Terrestrial – Ocean environmental change in the northwestern Pacific from the glacial times to Holocene     

Hodaka Kawahata  Hideaki Ohshima  Azumi Kuroyanagi 《Journal of Asian Earth Sciences》2011,40(6):430-1202

The Mixed Water Region (MWR) between the Oyashio Current and the Kuroshio Extension and surrounding terrestrial region have been affected by the global climatic change. The sedimentary core KR02-15 PC6 collected at 40°23.8871′N, 143°29.8663′E in the MWR provides detailed records of pollen and spores and alkenone sea surface temperature (SST) during the last 15 kyr, showing that both ocean and terrestrial environments have been appreciably linked. Abundance of Picea, a proxy for terrestrial cool climate, fluctuated, coinciding with the alkenone-SST change during the interstadial period (15.0–7.7 cal kyr B.P.). Alkenone-SST increased to the modern level at 8.0 cal kyr B.P. and remained almost constant until 2.0 kyr B.P. while the terrestrial warming still continued until 4.0 cal kyr B.P. The rainfall under terrestrial warm condition increased gradually from 7.9 cal kyr B.P. and rapidly from 2.0 cal kyr B.P. Both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold Oyashio Current.  相似文献   

论中国东部第四纪冷期植被与环境   总被引：8，自引：0，他引：8  

李文漪 《地理学报》1987,(4)

在第四纪的冷期,中国东部华北和东北植物区,因深受干旱因素影响,广泛发展了草原植被。当时在欧亚大陆上,草原、森林草原和苔原可能曾自南欧一直分布到东亚。在南方植物区,亚热带针叶林曾在平原和丘陵广为分布。同时,许多喜湿热的类群则被保存于避难所中。由此看来,第四纪寒冷气候南侵到中国东部的强度和范围,是有限的。  相似文献   

Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa     

Alfred Ngomanda  Dominique Jolly  Ilhem Bentaleb  Alex Chepstow-Lusty  M'voubou Makaya  Jean Maley  Michel Fontugne  Richard Oslisly  Nicaise Rabenkogo 《Quaternary Research》2007,67(3):411-425

Pollen and δ¹³C_TOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” ( 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ¹³C_TOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ¹³C_TOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available.  相似文献   

Human-ecosystem interactions in relation to Holocene environmental change in Port Joli Harbour,southwestern Nova Scotia,Canada   总被引：1，自引：0，他引：1  

Karen Neil  Konrad Gajewski  Matthew Betts 《Quaternary Research》2014

A high-resolution pollen record from Path Lake in Port Joli Harbour, Nova Scotia, Canada, provides a paleo-ecological perspective on Holocene climate and vegetation variability within the context of local archaeological research. Pollen assemblages in the early Holocene reflect a post-glacial forest dominated by Pinus, Tsuga, Betula and Quercus. During this time, a lower frequency of radiocarbon dated cultural material suggests lower human settlement intensity. Shallow water aquatic (Isoetes) and wetland (Alnus, Sphagnum) taxa increased after 3400 cal yr BP in response to a transition towards wetter climatic conditions. Culturally significant periods, where settlement intensity increased in the Maritimes and Maine, coincide with maximum values of reconstructed total annual precipitation, suggesting that environmental conditions may have influenced prehistoric human activity. European settlement, after 350 cal yr BP, was marked by a rise in Ambrosia. The impact of anthropogenic fire disturbances on the landscape was evidenced by peak charcoal accumulations after European settlement.  相似文献   

Holocene climate–fire–vegetation interactions at a subalpine watershed in southeastern British Columbia,Canada     

