølling/Allerød with the partial substitution of Betula by Marcescent and Evergreen Quercus, what probably indicates the arrival of temperate taxa to the area and the likely migration of birch to higher altitudes. The Younger Dryas Stadial shows a complex ecological response. Diatoms are very poorly preserved, but aquatic taxa reach their highest values. An increase in Marcescent Quercus during this cold stage lends further support to the hypothesis that this is a regional vegetation refuge. Low lake levels recorded during the EH affected the development and preservation of diatom communities. A delay in the onset of humid conditions for the EH is also supported by the vegetation composition, characterized by the maximum expansion of Juniperus

A multiple dating-method approach applied to the Sanabria Lake moraine complex (NW Iberian Peninsula, SW Europe)

New evidence in the NW region of the Iberian Peninsula (c. 42º N 6 ºW) of a glacial advance coeval with the global Last Glacial Maximum (LGM) of the Marine Isotope Stage 2 has been identified through a dataset of exposure ages based on 23 10Be concentration measurements carried out on boulder samples taken from a set of latero-frontal moraines. Results span the interval 19.2e15.4 10Be ka, matching the last deglaciation period when Iberia experienced the coldest and driest conditions of the last 25 ka, and are consistent with Lateglacial chronologies established in other mountain regions from SW Europe. The extent of the LGM stade identified in this work is similar to the local maximum ice extent stade recorded and dated as prior to 33 ka using radiocarbon and optically stimulated luminescence. This work showcases how multiple-dating approaches and detailed geomorphological mapping are required to reconstruct realistic palaeoglacier evolution models

Comment on "Climate in the Western Cordillera of the Central Andes over the last 4300 years", by Engel et al. (2014)

Engel et al. (2014) present a new approach to understand Holocene climate changes in the Central Andes. They reconstruct the relative temperature changes in the Western Cordillera for the last 4,300 years by characterizing the 13C composition of a plant species occurring in the Carhuasanta peat sedimentary record (Peru, 15º 30' S

Formation and evolution of back-barrier perched lakes in rocky coasts: an example of a Holocene system in NW Spain

Coastal back-barrier perched lakes are freshwater bodies that are elevated over sea-level and are not directly subjected to the inflow of sea-water. This study provides a detailed reconstruction of the Doniños back-barrier perched lake that developed at the end of a small river valley in the rocky coast of the northwest Iberian Peninsula during the Holocene transgression. Its sequence stratigraphy was reconstructed based on a core transect across the system, the analyses of its lithofacies and microfossil assemblages, and a high-resolution radiocarbon-based chronology. The Doniños perched lake was formed ca. 4.5 ka BP. The setting of the perched lake was favoured by Late Holocene sea-level stabilization and the formation of a barrier and back-barrier basin, which was contemporaneous with the high systems tract period. This basin developed over marine and lagoonal sediments deposited between 10.2 and 8.0 ka BP, during rapidly rising sea-level characteristic of the transgressive systems track period. At 1.1 ka BP, the barrier was breached and the perched lake was partially emptied, causing the erosion of the back-barrier basin sediments and a significant sedimentary hiatus. Both enhanced storminess and human intervention were likely responsible for this event. After 1 ka BP, the barrier reclosed and the present-day lake was reformed, with the water level reaching as high as 5 m amsl. The depositional evolution of the Doniños system serves as a model of coastal back-barrier perched lakes in coastal clastic systems that have developed over gently seaward-dipping rugged substrates at small distances from the shoreline and under conditions of rising sea-level and high sediment supply. A review of estuaries, back-barrier lagoons, pocket beaches and back-barrier perched lakes in the rocky coast of the northwest Spain shows that the elevation of the bedrock is the main factor controlling the origin and evolution of these systems

The influence of subaquatic springs in lacustrine sedimentation: Origin and paleoenvironmental significance of homogenites in karstic Lake Banyoles (NE Spain)

Banyoles (42°08′N, 2°45′E) is the largest and deepest lake of karstictectonic origin in the Iberian Peninsula. The lake comprises two basins and six sub-circularly shaped sub-basins fed by subaquatic springs. Periods of intense groundwater inflow in the deepest sub-basins lead to the fluidization and re-suspension of previously deposited sediments and subsequent settling forming homogenite deposits on the southern basin intermediate platforms. The multiproxy analysis of sediment cores combined with high resolution seismic stratigraphy (3.5 kHz pinger and multi-frequency Chirp surveys) allows a precise reconstruction of depositional environments and related hydrological variability and groundwater inflowduring the last ca. 7.6 cal kyr BP. According to the agemodel based on 137Cs, 210Pb and AMS 14C dating, homogenite deposition occurred between 7.2 and 5.5 cal kyr BP, stopped during the middle Holocene (5.52.8 cal kyr BP) and greatly increased during the last two millennia with a total of 17 homogenite layers individually up to 75 cm-thick. The onset of this unique sedimentation mode at ca. 3 cal kyr BP coincides with an increase in lake level, evidenced by the onlapping of fine-grained, distal sediments over coarser massive, carbonate-rich, littoral deposits. A detailed, multidisciplinary study of the homogenites (sedimentology, physical properties, high-resolution elemental geochemistry, mineral composition, grain-size, organic matter content and SEM) combined with seismic stratigraphy demonstrates that the fluidization events triggering the formation of the homogenites were caused by higher and more intense local groundwater inflow, related to increased rainfall during the Late Holocene and likely intensified by land use changes during the last millennium

