Late Devensian and Holocene relative sealevel changes at Loch nan Eala,near Arisaig,northwest Scotland

Pollen, diatom, radiocarbon and lithostratigraphical data from isolation basins in northwest Scotland are used to quantify the reference water (tide) level, indicative range and age of differenty types of isolation and connection contacts. Tendencies of sea-level movement and relative sea-level changes from the mid-Lateglacial Interstadial (11.8 ka BP) to the late Holocene are constructed from these data. Relative sea-level fell continuously from + 17.8 m OD at 11.8 ka BP to ca. + 5.2 m OD at 10.1 ka BP. From an unkown minimum between 10 ka and 9 ka BP relative sea-level then rose to +6.3 m OD at 8.3 ka BP. The maximum Holocene sea-level occurred within the range +6.6 m OD to +9.3 m OD between 6.6 ka BP and 4.0 ka BP before falling to present. Isobase, age-altitude and quantitative rebound models for northwest Scotland are tested using these sealevel data, but none of the published models shows close agreement with the new results.     

Variations in the pattern and rate of isostatic uplift indicated by a comparison of Holocene sea-level curves from Scotland

Differences in the timing of maxima and minima and shape between sea-level curves from the western Forth valley, lower Strathearn, inner Moray Firth and eastern Solway Firth areas of Scotland are interpreted as being due to differences in isostatic uplift and different methodologies used to interpret the basic data. Possible changes in the relative rates of uplift between areas suggest that the practice of applying the western Forth ‘model’ of relative sea-level change to other parts of Scotland must be questioned.     

Holocene tephra horizons at Klocka Bog,west‐central Sweden: aspects of reproducibility in subarctic peat deposits

This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west‐central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja‐1875, Hekla‐3, Kebister, Hekla‐4 and Lairg A tephras respectively. Radiocarbon‐based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west‐central Scandinavia. Long‐lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia. Copyright © 2004 John Wiley & Sons, Ltd.     

Holocene peat and carbon accumulation rates in the southern taiga of western Siberia

Although recent studies have recognized peatlands as a sink for atmospheric CO₂, little is known about the role of Siberian peatlands in the global carbon cycle. We have estimated the Holocene peat and carbon accumulation rate in the peatlands of the southern taiga and subtaiga zones of western Siberia. We explain the accumulation rates by calculating the average peat accumulation rate and the long-term apparent rate of carbon accumulation (LORCA) and by using the model of Clymo (1984, Philosophical Transactions of the Royal Society of London Series B 303, 605-654). At three key areas in the southern taiga and subtaiga zones we studied eight sites, at which the dry bulk density, ash content, and carbon content were measured every 10 cm. Age was established by radiocarbon dating. The average peat accumulation rate at the eight sites varied from 0.35 ± 0.03 to 1.13 ± 0.02 mm yr⁻¹ and the LORCA values of bogs and fens varied from 19.0 ± 1.1 to 69.0 ± 4.4 g C m⁻² yr⁻¹. The accumulation rates had different trends especially during the early Holocene, caused by variations in vegetation succession resulting in differences in peat and carbon accumulation rates. The indirect effects of climate change through local hydrology appeared to be more important than direct influences of changes in precipitation and temperature. River valley fens were more drained during wetter periods as a result of deeper river incision, while bogs became wetter. From our dry bulk density results and our age-depth profiles we conclude that compaction is negligible and decay was not a relevant factor for undrained peatlands. These results contribute to our understanding of the influence of peatlands on the global carbon cycle and their potential impact on global change.     

