Hypsithermal Period Research Articles

Climate change and long-term human behaviour in the Neotropics: an archaeological view from the Global South.

In this paper, we argue for the inclusion of archaeology in discussions about how humans have contributed to and dealt with climate change, especially in the long term. We suggest Niche Construction Theory as a suitable framework to that end. In order to take into account both human and environmental variability, we also advocate for a situated perspective that includes the Global South as a source of knowledge production, and the Neotropics as a relevant case study to consider. To illustrate this, we review the mid-Holocene Hypsithermal period in the southern Puna and continental Patagonia, both in southern South America, by assessing the challenges posed by this climate period and the archaeological signatures of the time from a Niche Construction Theory perspective. Finally, we emphasize the importance of these considerations for policymaking. This article is part of the theme issue 'Climate change adaptation needs a science of culture'.

Preface: Functional biogeography in Japanese cedar

Preface: Functional biogeography in Japanese cedar

Paleoenvironmental reconstruction of Quaternary valley-fill successions in summit paleosurfaces of southern Sierras Pampeanas (Córdoba Province, Argentina)

Climatic and environmental changes were inferred from the study of Late-Quaternary sequences that represent paleo-valleys filling in the summit pampas at the center-South of the Sierra de Comechingones, Córdoba Province, Argentina. A representative sedimentological section (P1) was described and sampled, and sediments age (14C), granulometric characteristics and organic matter content were determined. In the analyzed succession four main stratigraphic units were recognized and interpreted. The stratigraphic and pedological characteristics, diatom levels presence, geomorphological features and altitude conditions of the study area allow us to conclude that: 1) Valley-fill deposits are Holocene (from 8310 ± 110 yr BP to present days) and composed exclusively of loessic/loessoid material from surrounding areas. 2) The dominant transport mechanism could have been laminar and/or hyperconcentrated flows, mainly associated with slope evolution processes (sheet flow and high density flows). 3) Isolated swamps with important biological activity were the dominated environments in to the valleys. These environments suggest an alternating pedogenic cycles, were the most important was the Middle-Late Holocene, indicating a landscape stabilization tendency (4330 ± 130 yr BP). 4) Temperate-wet climatic conditions and high seasonality characterized Middle-Early Holocene (Hypsithermal period). More arid conditions dominated Late Holocene. From 1500 to 1000 BP to the present temperate-wet climatic conditions occurred, and this period was interrupted by the Little Ice Age. 5) In the mountains, both in wet and dry periods, the rainfalls were probably higher as well as the temperature must be lower than the surrounding plain, especially in winters, perhaps reaching periglacial conditions during more arid periods.

Peatland succession and long-term apparent carbon accumulation in central and northern Ontario, Canada

Despite their importance as globally significant carbon (C) stores, basic knowledge of post-glacial peatland history and C accumulation are lacking for the Canadian Boreal Shield and James Bay Lowland (JBL) of central and northern Ontario, Canada. Radiocarbon dates, plant macrofossil analysis, and soil C estimates from an eight-core transect of the JBL and surrounding regions are used to reconstruct the timings and patterns of fen to bog transitions, and the ranges and patterns of long-term apparent rate of C accumulation (LARCA). Peatland initiation lagged the retreat of the Laurentide ice sheet, the drainage of glacial lakes, and isostatic uplift by 810–6050 years. Transition from Carex-dominated fen to Sphagnum-dominated bog had a median timing of 3500 years following peatland establishment and ranged from 640 to 6970 years. LARCA was variable geographically and over time with median values ranging from 13.4 to 31.6 g C/m2/yr. LARCA anomalies were generally high ~6.1 kyr (kyr = 1000 calibrated years before present (cal. yr BP)) for southern sites, and ~2.5 kyr for the most northern sites, and may be associated with elevated moisture as inferred from a brief review of regional proxy reconstructions. Some sites displayed high LARCA anomalies, changes in plant ecology, or southern site initiation, which may have also been driven by a moist Hypsithermal Period occurring ~4.5 kyr. LARCA increases were not generally associated with high-temperature anomalies during the warm ‘Medieval Climate Anomaly’ compared with the cooler ‘Little Ice Age’; however, there is evidence that the establishment of modern permafrost during the late-Holocene negatively affected C accumulation.

