We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional ...humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.
We present a palaeoclimatic reconstruction of the last glacial cycle in Iberia (ca. 120,000–11,600cal yrs BP) based on multi-proxy reconstructions from lake sediments with robust chronologies, and ...with a particular focus on abrupt climate changes. The selected lake sequences provide an integrated approach from northern Iberia exploring temperature conditions, humidity variations and land-sea comparisons during the most relevant climate transitions of the last glacial period. Thus, we present evidence that demonstrates: (i) cold but relatively humid conditions during the transition from MIS 5 to MIS 4, which prevailed until ca. 60,000cal yrs BP in northern Iberia; (ii) a general tendency towards greater aridity during MIS 4 and MIS 3 (ca 60,000 to 23,500cal yrs BP) punctuated by abrupt climate changes related to Heinrich Events (HE), (iii) a complex, highly variable climate during MIS 2 (23,500 to 14,600cal yrs BP) with the “Mystery Interval” (MI: 18,500 to 14,600cal yrs BP) and not the global Last Glacial Maximum (LGM: 23,000 to 19,000cal yrs BP) as the coldest and most arid period. The last glacial transition starts in synchrony with Greenland ice records at 14,600cal yrs BP but the temperature increase was not so abrupt in the Iberian records and the highest humidity was attained during the Allerød (GI-1a to GI-1c) and not during the Bølling (GI-1e) period. The Younger Dryas event (GS-1) is discernible in northern Iberian lake records as a cold and dry interval, although Iberian vegetation records present a geographically variable signal for this interval, perhaps related to vegetation resilience.
The Marboré Cirque, which is located in the southern Central Pyrenees on the north face of the Monte Perdido Peak (42°40′0″N; 0.5°0″W; 3355 m), contains a wide variety of Holocene glacial and ...periglacial deposits, and those from the ‘Little Ice Age’ (‘LIA’) are particularly well developed. Based on geomorphological mapping, cosmogenic exposure dating and previous studies of lacustrine sediment cores, the different deposits were dated and a sequence of geomorphological and paleoenvironmental events was established as follows: (1) The Marboré Cirque was at least partially deglaciated before 12.7 kyr BP. (2) Some ice masses are likely to have persisted in the Early Holocene, although their moraines were destroyed by the advance of glaciers during the Mid Holocene and ‘LIA’. (3) A glacial expansion occurred during the Mid Holocene (5.1 ± 0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 kyr (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The ‘LIA’ represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and ad 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century. (7) A large rock avalanche occurred during the Mid Holocene, leaving a chaotic deposit that was previously considered to be a Late Glacial moraine.
Comparison of selected, well-dated, lacustrine, speleothem and terrestrial pollen records spanning the Holocene onset and the Early Holocene (ca. 11.7–8 cal kyrs BP) in the Iberian Peninsula shows ...large hydrological fluctuations and landscape changes with a complex regional pattern in timing and intensity. Marine pollen records from Alboran, the Mediterranean and off shore Atlantic sites show a step-wise increase in moisture and forest during this transition. However, available continental records point to two main patterns of spatial and temporal hydrological variability: i) Atlantic-influenced sites located at the northwestern areas (Enol, Sanabria, Lucenza, PRD-4), characterized by a gradual increase in humidity from the end of the Younger Dryas to the Mid Holocene, similarly to most North Atlantic records; and ii) continental and Mediterranean-influenced sites (Laguna Grande, Villarquemado, Fuentillejo, Padul, Estanya, Banyoles, Salines), with prolonged arid conditions of variable temporal extension after the Younger Dryas, followed by an abrupt increase in moisture at 10-9 cal kyrs BP. Different local climate conditions influenced by topography or the variable sensitivity (gradual versus threshold values) of the proxies analyzed in each case are evaluated. Vegetation composition (conifers versus mesothermophilous taxa) and resilience would explain a subdued response of vegetation in central continental areas while in Mediterranean sites, insufficient summer moisture availability could not maintain high lake levels and promote mesophyte forest, in contrast to Atlantic-influenced areas. Comparison with available climate models, Greenland ice cores, North Atlantic marine sequences and continental records from Central and Northern Europe and the whole Mediterranean region underlines the distinctive character of the hydrological changes occurred in inner Iberia throughout the Early Holocene. The persistent arid conditions might be explained by the intensification of the summer drought due to the high seasonality contrast at these latitudes caused by the orbital-induced summer insolation maximum. New records, particularly from western and southernmost Iberia, and palaeoclimate models with higher spatial resolution would help to constrain these hypotheses.
