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1.
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.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
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.  相似文献   

8.
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9.
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.  相似文献   

10.
This paper presents a lake‐level record for the Holocene at Lake Cerin (Jura Mountains, eastern France). It is based on a range of sedimentological techniques validated in previous studies, with a combination of systematic lithostratigraphic investigations of the infillings accumulated in the lacustrine basin, and sediment analyses of two selected cores. The chronology is based on 10 radiocarbon dates and pollen stratigraphy. On a millennial scale, the Cerin lake‐level record shows three distinct successive phases characterised by higher lake‐level conditions until ca. 9000 cal. a BP, followed by a maximal lowering at ca. 9000–8500 cal. a BP, and a progressive rise until the present. This rise was punctuated by centennial‐scale fluctuations, with major events around 4000, 2800 and after 1500 cal. a BP. Considered on a multimillennial scale, the general pattern of palaeohydrological changes reconstructed at Cerin reflects the impact of orbitally driven summer insolation. This is in agreement with other regional and extra‐regional palaeoclimatic records, although every record shows peculiarities in timing and shape depending on the proxy used for reconstruction. In this general context, centennial to multicentennial oscillations appear to have been second‐order events in comparison with the major influence of the orbital factor. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
Lithology, pollen, macrofossils, and stable carbon isotopes from an intermontane basin bog site in southern New Zealand provide a detailed late-glacial and early Holocene vegetation and climate record. Glacial retreat occurred before 17,000 cal yr B.P., and tundra-like grassland–shrubland occupied the basin shortly after. Between 16,500 and 14,600 cal yr B.P., a minor regional expansion of forest patches occurred in response to warming, but the basin remained in shrubland. Forest retreated between 14,600 and 13,600 cal yr B.P., at about the time of the Antarctic Cold Reversal. At 13,600 cal yr B.P., a steady progression from shrubland to tall podocarp forest began as the climate ameliorated. Tall, temperate podocarp trees replaced stress-tolerant shrubs and trees between 12,800 and 11,300 cal yr B.P., indicating sustained warming during the Younger Dryas Chronozone (YDC). Stable isotopes suggest increasing atmospheric humidity from 11,800 to 9300 cal yr B.P. Mild (annual temperatures at least 1°C higher than present), and moist conditions prevailed from 11,000 to 10,350 cal yr B.P. Cooler, more variable conditions followed, and podocarp forest was completely replaced by montane Nothofagus forest at around 7500 cal yr B.P. with the onset of the modern climate regime. The Cass Basin late-glacial climate record closely matches the Antarctic ice core records and is in approximate antiphase with the North Atlantic.  相似文献   

12.
Studies of Late Quaternary sediments in south and central Sweden have yielded a detailed tephrochronology for the Last Glacial–Interglacial transition (LGIT; ca. 15,000–10,000 cal. yr BP) and the Holocene. More than ten tephra layers have been detected and geochemically characterised. The most widespread tephra from the LGIT is the rhyolitic phase of the Vedde Ash (ca. 12,000 cal. yr BP) which has been found in lacustrine sediments and marine clays south of the Younger Dryas moraines in south Sweden. Other horizons from the LGIT identified to date include the Borrobol tephra (ca. 14,400 cal. yr BP), the Hässeldalen tephra (ca. 11,500 cal. yr BP), the 10-ka Askja tephra (ca. 11,300 cal. yr BP) and the Högstorpsmossen tephra (ca. 10,200 cal. yr BP). The most significant Holocene isochrones are Hekla-4 (ca. 4260 cal. yr BP), Hekla-Selsund/Kebister (ca. 3750 cal. yr BP), Hekla-3 (ca. 3000 cal. yr BP) and Askja-1875. Two new Late Holocene tephra horizons (the Stömyren tephra, ca. 2100 cal. yr BP and the Gullbergby tephra; ca. 2700 cal. yr BP) were identified in single sites and are so far less valuable as marker horizons, but are potentially important for the future.  相似文献   

