Lake‐level fluctuations at Lake Bourget (eastern France) around 4500–3500 cal. a BP and their palaeoclimatic and archaeological implications

On the basis of sedimentological analysis of two cores taken at Chatillon, Lake Le Bourget (northern French Pre‐Alps), and well dated by radiocarbon dates in addition to tree ring dates obtained from an archaeological layer, this paper presents a high‐resolution lake‐level record for the period 4500–3500 cal. a BP. The collected data provide evidence of a complex palaeohydrological (climatic) oscillation spanning the ca. 4300–3850 cal. BP time interval, with major lake‐level maxima at ca. 4200 and 4050–3850 cal. a BP separated by a lowering episode around 4100 cal. a BP. The lake‐level highstands observed at Chatillon between 4300 and 3850 cal. BP appear to be synchronous with (i) a major flooding period recorded in deep cores from the large lakes Le Bourget and Bodensee, and (ii) glacier advance and tree line decline in the Alps. Such wetter and cooler climatic conditions in west‐central Europe around 4000 cal. a BP may have been a nonlinear response to decrease and seasonal changes in insolation. They may also provide a possible explanation for the general abandonment of prehistoric lake dwellings north of the Alps between 4360 and 3750 cal. a BP. Copyright © 2012 John Wiley & Sons, Ltd.     

Millennial‐scale climate variability in northwest Patagonia over the last 15 000 yr

A pollen record from Lago Condorito (41°45'S, 73°07'W) shows prominent vegetation and climate changes at millennial time‐scales, superimposed on multimillennial trends in temperature and westerly activity in northwest Patagonia during the past 15 000 yr. The record shows that evergreen temperate rainforests have dominated the landscape over this interval, with floristic changes ranging from cold‐resistant North Patagonian forests with podocarp conifers to Valdivian forests with thermophilous, summer‐drought resistant species. The long‐term trend shows that cool‐temperate and humid conditions prevailed between 15 000 and 11 000 cal. yr BP, followed by an extreme warm and dry phase between 11 000 and 7600 cal. yr BP, and subsequent cooling events and increase in precipitation that peaked at ca. 5000 cal. yr BP, when Southern Hemisphere alpine glaciers achieved their first Neoglacial maximum. Modern conditions were established at ca. 1800 cal. yr BP, following a warm and dry phase between ca. 2900 and 1800 cal. yr BP. These results suggest that millennial‐scale climate variability during deglacial and post‐glacial times also affected the mid‐latitude region of the South Pacific, supporting the idea that changes in the tropical Pacific might be a key factor in the initiation and/or propagation of millennial‐scale climate variability at regional, hemispheric and global scales. Copyright © 2004 John Wiley & Sons, Ltd.     

Holocene environmental change in the West African Sahel: sedimentological and mineral‐magnetic analyses of lake sediments from Jikariya Lake,northeastern Nigeria

Previous studies have demonstrated long‐term changes in effective moisture in sub‐Saharan Africa. Here, we reconstruct Holocene environments using a ～7 m lake‐sediment sequence recovered from the northeastern Nigerian Sahel and attempt to distinguish basin‐specific changes from regional climatic variations. The sequence was analysed for sedimentological properties, mineral magnetism and pollen, and dated by ¹³⁷Cs, ²¹⁰Pb excess and ¹⁴C. Extremely arid conditions of the terminal Pleistocene ended ca. 11 500 cal. BP (calendar years) when climate ameliorated and a lake developed until the occurrence of an arid event leading to lake desiccation at ～11 200 cal. BP. Following this, climate ameliorated and a water body re‐emerged. Very wet conditions predominated 11 200–5600 cal. BP, followed by drought between 5600 and 5500 cal. BP and a return to moderate humidity from 5500 to 4000 cal. BP. After 4000 cal. BP, a marked deterioration occurred, culminating in lake desiccation at ca. 800 cal. BP. After this time the climate remained generally dry and the re‐emerging lake was shallow. Comparison of these results with other well‐dated sequences in the region demonstrates the importance of basin‐specific influences on the palaeolimnological records in addition to regional climatic controls. Disentangling these different controls, as well as the reconstruction of Holocene climate, therefore requires a multiple‐basin approach. Copyright © 2008 John Wiley & Sons, Ltd.     