Sea ice diatom contributions to Holocene nutrient utilization in East Antarctica

Combined high-resolution Holocene δ30Sidiat and δ13Cdiat paleorecords are presented from the Seasonal Ice Zone, East Antarctica. Both data sets reflect periods of increased nutrient utilization by diatoms during the Hypsithermal period (circa 7800 to 3500 calendar years (cal years) B.P.), coincident with a higher abundance of open water diatom species (Fragilariopsis kerguelensis), increased biogenic silica productivity (%BSi), and higher regional summer temperatures. The Neoglacial period (after circa 3500 cal years B.P.) is reflected by an increase in sea ice indicative species (Fragilariopsis curta and Fragilariopsis cylindrus, up to 50%) along with a decrease in %BSi and δ13Cdiat (< −18‰ to −23‰). However, over this period, δ30Sidiat data show an increasing trend, to some of the highest values in the Holocene record (average of +0.43‰). Competing hypotheses are discussed to account for the decoupling trend in utilization proxies including iron fertilization, species-dependent fractionation effects, and diatom habitats. Based on mass balance calculations, we highlight that diatom species derived from the semi-enclosed sea ice environment may have a confounding effect upon δ30Sidowncore compositions of the seasonal sea ice zone. A diatom composition, with approximately 28% of biogenic silica derived from the sea ice environment (diat-SI) can account for the increased average composition of δ30Sidiat during the Neoglacial. These data highlight the significant role sea ice diatoms can play with relation to their export in sediment records, which has implications on productivity reconstructions from the seasonal ice zone.

Sub-Boreal aggradation along the Apennine margin of the Central Po Plain: geomorphological and geoarchaeological aspects

The Apennine foothills at the southern limit of the Po Plain consist of a belt of coalescent, gravelly, alluvial fans, trending to the north, towards the depocenter of the plain. Their aggradation is generally considered to have been controled by climate and linked to the glacial periods of the Middle and Upper Pleistocene. At the transition from the Upper Pleistocene to the Holocene, aggradation of most of the alluvial fans stopped and their surface was subject to weathering, which resulted in deep, rubified Alfisols (Sols bruns fersiallitiques). These developed mainly during the Boreal and Atlantic periods. Beginning in the Sub-Boreal period, fine-textured alluvial deposits buried the distal margin of the alluvial fans and the soils developed on them. These deposits consist of fine-sized sediments of overbank facies, organised in fining upward sets and intercalated by buried Entisols, Inceptisols and Vertisols. The accumulation of alluvial sediments on the alluvial fans, after the prevailing weathering on their top, indicates a main change in the pedo-sedimentary processes and is related to the climatic change that occured between the end of the Postglacial Hypsithermal period and the beginning of the Neoglacial period. The soils on top of the alluvial fans and in later alluvial deposits show intensive human use and occupation from the Neolithic to the Early Bronze Age, and witness a significant change in land exploitation during the Atlantic/Sub-Boreal transition. During the Neolithic (Atlantic period), agricultural practices linked to shifting agriculture had minimal impact on the vegetation mantle and were limited to the plain areas. By contrast, during the Chalcolithic and the Early Bronze Age (Sub-Boreal period), a rather different mode of land use was adopted, as the result of the newly introduced transhumant pastoralism. Deforestation through slash and burn techniques was very intense and widespread, extending far beyond the boundary of the plain, deep inside the mountain range, affecting the Po Plain and the adjoining Apennines. This case study presents an argument for seeing climate change and human activity (deforestation by fire, agriculture and pastoralism) as synergic phenomena that shaped the prehistoric landscape.

