P. M. Anderson

Climate change and Arctic ecosystems: 2. Modeling, paleodata-model comparisons, and future projections

Large variations in the composition, structure, and function of Arctic ecosystems are determined by climatic gradients, especially of growing-season warmth, soil moisture, and snow cover. A unified circumpolar classification recognizing five types of tundra was developed. The geographic distributions of vegetation types north of 55degreesN, including the position of the forest limit and the distributions of the tundra types, could be predicted from climatology using a small set of plant functional types embedded in the biogeochemistry-biogeography model BIOME4. Several palaeoclimate simulations for the last glacial maximum (LGM) and mid-Holocene were used to explore the possibility of simulating past vegetation patterns, which are independently known based on pollen data. The broad outlines of observed changes in vegetation were captured. LGM simulations showed the major reduction of forest, the great extension of graminoid and forb tundra, and the restriction of low- and high-shrub tundra (although not all models produced sufficiently dry conditions to mimic the full observed change). Mid-Holocene simulations reproduced the contrast between northward forest extension in western and central Siberia and stability of the forest limit in Beringia. Projection of the effect of a continued exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects, suggests a potential for larger changes in Arctic ecosystems during the 21st century than have occurred between mid-Holocene and present. Simulated physiological effects of the CO2 increase (to >700 ppm) at high latitudes were slight compared with the effects of the change in climate.

Vegetation-pollen-climate relationships for the arcto-boreal region of North America and Greenland

We examine modem pollen, vegetation and climate relationships for the arcto-boreal region of North America using isopollen maps, scatter diagrams and re- sponse surfaces. These analyses are based on an array of 1119 modern pollen sites extending from Alaska to Green- land (excluding the Pacific-Cordillera region of western North America) and north of 42?N latitude. The pollen sum consists of thirty-one taxa selected for their abundance on the modern landscape or significance as indicators of par- ticular vegetation types. Response surfaces were calculated using a locally weighted-average procedure in order to display the percentages of the various taxa as a function of one to three climate variables. The isopoll maps accurately reflect taxa abundance and range limits, although the actual percentage at these limits may vary. Pollen of the major boreal taxa have optima at 10-20?C and dry (Pinus), moist (Abies) and intermediate (Picea) values of precipitation. Monospecific pollen taxa and those where the species have similar ecologies show a simple climate optimum, whereas pollen taxa with several species, such as Betula, show multiple optima. Each boreal taxon, even those with similar ranges, has a unique surface, suggesting that community level responses to climatic change, whether past or future, are likely to be complex and variable throughout North America.

Climate change and Arctic ecosystems: 1. Vegetation changes north of 55 degrees N between the last glacial maximum, mid-Holocene, and present

A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55°N at the last glacial maximum (LGM) and mid-Holocene (6000 years B.P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (∼200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (∼200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.

Thermoluminescence dating of an Arctic lake core from Alaska

Abstract Eight samples were selected from a 14 m core record from Squirrel Lake in the Alaskan Arctic for fine-grain, partial bleach thermoluminescence (TL) dating. Nine radiocarbon ( 14 C) ages were available for comparison. Three TL ages of 8.8 to 11.6 ka in the upper 2.5 m do not exceed calendar-corrected 14 C ages, suggesting that zeroing of light-sensitive TL in the detrital feldspars has been effective enough in this depositional environment to allow accurate dating of deeper core samples of similar sedimentology. TL ages of 60–65 ka for two samples in the 4.9–7 m depth range are consistent with an ‘infinite’ 14 C age of >38.6 ka at 5.8 m. TL ages from 83±11 to 125±31 for three samples in the depth range 11–13.5 m suggest that this core record encompasses the last interglacial period (80–130 ka). These first TL ages for sediments from an Arctic lake core demonstrate the potential of the method for providing a directly measured chronology beyond the radiocarbon dating range in the climatically sensitive Arctic regions.

Arctic Tundra Biodiversity: A Temporal Perspective from Late Quaternary Pollen Records

During the Quaternary (the last ca. 2 milhon years), the earth’s climate has oscillated between numerous predominantly warm or cold periods, causing dramatic changes in the distribution and composition of plant communities worldwide (Bradley 1885; Bartlein 1988; Bartlein and Prentice 1989). Arctic tundra has been particularly affected because large temperature fluctuations and the growth of continental ice sheets have extensively altered vegetation at high latitudes (Climap 1981; Bradley 1985). Since future warming is predicted to be greatest at high latitudes (e.g. Schlesinger and Mitchell 1987; Hansen et al. 1988), tundra will most likely continue to undergo significant change. Understanding the effects of potential chmatic change on tundra biodiversity requires a variety of research approaches. In this effort, information on long-term responses of tundra to past climatic variations can complement results of shorter-term observations and experiments on contemporary landscapes.

Continuous record of environmental changes in Chukotka during the last 350 thousand years

The comprehensive study of the upper 1283 cm of sediment from Lake El’gygytgyn, which formed nearly 4 Ma ago following a meteorite impact in northern Chukotka, yielded the first continuous record of the extreme changes in the Beringian climate and vegetation from the middle Middle Pleistocene to recent time (equivalent of marine isotope stages of 1–7 and the upper part of isotope stage 8). During this period, the climate was warmer than at present between 8600 and 10 7000 14C years and during the Late Pleistocene (isotope substage 5e, 116–128 ka ago). In 2003, the German-Russian-USA expedition continued studying sediments of Lake El’gygytgyn to obtain new evidence of the change in the vegetation cover in the Middle Pleistocene and the first information on the Middle Pleistocene interglacial (isotope stage 9; 297–347 ka ago). Pollen spectra characterizing the Middle Pleistocene interglacial are similar to spectra of the early stage of the Early Pleistocene interglacial and the climatic optimum in the Pleistocene to Holocene transitional period. The climatic history of Lake El’gygytgyn is basic for stratigraphic interpretations and correlations in the eastern sector of the Arctic. These data also expand our understanding of climatic changes that are studied within the framework of the “Pole-Equator-Pole Paleoclimate,” “Past Global Changes,” and other international projects.