Vegetation and climate changes over the last 30 000 years on the Leizhou Peninsula,southern China,inferred from the pollen record of Huguangyan Maar Lake

A pollen record from Huguangyan Maar Lake documents regional palaeovegetation and palaeoclimate changes in southern China over the last 30 000 years. Huguangyan Maar Lake is located close to the South China Sea (SCS) coastline and is influenced by the East Asian Monsoon (EAM). The pollen assemblages show a succession of vegetation and climate changes. During the Last Glaciation, 30–15.8 cal. ka BP, the Huguangyan area was dominated by subtropical evergreen‐deciduous forest with grassland surrounding the lake, indicating a colder and drier climate than today. During 15.8–11 cal. ka BP, the study area experienced several climatic fluctuations. From 11 to 2 cal. ka BP, the climate shifted to warmer and wetter conditions. After the Holocene Optimum in the early Holocene, the temperature and precipitation decreased. The sediment record of the last 2000 years cannot be used to interpret natural palaeoclimate changes due to the intense anthropogenic influences. Overall, however, the Huguangyan pollen archive highlights the rapid responses of subtropical vegetation to insolation changes in southern China.     

Abrupt climate change and early lake development – the Lateglacial diatom flora at Hässeldala Port,southeastern Sweden

The fossil diatom record from the Hässeldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13 900 and 11 200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open‐water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom‐based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13 900 to 12 500 cal. a BP. From 12 500 cal. a BP, coincident with the start of climate cooling, to 11 300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build‐up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.     

Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.     

Mid- to late Holocene environmental and climatic changes in New Caledonia, southwest tropical Pacific, inferred from the littoral plain Gouaro-Déva

Multiproxy analysis of three littoral cores from western New Caledonia supports the hypothesis that the main controlling factors of environmental changes are sea-level change, ENSO variability and extra-tropical phenomena, such as the Medieval Warm Period (MWP) marked by a tendency for La Niña-like conditions in the tropical Pacific. The record starts during the late Holocene sea-level rise when the terrestrial vegetation indicated wet and cool conditions. The site was a coastal bay definitely transformed into a freshwater swamp at around 3400 cal yr BP, after the rapid drawdown of sea level to its current level. Sediments and foraminiferal assemblages indicated subsequent episodes of freshwater infillings, emersion or very high-energy conditions, likely related to climatic changes and mostly controlled by ENSO variability. Between 2750 and 2000 cal yr BP, relatively dry and cool climate prevailed, while wetter conditions predominated between ca. 1800 and 900 cal yr BP. The Rhizophoraceae peak between ca. 1080 and 750 cal yr BP, coeval with the MWP, may indicate a global phenomenon. Microcharcoal particles present throughout the record increased after 1500 cal yr BP, suggesting an anthropogenic source. From ca. 750 cal yr BP the appearance of current type of vegetation marks the human impact.     

Hässeldala – a key site for Last Termination climate events in northern Europe

The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well‐constrained, multi‐proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi‐proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.     

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.     

Fire and vegetation history on Santa Rosa Island,Channel Islands,and long‐term environmental change in southern California

The long‐term history of vegetation and fire was investigated at two locations – Soledad Pond (275 m; from ca. 12 000 cal. a BP) and Abalone Rocks Marsh (0 m; from ca. 7000 cal. a BP) – on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800 cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900 cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500 cal. a BP, and at Abalone Rocks Marsh after ca. 3465 cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non‐native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000 cal. a BP, and especially after ca. 4500 cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene. Copyright © 2009 John Wiley & Sons, Ltd.     