Isotope characterisation of ground ice in northern Canada

AbstractThis paper reviews isotopic research on the characterisation and identification of various types of ground ice throughout the Canadian Arctic, including buried glacier ice, massive segregated ice, segregated ice lenses and offshore ice‐rich permafrost, as well as ice related to other cold‐region phenomena such as ice wedges, icings (aufeis), frost blisters and pingos. The formational age of ground ice bodies ranges from recent (seasonal ice in the active layer) to tens of thousands of years, when the region experienced widespread continental‐scale glaciation. Modern ice lenses generally have 18O/16O ratios of ‐18 to ‐22‰, while modern ice wedges usually range from ‐22 to ‐25‰. δ18O values as high as ‐14‰ are representative of the Hypsithermal period (4000 to 8000 years BP), while glacial‐age ice has been measured with 18O/16O ratios as low as ‐36‰. Buried glacier ice often preserves climatic variations from the time of snow deposition. Other massive ground ice bodies contain isotopic signatures (18O and 2H) that indicate variable fractionation of the isotopes during freezing of the source water at stationary freezing fronts in either open or closed systems. Placing the ice bodies into a time frame can be accomplished either through age dating of the enclosing sediments and encased organics, or by direct dating of the ice utilising tritium (3H) for relatively young ice and radiocarbon (14C) analysis of contained gas bubbles for older ice. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Mind the gap: an absence of valley-fill deposits identifying the Holocene hypsithermal period of enhanced flow regime in southeastern Australia

The Holocene sedimentary record in southeastern Australia is present in a range of landscape settings, such as upland swamps (dells), internally drained lake basins, alluvial fans, and mid-catchment and lowland floodplains. An assessment of the best-constrained basal radiocarbon dates in valley-fill locations between 30 and 42°S and upstream of last-glacial eustatic influences yields an intriguing pattern. The record for fluvial sites with catchment areas &gt; 30 km2 exhibits a distinct gap in the alluvial record between 8 and 4 ka BP (10—4.5 ka). In contrast, data for eleven upland-swamp sites with catchment areas &lt; 50 km2 exhibit a broader spectrum of basal ages, albeit with some reduction of activity during the alluvial gap. We suggest that the period 8—4 ka BP in the sedimentary record at the fluvial sites reflects the early to mid-Holocene climatic optimum independently recognized in proxy climate data in the region. It was a period of enhanced water discharges, stable well-vegetated catchments and low sediment yields, and therefore greatly limited sediment sequestration, and it has been termed the Nambucca Phase. In upland swamps, however, threshold-driven processes produce an episodic landscape responses during much of the Holocene. Contrasting results in upland compared with middle and lower basin locations demonstrate the nonuniform landscape response to climatic changes during the Holocene in southeastern Australia.

Population genetic consequences of geographic disjunction: a prairie plant isolated on Great Lakes alvars

Species may often exhibit geographic variation in population genetic structure due to contemporary and historical variation in population size and gene flow. Here, we test the predictions that populations on the margins of a species' distribution contain less genetic variation and are more differentiated than populations towards the core of the range by comparing patterns of genetic variation at five microsatellite loci between disjunct and core populations of the perennial, allohexaploid herb Geum triflorum. We sampled nine populations isolated on alvar habitat within the eastern Great Lakes region in North America, habitats that include disjunct populations of several plant species, and compared these to 16 populations sampled from prairie habitat throughout the core of the species' distribution in midwestern Canada and the USA. Alvar populations exhibited much lower within-population diversity and contained only a subset of alleles found in prairie populations. We detected isolation by distance across the species' range and within alvar and prairie regions separately. As predicted, genetic differentiation was higher among alvar populations than among prairie populations, even after controlling for the geographic distance between sampled populations. Low diversity and high differentiation can be accounted for by the greater contemporary spatial isolation of alvar populations. However, the genetic structure of alvar populations may also have been influenced by postglacial range expansion and contraction. Our results are consistent with alvar populations being founded during an expansion of prairie habitat during the warmer, hypsithermal period approximately 5000 bp and subsequently becoming stranded on isolated alvar habitat as the climate grew cooler and wetter.

歴史時代の気候変動に関する研究の展望

Recent studies on climate change during the historical period are reviewed in this paper. Firstly, methods, limitations and materials for reconstructing past climates are summarized. Historic diaries and old documents are useful particularly for the period of the past 500 years. Some indices for expressing the climatic conditions found in the historic materials are introduced. Historic documents and materials found in China since 4, 000 BP were published in 2004. On the other hand, daily weather data at several stations for the 15 and 16 centuries in Japan were published in 2004 and 2006, respectively. Secondly, the “Little hypsithermal (warm) period” during the period from the 4th century to the 10th century is described. In the final part of the present paper, examples of an ancient central government in Japan, planning of Heijoukyou (an old center of government), settlements developed on the Boso Peninsula, Chiba, Japan, and parallel activities in Southeast Asia are discussed in relation to the changing climate during the “Little climatic optimum” from the 8th century to 9th century, which was the peak of the “Little hypsithermal (warm) period”. It is pointed out that the changes were roughly in parallel.

Millennial surface water dynamics in the Ría de Vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers

A combined study of coccolith assemblages and biomarkers in a gravity core collected from the Ría de Vigo (NW Spain) allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years. The quantitative distribution of coccolithophore species points to three different intervals within the core, dated by AMS radiocarbon measurements. The first interval (ca. 975 BC–252 AD), characterized by high abundances of Calcidiscus leptoporus and Gephyrocapsa muellerae, is thought to represent moderate water temperatures, suggesting a transition from a warmer to a cooler period. The second interval (ca. 252–1368 AD), characterized by the dominance of Coccolithus pelagicus, Helicosphaera carteri and Syracosphaera spp., and a high concentration of hexacosanol linked to terrestrial input, is interpreted as having been a humid period with fluvial input. The third interval (ca. 1368 AD–1950) is characterized by a high abundance of Gephyrocapsa oceanica, high alkenone values and low values of hexacosanol, and is thought to represent a period dominated by oceanic conditions within the Ría. Taking into account the ocean–atmospheric system affecting the region studied, here we propose an alternation in the mean state of North Atlantic Oscillation (NAO) at millennial time scales. A well-developed upwelling system and an active Ría–ocean connection during the warmer interval I suggest a NAO+ phase influenced by a Hypsithermal period. The occurrence of the humid and relatively warm interval II is consistent with a negative phase in the NAO, as well as a relative restriction in ocean–Ría exchange. Interval III, which was drier and more productive, again suggests the dominance of a positive phase in the NAO, with a more intense oceanic connection and more energized upwelling.

Endostromatolites from permafrost karst, Yukon, Canada: paleoclimatic proxies for the Holocene hypsithermal

A remarkable biogenic calcite precipitate forms carpets of finely laminated ~1 mm diameter columns lining fissures within limestone bedrock in the permafrost regions of the northern Yukon. This material, "endostromatolite," for its laminated morphology and growth hidden within the carbonate rock, is ubiquitous within limestone terrains of the Arctic and grew during the early Holocene hypsithermal. Dissolution on the interior fissure faces is accompanied by biomineralization of the opposing faces; a previously unrecognized weathering process in permafrost regions. Occurrence is restricted to outcrops with a southern orientation in permafrost regions, in this case, from the Ogilvie Mountains, northern Yukon. Growth occurs in water-saturated talik during periods of permafrost degradation during insolation maxima. Their enriched δ13C values (–1.7‰ to 11.4‰) are generated in a methanogenic environment during anaerobic degradation of soil-derived organic carbon. A paleotemperature signal extracted from the δ18O values demonstrates that growth occurred during a hypsithermal period with an average summer air temperature 7 ± 2 °C higher than today. Corrected radiocarbon age measurements of the calcite and organic matter preserved within the endostromatolites indicate that biomineralization occurred during the late Pleistocene – early Holocene hypsithermal event. Profiles along the columns document late Pleistocene climate improvement, with maximum warmth coincident with the insolation maximum for 65°N, followed by cooling and end of growth in the mid to late Holocene.