First Lake Record of Holocene Climate and Vegetation Change of the Northern Kuril Islands

Investigation of Pernatoe Lake sediments in the south of Paramushir Island has enabled us to obtain the first continuous pollen record of climate and vegetation changes in the north of the Kurile archipelago during the Holocene. Series of radiocarbon datings of between 10 000 ± 40 and 2180 ± 40 years ago are evidence that the beginning of sediments accumulation, found after borehole development, is related to the Early Holocene. Diatom analysis has shown several stages in the lake development: raised bog on the border of the Pleistocene and Holocene, lagoon formation resulting from the sea level rise over 9–6 ky, and freshwater lake formation 6 ky and up to the present. Climate warming during the period attributed to the boreal and Atlantic periods of the Holocene is reflected by the dominance of Pinus pumila and Alnus serrulata assemblages in vegetation cover. Wide dune fields were formed in the Sea of Okhotsk and the Pacific shores of Paramushir Island 5–4 ky. Strengthening of atmogenic processes is related to cooling of the climate and drying of some areas of the underwater slope.

Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

ABSTRACT Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000–11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000–9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000 and 9000 cal. yr BP.

First data on the expansion of Larix gmelinii (Rupr.) Rupr. into arctic regions of Beringia during the early Holocene

The international program on paleoclimates of El’gygytgyn Lake contemplates the study of different genetic types of sediments established in its basin. The lake, which provided one of the longest continuous climatic records of the Arctic Region, was formed about 4 Ma ago when a meteorite fell in the northern Chukchi Peninsula in the region of 67 ° 30 � N, 172 ° 05 � E [1]. The region belongs to a mountainous variant of a typical tundra subzone [2]. Slopes of the Anadyr Tableland surrounding the lake are occupied by the undershrub‐ lichen tundra. Dwarf birch and willow are encountered on protected areas in valleys of the Enmyvaam River flowing out of the lake and its tributaries (the Anadyr River system). Present-day climatic parameters for El’gygytgyn Lake are as follows: the average temperature is +8.3 ° C for July and ‐28.4 ° C for January; average precipitation is 47.4 mm in July and 21.5 mm in January. A series of radiocarbon ages (figure) accompanies the palynological and paleocarpological analyses of loose deposits exposed in the scarp of the 4-m terrace of the Ol’ga Creek running into the Enmyvaam River on the left at a distance of 1 km from the lake (67 ° 26 � 45 � N, 172 ° 13 � 14 � E). The first age (9125 ± 30 years ago, MAG-994) in this series was established for a large trunk of alder ( Duschekia fruticosa ) found in peat at the depth of 163 cm (figure). This age and two other ages for fragments of shrub branches: 9250 ± 90 years ago (MAG-1477), at the depth of 172 cm, and 8120 ± 25 years ago (MAG-1478), at the depth of 150 cm, allow for correlating the peat formation time with the Boreal interval of the Holocene. The age 7770 ± 50 years ago (MAG-1480) established for plant remains from the depth of 109 cm indicates that peat with sand lenses (figure, Bed 5) formed during the period corresponding to the Atlantic interval of the Holocene. The spore-and-pollen diagram of deposits on the terrace comprises three pollen zones (figure). Subdivision of zones is determined by variations in the content of main pollen taxons and each spore taxon calculated in percent out of the total pollen. It is significant that in contrast to spectra of sediments from El’gygytgyn Lake represented by pollen brought by wind from the Anadyr Tableland [1], peat spectra reflect local plant communities. Pollen zone 1 is distinguished as a zone of birch (figure). It is similar to birch pollen zones in climatic records of Beringia lakes and reflects a response of the vegetation cover to climate warming in the period transitional from the Pleistocene to the Holocene [3]. Spore-and-pollen spectra of the zone underline a wide distribution of such shrubby birch species as Betula middendorffii, B. exilis, and B. fruticosa that replaced herb communities of the Last Glaciation [3].

Rock magnetic properties of the lake Pernatoe sediments (Paramushir Island) as an indicator of the changes in sedimentation conditions

Lake Pernatoe is located on Paramushir Island, Kuril Arc, in the area of sand dunes. The 7-m-thick sediments of this lake pertain to the Holocene and contain palustrine, marine, and lacustrine facies. The rock magnetic properties of the sediments are analyzed for tracking the changes in sedimentation conditions. Marine facies are noted with low content of magnetic minerals; their magnetization is dominated by the paramagnetic component; pseudo-single-domain particles of magnetic material and iron sulfides (pyrite) are present. Pyrite frequently occurs in diatoms in the form of chains, spherules, and crystals. The lacustrine facies show high values of the magnetic parameters; they contain multidomain particles, mostly titanomagnetite and magnetite. Sands and sandy silts have the maximum values of magnetic parameters and reflect the stages of aeolian activity, corresponding to climatic cooling and marine regressions. On the basis of magnetic properties, four stages of active aeolian sedimentation are identified in the Holocene.