Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age

No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO2) concentration variability over glacial–interglacial cycles. A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum. However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO2 concentration increased rapidly, reflecting—at least in part— a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our records show that the observed covariation between atmospheric CO2 concentration and abyssal Southern Ocean oxygenation was maintained throughout most of the past 80,000 years. This suggests that on millennial timescales deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in modifying atmospheric CO2 concentration.

A refined TALDICE-1a age scale from 55 to 112 ka before present for the Talos Dome ice core based on high-resolution methane measurements

A precise synchronization of different climate records is indispensable for a correct dynamical interpretation of paleoclimatic data. A chronology for the TALDICE ice core from the Ross Sea sector of East Antarctica has recently been presented based on methane synchronization with Greenland and the EDC ice cores and δ18Oice synchronization with EDC in the bottom part (TALDICE-1). Using new high-resolution methane data obtained with a continuous flow analysis technique, we present a refined age scale for the age interval from 55–112 thousand years (ka) before present, where TALDICE is synchronized with EDC. New and more precise tie points reduce the uncertainties of the age scale from up to 1900 yr in TALDICE-1 to below 1100 yr over most of the refined interval and shift the Talos Dome dating to significantly younger ages during the onset of Marine Isotope Stage 3. Thus, discussions of climate dynamics at sub-millennial time scales are now possible back to 110 ka, in particular during the inception of the last ice age. Calcium data of EDC and TALDICE are compared to show the impact of the refinement to the synchronization of the two ice cores not only for the gas but also for the ice age scale.

Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core

High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (Δage) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP Δdepth (5.49 to 5.85 m) and Δage (498 to 601 yr) at the warming onset of GI-21 as well as the Δage range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ15N proxy) increases before CH4 concentration by no more than a few decades.

Direct north-south synchroniszation of abrupt climate change record in ice cores using Beryllium 10

A new, decadally resolved record of the 10Be peak at 41 kyr from the EPICA Dome C ice core (Antarctica) is used to match it with the same peak in the GRIP ice core (Greenland). This permits a direct synchronisation of the climatic variations around this time period, independent of uncertainties related to the ice age-gas age difference in ice cores. Dansgaard-Oeschger event 10 is in the period of best synchronisation and is found to be coeval with an Antarctic temperature maximum. Simulations using a thermal bipolar seesaw model agree reasonably well with the observed relative climate chronology in these two cores. They also reproduce three Antarctic warming events observed between A1 and A2.

The onset of Neoglaciation 6000 years ago in western Mongolia revealed by an ice core from the Tsambagarav mountain range

Glacier highstands since the Last Glacial Maximum are well documented for many regions, but little is known about glacier fluctuations and lowstands during the Holocene. This is because the traces of minimum extents are difficult to identify and at many places are still ice covered, limiting the access to sample material. Here we report a new approach to assess minimal glacier extent, using a 72-m long surface-to-bedrock ice core drilled on Khukh Nuru Uul, a glacier in the Tsambagarav mountain range of the Mongolian Altai (4130 m asl, 48°39.338′N, 90°50.826′E). The small ice cap has low ice temperatures and flat bedrock topography at the drill site. This indicates minimal lateral glacier flow and thereby preserved climate signals. The upper two-thirds of the ice core contain 200 years of climate information with annual resolution, whereas the lower third is subject to strong thinning of the annual layers with a basal ice age of approximately 6000 years before present (BP). We interpret the basal ice age as indicative of ice-free conditions in the Tsambagarav mountain range at 4100 m asl prior to 6000 years BP. This age marks the onset of the Neoglaciation and the end of the Holocene Climate Optimum. The ice-free conditions allow for adjusting the Equilibrium Line Altitude (ELA) and derive the glacier extent in the Mongolian Altai during the Holocene Climate Optimum. Based on the ELA-shift, we conclude that most of the glaciers are not remnants of the Last Glacial Maximum but were formed during the second part of the Holocene. The ice core derived accumulation reconstruction suggests important changes in the precipitation pattern over the last 6000 years. During formation of the glacier, more humid conditions than presently prevailed followed by a long dry period from 5000 years BP until 250 years ago. Present conditions are more humid than during the past millennia. This is consistent with precipitation evolution derived from lake sediment studies in the Altai.