Relative sea‐level changes since 15 000 cal. yr BP in the Nanortalik area,southern Greenland

We present new results for relative sea‐level change for southern Greenland for the interval from 9000 cal. yr BP to the present. Together with earlier work from the same region this yields a nearly complete record from the time of deglaciation to the present. Isolation and/or transgression sequences in one lake and five tidal basins have been identified using lithostratigraphic analyses, sedimentary characteristics, magnetic susceptibility, saturated induced remanent magnetisation (SIRM), organic and carbonate content, and macrofossil analyses. AMS radiocarbon dating of macrofossils and bulk sediment samples provides the timescale. Relative sea level fell rapidly and reached present‐day level at ～9300 cal. yr BP and continued falling until at least 9000 cal. yr BP. Between 8000 and 6000 cal. yr BP sea level reached its lowest level of around ～10 m below highest astronomical tide. At around 5000 cal. yr BP, sea level had reached above 7.8 m below highest astronomical tide and slowly continued to rise, not reaching present‐day sea level until today. The isostatic rebound caused rapid isolation of the basins that are seen as distinct isolation contacts in the sediments. In contrast, the late Holocene transgressions are less well defined and occurred over longer time intervals. The late Holocene sea‐level rise may be a consequence of isostatic reloading by advancing glaciers and/or an effect of the delayed response to isostatic rebound of the Laurentide ice sheet. One consequence of this transgression is that settlements of Palaeo‐Eskimo cultures may be missing in southern Greenland. Copyright © 2006 John Wiley & Sons, Ltd.     

Holocene vegetation change in northernmost Fennoscandia and the impact on prehistoric foragers 12 000–2000 cal. a BP – A review

While single pollen records are widely used in reconstructing the environment for nearby prehistoric settlements, they are less helpful when addressing large‐scale issues of variation in human settlement patterns. In order to assess the impact of vegetation change on regional prehistoric settlement and subsistence patterns in an ecotone sensitive area, we inferred the general change in main vegetation types based on palaeobotanical investigations from across northernmost Fennoscandia. Tundra vegetation was predominant during the Lateglacial and earliest parts of the Holocene. Maritime birch forests rich in ferns started to expand c. 11 000 cal. a BP and became dominant from 10 000 cal. a BP. Pine expanded from the NE of the investigation area and pine‐birch forest dominated in the inland around 8000 cal. a BP. A gradual degeneration of forest towards more open birch woodland started c. 6000 cal. a BP with the most marked change around 3500 cal. a BP. Along the northern outer coast, this eventually led to open heathland. Comparison with the archaeological setting suggests a general correlation between low forest cover and extensive mobility patterns, while widespread and varied forest cover appear to have led to a more sedentary way of life. The background for this is arguably that the forested landscapes hosted a larger diversity of resources within a shorter foraging distance, while areas and periods with low forest cover required longer travels to obtain the desired prey and materials.     

"8.2 ka BP冷事件"的研究现状展望

统计了全新世早期气候突变事件"8.2 ka BP冷事件", 并对其触发机制及区域气候响应做了较深入的分析. 从各种气候记录的分布情况来看, 全新世早期的这次冷事件是全球性气候事件, 并非是一种局部气候变冷事件. 全新世早期Agassiz和Ojibway阻塞湖在大约8.47 cal ka BP时突然排泄, 可能是造成8.4～8.0 cal ka BP时期北大西洋地区突然降温的主要原因;另外, 8.4～8.0 cal ka BP期间的太阳辐射量减小或太阳活动减弱, 也可能对全新世早期的这次冷事件有一定强化作用. 由于西风带南移和季风环流减弱等原因的影响, 使得这次冷事件区域气候响应有明显的不同, 欧洲的中高纬度地区、东亚地区呈现一种冷干的气候状态;北美洲三分之二的地区降水量减少、风力加强;中美洲、非洲的大部分地区和阿拉伯半岛均以干旱为主;东欧、地中海地区呈现普遍的冷湿气候环境, 亚马逊盆地、智利玻利维亚高原呈现低湿的气候状况.     

