Climatic influence on peatland formation and lateral expansion in sub‐arctic Fennoscandia

Weckström, J., Seppä, H. & Korhola, A. 2010: Climatic influence on peatland formation and lateral expansion in sub‐arctic Fennoscandia. Boreas, Vol. 39, pp. 761–769. 10.1111/j.1502‐3885.2010.00168.x. ISSN 0300‐9843. The initiation and lateral expansion patterns of five small sub‐arctic peatlands in the Fennoscandian tree‐line region were studied by 21 accelerator mass spectrometry (AMS) ¹⁴C‐dated basal‐peat samples representing three to six dates per site. The radiocarbon dates were converted to calendar years and are based on the median probability. When combined with earlier basal‐peat dates from the region, four distinctive periods can be observed in the cumulative record of the dates. The early Holocene, from c. 10 000 to 8000 cal. yr BP, was characterized by the fast initiation and rapid expansion of peatlands, whereas at 8000–4000 cal. yr BP lateral expansion was modest. The most intensive period of peatland expansion occurred at the beginning of the late Holocene at c. 4000 to 3000 cal. yr BP, after which it slowed down towards the present. All these periods are in rough agreement with the main Holocene climatic periods in the area, namely the relatively warm and moist early Holocene, the warm and dry Holocene thermal maximum (HTM) at 8000–4000 cal. yr BP, and the start of the cooler and moister trend (neoglacial cooling) from c. 4000 cal. yr BP to the present, indicating a broad‐scale climatic control on the lateral growth of sub‐arctic peatlands in Fennoscandia. In order to study the lateral expansion of peatlands and to evaluate their Holocene succession patterns, more studies based on multiple dates from the same peatland are needed.     

Post‐glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut,Canada

Climate models suggest that the global warming during the early to mid‐Holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo. We investigated the Holocene vegetation history of low arctic continental Nunavut, Canada, from a radiocarbon‐dated sediment core from TK‐2 Lake, a small‐lake ca. 200 km north of the limit of the forest‐tundra. The pollen and loss‐on‐ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca. 9000 cal. yr BP with dominance of Betula, especially since 8700 cal. yr BP. At 8100–7900 cal. yr BP the dominance of the shrub tundra was punctuated by a transient decline of Betula and coincident increases of Ericaceae undiff., Vaccinium‐type, and Gramineae. This suggests an abrupt disturbance of the Betula glandulosa population, approximately simultaneously with the sudden 8200 cal. yr BP event in the North Atlantic. However, in the absence of other sites studied in the area, linkage to the 8200 cal. yr BP event remains tentative. The lack of any evidence of forest‐tundra in the region constrains the northern limit of the mid‐Holocene advance of the forest‐tundra boundary in central northern Canada. Consequently, our results show that the climate models imposing a mid‐Holocene advance of the limit of the forest‐tundra to the arctic coast of Canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

Changing marine productivity off northern Chile during the past 19 000 years: a multivariable approach

A multivariable approach utilising bulk sediment, planktonic Foraminifera and siliceous phytoplankton has been used to reconstruct rapid variations in palaeoproductivity in the Peru–Chile Current System off northern Chile for the past 19 000 cal. yr. During the early deglaciation (19 000–16 000 cal. yr BP), our data point to strongest upwelling intensity and highest productivity of the past 19 000 cal. yr. The late deglaciation (16 000–13 000 cal. yr BP) is characterised by a major change in the oceanographic setting, warmer water masses and weaker upwelling at the study site. Lowest productivity and weakest upwelling intensity are observed from the early to the middle Holocene (13 000–4000 cal. yr BP), and the beginning of the late Holocene (<4000 cal. yr BP) is marked by increasing productivity, mainly driven by silicate‐producing organisms. Changes in the productivity and upwelling intensity in our record may have resulted from a large‐scale compression and/or displacement of the South Pacific subtropical gyre during more productive periods, in line with a northward extension of the Antarctic Circumpolar Current and increased advection of Antarctic water masses with the Peru–Chile Current. The corresponding increase in hemispheric thermal gradient and wind stress induced stronger upwelling. During the periods of lower productivity, this scenario probably reversed. Copyright © 2004 John Wiley & Sons, Ltd.     