Colin J. Courtney Mustaphi  Michael F.J. Pisaric 《Quaternary Research》2014

Vegetation assemblages and associated disturbance regimes are spatially heterogeneous in mountain ecosystems throughout the world due to the complex terrain and strong environmental gradients. Given this complexity, numerous sites describing postglacial vegetation and fire histories are needed to adequately understand forest development and ecosystem responses to varying climate and disturbance regimes. To gain insight into long-term historical climate–fire–vegetation interactions in southeastern British Columbia, Canada, sedimentological and paleoecological analyses were performed on a sediment core recovered from a small subalpine lake. The pollen assemblages, stomata, and macroremains indicate that from 9500 to 7500 cal yr BP, Pinus-dominated forests occurred within the catchment and Alnus was also present. Climate was an important control of fire and fire frequency was highest at this time, peaking at 8 fires 1000 yr^− 1, yet charcoal accumulation rates were low, indicative of low terrestrial biomass abundance. From 7500 to 4600 cal yr BP, Pinus decreased as Picea, Abies and Larix increased and fire frequencies decreased to 3–6 fires 1000 yr^− 1. Since 7500 cal yr BP the fire regime varied at a millennial scale, driven by forest biomass abundance and fuel accumulation changes. Local scale (bottom-up) controls of fire increased in relative importance since at least 6000 cal yr BP.  相似文献   

A multiple profile approach to the palynological reconstruction of Norse landscapes in Greenland's Eastern Settlement     

Paul M. Ledger  Kevin J. Edwards  J. Edward Schofield 《Quaternary Research》2014

Palynological research is increasingly revealing the landscape impacts of Norse colonisation in southern Greenland. Typically, although not exclusively, these studies are from depositional environments with highly localised pollen source areas close to fjord-side centres of medieval power. In contrast, this paper presents data from Vatnahverfi, an inland district of the Eastern Settlement, and explores the emergence of a cultural landscape through three pollen sequences at variable distances from Norse farms. Two are from mires with small pollen source areas close to (< 100 m) and distant from (≥ 1500 m) probable farming activities. The other provides a more regional signal of vegetation change, albeit one located close to a Norse settlement. Landnám is marked primarily through an increase in microscopic charcoal and the appearance of pollen from Rumex acetosella, although significant differences between profiles are noted. Close to Norse ruins, pollen productivity from grassland communities increases and woodland and scrub representation declines. Further from archaeological remains, palynologically inferred human activity is primarily characterised by decreased productivity, notably declining influx from woodland and scrub species, reflecting grazing herbivores or coppicing. Abandonment of Vatnahverfi is indicated from the late 14th to early 15th century AD.  相似文献   

Vegetation and fire history since the last glacial maximum in an inland area of the western Mediterranean Basin (Northern Iberian Plateau,NW Spain)     

César Morales-Molino  Mercedes García-Antón 《Quaternary Research》2014

We reconstructed vegetation responses to climate oscillations, fire and human activities since the last glacial maximum in inland NW Iberia, where previous paleoecological research is scarce. Extremely sparse and open vegetation composed of steppic grasslands and heathlands with scattered pioneer trees suggests very cold and dry conditions during the Oldest Dryas, unsuitable for tree survival in the surroundings of the study site. Slight woodland expansion during the Bølling/Allerød was interrupted by the Younger Dryas cooling. Pinewoods dominated for most of the early Holocene, when a marked increase in fire activity occurred. Deciduous trees expanded later reaching their maximum representation during the mid-Holocene. Enhanced fire activity and the presence of coprophilous fungi around 6400–6000 cal yr BP suggest an early human occupation around the site. However, extensive deforestation only started at 4500 cal yr BP, when fire was used to clear the tree canopy. Final replacement of woodlands with heathlands, grasslands and cereal crops occurred from 2700 cal yr BP onwards due to land-use intensification. Our paleoecological record can help efforts aimed at restoring the natural vegetation by indicating which communities were dominant at the onset of heavy human impact, thus promoting the recovery of currently rare oak and alder stands.  相似文献   

Testing the reliability of pollen-based diversity estimates   总被引：2，自引：2，他引：0  

Matthew Charles Peros  Konrad Gajewski 《Journal of Paleolimnology》2008,40(1):357-368

Rarefaction analysis is a common tool for estimating pollen richness. Using modern and fossil pollen data from the Canadian Arctic and Greenland, we examine the effects of pollen concentration (grains/cc) and evenness (the distribution of species abundances) on palynological richness. Our results show that pollen richness and concentration have a strong negative correlation at low pollen concentrations. There is a positive correlation between pollen evenness and richness, although the strength of this relationship is difficult to determine. Rarefaction analysis on samples of low concentration or high evenness is likely to lead to pollen richness being less underestimated than on samples of high concentration or low evenness. These findings corroborate theoretical research on these issues.  相似文献   

Coupling relationships: Hillslope–fluvial linkages in the Hodder catchment, NW England     

R.C. Chiverrell  G.C. Foster  P. Marshall  A.M. Harvey  G.S.P. Thomas 《Geomorphology》2009,109(3-4):222-235

Variations in the coupling of sediment transfer between different parts of a fluvial catchment, e.g., hillslope to axial stream, can hamper understanding but are an integral part of the geomorphological record. Depositional environments respond to a combination of land use, climate, storms (floods), and autogenic conditioning. The distribution of sediment in the upland landscapes of NW England is out of equilibrium with contemporary climate and geomorphological processes; more a function of peri- and paraglacial mobilisation of glacigenic deposits. Soil and vegetation development after deglaciation have interrupted any progression toward sediment exhaustion with sediment release controlled largely by extrinsic perturbation, with late Holocene anthropogenic activity, climate and extreme hydrological events the likely candidates. This paper presents a new radiocarbon-dated Holocene geomorphological succession for the River Hodder (NW England), alongside evaluating new palaeoecological and geoarchaeological data to discern the impacts of human activity. These data show a late Holocene expansion in human occupation and use of the landscape since the Iron Age (700–0 cal. B.C.), with more substantial changes in the character and intensity of upland land use in the last 1300 years. The geomorphological responses in the uplands were the onset of considerable and widespread hillslope erosion (gullying) and associated alluvial fan development. Interpretation of the regional radiocarbon chronology limits gullying to four, more extensive and aggressive phases after 500 cal. B.C. The downstream alluvial system has responded with considerable valley floor deposition and lateral channel migration that augmented sediment supply by remobilising the existing floodplain terraces and led to the aggradation of a series of inset alluvial terraces. The timing of these changes between states of aggradation and incision in alluvial reaches reflects the increased connectivity between the hillslope and alluvial systems. Aspects of both the regional climate and land use histories are conducive to increasing discharge and sediment flux, but the region wide lowering of erosion thresholds appears a key driver conditioning these sediment-rich conditions and producing a landscape that was more susceptible to erosion under lower magnitude flows.  相似文献   

Stratigraphy of a Lateglacial lake basin sediment sequence at Turret Bank,upper Glen Roy,Lochaber: implications for the age of the Turret Fan     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(1):110-124

New lithostratigraphical, pollen-stratigraphical and tephrostratigraphical data are presented for a sediment sequence at Turret Bank, a site that lies close to the confluence of the River Turret with the River Roy in Lochaber, the western Scottish Highlands. The site is also adjacent to the inner margin of a major gravel fan, the Glen Turret Fan, the age of which has been debated and has a crucial bearing on the overall sequence of events in Glen Roy, especially concerning the maximum limit of Loch Lomond Readvance (Younger Dryas) ice. Several lines of evidence point to the sediment sequence at Turret Bank having been wholly deposited during the Loch Lomond Stadial-early Holocene transition: (i) the pollen sequence is typical for this transitional period; (ii) varved deposits preserved in the sequence bear a strong resemblance to mid-Stadial varves in a regional master varve scheme for Glen Roy and vicinity (the Lochaber Master Varve Chronology); and (iii) an early Holocene tephra – the Askja-S Tephra – is preserved within the sequence. Some limitations with the new data are considered, but it is concluded that the coherent integration of lithostratigraphic, geomorphological, pollen-stratigraphical and tephrostratigraphical data point to the likelihood that Loch Lomond Readvance ice extended to the inner margin of the Glen Turret Fan, and that the fan was probably constructed by glacial meltwaters at this time.  相似文献