William N. Mode

Stratified interglacial lacustrine sediments from Baffin Island, Arctic Canada: chronology and paleoenvironmental implications

Thirteen of 18 piston cores recovered from ‘Robinson Lake’ in the mid-Arctic vegetation zone of Baffin Island, Arctic Canada, penetrated stratified lacustrine sediment beneath a thin over-consolidated diamict (till) and postglacial lacustrine sediment. The sub-till lacustrine units are up to 120 cm thick, of which the upper several decimeters frequently contain thick, layered mats of aquatic moss; pollen and diatoms are common throughout both lacustrine units. A series of 23 AMS 14C dates defines the chronology of the postglacial sequence, which records a succession from a pioneer grass- and Oxyria-dominated tundra between 10.4 and 8 ka BP, to a sedge-dominated tundra after 8 ka BP. Limiting 14C dates place the sub-till lacustrine sediments more than 40 ka BP; 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage (OIS) 5. The dominance of shrub and tree pollen, especially shrub birch and alder, in sub-till lacustrine samples, indicates low-arctic tundra farther north than at any time during the Holocene. Pollen concentrations are comparable to or higher than in the Holocene units. Cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section. Diatom floras in both the sub-till and postglacial lacustrine sequences indicate similar development of lake-water chemistry, but input of silica and weathering products was greater in the older lake cycle, suggesting more vigorous catchment processes. Macrofossils in the sub-till units are characteristic of lakes ice-free in summer. Based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the Holocene, we interpret the sub-till lacustrine units to be of interglacial character. By analogy with Holocene plant succession in central and eastern Canada, all of Keewatin and Labrador/Ungava must have been ice free throughout this interval, suggesting essentially complete deglaciation of the Laurentide Ice Sheet at the time.

Deglaciation and postglacial timberline in the San Juan Mountains, Colorado

Lake Emma, which no longer exists because of a mining accident, was a tarn in a south-facing cirque near the headwaters of the Animas River in the San Juan Mountains of southwestern Colorado. During the Pinedale glaciation, this area was covered by a large transection glacier centered over the Lake Emma region. Three radiocarbon dates on basal organic sediment from Lake Emma indicate that by ca. 15,000 yr B.P. this glacier, one of the largest in the southern Rocky Mountains, no longer existed. Twenty-two radiocarbon dates on Picea and Abies krummholz fragments in the Lake Emma deposits indicate that from ca. 9600 to 7800 yr B.P., from 6700 to 5600 yr B.P., and at 3100 yr B.P. the krummholz limit was at least 70 m higher than present. These data, in conjunction with Picea:Pinus pollen ratios from both the Lake Emma site and the Hurricane Basin site of J. T. Andrews, P. E. Carrara, F. B. King, and R. Struckenrath (1975, Quaternary Research 5, 173–197) suggest than from ca. 9600 to 3000 yr B.P. timberline in the San Juan Mountains was higher than present. Cooling apparently began ca. 3000 yr B.P. as indicated by decreases in both the percentage of Picea pollen and Picea:Pinus pollen ratios at the Hurricane Basin site (Andrews et al., 1975). Cooling is also suggested by the lack of Picea or Abies fragments younger than 3000 yr B.P. at either the Lake Emma or the Hurricane Basin site.

HOLOCENE CLIMATE BASED ON POLLEN TRANSFER FUNCTIONS, EASTERN CANADIAN ARCTIC

Transfer functions are developed for a north-south transect in the eastern Canadian Arctic (from Clyde River to Fort Chimo) based on surface pollen samples. The Imbrie/Kipp and multiple stepwise linear regression models are used to show the statistical association between percentages of 19 pollen taxa and climatic variables (January, June, July, and summer temperatures, Youngs index of summer warmth, and summer UJJA] precipitation). Multiple correlation

Land/ocean correlations during the last interglacial/glacial transition, Baffin Bay, northwestern North Atlantic: A review

Abstract Evidence from terrestrial sections, ice cores, and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest North Atlantic during marine isotope stages 5 and 4. The critical physical link between the landbased glacial chronology and marine events in Baffin Bay is the presence of carbonate rich drift along the Baffin Bay coast of Bylot Island and a detrital carbonate facies (Facies B) in Baffin Bay sediments. Cores from Baffin Bay/Labrador Sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards. One occurrence of Facies B is dated between late stage 5 and stage 4 and we correlate this event with the Eclipse Glaciation of Bylot Island and the Ayr Lake stade of the Foxe Glaciation of Baffin Island (= Kogalu aminozone). In contrast on West Greenland, amino acid racemization evidence suggests that the Greenland Ice Sheet developed throughout stage 4 and reached a maximum in stage 3 (Svartenhuk advance >40 ka). The oxygen isotope record in the Devon Island Ice Cap (northwest Baffin Bay) indicates that Baffin Bay was largely open during marine isotope stage 5. Analyses of shallow water molluscan and foraminiferal assemblages, deep-water foraminifera, pollen from Iand sections and deep-sea cores, and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage 5 4 glaciation.

Modern and late Quaternary pollen spectra of fiord sediments, eastern Baffin Island, Arctic Canada

Abstract Pollen spectra of thirty surface samples from Baffin Island fiords are dominated by aBetula/Filicales/Cyperaceae/Gramineae association that is somewhat representative of local or regional vegetation. However,Betula and Filicales are over-represented andSalix, Cyperaceae and Ericales are under-represented compared to their importance in the present vegetation. Two possible causes for this disparity, related to the fluvial processes that furnish most pollen to fiords, are: (1) fluvial reworking of older sediment that contains abundantBetula and Filicales; and (2) greater resistance of these taxa to corrosion and degradation during fluvial transport. The pollen stratigraphy of five piston cores from fiords contains two types of pollen assemblages. In the lower portions of the cores, exotic pollen types and pre-Quaternary palynomorphs are abundant. The upper portions of the cores contain an assemblage roughly representative of the present vegetation, in which Cyperaceae and Gramineae are abundant and exotic and pre-Quaternary types are reduced or absent. The lower assemblage was deposited during the late glacial/deglacial transition and deglaciation ca. 12,000 to 6000 B.P., when eastern Baffin Island had little vegetation cover and long-distance transport and reworking were virtually the only pollen sources. A feature of several cores is a major peak in Dinoflagellates about 5000 B.P. This event may be related to the postglacial marine climatic optimum in the eastern Canadian Arctic between 5000 and 3000 B.P.

A 1400-Year Bølling-Allerød Tree-Ring Record from the U.S. Great Lakes Region

Abstract Since the late 19th Century, geologists and naturalists working in the US Midwest have reported an abundance of tree macrofossils embedded in glacial and lacustrine deposits formed after the Last Glacial Maximum. The most widely-known of these sites is the Two Creeks type locality in Wisconsin. We report progress on development of a long tree-ring record from this subfossil wood in the US Great Lakes region, employing samples collected during a decade-long series of field campaigns at recently eroded lake shorelines, construction projects, and excavations, along with acquisition of archived samples collected from the 1950s to the 1980s during past lake erosion events. A previously-reported tree-ring chronology from the Two Creeks type locality reached ca. 250 years in length; here we used radiocarbon dates and tree-ring crossdating to develop a 1408-year tree-ring chronology (mainly spruce [Picea spp.] with some tamarack [Larix]) comprising a total of 135 overlapped tree-ring width series in three clusters from nine locations in eastern Wisconsin. The calendar age of the record is estimated with 46 14C dates to between 14,500 to 13,100 cal BP. This is currently the oldest and only long tree-ring record in North America from the boreal environments of the Bølling-Allerød warm period during the transition from the Late Glacial to the Holocene.