Widespread middle Holocene dune formation in the eastern Upper Peninsula of Michigan and the relationship to climate and outlet-controlled lake level

Research Article| January 01, 2002 Widespread middle Holocene dune formation in the eastern Upper Peninsula of Michigan and the relationship to climate and outlet-controlled lake level Alan F. Arbogast; Alan F. Arbogast 1Department of Geography, Michigan State University, East Lansing, Michigan 48824-1115, USA Search for other works by this author on: GSW Google Scholar Ann G. Wintle; Ann G. Wintle 2Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK Search for other works by this author on: GSW Google Scholar Susan C. Packman Susan C. Packman 2Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Alan F. Arbogast 1Department of Geography, Michigan State University, East Lansing, Michigan 48824-1115, USA Ann G. Wintle 2Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK Susan C. Packman 2Institute of Geography and Earth Sciences, University of Wales, Aberystwyth SY23 3DB, UK Publisher: Geological Society of America Received: 19 Apr 2001 Revision Received: 27 Aug 2001 Accepted: 12 Sep 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2002) 30 (1): 55–58. https://doi.org/10.1130/0091-7613(2002)030<0055:WMHDFI>2.0.CO;2 Article history Received: 19 Apr 2001 Revision Received: 27 Aug 2001 Accepted: 12 Sep 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alan F. Arbogast, Ann G. Wintle, Susan C. Packman; Widespread middle Holocene dune formation in the eastern Upper Peninsula of Michigan and the relationship to climate and outlet-controlled lake level. Geology 2002;; 30 (1): 55–58. doi: https://doi.org/10.1130/0091-7613(2002)030<0055:WMHDFI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Dating of five widely spaced (noncoastal) dunes in eastern upper Michigan by optically stimulated luminescence of quartz establishes that eolian sand was last mobilized between ca. 7 and 5.5 ka in the region. Although this interval corresponds to the drier Altithermal- Hypsithermal period, climate alone may not have been sufficiently arid to cause dune formation in this area. Instead, it appears that dune formation may also be linked to depressed water tables, associated with outlet-controlled low levels in Lakes Michigan and Superior. Following dune stabilization, peat began to accumulate in interdune areas ca. 4.4 ka. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleoecology and its application to fire and vegetation management in Kootenay National Park, British Columbia

High-resolution analysis of macroscopic charcoal and pollen ratios were used to reconstruct a 10,000 yr history of fire and vegetation change around Dog Lake, now in the Montane Spruce biogeoclimatic zone of southeastern British Columbia. Lake sediment charcoal records suggest that fire was more frequent in the early Holocene from 10,000 to 8200 calendar yrs BP, when climate was warmer and drier than today and forest fuels were limited. Fire frequency increased and reached its maximum during the early to mid-Holocene from 8200 to 4000 calendar yrs BP, corresponding to the dry and warm Hypsithermal period in the Rocky Mountains. During the Hypsithermal period forests around Dog Lake were dominated by Pseudotsuga/Larix,Pinus and open meadows of Poaceae that were subject to frequent fire. From 4000 calendar yrs BP to present, fires became less frequent with the onset of cooler and wetter Neoglacial climate and an increase in wet-closed Picea and Abies forests in the valley. Changes in fire frequency are supported by dry-open/wet-closed pollen ratio data indicating that forest type and disturbance regimes vary with changing climate. The fire frequency and forest cover reconstructions from Dog Lake are a first attempt at defining a range of natural variability for Montane Spruce forests in southeastern British Columbia. Fire and vegetation management in Kootenay National Park can now use this century to millennial-scale range of variability to define the context of current forest conditions and potential changes under global warming scenarios.