13.
We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS 14C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.  相似文献   

14.
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   

15.
Wohlfarth, B. 2010: Ice‐free conditions in Sweden during Marine Oxygen Isotope Stage 3? Boreas, 10.1111/j.1502‐3885.2009.00137.x. ISSN 0300‐9483 Published and unpublished 14C dates for Sweden older than the Last Glacial Maximum ice advance were evaluated. Acceptable 14C dates indicate that age ranges for interstadial organic material in northern and central Sweden are between c. 60 and c. 35 cal. kyr BP and for similar deposits in southern Sweden are between c. 40 and c. 25 cal. kyr BP, which is in good agreement with recently derived Optical Stimulated Luminescence ages. 14C dates on mammoth remains show a larger scatter, possibly as a result of incomplete laboratory pretreatment. A possible scenario based on calibrated 14C dates from interstadial deposits is that central and northern Sweden was ice‐free during the early and middle part of Marine Oxygen Isotope Stage 3 and that southern Sweden remained ice‐free until c. 25 cal. kyr BP. A first ice advance into northern and central Sweden might have occurred as late as around 35 cal. kyr BP, more or less coeval with the Last Glacial Maximum ice advance onto the Norwegian shelf. To test the conclusions drawn here, new multi‐proxy and high‐resolution investigations of several key sites in north, central and south Sweden are required.  相似文献   

16.
This paper presents a Holocene pollen record from an ombrotrophic bog in Southland, New Zealand, together with multiproxy data (testate amoebae, peat humification and plant macrofossils) from the same core to establish an independent semiquantitative record of peatland surface moisture. Linkages between reconstructed peatland surface moisture and regional forest composition are investigated using redundancy analysis of the forest pollen data constrained with predicted bog water‐table depths. Over 32% of the pollen data variance can be explained by surface moisture changes in the bog, suggesting a common cause of water‐table and regional vegetation change. Water tables were higher during the early to mid‐Holocene when the forest was dominated by podocarp taxa. Water tables lowered after about 3300 cal. yr BP coevally with the expansion of Nothofagus species, culminating with the dominance of Nothofagus subgenus Fuscospora in the past 1200 cal. yr BP. This is in apparent opposition to the warm/dry to cool/wet trend suggested by subjective interpretation of pollen data alone, from this and other studies. We suggest that during the late Holocene, drier summers associated with shifts in solar insolation caused reduced surface wetness and summer humidity, which together with a trend to cooler winters, apparently favoured the regeneration of Nothofagus species. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
Three pollen and charcoal records from three lakes lying at 3400 m elevation in southern Peru provided a record of landscape change spanning the last ca.18 000 cal. a BP. The tree line lay close to the site between ca. 16 000 and 12 000 cal. a BP, with Polylepis woodlands growing near the lakes. Progressively drying conditions led to increased fire after 12 000 cal. a BP, coinciding with a decline in Polylepis cover and Andean forest relicts as puna grasslands expanded. A strong decrease in the rate of sediment deposition between ca. 12 000 and ca. 4400 cal. a BP was interpreted to indicate the presence of sedimentary hiatuses. With the return of wet conditions after 4400 cal. a BP, forests did not reassemble around the lakes. Instead, fire‐maintained grasslands dominated the landscape. Humans probably induced the intensified fire activity during the late Holocene and thereby deflected local successions. The modern fragmented landscape, with Polylepsis woodlands existing in fire‐resistant pockets above the general limit of the Andean tree line, resulted from the intensification of human land use practices during the last 4400 cal. a BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
This study presents a multi‐proxy record from Lake Kotokel in the Baikal region at decadal‐to‐multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000‐year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, cold steppe associations typical for northern Mongolia, and mountain tundra vegetation. The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase (c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid‐based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice‐cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity.  相似文献   

20.
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.  相似文献   

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