El registro sedimentario del lago Sant Maurici (Pirineos Centrales)

[spa] El Lago de St. Maurici (1.004818 E, 42.580801 N, 1924 m s.n.m) se localiza en la zona oriental del 'Parc Nacional d'Aigüestortes i Estany de Sant Maurici', Pirineos Centrales, Catalunya. El lago ocupa una cuenca de sobre- excavación detrás de una morrena terminal. El objetivo de este trabajo es reconstruir la evolución de los ambientes de depósito y su relación con la variabilidad climática desde la deglaciación hasta la actualidad, basándose en un sondeo de 8,7 m de longitud de la zona profunda del lago y un modelo de edad preliminar con tres dataciones AMS 14C. Tras la retirada del glaciar, se sedimentó una secuencia de arenas carbonatadas muy finas y limos arcillosos sin materia orgánica, propios de un lago proglacial. El Holoceno temprano se caracteriza por facies de arenas finas masivas que pasan a facies de limos arenosos laminados con un aumento progresivo del contenido en materia orgánica y con algunas capas de arenas. La secuencia presenta un hiato sedimentario durante el Holoceno medio. Desde el re-inicio de la sedimentación en el Holoceno tardío (ca. 4 ka) se han depositado facies organógenas.[eng] The St. Maurici Lake (1.004818 E, 42.580801 N, 1924 m a.s.l.) is located in the eastern area of 'Parc Nacional d'Aigüestortes i Estany de Sant Maurici', Central Pyrenees, Catalonia. The lake occupies an overexcavated basin behind a terminal moraine. This paper aims to reconstruct the evolution of depositional environments and their relation to climate evolution since deglaciation to the present, based on a 8.7-m long sequence retrieved in the deepest part of the lake and a preliminary chronological model with three 14C AMS dates. After the glacial retreat carbonatic very fine sands and silts without organic matter were deposited in a proglacial environment. Early Holocene sediments are massive fine sands to laminated sandy silts with increasing organic content and some sand layers. A sedimentary hiatus occurred during the mid Holocene and the sedimentation re-started after ca. 4 ka with deposition of organic facies. Changes in clastic content reflect centennial scale run-off variability during the last millennia

Centennial-scale precipitation anomalies in the southern Altiplano (18° S) suggest an extra-tropical driver for the South American Summer Monsoon during the late Holocene

Modern precipitation anomalies in the Altiplano region of South America are closely linked to the strength of the South American Summer Monsoon (SASM) which is influenced by large-scales climate features sourced in the tropics such as latitudinal shifts of the Intertropical Convergence Zone (ITCZ) and El Niño-Southern Oscillation (ENSO). However, the timing, direction and spatial extent of precipitation changes prior to the instrumental period are still largely unknown, preventing a better understanding of the long-term drivers of the SASM and their effects over the Altiplano. Here we present a detailed pollen reconstruction from a sedimentary sequence covering the period between 4500-1000 cal yr BP in Lago Chungará (18° S; 4570 masl), a high elevation lake in the southwestern margin of the Altiplano where precipitation is delivered almost exclusively during the mature phase of the SASM in the austral summer. We distinguish three well-defined centennial-scale anomalies, with dry conditions between 4100-3300 and 1600-1000 cal yr BP, and a conspicuous humid interval between 2400-1600 cal yr BP; which resulted from weakening and strengthening of the SASM respectively. Comparisons with other climate reconstructions from the Altiplano, the Atacama Desert, the Tropical Andes and the southwestern Atlantic coast reveal that - unlike the modern climatological controls - past precipitation anomalies at Lago Chungará were largely decoupled from north-south shifts in the ITCZ and ENSO. A regionally coherent pattern of centennial-scale SASM variations and a significant latitudinal gradient in precipitation responses suggest the contribution of an extra-tropical moisture source for the SASM, with significant effects over precipitation variability in the Southern Altiplano

Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27ºS)

Easter Island (SE Pacific, 27ºS) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Climates in the mid- to lowlatitude region of the eastern South Pacific Ocean are controlled by fluctuations in the Westerlies winds, the South Pacific Convergence Zone and the South Pacific Anticyclone. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34000 years based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 to 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest in the watershed during the Glacial period and a cold and relatively humid climate. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major floods due to the erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca. 9.5 cal kyr BP) and peatbog and shallow lake conditions dominated till mid Holocene, partially favored by the colmatation of the lacustrine basin. During the mid to late Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The human colonization of the island coincides with a new humid episode that started 800 yrs ago. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2 to 0.8 cal kyr BP sedimentary gap. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake