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1.
A proxy climate record from a raised bog in County Fermanagh, Northern Ireland, is presented. The record spans the interval between 2850 cal. yr BC and cal. yr AD 1000 and chronological control is achieved through the use of tephrochronology and 14C dating, including a wiggle‐match on one section of the record. Palaeoclimatic inferences are based on a combination of a testate amoebae‐derived water table reconstruction, peat humification and plant macrofossil analyses. This multiproxy approach enables proxy‐specific effects to be identified. Major wet shifts are registered in the proxies at ca. 1510 cal. yr BC, 750 cal. yr BC and cal. yr AD 470. Smaller magnitude shifts to wetter conditions are also recorded at ca. 380 cal. yr BC, 150 cal. yr BC, cal. yr AD 180, and cal. yr AD 690. It is hypothesised that the wet shifts are not merely local events as they appear to be linked to wider climate deteriorations in northwest Europe. Harmonic analysis of the proxies illustrates statistically significant periodicities of 580, 423–373, 307 and 265 years that may be related to wider Holocene climate cycles. This paper illustrates how the timing of climate changes registered in peat profiles records can be precisely constrained using tephrochronology to examine possible climatic responses to solar forcing. Relying on interpolated chronologies with considerable dating uncertainty must be avoided if the climatic responses to forcing mechanisms are to be fully understood. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

2.
In this study, a ca. 4000 cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. δ18O and δ13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC–AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial‐scale climatic events were revealed, with the wettest spell during AD 450–550, and a relatively wetter interval between AD 930–1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200 yr, ca. 120 yr, ca. 90 yr, ca. 45 yr and ca. 33 or 30 yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal‐ and centennial‐scale climate variations in the study area. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
This paper investigates evidence for palaeoclimatic changes during the period ca. 1500–500 cal. yr BC through peat humification studies on seven Irish ombrotrophic bogs. The sites are well‐correlated by the identification of three mid‐first millennium BC tephras, which enable the humification records at specific points in time to be directly compared. Phases of temporarily increased wetness are suggested at ca. 1300–1250 cal. yr BC , ca. 1150–1050 cal. yr BC , ca. 940 cal. yr BC and ca. 740 cal. yr BC . The last of these is confirmed to be synchronous at five sites, suggesting external forcing on a regional scale. The timing of this wet‐shift is constrained by two closely dated tephras and is demonstrated to be distinct from the widely reported changes to cooler/wetter conditions associated with a solar minimum at 850–760 cal. yr BC , at which time the Irish sites appear instead to experience drier conditions. The results suggest the possibility of either non‐uniform responses to solar forcing in northwest Europe at this time, or the existence of unrelated climate events in the early first millennium BC . The findings caution against the correlation of loosely dated palaeoclimate data if the effects of forcing mechanisms are to be understood. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

4.
From the Sellevollmyra bog at Andøya, northern Norway, a 440‐cm long peat core covering the last c. 7000 calendar years was examined for humification, loss‐on‐ignition, microfossils, macrofossils and tephra. The age model was based on a Bayesian wiggle‐match of 35 14C dates and two historically anchored tephra layers. Based on changes in lithology and biostratigraphical climate proxies, several climatic changes were identified (periods of the most fundamental changes in italics): 6410–6380, 6230–6050, 5730–5640, 5470–5430, 5340–5310, 5270–5100, 4790–4710, 4890–4820, 4380–4320, 4220–4120, 4000–3810, 3610–3580, 3370–3340 (regionally 2850–2750; in Sellevollmyra a hiatus between 2960–2520), 2330–2220, 1950, 1530–1450, 1150–840, 730? and c. 600? cal. yr BP. Most of these climate changes are known from other investigations of different palaeoclimate proxies in northern and middle Europe. Some volcanic eruptions seemingly coincide with vegetation changes recorded in the peat, e.g. about 5760 cal. yr BP; however, the known climatic deterioration at the time of the Hekla‐4 tephra layer started some decades before the eruption event.  相似文献   

5.
Sillasoo, Ü., Mauquoy, D., Blundell, A., Charman, D., Blaauw, M., Daniell, J. R. G., Toms, P., Newberry, J., Chambers, F M. & Karofeld, E. 2007 (January): Peat multi‐proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia. Boreas, Vol. 36, pp. 20–37. Oslo. ISSN 0300–9483. As part of a wider project on European climate change over the past 4500 years, a 4.5‐m peat core was taken from a lawn microform on Männikjärve bog, Estonia. Several methods were used to yield proxy‐climate data: (i) a quadrat and leaf‐count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water‐table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100,3010–2990,2300, 1750–1610, 1510, 1410, 1110, 540 and 310 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP, the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Mannikjarve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog micro‐depressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.  相似文献   

6.
《Quaternary Science Reviews》2005,24(10-11):1261-1277
Analyses of plant macrofossils, testate amoebae and humification have been carried out on a 2800-year core from Tore Hill Moss, a raised bog in the Strathspey region of Scotland. All three analyses were carried out at the same 4 cm intervals allowing exact correlation, and the core was dated by nine Accelerator mass spectrometry radiocarbon dates and the Glen Garry tephra layer. The results have been combined and compared to present a bog surface wetness (BSW) record within which the limitations of each proxy method can be assessed and this has highlighted the advantages of a combined rather than a single proxy approach. Significant wet shifts are recorded at ca cal. 560 BC, 60 BC, AD 430, AD 570, AD 700, AD 1090 and AD 1640. Significant shifts to drier periods are also suggested ca cal. AD 220, AD 500 and AD 820. Some of the recorded shifts and phases are related to phases of wetter and drier climate such as the Sub-boreal/Sub-atlantic transition, the Dark Age deterioration and the Romano-British Warm Period. The Dark Ages are notable as a period of rapid peat accumulation and frequent water table fluctuations. Time-series analysis revealed a significant wet-shift cycle of 560 years from the testate amoebae data.  相似文献   

7.
Two new peat‐based climate records from Ireland covering the late Holocene are presented. The sequences are dated by a strong chronological framework formed by AMS radiocarbon dates and SCPs. Three proxy indicators (testate amoebae, macrofossils and humification) have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness (BSW) record for both sites. Age–depth models take into account the potential for accumulation rates to vary with bog vegetation. The records from each site have been used to derive a combined BSW record that displays changes to a wetter/cooler climate from ca. AD 30 (1920 BP), ca. AD 310 (1640 BP), ca. AD 805 (1145 BP), ca. AD 1040 (910 BP) and ca. AD 1300 (650 BP). Changes follow closely those identified in a northern Britain composite BSW record and largely correspond with lake‐level data in central France suggesting the main changes in water balance were coherent over a large region. Correspondence with increases in IRD and slower Iceland‐Scotland Overflow Water (ISOW) suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over Ireland. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi‐quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. 14C dates provide the chronology for the stratigraphy. Differences were encountered between AMS 14C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

9.
Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to 14C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.  相似文献   

10.
The Iberian-Roman Humid Period (IRHP, 2600-1600 cal yr BP), is the most humid phase of the last 4000 yr in southern Spain as recorded in the sedimentary sequence of Zoñar Lake (37°29′00″N, 4°41′22″ W, 300 m a.s.l.). A varve chronology supported by several AMS 14C dates allows study of the lake evolution at annual scale in response to human impact and climate changes. There are four climate phases within this period: i) gradual transition (2600-2500 yr ago, 650-550 BC) from a previous arid period; ii) the most humid interval during the Iberian-Early Roman Epoch (2500-2140 yr ago, 550-190 BC); iii) an arid interval during the Roman Empire Epoch (2140-1800 yr ago, 190 BC AD 150); and iv) a humid period synchronous with the decline of the Roman Empire (1800-1600 yr ago, AD 150-350). Varve thickness and geochemical proxies show a multi-decadal cyclicity similar to modern North Atlantic Oscillation (NAO) (60, 20 years) and solar variability cycles (11 yr). The timing and the structure of this humid period is similar to that described in Eastern Mediterranean and northern European sites and supports the same large-scale climate control for northern latitudes and the Mediterranean region.  相似文献   

11.
A wide range of palaeoenvironmental evidence from the Holocene has suggested periodicities in the Earth's climate of 10s to 1000s of years. Identifying these millennial‐, century‐ and decadal periodicities, and their impacts, is critical in developing a fuller understanding of natural climate variability. Any solar‐induced climatic change needs to be distinguished from other causes of natural climate variability and from short‐term catastrophic events induced either by external or internal processes. Such events might themselves generate a periodicity, or in combination with other forcing factors they may contribute towards a periodicity (and so spuriously imply a universal and continuing periodicity in the climate record), or they may resonate with a solar‐induced periodicity. Here, evidence from peat records for periodicity in climate change over the mid to late Holocene is reviewed and this is followed by a test of the replicability of claimed periodicities using blanket peat data covering the past 2000 yr from four sites in the British Isles. Results suggest that the mires studied do go through phases of being responsive to periodic forcing factors, with ca. 200, ca. 80 and 60–50 yr wavelengths reflected in some data sets. However, the patterns shown are not consistent. This could be the result of local conditions at individual mires (human impact, sensitivity and vegetation succession) or of changes in the strength or nature of global forcing factors. Assessing a solar–mire link remains difficult because the century‐scale variations of the Sun show different intervals between solar minima, the durations of which are themselves unequal, and because the proxy‐climate data‐sets from peat profiles may themselves not be dated with sufficient precision and/or accuracy. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

