‘‘Lifetime Achievement Awards’’ were presented to Walt Dean, Dan Livingstone, Frank Oldfield, and Herb Wright by the International Paleolimnology Association (IPA) at the 11th International Paleolimnology Symposium in Guadalajara, Mexico, in December 2009. Acceptance speeches of the recipients were published in Volume 44 (No. 2) of the Journal of Paleolimnology. All four submissions should have been published as Notes.

Dzhangyskol is a small lake of glacial origin in the central part of the Altai Mountains in southern Siberia. Pollen stratigraphies and chronologies of two cores record the vegetational development of the area from the Late Glacial treeless landscape to the forest and steppe of today. The modern lake is a remnant of a much larger ice-dammed lake, which was reduced in size and then temporarily drained after diversion of the inflowing mountain meltwater stream, which had low δ18O values. The dry lake floor allowed development of permafrost and small pingos (frozen mounds of lake sediments). With the onset of greater climatic humidity in the mid-Holocene, the input of local water with higher δ18O caused a rise in lake level, drowning the earlier pingos. Growth of a broad fen on the margin of the lake led to formation of a modern pingo complex.

Two lakes of glacial origin (Grusha at 2413 m and Akkol at 2204 m) are located on a broad high-mountain plateau on the dry eastern end of the Russian Altai Mountains in the Republic of Tuva, just north of Mongolia. The present vegetation of the area is an open high-mountain tundra–steppe mosaic, with patches of Larix and Pinus sibirica forests on north-facing slopes 30 km northwest of the lakes. Alpine meadows occur near streams and snow patches. Pollen diagrams and radiocarbon dates (16 for Grusha and 12 for Akkol) were used to reconstruct the vegetational history since the last glaciation. The core from Grusha contains about 50 cm of Late Glacial sediment of relatively low organic content, mostly correlated with the Younger Dryas episode because of the high percentages of Artemisia, Gramineae, and Chenopodiaceae, along with a diversity of non-arboreal pollen types indicating tundra–steppe and meadow-steppe. In the earliest Holocene, starting with increased organic matter at about 195 cm (12,000 cal. yr BP), the Artemisia–Gramineae–Chenopodiaceae pollen assemblage continued, along with an increase in shrub Betula but without the diversity of minor non-arboreal types. The interpretation of dry and warm climate at this time is supported by the unconformity at Akkol, implying a dried lake. Then after about 1000 years the increase of Pinus sibirica, P. sylvestris, Picea obovata, and Abies sibirica suggests that forests developed in response to increased humidity, first at the higher-elevation Grusha, and then at Akkol. After about 6000 cal. yr BP the role of forests decreased sharply in the area. The Picea and Abies components almost disappeared, as they did also in more westerly areas of the Altai Mountains. Steppe elements increased along with alpine herbs, especially after 2000 cal. yr BP as a result of cooling or increased aridity, as well as probable human activity. Correlation of the vegetation sequence for the Tuva sites with those to the west in the central Altai Mountains indicates that the Late Glacial open landscapes persisted in the earliest Holocene but then were invaded by coniferous forests as a result of increased moisture and temperature associated with Atlantic storm systems as well as with insolation-enhanced Asian monsoon. Cooling and drying after about 6000 cal. yr BP brought the decline of Abies and Picea and the expansion of tundra–steppe.

Recognition that Earth/Sun orbital changes are the basic cause for Quaternary climatic variations provides a context for explaining global environmental changes, many of which are preserved in the stratigraphic and geomorphic record of lakes. Paleoclimatic numerical models suggest the mechanisms. In subtropical latitudes such as North Africa the enhanced summer insolation culminating about 10 000 years ago resulted in the increased monsoonal rains that explain the widespread expansion of lakes in now-desert basins. But in the American Southwest lake expansion dates to 18 000–15 000 years ago, when storm tracks were displaced to the south by the ice sheets—themselves a product of earlier orbital changes. The dynamics in the resopnse of different components of the natural system to climatic change are recorded in the stratigraphy of lake sediments, not only by their pollen content as a manifestation of the regional vegetation but also by their microfossils and chemical composition as reflections of lake development.