Climatic changes in the South American plains: Records of a continent-scale oscillation

Abstract The last glacial/interglacial cycle produced a variety of climates and landscape responses in South America. The present contribution is an attempt to establish broad trends within this complex period. Two points are clear: (a) In the Cordillera de los Andes temperature variations produced advances and retreats of glaciers, which were coherent with the global climatic changes recorded in other continents. (b) The lowlands experienced a series of dry and humid periods. Humid intervals in the north of the continent (extending to latitude 10°S) are coeval with dry conditions in the south and vice versa. The broad climatic sequence is as follows: 1. Isotope stage 4 – A massive glaciation affected the whole Cordillera. Humid climate in the north. A large desert developed in the south, associated with wind-blown silts which reached a latitude of 25°S in SE Brazil. 2. Isotope Stage 3 – Mountain glaciers were of modest extent in the Andes. A humid climate with soil development and dune degradation prevailed in the south (Pampa and Chaco) while dry conditions dominated the north (Colombia and Amazonas). 3. Isotope Stage 2 – General advance of glaciers in the Andes, although smaller than in IS4. Dry and cold in the south, with extension of the Patagonian climate to the NE. Humid in Amazonas. The waning of the glaciation was accompanied by a humid environment (pedogenesis) in the Pampa and by a dry phase in the north (forest retreat in Carajas and in the Colombian Andes). Within the period 14,000 BP to 8500 BP (sensu lato Younger Dryas) a glacial advance occurred, with humid conditions in the north (pedogenesis in the Orinoco and forest readvance in Amazonas) and a dry climate characterized by strong westerly winds in the Pampa. 4. The Hypsithermal period was humid in the south and dry in the north of the continent.

Upper Quaternary geology of the lower Carcarañá Basin, North Pampa, Argentina

The geological evolution of the lower Carcarañá Basin reflects a sequence of dry and humid climates. From a geomorphological point of view, the area belongs to the Pampean Eolian System. The geomorphological units comprise several fluvial geoforms, partially masked by a loess carpet, on which eolian erosive forms developed. The sedimentary record is not simple. The typical profile begins with a predominantly eolian unit, composed of silty sand and including two pedogenic levels (Carcarañá Fm). The formation is the result of the reworking of a dune field in the Pampean Sand Sea (IS4). It is upper Pleistocene in age (IS 3). Another, somewhat different, climatic deterioration followed (related to the begining of the Last Glacial Maximum -IS 2), which caused the deposition of a loessic mantle (Tezanos Pinto Fm). Subsequent evolution of the climate involved a shift to humid conditions during the Hypsithermal period, generating a well-developed soil at the top of the formation. An upper Holocene eolian layer (San Guillermo Fm) covers the whole sequence. At the river margins of the basin the late Pleistocene/lower Holocene eolian deposits are replaced by a complex silty–clayey sequence, mainly paludal, with a soil complex in the middle of the section (Lucio Lopez Fm).

The Holocene in the South-Eastern region of the Province Jujuy, North-West Argentina

Abstract The results reported are from three sedimentary sections bordering the Rio Grande and its tributary in San Salvador de Jujuy and surrounding areas. The prevailing precipitation in the area of investigation, at 1200 m elevation, is about 900 mm/yr and increases with altitude to 1300 mm/yr at 1700 m elevation. On the basis of these sections it is possible to recognize two Holocene dry phases and two humid phases. A dry period, from the Late Pleistocene until 8900 yr BP, is evident in the section Los Perales, in the form of a 3 m loess bed, rich in volcanic glass. The Hypsithermal period, beginning 8900 yr BP and ending 6400 yr BP or even later, is identified by two different fossil soil developments in the section Los Perales, as well as by several peat horizons in the section Rio Chico. In the first case, we can recognize intensive soil development in the Early Holocene levels, which can be separated into two soil development phases. These phases are represented by two B-horizons separated by a 15 cm thick loess bed, and are dated by C 14 to 8180±130 yr BP and 6470±100 yr BP. In the case of the Rio Chico section, the peat below a gravel bed was radiocarbon dated to 8930±130 yr BP 7610±130 yr BP, 6970±100 yr BP and 6470±110 yr BP. The middle Holocene in section Los Perales is characterized by a 45 cm thick loess deposit, which reflects predominantly dry conditions. The recurrence of moister conditions and corresponding soil development into vertisols is documented by several palaeosols, the older ones dating to 1340±50 yr BP.