12.
Plant macrofossil remains have been analysed from two raised peat bogs in northern Germany and Denmark. The quantified vegetation reconstructions of each profile were subjected to multivariate analyses to extract records of changing bog surface wetness (BSW), which are interpreted in these rain-fed bogs as being proxy climate signals. Age/depth models were constructed using radiocarbon dates and a number of drier and wetter phases were defined. The records both register cooler/wetter conditions around 2700, 1800 and 1400 cal. yr BP, and at the beginning of the Little Ice Age around AD 1250–1350. These rising bog water tables must have been reflected in poorer conditions for agriculture, and in particular near Dosenmoor where the profile records a catastrophic change to such conditions culminating at 2750–2600 cal. yr BP.  相似文献   

13.
Pollen analysis from a peat core 7.0 m in length, taken from a bog near Bisoca, in a mid-altitude area of the Buzăului Subcarpathian mountains, is used to reconstruct the postglacial vegetation history of the region. The vegetation record, which is supported by twelve 14C dates, starts at the end of the Late Glacial period. At the Late Glacial/Holocene transition, open vegetation was replaced by forest, suggesting a fast response to climatic warming. The Holocene began with the expansion of Betula, Pinus and Ulmus, followed, after 11,000 cal yr BP, by Fraxinus, Quercus, Tilia and Picea. The rapid expansion of these taxa may be due to their existence in the area during the Late Glacial period. At ca. 9200 cal yr BP, Corylus expanded, reaching a maximum after 7600 cal yr BP. The establishment of Carpinus occurred at ca. 7200 cal yr BP, with a maximum at ca. 5700 cal yr BP. Fagus pollen is regularly recorded after 7800 cal yr BP and became dominant at ca. 2000 cal yr BP. The first indications of human activities appear around 3800 cal yr BP.  相似文献   

14.
《地学前缘(英文版)》2020,11(5):1461-1475
A high resolution core(9.7 yr cm~(-1)) from the Chao de Veiga Mol raised bog(NW Iberian Peninsula) was analyzed to identify plant macrofossils,estimate peat humification and calculate hydroclimatic indices based on current bog species,with the overall aim of determining the climate conditions associated with evolution of the bog during the Medieval Climate Anomaly and the Little Ice Age.These proxies,together with historical and climate data,proved to be good indicators of the changes in bog surface wetness.Analysis:of the core led to identification of 9 different periods:two corresponding to the so-called Medieval Climate Anomaly(930 to 1345 AD,1075-665 calibrated years before present [cal.yr BP]);four corresponding to the Little Ice Age(1345 to 1905 AD;665-105 cal yr BP);and three corresponding to the last century(1905 to2000 AD).The findings revealed a generally dry climate that lasted until the 14 th century,followed by a transition to a long period with a more humid,but characteristically very variable climate,which ended at the beginning of the 20 th century and was followed by a rapid transition to more humid conditions and finally,a change to drier conditions.The Medieval Climate Anomaly was indicated by the abundance of dry-adapted mosses(Leucobryum glaucum,Hypnum cupressiforme) and characterized by warm dry conditions and high levels of peat humification,with alternating wet phases.The LIA period was dated by a large abundance of Sphagnum species(an indicator of wetness) and a gradual increase in the humification index.However,four different climate phases were differentiated in this period.High-resolution reconstruction of the evolution of the CVM bog and the multiproxy approach have together enabled a more detailed identification of climatic variations in this area,which are generally consistent with the global models,as well as better definition of the elusive climatic oscillations in the last millennium and confirmation of the importance of local modulation of global models.The study provides new information and a detailed chronology of climatic events that will help to refine local modulation of the climate evolution model in the still quite unexplored region of the NW Iberian Peninsula,a key area for understanding the paleoclimatic dynamics in SW Europe.  相似文献   