Holocene sea-level changes and crustal movements in Morecambe Bay,northwest England

Holocene stratigraphy from Skelwith Pool, on the northern side of Morecambe Bay, is described. Diatom and pollen analyses and radiocarbon dating have been undertaken for three sampling sites, from which eight sea-level index points have been obtained. These index points come from a small homogeneous area and similar palaeoenvironments. Some published sea-level index points from Morecambe Bay have been re-evaluated and validated by means of diatom analysis. An enhanced sea-level database with 28 index points has been used for the reconstruction of Holocene sea-level history. Relative sea-level rose rapidly around 6870–6510 BC at a maximum rate of +36.7 mm yr⁻¹. Subsequently, the rate of sea-level change has varied between −8 mm yr⁻¹ and +12 mm yr⁻¹. The rate of relative sea-level changes for the last 3500 years is not clear. Uplift driven by deglaciation is believed to have been interrupted in the early Holocene by a rapid rise in relative sea-level. Uplift restarted at 6510 BC but soon declined as glacio-isostatic recovery ended around 3800 BC in the Morecambe Bay area. Since then, crustal movements in the Morecambe Bay area have been minimal. Factors affecting the attitudes of the index points such as sediment compaction of the basal peat and variations in palaeotidal range during the Holocene have been considered. © 1996 John Wiley & Sons, Ltd.     

Hydrological changes in the European midlatitudes associated with freshwater outbursts from Lake Agassiz during the Younger Dryas event and the early Holocene

Recent studies of lake-level fluctuations during the last deglaciation in eastern France (Jura Mountains and Pre-Alps) and on the Swiss Plateau show distinct phases of higher water level developing at the beginning and during the latter part of Greenland Stade 1 (i.e., Younger Dryas event) and punctuating the early Holocene period at 11,250-11,050, 10,300-10,000, 9550-9150, 8300-8050, and 7550-7250 cal yr B.P. The phases at 11,250-11,050 and 8300-8050 cal yr B.P. appear to be related to the cool Preboreal Oscillation and the 8200 yr event assumed to be associated with deglaciation events. A comparison of this mid-European lake-level record with the outbursts from proglacial Lake Agassiz in North America suggests that, between 13,000 and 8000 cal yr B.P., phases of positive water balance were the response in west-central Europe to climate cooling episodes, which were induced by perturbation of the thermohaline circulation due to sudden freshwater releases to oceans. This probably was in response to a southward migration of the Atlantic Westerly Jet and its associated cyclonic track. Moreover, it is hypothesized that, during the early Holocene, varying solar activity could have been a crucial factor by amplifying or reducing the possible effects of Lake Agassiz outbursts on the climate.     

A multiproxy record of Holocene environmental changes in the central Kola Peninsula,northwest Russia

A sediment core from Chuna Lake (Kola Peninsula, northwest Russia) was studied for pollen, diatoms and sediment chemistry in order to infer post‐glacial environmental changes and to investigate responses of the lake ecosystem to these changes. The past pH and dissolved organic carbon (DOC) of the lake were inferred using diatom‐based transfer functions. Between 9000 and 4200 cal. yr BP, slow natural acidification and major changes in the diatom flora occurred in Chuna Lake. These correlated with changes in regional pollen, the arrival of trees in the catchment, changes in erosion, sediment organic content and DOC. During the past 4200 yr diatom‐based proxies showed no clear response to changes in vegetation and erosion, as autochthonous ecological processes became more important than external climate influences during the late Holocene. The pollen stratigraphy reflects the major climate patterns of the central Kola Peninsula during the Holocene, i.e. a climate optimum between 9000 and 5400/5000 cal. yr BP when climate was warm and dry, and gradual climate cooling and an increase in moisture during the past 5400/5000 yr. This agrees with the occurrence of the north–south humidity gradient in Fennoscandia during the Holocene. Copyright © 2002 John Wiley & Sons, Ltd.     