Kråkenes is the site of a small lake on the west coast of Norway that contains a long sequence of late-glacial sediments. The Younger Dryas is well represented, as a cirque glacier developed in the catchment at this time. This site offers unique opportunities to reconstruct late-glacial environments from independent sources of evidence; physical evidence (glacial geomorphology, sedimentology, palaeomagnetism, radiocarbon dating), and biological evidence from the remains of animals and plants derived from both the terrestrial and aquatic ecosystems. This report describes the background to the site, and the international multidisciplinary project to reconstruct late-glacial and early Holocene environmental and climatic changes at Kråkenes.

One of the more enduring controversies surrounding management of Yellowstone National Park is whether historic fluctuations in elk numbers have resulted in overgrazing and accelerated erosion of range lands in the northern part of the Park. Our recent paleolimnological analysis of eight small lakes in this northern winter range found little evidence that environmental conditions prior to park establishment (1872) were substantially different from those of recent decades (Engstrom et al., 1991; Whitlock et al., 1991). As a response to

New fossil pollen records from the central Peruvian Andes at elevations above 4000 m including pollen-concentration data and additional radiocarbon dates, provide information on late Quaternary vegetation change for the region. A pollen assemblage typical of superpuna plus low pollen concentrations, and % organics in the late glacial section of Laguna Tuctua indicate a cold/dry climate, but strong evidence for a late glacial climate reversal, i.e., the Younger Dryas, is not presently confirmed. An abrupt increase in Urticales pollen as Compositae and Polylepis-Acaena type pollen decline signals the beginning of the Holocene. Subsequent increases in Urticales and Plantago rigida type pollen point to increased moisture as well as higher temperatures from about 11,000 to 7000 yr B.P. A possible correlation exists between the rapid expansion of puna and closed continuous forest and the rise in importance of camelids in the early Holocene. In the mid-Holocene Plantago rigida cushion bogs and continuous montane forest elements decline, suggesting a drier climate. Grasses and Cheno-Ams then increase, reaching maxima about 4000 yr B.P. Pastoralism and agriculture are thought to have developed at this time, according to ethnobotanical studies from this area, and pollen evidence seems to support these findings. Between 3000 and 2000 yr B.P. pollen percentages of Poaceae, Plantago rigida type, and other local taxa decline as glacial activity was renewed in the higher mountains. Zea mays is present by 2000 yr B.P., and pollen of weeds and secondary successional plants associated with increasing agricultural disturbance are evident.

are dynamic on certain time scales. Thus the dual concepts of the evolution of landforms and succession in ecosystems have always been of interest in natural history. The grand theory of landform evolution by William Morris Davis was matched soon after by the grand synthesis of vegetational succession represented by the works of Frederic Clements, and ever since then they have been discussed and evaluated as new insights have come with research in geomorphology and Earth history and in ecology and palaeoecology. But when it comes down to details of the facts and mechanisms

COHMAP (Cooperative Holocene Mapping Project) had its start in the 1970s with the intent to compare atmospheric general circulation models with quantitative palaeoclimatic reconstructions based on stratigraphic pollen analysis. As the sophistication of the models increased and as additional palaeoclimatic indicators (lake levels, marine microfossils) were incorporated in the reconstructions, the programme expanded to global coverage through the participation of numerous collaborators. The carefully nurtured dual approach of modelling and data analysis was strengthened by continued testing of one against the other, with emphasis on interdisciplinary understanding fostered by workshops. With the development of new computer models that have higher spatial resolution and improved boundary conditions, and with diversification and enlargement of the geographic and temporal coverage of field and analytical data, substantial refinements can be anticipated in the understanding of global climatic changes since the last glacial maximum.