15.
The harp seal ( Phoca groenlandica ) is a low-arctic species that is currently a rare visitor to Danish waters. However, bone remains from archaeological and geological deposits in Denmark and the Baltic Sea testify to a regular presence of harp seals in this region during the mid-Holocene. The paradox of the presence of a low-arctic seal species in southern Scandinavia during the mid-Holocene thermal maximum has been widely discussed. In order to improve the Holocene chronology for the presence of harp seal in Denmark, 24 bone remains of the species were radiocarbon dated. The oldest date is around 4100 cal. yr BC, indicating that the harp seal arrived several millennia after fully marine conditions were established in Danish waters. The majority of the dated specimens fall within two age groups, one centred around 3900 cal. yr BC (11 dates), the other around 2700 cal. yr BC (7 dates). It is argued that these two groups may reflect periods with suitable living conditions for the harp seal in Danish waters and that this is connected with an enhanced inflow of high-salinity North Sea water and higher biological productivity. Six dates show a scattered distribution between c . 1400 cal. yr BC and c . AD 1000, suggesting sporadic visits of the harp seal to Danish waters during the late Holocene.  相似文献   

16.
We present a record of peatland development in relation to climate changes and human activities from the Palomaa mire, a remote site in northern Finland. We used fine‐resolution and continuous sampling to analyse several proxies including pollen (for vegetation on and around the mire), testate amoebae (TA; for mire‐wetness changes), oxygen and carbon isotopes from Sphagnum cellulose (δ18O and δ13C; for humidity and temperature changes), peat‐accumulation rates and peat‐colour changes. In spite of an excellent accumulation model (30 14C dates and estimated standard deviation of sample ages <1 year in the most recent part), the potential to determine cause–effect (or lead–lag) relationships between environmental changes and biotic responses is limited by proxy‐specific incorporation processes below the actively growing Sphagnum surface. Nevertheless, what emerges is that mire development was closely related to water‐table changes rather than to summer temperature and that water‐table decreases were associated with increasing peat‐accumulation rates and more abundant mire vegetation. A rapid fen‐to‐bog transition occurred within a few years around AD 1960 when the water table decreased beyond the historical minimum, supporting the notion that mires can rapidly shift into bogs in response to allogenic factors. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

17.
A Holocene record of pollen, macrofossils, testate amoebae and peat humification is presented from a small montane bog. Sediment accumulation began before 9000 yr BP, but peat growth not until ca. 7000 BP. From 12 000 to 7000 yr BP, a shrub–grassland dominated under a dry climate, with increasing conifer forest and tall scrub from ca. 9600 yr BP. At 7000 yr BP a dense montane–subalpine low conifer forest established under a moist, cool climatic regime. Between 7000 and 700 yr BP the bog surface was shrubby, tending to be dry but with highly variable surface wetness. The catchment was affected by major fire at least four times between 4000 and 1000 yr BP. Both fire and bog surface wetness may have been linked to ENSO-caused variations in rainfall. Cooler, cloudier winters and disturbance by fire promoted the expansion of the broadleaf tree Nothofagus menziesii between 4000 yr BP and 1300 yr BP at the expense of the previous conifer forest–scrub vegetation. Polynesian fires (ca. 700 yr BP) reduced the vegetation to tussock grassland and bracken. Deforestation did not markedly affect the hydrology of the site. European pastoralism since ad 1860 has increased run-off and rising water tables in the bog have led to a Sphagnum-dominated cover. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

18.
Botanical macrofossil analysis of a more than 9000 years old, radiocarbon dated peat sequence of a moss peat bank from South Georgia, shows a clear evolution in the vegetation. Seven ecological phases could be distinguished and they can be interpreted in terms of climate development during the Holocene. Until 2200 years ago, Warnstorfia fontinaliopsis was the dominant moss species pointing to a wet environment. Lower numbers of this species in association with the presence of drier species are assumed to indicate drier periods, such as occurring between ca 6000–5200 and 4400–3400 cal yr BP. The most prominent and definitive vegetation change took place around 2200 cal yr BP. A Polytrichum–Chorisodontium moss peat bank was formed, which is still growing there today. The forcing mechanism for this vegetation change is thought to be a temperature decrease, rather than a precipitation decrease. This conclusion is mainly based on the fact that, today, moss peat banks have their optimal occurrence range in the maritime Antarctic, a region were the mean annual temperature is ca 4 °C lower than on South Georgia. The remarkable change in the moss bank vegetation at 2200 cal yr BP raises the question whether this moment was only a short climatic deterioration, or a definitive change to a cooler and wetter climate after a Holocene climatic optimum period.  相似文献   

19.
Simulated Holocene sediment discharges from a high‐resolution cellular model of river evolution in northern England, driven by a peat‐bog proxy climate and palynological based land‐cover record, show a very close similarity to alluviation phases evident in British river valleys. Independent validation of the model indicates that British river systems have been surprisingly sensitive to short term (ca. 102 yr) climate fluctuations, although river dynamics also have been modulated by land‐use change and sediment supply. This has important implications for understanding alluvial system evolution, establishing controlling factors and, most importantly, forecasting river response to future climate and land‐use changes. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

20.
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

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