A multi‐proxy record of changing environments from ca. 30 000 to 9000 cal. a BP: Onepoto maar palaeolake,Auckland, New Zealand

We present a high‐resolution record of lacustrine sedimentation spanning ca. 30 000 to 9000 cal. a BP from Onepoto maar, northern North Island, New Zealand. The multi‐proxy record of environmental change is constrained by tephrochronology and accelerator mass spectrometric ¹⁴C ages and provides evidence for episodes of rapid environmental change during the Last Glacial Coldest Period (LGCP) and Last Glacial–Interglacial Transition (LGIT) from northern New Zealand. The multi‐proxy palaeoenvironmental record from Onepoto indicates that the LGCP was cold, dry and windy in the Auckland region, with vegetation dominated by herb and grass in a beech forest mosaic between ca. 28 500 and 18 000 cal. a BP. The LGCP was accompanied by more frequent fires and influx of clastic sediment indicating increased erosion during the LGCP, with a mid‐LGCP interstadial identified between ca. 25 000 and 23 000 cal. a BP. Rapid climate amelioration at ca. 18 000 cal. a BP was accompanied by increased terrestrial biomass exemplified by the expansion of lowland podocarp forest, especially Dacrydium cupressinum. Increasing biomass production is reversed briefly by LGIT perturbations which are apparent in many of the proxies that span ca. 14 000–10 500 cal. a BP, suggesting generally increased wetness and higher in situ aquatic plant productivity with reduced terrestrial organic matter and terrigenous detrital influx. Furthermore, conditions at that time were probably warmer and frosts rare based on the increasing importance of Ascarina. The subsequent early Holocene is characterised by podocarp conifer forest and moist mild conditions. Postglacial sea‐level rise breached the crater rim and deposited 36 m of estuarine mud after ca. 9000 cal. a BP. Copyright © 2011 John Wiley & Sons, Ltd.     

A record of Holocene climate change from lake geochemical analyses in southeastern Arabia

Lacustrine sediments from southeastern Arabia reveal variations in lake level corresponding to changes in the strength and duration of Indian Ocean Monsoon (IOM) summer rainfall and winter cyclonic rainfall. The late glacial/Holocene transition of the region was characterised by the development of mega-linear dunes. These dunes became stabilised and vegetated during the early Holocene and interdunal lakes formed in response to the incursion of the IOM at approximately 8500 cal yr BP with the development of C3 dominated savanna grasslands. The IOM weakened ca. 6000 cal yr BP with the onset of regional aridity, aeolian sedimentation and dune reactivation and accretion. Despite this reduction in precipitation, the lake was maintained by winter dominated rainfall. There was a shift to drier adapted C4 grasslands across the dune field. Lake sediment geochemical analyses record precipitation minima at 8200, 5000 and 4200 cal yr BP that coincide with Bond events in the North Atlantic. A number of these events correspond with changes in cultural periods, suggesting that climate was a key mechanism affecting human occupation and exploitation of this region.     

A record of Lateglacial/Holocene environmental change from a high‐elevation site in the Intermountain West,USA

Records of past vegetation and fire history can be complicated by changes in the depositional environment of a sampling location. However, these changes can alternatively be used as a measure of climate variability. Our study site, ca. 18.0 cal. ka BP record from Little Brooklyn Lake, Wyoming, located near the crest of the Snowy Range, records three moisture states. Initially, the lake was likely a glacier‐fed pond indicated by the presence of Pediastrum algae colonies. Around 13.0 cal. ka BP this pond transitioned to a meadow environment, suggested by the loss of Pediastrum algae colonies and slow sedimentation rates. Meadow conditions were maintained until ca. 5.0 cal. ka BP when Pediastrum algae colony abundance increased,indicating the formation of a shallow lake. From 18.0 to ca. 5.0 cal. ka BP, the pollen record is suggestive of alpine vegetation conditions with relatively high spruce and herbaceous taxa. Low charcoal influx also characterizes the period between 18.0 and 5.0 cal. ka BP. After 5.0 cal. ka BP, the coincidence of the formation of shallow lake and pollen data, indicating a shift to a spruce and fir forest, suggests an increase in effective moisture. Fire remained rare in this basin over the entire record, however, once the lake established sedimentation rates and charcoal influx increased. Copyright © 2013 John Wiley & Sons, Ltd.     