The Holocene pollen sequence in the Minnesota area is “asymmetric” around the so-called prairie period: the early Holocene is dominated by elm (with pine in the north) and the late Holocene by oak. The elm zone is interpreted as a manifestation of summer monsoonal rains enhanced by the Milankovitch insolation maximum, and the pine in the north is interpreted as a result of summer cooling near the retreating ice sheet. As the summer insolation waned during the Holocene, its associated monsoonal rains from the Caribbean moisture source lasted longer in the south (northeastern Iowa and southern Wisconsin), where the inferred mesic elm forest changed to prairie as late as 5000 yr B.P., compared to 8000 yr. B.P. in Minnesota (and 9000 yr B.P. in the Dakotas).

This commentary is intended as a practical guide for the non-motorized use of piston corers to obtain undisturbed sections of lake sediments. Good recovery is essential for accurate reconstruction of environmental and limnological history. Emphasis is placed on the square-rod piston corer, which is widely used for acquisition of sediment cores in meter-long sections from lakes as much as 30 m deep. Coring platforms for open water can be easily prepared on pairs of boats or canoes or (in water depth up to 15 m) even a single small rubber raft, but firm anchoring is essenial to maintain the vertical position of the casing and to assure re-entry into a single hole. Incomplete recovery on individual drives is not a result of sediment compaction but rather the build-up of friction on the tube interior, by which the core forms a plug that prevents further recovery.

Recent sediments of eight small lakes in the northern winter range of Yellowstone National Park were cored to examine stratigraphic records of past changes in limnology and local environment that might be attributed to grazing and other activities of elk, bison, and other large ungulates. Cores of undisturbed sediment were analyzed at close intervals to depths covering the last 100–150 years according to chronologies established by lead-210 dating. Pollen analyses were made to show change in regional vegetation, and diatom and geochemical analyses were made to reveal possible limnological changes resulting from soil erosion and nutrient input from the lake catchments.

Lake St Croix at the downstream end of the St Croix River was formed when a natural dam was constructed across its mouth by the Mississippi River, which has aggraded its floodplain in Holocene time since the termination of deep erosion by the Glacial River Warren, the outlet for Glacial Lake Agassiz until about 9500 BP. Pollen analysis and radiocarbon dating of a 19 m core from the uppermost basin of the lake shows a rapidly increasing rate of sedimentation and pollen influx since 3000 BP and especially since 1300 BP, as the delta of the St Croix River approached the coring site. The pollen sequence closely resembles that for Lily Lake which is located on the moraine upland a few kilometres to the west. Its pollen assemblage differs from that for Lake St Croix more because of its upland location slightly to the west than to influx of river sediment in Lake St Croix.

Bog development, in terms of the rates of horizontal and vertical accumulation of peat and the timing of landform development of open—water pools, was examined on two concentric raised bogs in central Sweden. The results are compared with three models (allogenic, autogenic, and neutral models) of bog development in order to evaluate the relative contribution of environmental factors vs. ecosystem control of developmental processes. Both mires began to grow on discrete upland sites °6000 BP and then spread concentrically and accumulated peat vertically at approximately continuous rates to the present. Radiocarbon dates from pool sediments are progressively younger from the center to the margin of the mire, suggesting that pool formation is triggered autogenically by changes in hydrology. The results conform to hydrological models of mire formation based on groundwater mound equations and suggest that autogenic processes exert a major control over bog expansion, landform development, and the formation of conspicuous features in the stratigraphic record.

Interest in significant climatic fluctuations affecting large geographic areas but having a time range that is too brief to adduce the Milankovitch radiation cycles has focused on the Alleröd/Younger Dryas event, which is a well-established phenomenon of western Europe manifested by glacial and vegetational reconstructions. It is also shown by the foraminiferal evidence for shifts in the polar front in the North Atlantic. Recent pollen and lithostratigraphic investigations in the Maritime Provinces of eastern Canada and in the till plains of west-central Ohio on opposite sides of the late-glacial spruce forest indicate that the event also left a record in eastern North America. Experiments with an atmospheric general circulation model, with the temperature of North Atlantic surface waters depressed to full-glacial levels, lowered summer temperatures in ‘upwind’ periglacial eastern North America by 2°C — just as far inland as they did downwind in western Europe, where the paleoecological record of cooling is clear.