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•Review of available high-resolution paleoenvironmental records of the Iberian Peninsula extending back to the late glacial.•A large spatial and temporal variability of hydrological conditions during the Early Holocene has been recorded.•A multidisciplinary approach, including lake, speleothem and pollen records, has been used.•Atlantic-influenced sites experienced a gradual increase in humidity from the end of the Younger Dryas to the Mid Holocene.•Continental and Mediterranean-influenced areas recorded prolonged aridity after the Younger Dryas until 10 to 9 cal kyrs BP.
Abstract
Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. ...Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America.
The North Atlantic Oscillation (NAO) exerts a major influence on the climate of the North Atlantic region. However, other atmospheric circulation modes (ACMs), such as the East Atlantic (EA) and ...Scandinavian (SCAND) patterns, also play significant roles. The dynamics of lakes on the Iberian Peninsula are greatly controlled by climatic parameters, but their relationship with these various ACMs has not been investigated in detail. In this paper, we analyze monthly meteorological and limnological long-term datasets (1950–2011 and 1992–2011, respectively) from two lakes on the northern and central Iberian Peninsula (Sanabria and Las Madres) to develop an understanding of the seasonal sensitivity of these freshwater systems to the NAO, EA and SCAND circulation modes. The limnological variability within Lake Sanabria is primarily controlled by fluctuations in the seasonal precipitation and wind, and the primary ACMs associated with the winter limnological processes are the NAO and the SCAND modes, whereas only the EA mode appears to weakly influence processes during the summer. However, Lake Las Madres is affected by precipitation, wind and, to a lesser extent, temperature, whereas the ACMs have less influence. Therefore, we aim to show that the lakes of the Iberian Peninsula are sensitive to these ACMs. The results presented here indicate that the lake dynamics, in some cases, have a higher sensitivity to variations in the ACMs than single local meteorological variables. However, certain local features, such as geography, lake morphology and anthropic influences, are crucial to properly record the signals of these ACMs.
Lake Arreo sequence (western Ebro Basin, Spain) illustrates the century-scale climatic variability and human interactions in the landscape during the last 2.5kyr in the low lands of northern Spain. ...Two sediment cores from shallow-water and deep-water environments were analyzed using sedimentological, geochemical, mineralogical, biological – diatoms, pollen and charcoal content – and radiometric techniques for absolute dating. The shallow-water sequence indicates a rapid evolution from an alluvial-influenced wetland prior to 7th century BC to a wetland during the Ibero-Roman Humid Period (BC 630–AD 465) and a deeper, carbonate producing lake during the Dark Ages Cold Period (AD 465–890). The deep-water core shows the transition from a more saline lake during the arid Medieval Climate Anomaly (MCA, AD 890–1300) to less saline, meromictic conditions, particularly since the onset of the Little Ice Age (LIA, AD 1300–1870). During the last 2.5kyr, arid conditions occurred prior to 1st century AD, during the MCA and late 19th–mid 20th century while colder temperatures and relatively more humid conditions were more frequent during the Dark Ages, particularly the 7th century AD and the LIA. The evolution of the lake also reflects changes in grazing and agricultural practices since the Roman Period associated to the exploitation of nearby salt mining. Periods of intense human pressure on the lake watershed occurred during the High Middle Ages (AD 890–1180) and the Modern Period (AD 1600–1830).