Holocene palaeoflood events recorded by slackwater deposits along the middle Beiluohe River valley,middle Yellow River basin,China

Palaeohydrological investigations were carried out in the middle Beiluohe River valley in the middle Yellow River basin. Palaeoflood slackwater deposits (SWDs) are natural records of overbank flooding and are often identified in the Holocene aeolian loess–soil profiles along the river valley. Three bedsets of palaeoflood SWDs were found within the mid‐Holocene Climatic Optimum palaeosol (S₀) on the right riverbank. Both the sedimentary and the analytical results, including magnetic susceptibility, grain‐size distribution and concentrations of chemical elements, indicate that these palaeoflood SWDs were deposited from the suspended sediment load of overbank flooding. We identified three episodes of extraordinary overbank flooding events. These hydro‐climatic events were dated to 7600–7400, 5800–5000 and 4200–4000 a BP, from optically stimulated luminescence (OSL) dating and pedostratigraphical correlation. The minimum flood peak discharges were estimated to have been between 12 600 and 14 100 m³ s^?1 using the slope–area method. These hydro‐climatic events are considered to be a regional expression of known climatic events and demonstrate that the mid‐Holocene climate was far from stable. These results show that the magnitudes of floods are highly sensitive to climate change in semi‐arid and sub‐humid regions with a monsoonal climate.     

River sediments,great floods and centennial‐scale Holocene climate change

A new analysis of all 346 published ¹⁴C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd.     

Patterns of human occupation during the early Holocene in the Central Ebro Basin (NE Spain) in response to the 8.2 ka climatic event

The Central Ebro River Basin (NE Spain) is the most northern area of truly semi-arid Mediterranean climate in Europe and prehistoric human occupation there has been strongly influenced by this extreme environmental condition. Modern climate conditions single out this region due to the harsh environment, characterised by the highest absolute summer temperatures of the Ebro River Basin. The Bajo Aragón region (SE Ebro River Basin) was intensively populated during the Early Holocene (9400-8200 cal yr BP) but the settlements were abandoned abruptly at around 8200 cal yr BP. We propose that this “archaeological silence” was caused by the regional impact of the global abrupt 8.2 ka cold event. Available regional paleoclimate archives demonstrate the existence of an aridity crisis then that interrupted the humid Early Holocene. That environmental crisis would have forced hunter-gatherer groups from the Bajo Aragón to migrate to regions with more favourable conditions (i.e. more humid mountainous areas) and only return in the Neolithic. Coherently, archaeological sites persist during this crisis in the nearby Iberian Range (Maestrazgo) and the North Ebro River area (Pre-Pyrenean mountains and along the northwestern Ebro Basin).     

Holocene temperatures in Bohuslän, southwest Sweden: a quantitative reconstruction from fossil pollen data

Inferred mean annual temperatures (Tann) from a radiocarbon-dated fossil pollen stratigraphy obtained from Lake Trehörningen, southwest Sweden, provide evidence of climate variability during the Holocene in the boreal-nemoral zone of Sweden. The record indicates low early Holocene temperatures, followed by a rising trend and maximum temperature values from about 7000 to 4000 cal. yr BP. During the later part of the Holocene until present day, a cooling trend is reflected in the temperature record. At about 8200 cal. yr BP, temperatures temporarily drop, and at 8000 cal. yr BP the rising temperature trend is recovered. Inferred mid-Holocene temperatures are about 2.5-3°C higher than at present, and also higher than other pollen-inferred mid-Holocene temperatures of 1.5-2.5°C further to the north and east in Scandinavia. The reconstructed long-term climate pattern in Trehörningen has an overall consistency with temperature reconstructions from Scandinavia, suggesting a regional climate link for the Holocene variability in Sweden. Holocene climate trends in Trehörningen also show a remarkably similar pattern with the classic work on postglacial climate change by Sernander (1893, Sernander 1909), Andersson (1909) and von Post (1924).     

Holocene colluvial (debris‐flow and water‐flow) processes in eastern Norway: stratigraphy,chronology and palaeoenvironmental implications

Very little is known about the temporal pattern and the palaeoenvironmental implications of Holocene colluvial processes (debris‐flow and water‐flow processes) in eastern Norway. In this study, well‐dated sedimentary successions from 19 deep excavations are used to reconstruct Holocene colluvial activity in upper Gudbrandsdalen, eastern Norway. Following deglaciation, debris‐flow and water‐flow events have been common in upper Gudbrandsdalen throughout the Holocene, with 62% of the recognised debris‐flow and water‐flow units deposited prior to 5000 cal. yr BP. Relatively high colluvial activity is recorded at ca. 8600–7400, 2400–1900 and 800–400 cal. yr BP, with a conspicuous peak at ca. 8500–8100. Periods of relatively low colluvial activity are recorded at ca. 7100–6500, 5900–5300 and 3500–2500 cal. yr BP. Two different weather situations, unusually heavy rains and warm periods during the snowmelt season, are responsible for triggering colluvial processes in this area. These different weather situations may in turn be related to different climatic conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Stable carbon and oxygen isotopic evidence for late Pleistocene to middle Holocene climatic fluctuations in the interior of southern Africa

Stable carbon and oxygen isotope analyses of ungulate grazers from four archaeological sites located in different environs within the Caledon River Valley have provided a relatively well‐dated proxy palaeoenvironmental and palaeoclimatic sequence for the period between 16 000 and 6000 calendar (cal.) yr BP. Within the overall trend towards hot mid‐Holocene temperatures and a summer rainfall pattern, stable carbon isotope results show that there were three periods when growth season temperatures were cool enough for C₃ grasses to be present: 16 000–14 000; 10 200–9600, and 8400–8000 cal. yr BP. Similar trends were recorded in stable oxygen isotope values, reflecting shifts in either temperature or available moisture. Although having a similar pattern to that of the lower altitude site, sites situated in foothills and montane portions of the valley consistently maintained lower temperatures until the mid‐Holocene altithermal. At this time growth season temperatures warmed sufficiently for a 100% C₄ grassland to expand in altitude from the warmer low lying localities. In relation to present understanding of synoptic and global climatic patterning, these findings suggest that the early to middle Holocene transition was not a gradual warming trend, but rather it was marked by a series of climatic fluctuations. Of particular note is the possible global, rather than regional, occurrence of the 8200 cal. yr BP ‘event’. Copyright © 2002 John Wiley & Sons, Ltd.     

Late Devensian and Holocene relative sea‐level changes on the Isle of Skye,Scotland, UK

Detailed litho‐ and biostratigraphical analyses from three coastal sites in contrasting coastal settings on the Isle of Skye, Scotland, UK, reveal evidence for several changes in relative sea level during the Late Devensian and Holocene. At the start of the record, relative sea level in the area was high at ca. 12 500 ¹⁴C (ca. 14 800 cal.) yr BP but then fell, reaching a low point during the Younger Dryas, at ca. 11 000–10 000 ¹⁴C (ca. 13 000–11 600 cal.) yr BP, when a rock platform, correlated with the Main Rock Platform, was formed. In the early–middle Holocene, relative sea level was rising by ca. 8000 ¹⁴C (ca. 8800 cal.) yr BP and in northeast Skye a lagoonal surface, correlated with the Main Postglacial Shoreline, was formed at ca. 6600 ¹⁴C (ca. 7500 cal.) yr BP. By the late Holocene, relative sea level was again falling, but a rise, registered at at least two sites, began probably before ca. 4000 ¹⁴C (ca. 4500 cal.) yr BP, and a second lagoonal surface in northeast Skye, correlated with the Blairdrummond Shoreline, was formed, although by ca. 3000 ¹⁴C (ca. 3200 cal.) yr BP relative sea level in the area had resumed its downward trend. The pattern of relative sea‐level changes disclosed is compared with evidence elsewhere in Scotland. Copyright © 2006 John Wiley & Sons, Ltd.     

Changes of treelines and alpine vegetation in relation to post‐glacial climate dynamics in northern Fennoscandia based on pollen and chironomid records

Palaeoclimatic records derived from a variety of independent proxies provide evidence of post‐glacial changes of temperature and soil moisture in northern Fennoscandia. We use pollen percentage, pollen influx, stomatal and chironomid records from Toskaljavri, a high‐altitude lake in northern Finland, to assess how treelines and alpine vegetation there have responded to these climate changes. The evidence suggests that the cool, moist climate of the early Holocene supported birch forest in the area 9600 cal. yr BP onwards and that a rise of temperature triggered the immigration of pine at 8300 cal. yr BP. At 6100–4000 cal. yr BP altitudinal treeline in the area was formed by pine, in contrast to the modern situation where mountain birch reaches a higher elevation. Alpine vegetation also demonstrates clear changes. Plant communities typical of dry, oligotrophic heaths of northern Fennoscandia expanded during the dry climatic period at 7000–4000 cal. yr BP and decreased in response to cooler and moister conditions after 4000 cal. yr BP. Alpine plant communities favouring moist sites show an inverse pattern, expanding after a change towards moister climate after 4000 cal. yr BP. In a redundancy analysis (RDA), a statistically significant proportion of the variability in the total chironomid assemblages was captured by changes in the pollen types reflecting alpine vegetation typical of moist sites. Although chironomid community changes appeared to follow the major patterns in the alpine vegetation succession, the present study does not support a direct link between the changing treeline position and chironomid stratigraphy. Rather, the data indicate that the terrestrial and aquatic environments have each responded directly to the same ultimate cause, namely changing Holocene climate. Copyright © 2002 John Wiley & Sons, Ltd.     

Rapid change in early Holocene environments inferred from Lake Pupuke,Auckland City,New Zealand

Sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high‐resolution millennial to centennial‐scale record of changing climate and catchment hydrology spanning the past ca. 10 000 years. Here, we focus on the period between 9500 ± 25 and 7000 ± 155 cal. yr BP during which grain size, diatom palaeoecology, biogenic silica concentrations, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions, with a significant event commencing at ca. 8240 cal. yr BP, commensurate with a lowering of lake level, faster erosion rates and increased sediment influx with a duration of ca. 360 yrs. However, the changes in the lake are not reflected in the terrestrial vegetation, where the pollen record indicates that podocarp forest dominated the Auckland region, with apparent environmental stability during this part of the early Holocene. The synchronous change in most of the proxies between ca. 8240 and 7880 cal. yr BP at Lake Pupuke indicates the presence of a sustained episode of relatively low lake level and concomitant increased rate of erosion in the early Holocene that appears to be at least partly coeval with the 8200 cal. yr BP meltwater event proposed for the North Atlantic region. Copyright © 2008 John Wiley & Sons, Ltd.     

Holocene vegetation, fire and climate history of the Sawtooth Range, central Idaho, USA

The paucity of low- and middle-elevation paleoecologic records in the Northern Rocky Mountains limits our ability to assess current environmental change in light of past conditions. A 10,500-yr-long vegetation, fire and climate history from Lower Decker Lake in the Sawtooth Range provides information from a new region. Initial forests dominated by pine and Douglas-fir were replaced by open Douglas-fir forest at 8420 cal yr BP, marking the onset of warmer conditions than present. Presence of closed Douglas-fir forest between 6000 and 2650 cal yr BP suggests heightened summer drought in the middle Holocene. Closed lodgepole pine forest developed at 2650 cal yr BP and fires became more frequent after 1450 cal yr BP. This shift from Douglas-fir to lodgepole pine forest was probably facilitated by a combination of cooler summers, cold winters, and more severe fires than before. Five drought episodes, including those at 8200 cal yr BP and during the Medieval Climate Anomaly, were registered by brief intervals of lodgepole pine decline, an increase in fire activity, and mistletoe infestation. The importance of a Holocene perspective when assessing the historical range of variability is illustrated by the striking difference between the modern forest and that which existed 3000 yr ago.     

Late Quaternary deglaciation and climate history of the Larsemann Hills (East Antarctica)

The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.     

Post‐Glacial immigration of the harbour porpoise (Phocoena phocoena) into the Baltic Sea*

At the end of the Pleistocene, environmental conditions in the Baltic Basin were affected by the melting glaciers and the resultant freshwater bodies. In contrast to various seal species, there is no subfossil evidence of the harbour porpoise (Phocoena phocoena) from the early Holocene stages of the Baltic Basin. This article is an attempt to clarify the colonization of the harbour porpoise into the Baltic Sea and to reveal the ecological background of this process. All published Holocene subfossil records from the porpoise in the Baltic region were sought and supplemented with those from museums and zoological collections; 148 records document the porpoise's occurrence. The earliest records of the harbour porpoise date from the time between 9600 and 7000 cal. yr BP and originate from the early and middle Mesolithic coastal settlements of the Maglemose and Kongemose culture during the early Littorina stage. Around 7500–5700 cal. yr BP, the porpoise is recorded frequently at many localities from late Mesolithic (Ertebølle culture) and Neolithic in the coastal areas of the western Baltic Sea, as well as for the first time in the Gulfs of Bothnia and Finland. Since 4000 cal. yr BP, P. phocoena has only been recorded in the western Baltic. We suggest that immigration and dispersion of P. phocoena into the Baltic Sea was connected with the Littorina transgression beginning around 9000 cal. yr BP. The continuous influx of seawater and the associated ecological changes led to a new, very species‐rich, fish community and adequate living conditions for the harbour porpoise.     

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.     

Environmental change and cultural response between 8000 and 4000 cal. yr BP in the western Loess Plateau,northwest China

Two ancient swamps in the western Loess Plateau, northwest China record the climate history between 8000 and 4000 cal. yr BP. Grain size, CaCO₃, organic matter, mollusc fauna and pollen assemblages show that climate was wet between 8300 and 7400 cal. yr BP, distinctly humid and warm between 7400 and 6700 cal. yr BP, semi‐humid from 6700 to 6300 cal. yr BP, and semi‐arid between 6300 and 4000 cal. yr BP. The temporal and spatial distribution of archaeological sites shows that the prosperity of the neolithic cultures in the western part of the Chinese Loess Plateau did not appear until the climate changed to semi‐arid, implying that the semi‐arid climate was more favourable than wet and humid climate to neolithic peoples, whose subsistence was based on cereals adapted to arid environments. Copyright © 2004 John Wiley & Sons, Ltd.     

Climatic change recorded by stable isotopes and trace elements in a British Holocene tufa

Combined stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg, Sr) geochemistry from bulk tufa calcite and ostracod shell calcite from an early Holocene British tufa reveal clear records of Holocene palaeoclimatic change. Variation in δ¹⁸O is caused principally by change in the isotopic composition of Holocene rainfall (recharge), itself caused mainly by change in air temperature. The δ¹³C variability through much of the deposit reflects increasing influence of soil‐zone CO₂, owing to progressive woodland soil development. Bulk tufa Mg/Ca and Sr/Ca are controlled by their concentrations in the spring water. Importantly, Mg/Ca ratios are not related to δ¹⁸O values and thus show no temperature dependence. First‐order sympathetic relationships between δ¹³C values and Mg/Ca and Sr/Ca are controlled by aquifer processes (residence times, CO₂ degassing and calcite dissolution/reprecipitation) and probably record intensity of palaeorainfall (recharge) effects. Stable isotope records from ostracod shells show evidence of vital effects relative to bulk tufa data. The ostracod isotopic records are markedly ‘spiky’ because the ostracods record ‘snapshots’ of relatively short duration (years), whereas the bulk tufa samples record averages of longer time periods, probably decades. The δ¹⁸O record appears to show early Holocene warming, a thermal maximum at ca. 8900 cal. yr BP and the global 8200 yr BP cold event. Combined δ¹³C, Mg/Ca and Sr/Ca data suggest that early Holocene warming was accompanied by decreasing rainfall intensity. The Mg/Ca data suggest that the 8200 yr BP cold event was also dry. Warmer and wetter conditions were re‐established after the 8200 yr BP cold event until the top of the preserved tufa sequence at ca. 7100 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Lateglacial and Holocene terrestrial and marine proxies reflecting climate changes in the Malangen fjord area, Norway, northeast North Atlantic

A high-resolution Younger Dryas–late Holocene record of climate and environment from the Malangen fjord has been established on the basis of two marine sediment cores. Five pollen-spore assemblage zones have been defined covering the period c . 11 500 cal. yr BP (10 200 ¹⁴C yr BP) to c . 1600 cal. yr BP (1600 ¹⁴C yr BP) with a hiatus of c . 2000 cal. years between c . 10 200 and 8100 cal. yr BP (9000 and 7300 ¹⁴C yr BP). The Holocene vegetation development from pioneer vegetation to forest development, identified in the marine pollen record, correlates well with pollen records from terrestrial sections of northern Norway. The marine pollen record was also correlated directly with marine proxy records of the bottom water temperature investigated in the same sediment cores. Correlation between the marine and terrestrial proxies suggests that changes in the influx of warm Atlantic Water to the fjord led to an instant change in the vegetation of the surrounding land area. The results thus support a strong link between marine and atmospheric mean climatic states in the North Atlantic region throughout the Holocene.