Spatial gradients of temperature, accumulation and delta18O-ice in Greenland over a series of Dansgaard-Oeschger events

Air and water stable isotope measurements from four Greenland deep ice cores (GRIP, GISP2, NGRIP and NEEM) are investigated over a series of Dansgaard–Oeschger events (DO 8, 9 and 10), which are representative of glacial millennial scale variability. Combined with firn modeling, air isotope data allow us to quantify abrupt temperature increases for each drill site (1σ = 0.6 °C for NEEM, GRIP and GISP2, 1.5 °C for NGRIP). Our data show that the magnitude of stadial–interstadial temperature increase is up to 2 °C larger in central and North Greenland than in northwest Greenland: i.e., for DO 8, a magnitude of +8.8 °C is inferred, which is significantly smaller than the +11.1 °C inferred at GISP2. The same spatial pattern is seen for accumulation increases. This pattern is coherent with climate simulations in response to reduced sea-ice extent in the Nordic seas. The temporal water isotope (δ18O)–temperature relationship varies between 0.3 and 0.6 (±0.08) ‰ °C−1 and is systematically larger at NEEM, possibly due to limited changes in precipitation seasonality compared to GISP2, GRIP or NGRIP. The gas age−ice age difference of warming events represented in water and air isotopes can only be modeled when assuming a 26% (NGRIP) to 40% (GRIP) lower accumulation than that derived from a Dansgaard–Johnsen ice flow model.

Impact of Holocene climate changes on alpine and treeline vegetation at Sanetsch Pass, Bernese Alps, Switzerland

In order to infer reactions of treeline and alpine vegetation to climatic change, past vegetation changes are reconstructed on the basis of pollen, macrofossil and charcoal analysis. The sampled sediment cores originate from the small pond Emines, located at the Sanetsch Pass (connecting the Valais and Bern, Switzerland) at an altitude of 2288 m a.s.l. Today's treeline is at ca. 2200 m a.s.l. in the area, though due to special pass (saddle) conditions it is locally depressed to ca. 2060 m a.s.l. Our results reveal that the area around Emines was covered by treeless alpine vegetation during most of the past 12,000 years. Single individuals of Betula, Larix decidua and possibly Pinus cembra occurred during the Holocene. Major centennial to millennial-scale responses of treeline vegetation to climatic changes are evident. However, alpine vegetation composition remained rather stable between 11,500 and 6000 cal. BP, showing that Holocene climatic changes of +/− 1 °C hardly influenced the local vegetation at Emines. The rapid warming of 3–4 °C at the Late Glacial/Holocene transition (11,600 cal. BP) caused significant altitudinal displacements of alpine species that were additionally affected by the rapid upward movement of trees and shrubs. Since the beginning of the Neolithic, vegetation changes at Sanetsch Pass resulted from a combination of climate change and human impact. Anthropogenic fire increase and land-use change combined with a natural change from subcontinental to more oceanic climate during the second half of the Holocene led to the disappearance of P. cembra in the study area, but favoured the occurrence of Picea abies and Alnus viridis. The mid- to late-Holocene decline of Abies alba was primarily a consequence of human impact, since this mesic species should have benefitted from a shift to more oceanic conditions. Future alpine vegetation changes will be a function of the amplitude and rapidity of global warming as well as human land use. Our results imply that alpine vegetation at our treeline pass site was never replaced by forests since the last ice-age. This may change in the future if anticipated climate change will induce upslope migration of trees. The results of this study emphasise the necessity of climate change mitigation in order to prevent biodiversity losses as a consequence of unprecedented community and species displacement in response to climatic change.

Bacterial GDGTs in Holocene sediments and catchment soils of a high Alpine lake: application of the MBT/CBT-paleothermometer

A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.

Cascading climate effects and related ecological consequences during past centuries

The interface between climate and ecosystem structure and function is incompletely understood, partly because few ecological records start before the recent warming phase. Here, we analyse an exceptional 100-yr long record of the great tit (Parus major) population in Switzerland in relation to climate and habitat phenology. Using structural equation analysis, we demonstrate an uninterrupted cascade of significant influences of the large-scale atmospheric circulation (North-Atlantic Oscillation, NAO, and North-sea – Caspian Pattern, NCP) on habitat and breeding phenology, and further on fitness-relevant life history traits within great tit populations. We then apply the relationships of this analysis to reconstruct the circulation-driven component of fluctuations in great tit breeding phenology and productivity on the basis of new seasonal NAO and NCP indices back to 1500 AD. According to the structural equation model, the multi-decadal oscillation of the atmospheric circulation likely led to substantial variation in habitat phenology, productivity and consequently, tit population fluctuations with minima during the "Maunder Minimum" (∼ 1650–1720) and the Little Ice Age Type Event I (1810–1850). The warming since 1975 was not only related with a quick shift towards earlier breeding, but also with the highest productivity since 1500, and thus, the impact of the NAO and NCP has contributed to an unprecedented increase of the population. A verification of the structural equation model against two independent data series (1970–2000 and 1750–1900) corroborates that the retrospective model reliably depicts the major long-term NAO/NCP impact on ecosystem parameters. The results suggest a complex cascade of climate effects beginning at a global scale and ending at the level of individual life histories. This sheds light on how large-scale climate conditions substantially affect major life history parameters within a population, and thus influence key ecosystem parameters at the scale of centuries.