A 100 000‐year record of annual and seasonal rainfall and temperature for northwestern Australia based on a pollen record obtained offshore

Pollen recovered from core tops of deep‐sea cores from offshore northwestern Western Australia were used to build climatic transfer functions applied to sediment samples from major rivers bordering the ocean in the same region and a deep‐sea core offshore Northwest Cape. Results show for the last 100 000 years, with a gap in the record spanning the 64 000 to 46 000 years interval, that from about 100 000 to 82 000 yr BP, climatic conditions represented by rainfall, temperature and number of humid months, were significantly higher than today's values. For the entire record, the coldest period occurred about 43 000 to 39 000 yr BP but it was wetter than today, whereas the Last Glacial Maximum saw a significant reduction in summer rainfall, interpreted as a result of the absence of monsoonal activity in the region. The Holocene can be divided into two distinct phases: one peaking around 6000 cal. yr BP with highest rainfall and summer temperatures; the second one commencing at 5000 cal. yr BP and showing a progressive decrease in summer rainfall in contrast to an increase in winter rainfall, paralleled by a progressive decrease in temperatures. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydrological changes during the Roman Climatic Optimum in northern Tuscany (Central Italy) as evidenced by speleothem records and archaeological data

Study of the climate in the Mediterranean basin during different historical periods has taken on a particular importance, particularly regarding its role (together with other factors) in the evolution of human settlement patterns. Although the Roman age is traditionally considered a period with a favourable climate, recent studies have revealed considerable complexity in terms of regional climate variations. In this paper, we compare the hydrological change from speleothem proxy records with flood reconstructions from archaeological sites for Northern Tuscany (central Italy). We identify a period of oscillating climatic conditions culminating in a multidecadal dry event during the 1st century bc , followed by a century of increased precipitation at the beginning of the Roman Empire and subsequently a return to drier conditions in the 2nd century ad. The period of rainfall increase documented by the speleothems agrees with both the archaeological flood record as well as historical flood data available for the Tiber River, ca. 300 km to the south. These data also suggest a return to wetter conditions following the 3nd and 4rd centuries ad.     

Evidence for an extreme climatic event on Achill Island,Co. Mayo,Ireland around 5200–5100 cal. yr BP

A range of detailed palaeoenvironmental analyses carried out on a series of three peat profiles from Achill Island, Co. Mayo, western Ireland, reveal evidence for an extreme climatic event, probably a storm or series of storms, around 5200–5100 cal. yr BP that caused the deposition of an extensive layer of silt across blanket peat. This event followed a period of relatively dry climate during which Neolithic communities expanded in the region. There was a subsequent period of continuing dry conditions allowing extensive colonisation of the peat by Pinus before a shift to wetter conditions characteristic of the later Holocene. The extreme climatic event is possibly linked to human abandonment of the area comparable to that observed from the work on the internationally significant Céide Fields in the same region. Copyright © 2005 John Wiley & Sons, Ltd.     

Reconstructing Holocene palaeoclimate and palaeoceanography in Ìsafjarðardjúp,northwest Iceland,from two fjord records overprinted by relative sea‐level and local hydrographic changes

We reconstruct palaeoclimate and palaeoceanography of the Ísafjarðardjúp fjord system from two cores – one from the inner fjord and one near the fjord mouth – while separating the potential overprinting of relative sea‐level (RSL) and local fjord hydrographic changes on these records. The inner fjord core (B997‐339) reflects local fjord hydrography; the outer fjord core (MD99‐2266) reflects the regional oceanic signal. Glacial marine conditions ended at ca. 10 200 cal. a BP, indicated by both ice‐rafted debris records. The other proxy records show spatial and temporal variability within the fjord system. At the inner fjord site (B997‐339) foraminiferal assemblages and the δ¹⁸O record indicate lowered RSL between ca. 10 600 and 8900 cal. a BP and document the onset of fjord water overturning at ca. 8900 cal. a BP, which obscured the climate record. At the fjord mouth (MD99‐2266) mass accumulation rates suggest lowered RSL between ca. 10 200 and 5500 cal. a BP and local freshwater and/or reduced salinities of the Irminger Current water masses affected the δ¹⁸O signal between ca. 10 200 and 7900 cal. a BP. At MD99‐2266, foraminiferal fauna record the Holocene Thermal Maximum between ca. 8000 and 5700 cal. a BP and the onset of modern oceanic circulation at ca. 7000 cal. a BP. Copyright © 2010 John Wiley & Sons, Ltd.