Climate drying and associated forest decline in the lowlands of northern Guatemala during the late Holocene

Palynological studies document forest disappearance during the late Holocene in the tropical Maya lowlands of northern Guatemala. The question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation, as previously suggested, or whether it was partly attributable to climate changes. We report multiple palaeoclimate and palaeoenvironment proxies (pollen, geochemical, sedimentological) from sediment cores collected in Lake Petén Itzá, northern Guatemala. Our data indicate that the earliest phase of late Holocene tropical forest reduction in this area started at ∼ 4500 cal yr BP, simultaneous with the onset of a circum-Caribbean drying trend that lasted for ∼ 1500 yr. This forest decline preceded the appearance of anthropogenically associated Zea mays pollen. We conclude that vegetation changes in Petén during the period from ∼ 4500 to ∼ 3000 cal yr BP were largely a consequence of dry climate conditions. Furthermore, palaeoclimate data from low latitudes in North Africa point to teleconnective linkages of this drying trend on both sides of the Atlantic Ocean.     

贵州草海南屯泥炭记录的中全新世以来的气候变化

通过贵州草海南屯泥炭沉积中的腐殖化度、烧失量两个指标时间序列的综合分析,重建了草海地区自7.1cal.ka B.P.以来的古气候演变特征。结果表明,约7.1~4.5cal.ka B.P.期间,气候波动较为和缓,总体表现为由暖湿逐渐向干冷转变;4.5~2.4cal.ka B.P.期间,气候先出现了两次明显的波动下降,后来快速回升,波动较为剧烈;2.4cal.ka B.P.以后降水逐渐减少,气候总体干冷,但干湿波动频繁。通过区域对比发现,贵州草海地区反映的突变事件与红原、董哥洞、哈尼以及北大西洋地区古环境记录的气候突变事件有较好的对应;同时发现厄尔尼诺的活动强度与西南季风的强弱呈现明显的反相关关系,西南季风的气候波动很可能是ENSO事件驱动的结果,西南季风区受高纬驱动影响相对较小而受低纬驱动影响显著;另外,功率谱分析结果发现气候变化与太阳活动较为一致的周期有1108a、405a和205a,因此太阳活动是全新世西南季风波动主要的自然控制因子。研究结果表明太阳活动与低纬度因子（El Niño等）是中全新世以来西南地区气候变化的重要驱动力。

     

Temporal changes in Holocene δ18O records from the northwest and central North Iceland Shelf

The region of north Iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts. In this study we present total carbonate and δ¹⁸O records of benthic and planktic Foraminifera from nine sediment cores from the North Iceland Shelf. The results of this work indicate that the deglaciation of the Vestfirdir Peninsula was completed by 10 200 cal. yr BP. The 8200 cal. yr BP cold event is present only as a minor isotopic event, and seems not to have had much of a cooling effect on the bottom waters of the northwest Iceland shelf. The Holocene maximum warmth, attributed to a stronger North Icelandic Irminger Current, occurred between ca. 7800 and 6200 cal. yr BP. Over the past 4500 cal. yr BP a general cooling trend has occurred on the North Iceland Shelf, and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf. Relatively cooler waters were present at 4200–4000 cal. yr BP, 3200–2900 cal. yr BP, 2500–2350 cal. yr BP and 600–200 cal. yr BP, whereas relatively warmer waters were present on the shelf at 3750–3450 cal. yr BP, 2800–2600 cal. yr BP and 1700–1000 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

山西宁武地区高山湖泊全新世湖相地层划分及干海组的建立

通过山西宁武地区高山湖泊湖相沉积地层的浅井挖掘,在天池湖泊群一带发现了厚度大于6m的以草炭、泥炭、粘土及砂层为主的湖相沉积物。根据实测的干海、天池和琵琶海3条剖面,将分布于高山湖盆区内的湖相地层划分为12层,层序地层显示出以干海为代表的古湖泊由浅湖→滨湖→沼泽的演化趋势。湖相沉积的14C法测年结果为10950～260aBP,ESR法年龄测定结果为(9±3～8±1)ka,这表明高山湖盆内湖相沉积的形成时代为全新世。根据沉积相、岩相组合等特征,结合同位素测年、孢粉分析、微体古生物鉴定等资料,首次建立了山西宁武地区高山湖泊全新世湖相沉积地层序列,并将该套地层命名为干海组。     

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

Two ¹⁴C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm^?1, ～1310 yr old, 34 ¹⁴C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm^?1, ～5250 yr old, 42 ¹⁴C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.     