•A multiproxy study from Lake Arreo sediment cores (N Iberian Peninsula)•Synergies between climate and human activities since the Roman Period•Arid intervals prior to 1st century AD, between AD 890–1300 and the XXth century•Cold and humid phases occurred between AD 640–790 and AD 1300–1700•Strong impact of salt mining on the environment during the last 2ka
During the period of instrumental records, the North Atlantic Oscillation (NAO) has strongly influenced inter-annual precipitation variations in the western Mediterranean, while some eastern parts of ...the basin have shown an anti-phase relationship in precipitation and atmospheric pressure. Here we explore how the NAO and other atmospheric circulation modes operated over the longer timescales of the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). High-resolution palaeolimnological evidence from opposite ends of the Mediterranean basin, supplemented by other palaeoclimate data, is used to track shifts in regional hydro-climatic conditions. Multiple geochemical, sedimentological, isotopic and palaeoecological proxies from Estanya and Montcortés lakes in northeast Spain and Nar lake in central Turkey have been cross-correlated at decadal time intervals since AD 900. These dryland lakes capture sensitively changes in precipitation/evaporation (P/E) balance by adjustments in water level and salinity, and are especially valuable for reconstructing variability over decadal–centennial timescales. Iberian lakes show lower water levels and higher salinities during the 11th to 13th centuries synchronous with the MCA and generally more humid conditions during the ‘LIA’ (15th–19th centuries). This pattern is also clearly evident in tree-ring records from Morocco and from marine cores in the western Mediterranean Sea. In the eastern Mediterranean, palaeoclimatic records from Turkey, Greece and the Levant show generally drier hydro-climatic conditions during the LIA and a wetter phase during the MCA. This implies that a bipolar climate see-saw has operated in the Mediterranean for the last 1100years. However, while western Mediterranean aridity appears consistent with persistent positive NAO state during the MCA, the pattern is less clear in the eastern Mediterranean. Here the strongest evidence for higher winter season precipitation during the MCA comes from central Turkey in the northeastern sector of the Mediterranean basin. This in turn implies that the LIA/MCA hydro-climatic pattern in the Mediterranean was determined by a combination of different climate modes along with major physical geographical controls, and not by NAO forcing alone, or that the character of the NAO and its teleconnections have been non-stationary.
► High-resolution lake climate records from Spain and Turkey show opposite trends during the last 1100 years. ► In this bipolar climate see-saw the MCA was overall dry (wet) and the LIA wet (dry) in the western (eastern) Mediterranean. ► Western Mediterranean dryness during the MCA is consistent with a persistent positive NAO state. ► The eastern Mediterranean pattern, on the other hand, cannot be explained by recent NAO teleconnections alone.
The molecular biomarker composition of two sediment cores from Sanabria Lake (NW Iberian Peninsula) and a survey of modern plants in the watershed provide a reconstruction of past vegetation and ...landscape dynamics since deglaciation. During a proglacial stage in Lake Sanabria (prior to 14.7 cal ka BP), very low biomarker concentration and carbon preference index (CPI) values ~1 suggest that the
n
-alkanes could have derived from eroded ancient sediment sources or older organic matter with high degree of maturity. During the Late glacial (14.7–11.7 cal ka BP) and the Holocene (last 11.7 cal ka BP) intervals with higher biomarker and triterpenoid concentrations (high %
n
C
29
, n
C
31
alkanes), higher CPI and average carbon length (ACL), and lower P
aq
(proportion of aquatic plants) are indicative of major contribution of vascular land plants from a more forested watershed (e.g. Mid Holocene period 7.0–4.0 cal ka BP). Lower biomarker concentrations (high %
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C
27
alkanes), CPI and ACL values responded to short phases with decreased allochthonous contribution into the lake that correspond to centennial-scale periods of regional forest decline (e.g. 4–3 ka BP, Roman deforestation after 2.0 ka, and some phases of the LIA, seventeenth–nineteenth centuries). Human activities in the watershed were significant during early medieval times (1.3–1.0 cal ka BP) and since 1960 CE, in both cases associated with relatively higher productivity stages in the lake (lower biomarker and triterpenoid concentrations, high %
n
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23
and %
n
C
31
respectively, lower ACL and CPI values and higher P
aq
). The lipid composition of Sanabria Lake sediments indicates a major allochthonous (watershed-derived) contribution to the organic matter budget since deglaciation, and a dominant oligotrophic status during the lake history. The study constrains the climate and anthropogenic forcings and watershed versus lake sources in organic matter accumulation processes and helps to design conservation and management policies in mountain, oligotrophic lakes.