The origin of the European Medieval Warm Period"

Proxy records and results of a three dimensional climate model show that European summer temperatures roughly a millennium ago were comparable to those of the last 25 years of the 20th century, supporting the existence of a summer "Medieval Warm Period" in Europe. Those two relatively mild periods were separated by a rather cold era, often referred to as the "Little Ice Age". Our modelling results suggest that the warm summer conditions during the early second millennium compared to the climate background state of the 13th–18th century are due to a large extent to the long term cooling induced by changes in land-use in Europe. During the last 200 years, the effect of increasing greenhouse gas concentrations, which was partly levelled off by that of sulphate aerosols, has dominated the climate history over Europe in summer. This induces a clear warming during the last 200 years, allowing summer temperature during the last 25 years to reach back the values simulated for the early second millennium. Volcanic and solar forcing plays a weaker role in this comparison between the last 25 years of the 20th century and the early second millennium. Our hypothesis appears consistent with proxy records but modelling results have to be weighted against the existing uncertainties in the external forcing factors, in particular related to land-use changes, and against the uncertainty of the regional climate sensitivity. Evidence for winter is more equivocal than for summer. The forced response in the model displays a clear temperature maximum at the end of the 20th century. However, the uncertainties are too large to state that this period is the warmest of the past millennium in Europe during winter.

How stable are 20th century calibration models? A high-resolution summer temperature reconstruction for the eastern Swiss Alps back to A.D. 1580 derived from proglacial varved sediments

We found a significant positive correlation between local summer air temperature (May-September) and the annual sediment mass accumulation rate (MAR) in Lake Silvaplana (46°N, 9°E, 1800 m a.s.l.) during the twentieth century (r = 0.69, p < 0.001 for decadal smoothed series). Sediment trap data (2001-2005) confirm this relation with exceptionally high particle yields during the hottest summer of the last 140 years in 2003. On this base we developed a decadal-scale summer temperature reconstruction back to AD 1580. Surprisingly, the comparison of our reconstruction with two other independent regional summer temperature reconstructions (based on tree-rings and documentary data) revealed a significant negative correlation for the pre-1900 data (ie, late ‘Little Ice Age’). This demonstrates that the correlation between MAR and summer temperature is not stable in time and the actualistic principle does not apply in this case. We suggest that different climatic regimes (modern/‘Little Ice Age’) lead to changing state conditions in the catchment and thus to considerably different sediment transport mechanisms. Therefore, we calibrated our MAR data with gridded early instrumental temperature series from AD 1760-1880 (r = -0.48, p < 0.01 for decadal smoothed series) to properly reconstruct the late LIA climatic conditions. We found exceptionally low temperatures between AD 1580 and 1610 (0.75°C below twentieth-century mean) and during the late Maunder Minimum from AD 1680 to 1710 (0.5°C below twentieth-century mean). In general, summer temperatures did not experience major negative departures from the twentieth-century mean during the late ‘Little Ice Age’. This compares well with the two existing independent regional reconstructions suggesting that the LIA in the Alps was mainly a phenomenon of the cold season.

A 700-year paleoecological record of boreal ecosystem responses to climatic variation from Alaska

Recent observations and model simulations have highlighted the sensitivity of the forest - tundra ecotone to climatic forcing. In contrast, paleoecological studies have not provided evidence of tree-line fluctuations in response to Holocene climatic changes in Alaska, suggesting that the forest - tundra boundary in certain areas may be relatively stable at multicentennial to millennial time scales. We conducted a multiproxy study of sediment cores from an Alaskan lake near the altitudinal limits of key boreal-forest species. Paleoecological data were compared with independent climatic reconstructions to assess ecosystem responses of the forest - tundra boundary to Little Ice Age (LIA) climatic. uctuations. Pollen, diatom, charcoal, macrofossil, and magnetic analyses provide the first continuous record of vegetation -. re - climate interactions at decadal to centennial time scales during the past 700 years from southern Alaska. Boreal-forest diebacks characterized by declines of Picea mariana, P. glauca, and tree Betula occurred during the LIA ( AD 1500 - 1800), whereas shrubs ( Alnus viridis, Betula glandulosa/nana) and herbaceous taxa (Epilobium, Aconitum) expanded. Marked increases in charcoal abundance and changes in magnetic properties suggest increases in. re importance and soil erosion during the same period. In addition, the conspicuous reduction or disappearance of certain aquatic ( e. g., Isoetes, Nuphar, Pediastrum) and wetland ( Sphagnum) plants and major shifts in diatom assemblages suggest pronounced lake-level. uctuations and rapid ecosystem reorganization in response to LIA climatic deterioration. Our results imply that temperature shifts of 1 - 2 degrees C, when accompanied by major changes in moisture balance, can greatly alter high-altitudinal terrestrial, wetland, and aquatic ecosystems, including conversion between boreal-forest tree line and tundra. The climatic and ecosystem variations in our study area appear to be coherent with changes in solar irradiance, suggesting that changes in solar activity contributed to the environmental instability of the past 700 years.

Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years

The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km2 have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost 41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier elevation in the Northern Tien Shan since the Little Ice Age maximum.

1200 years of decadal-scale variability of Mediterranean vegetation and climate at Pantelleria Island, Italy

A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from ad 800 to 1000 that corresponds to the ‘Medieval Warm Period’ (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at ad 1000, when carbonate content became very low suggesting wetter conditions until ad 1850–1900. Broadly, this period coincides with the ‘Little Ice Age’ (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around ad1750.

North-south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

On the basis of a multi-proxy approach and a strategy combining lacustrine and marine records along a north–south transect, data collected in the central Mediterranean within the framework of a collaborative project have led to reconstruction of high-resolution and well-dated palaeohydrological records and to assessment of their spatial and temporal coherency. Contrasting patterns of palaeohydrological changes have been evidenced in the central Mediterranean: south (north) of around 40° N of latitude, the middle part of the Holocene was characterised by lake-level maxima (minima), during an interval dated to ca. 10 300–4500 cal BP to the south and 9000–4500 cal BP to the north. Available data suggest that these contrasting palaeohydrological patterns operated throughout the Holocene, both on millennial and centennial scales. Regarding precipitation seasonality, maximum humidity in the central Mediterranean during the middle part of the Holocene was characterised by humid winters and dry summers north of ca. 40° N, and humid winters and summers south of ca. 40° N. This may explain an apparent conflict between palaeoclimatic records depending on the proxies used for reconstruction as well as the synchronous expansion of tree species taxa with contrasting climatic requirements. In addition, south of ca. 40° N, the first millennium of the Holocene was characterised by very dry climatic conditions not only in the eastern, but also in the central- and the western Mediterranean zones as reflected by low lake levels and delayed reforestation. These results suggest that, in addition to the influence of the Nile discharge reinforced by the African monsoon, the deposition of Sapropel 1 has been favoured (1) by an increase in winter precipitation in the northern Mediterranean borderlands, and (2) by an increase in winter and summer precipitation in the southern Mediterranean area. The climate reversal following the Holocene climate optimum appears to have been punctuated by two major climate changes around 7500 and 4500 cal BP. In the central Mediterranean, the Holocene palaeohydrological changes developed in response to a combination of orbital, ice-sheet and solar forcing factors. The maximum humidity interval in the south-central Mediterranean started ca. 10 300 cal BP, in correlation with the decline (1) of the possible blocking effects of the North Atlantic anticyclone linked to maximum insolation, and/or (2) of the influence of the remnant ice sheets and fresh water forcing in the North Atlantic Ocean. In the north-central Mediterranean, the lake-level minimum interval began only around 9000 cal BP when the Fennoscandian ice sheet disappeared and a prevailing positive NAO-(North Atlantic Oscillation) type circulation developed in the North Atlantic area. The major palaeohydrological oscillation around 4500–4000 cal BP may be a non-linear response to the gradual decrease in insolation, with additional key seasonal and interhemispheric changes. On a centennial scale, the successive climatic events which punctuated the entire Holocene in the central Mediterranean coincided with cooling events associated with deglacial outbursts in the North Atlantic area and decreases in solar activity during the interval 11 700–7000 cal BP, and to a possible combination of NAO-type circulation and solar forcing since ca. 7000 cal BP onwards. Thus, regarding the centennial-scale climatic oscillations, the Mediterranean Basin appears to have been strongly linked to the North Atlantic area and affected by solar activity over the entire Holocene. In addition to model experiments, a better understanding of forcing factors and past atmospheric circulation patterns behind the Holocene palaeohydrological changes in the Mediterranean area will require further investigation to establish additional high-resolution and well-dated records in selected locations around the Mediterranean Basin and in adjacent regions. Special attention should be paid to greater precision in the reconstruction, on millennial and centennial timescales, of changes in the latitudinal location of the limit between the northern and southern palaeohydrological Mediterranean sectors, depending on (1) the intensity and/or characteristics of climatic periods/oscillations (e.g. Holocene thermal maximum versus Neoglacial, as well as, for instance, the 8.2 ka event versus the 4 ka event or the Little Ice Age); and (2) on varying geographical conditions from the western to the eastern Mediterranean areas (longitudinal gradients). Finally, on the basis of projects using strategically located study sites, there is a need to explore possible influences of other general atmospheric circulation patterns than NAO, such as the East Atlantic–West Russian or North Sea–Caspian patterns, in explaining the apparent complexity of palaeoclimatic (palaeohydrological) Holocene records from the Mediterranean area.