Identification of Icelandic tephras from the last two millennia in the White Sea region (Vodoprovodnoe peat bog,northwestern Russia)

The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.     

The subfossil tree deposits from the Garonne Valley and their implications on Holocene alluvial plain dynamics

Subfossil tree trunks deposits are common in large rivers, but their status as a source for dating alluvial sequences and palaeoenvironmental studies is still discussed. Particularly their origin and the process(es) of deposition as well as a possible remobilization were pointed as a limit to their use to document river alluvial changes. In this work we report the discovery of the largest subfossil trunks deposits in the Garonne valley. These new data are compared to the previous ones. A set of 17 tree trunks and more than 300 smaller wood fragments were collected. The xylologic study shows the prevalence of Quercus and a single occurrence of Ulmus. These two hardwood species are commonly associated with riparian forest. The ¹⁴C dating carried out on seven trunks and a single branch of Quercus on the outermost identified growth rings, indicates age ranging from 8400–8000 cal. BP for the oldest fragment (bough) to 4300–4000 cal. BP for the most recent tree trunk. Radiocarbon ages of the trunks are aggregated into two main periods: 5300–5600 cal. BP (four trunks) and 4300–4000 cal. BP (three trunks). The radiocarbon (charcoal) dating of the top of the alluvial sequence overlaying the trunks gives an age between 1965–1820 and 1570–1810 cal. BP, i.e. between the 2nd and the 5th c. AD. In addition, the discovery of two unpublished subfossil tree trunks deposits in Finhan are reported (six trunks). At the light of these results, we discuss previously proposed models for the Garonne floodplain building.     

Stratigraphy of peat bog in the Gorobets River valley and development of natural environments of Shikotan Island (Lesser Kurile Ridge) in the Holocene

The stratigraphic subdivision of peat in the Gorobets River valley, the largest river on Shikotan Island, is conducted based on the study of palynological and diatom assemblages, tephrostratigraphy, and radiocarbon dating. The study object is one of the oldest peats in the South Kurile region and reflects the development of natural environments beginning from the early Holocene. Nine phases are distinguished in the development of vegetation on Shikotan Island. The changes in vegetable communities were determined by climatic fluctuations during the Holocene. Their ages, the factors responsible for the appearance and extinction of particular coniferous, small-, and broad-leaved taxa, and changes in their landscape-forming role during different periods of the Holocene, as well as specific features in the formation of the present-day vegetation on the Lesser Kurile Ridge representing a separate floral area, are established. In addition to the climatic and sea-level fluctuations, the development of the island landscapes was determined to a significant extent by its topography, size, and isolation.     

钱塘江下切河谷SE2孔全新世沉积物黏土矿物特征及其意义*

通过X射线衍射系统分析了杭州湾地区SE2孔全新世沉积物的黏土矿物组成,结果显示研究层段黏土矿物主要由伊利石、绿泥石、高岭石和蒙脱石组成;伊利石结晶度较好,化学风化指数普遍大于0.5,表明以化学风化为主,且风化趋势自下而上呈递减趋势。通过对比中国东南部主要河流沉积物的黏土矿物组成,认为钱塘江下切河谷全新世沉积物的黏土矿物组成具有较好的物源指示意义: 全新世 Ⅰ 段(即古河口湾和河漫滩)沉积物主要来自钱塘江上游,特征黏土矿物为高岭石,河口外物质贡献不大;Ⅱ 段(即现代河口湾和近岸浅海)沉积物包含较多蒙脱石,表明不仅包括钱塘江上游物质,河口外长江物质也开始进入钱塘江河口。黏土矿物中,高岭石对气候有较好的指示作用:中全新世高岭石含量达到最高值,反映气候最为湿热,化学风化程度最高;晚全新世含量逐渐降低,反映气候逐渐回冷,化学风化强度降低。