Holocene lake level and climate change inferred from marl stratigraphy of the Cayuga Lake basin, New York

ABSTRACT A series of 12 radiocarbon-dated sediment cores (up to 15 m long) were used to define the Holocene stratigraphy beneath the Cayuga Lake basin in central New York State in order to evaluate the stability of Holocene climate in the northeastern United States. These cores contain an abundance of thick lacustrine marls (> 30% CaCO3) that were used to reconstruct century- to millennium-scale changes in lake levels and, thus, paleoclimates. The oldest sediments recovered (> 11.2 ka) consist of pink, proglacial clays that were deposited in Glacial Lake Iroquois between ~ 12.5 and 11.3 ka. Lacustrine sediment (non-marl) of Killarney-Younger Dryas age (11.2-10.3 ka) was recovered both north and south of modern Cayuga Lake, indicating relatively high lake levels during this well-known cold-climate phase. Following a brief ( The Holocene Hypsithermal period (~ 9-4 ka) in the Cayuga Lake basin was characterized by widespread deposition of marl that locally contains as much as 90% CaCO3. These marls document a broad, first-order warming-cooling trend throughout the Hypsithermal, with the climatic optimum at ~ 7 ka. This long-term trend is consistent with insolation data as well as ice-core records from Greenland, and likely was a response to Milankovitch orbital forcing. Lake levels throughout the Finger Lakes region were relatively high during the Holocene Hypsithermal, implying an overall warm and wet climate in contrast to the traditional view of mid-Holocene drought. However, Hypsithermal climate and lake levels in the Finger Lakes region were not stable; rather they were characterized by significant century- to millennium-scale variability, implying short-term climate changes. Marl deposition in the Cayuga Lake basin ceased at ~ 3.4 ka when lake levels dropped as global cooling set in at the end of the Hypsithermal. However, there was a brief return to a warm and wet climate at ~ 1 ka, during the Medieval Warm Period prior to the onset of anthropogenic effects.

Ice wedges on hillslopes and landform evolution in the late Quaternary, western Arctic coast, Canada

In rolling to hilly areas of the western Arctic coast of Canada, anti-syngenetic wedges, which by definition are those that grow on denudational slopes, are the most abundant type of ice wedge. Through prolonged slope denudation, hilltop epigenetic wedges can evolve into hillslope anti-syngenetic wedges, and some bottom-slope anti-syngenetic wedges, by means of deposition from upslope, can evolve into bottom-slope syngenetic wedges. The axis of a hillslope wedge is oriented perpendicular to the slope, so the wedge foliation varies according to the trend of the wedge with respect to the slope. Because the tops of hillslope wedges are truncated by slope recession, the mean chronological age of anti-syngenetic wedge ice decreases with time, so the growth record for an old wedge is incomplete. Summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the troughs relative to the slope. Wedge-ice uplift, probably diapiric, has been measured. Some hillslope polygon patterns may predate the development of the present topography. Many Wisconsinan wedges, truncated and buried during the Hypsithermal period, have been reactivated by upward cracking.

The Role of Fire in the Development of Sphagnum-Dominated Peatlands in Western Boreal Canada

1 The effect of fire on vegetation development and accumulation rates in Sphagnumdominated peatlands of western boreal Canada was studied through plant macrofossil and physicochemical analyses of two Holocene peat sequences characterized by a large number of macroscopic charcoal layers. 2 Field observations and detailed macrofossil analyses of charcoal horizons indicate that these layers represent local fires that burnt the superficial peat deposit. 3 Peat surface fires do not influence the long-term vegetation development of Sphagnum-dominated boreal peatlands. Vegetation response such as species composition changes in moss cover, if any, is generally limited to a few decades after the fire event. 4 Accumulation rates in Sphagnum-dominated boreal peatlands decrease significantly with increasing fire frequencies. Rates of height of peat accumulation and carbon accumulation would approximate zero with a fiveto sevenfold increase in the frequency of peat surface fires, compared to the average frequency of this type of fire during the last 2500 years. 5 The frequency of peat surface fires at 7000 years BP, in the Hypsithermal period, was about twice as high as during the period 0-2500 BP, in the Late Holocene.