Jocelyne Bourgeois

Seasonal and interannual pollen variability in snow layers of arctic ice caps

Abstract The pollen content of snow, deposited at the summit of three ice caps and a small glacier in the Canadian Arctic and at one ice cap in the Russian Arctic, was determined for periods ranging from one to 13 years. On the ice caps, boreal forest trees and low arctic shrubs account, on average, for 26% to 49% of the total pollen. On the small glacier, the assemblages are characterized by about 90% tundra pollen types. Sphagnum , which is rare in the region, is sometimes one of the major components of the assemblages at these sites. The concentration of the various pollen types varies in the annual snow pack. The concentration of tundra pollen usually increases in the summer melt layer, but on some ice caps the highest concentrations are found in snow deposited after the melt season. Concentrations of tree/shrub pollen increase substantially in the late winter/spring snow layer and/or in the summer melt layer. The number of tree/shrub pollen reaching the ice caps varies considerably from year to year, and this variability increases with decreasing distance to treeline.

Paleoenvironments of the Canadian high arctic derived from pollen and plant macrofossils: Problems and potentials

Abstract Analyses of peat sections, lake sediments and ice cores provide information about Late-Quaternary arctic environments. Palynomorphs and plant macrofossils from each of these three types of sediments record different aspects of the environment with particular spatial and temporal scales of resolution. In the Arctic, the limits to the interpretation of past environments are particularly significant. Problems of low pollen concentrations, long-distance transport, stratigraphic inversions and contamination by fossils from older deposits are more serious in this region due to the biogeographic context that characterizes these high latitudes and influences the particular ecological and geomorphological processes. However, recent work has shown that past environments can be reconstructed from evidence preserved in high arctic sediments and ice cores, if these problems are taken into account before their interpretation.

Natural variability of Arctic sea ice over the Holocene

The area and volume of sea ice in the Arctic Ocean is decreasing, with some predicting ice-free summers by 2100 A.D. [Johannessen et al., 2004]. The implications of these trends for transportation and ecosystems are profound; for example, summer shipping through the Northwest Passage could be possible, while loss of sea ice could cause stress for polar bears. Moreover, global climate may be affected through albedo feedbacks and increased sea ice production and export. With more open water, more new sea ice forms in winter, which melts and/or gets exported out of the Arctic.

Spatial patterns of pollen deposition in arctic snow

The pollen content of 77 snow samples, collected at 41 sites in the Canadian Arctic, the adjacent Arctic Ocean and Greenland can be used to identify source regions that produced the assemblages. The major vegetation zones of northern Canada produce distinctive pollen assemblages, and principal components analysis (PCA) indicate that these assemblages are retained even in snow on the sea ice surface. It is shown that pollen percentages and concentrations are related to the density of the regional vegetation and to the distance to the source of more productive regions. Because the pollen grains may be transported for great distances (even to the central regions of the Arctic Ocean), they may be used to indicate the source of that pollen and the trajectory of the air masses that carried and deposited them. Pine is particularly valuable in this sense because it has longer trajectories than other tree pollen. For example, there are indications of “over-the-pole” transport of pollen from higher pine pollen concentrations at the North Pole than on northern Ellesmere Island. Pollen concentrations of certain taxa change significantly at ∼75°N, north of which the concentrations become lower, thereby suggesting that there is a climatic boundary at that latitude. Therefore it would appear that studies of the concentration of pollen in snow have the potential for determining past and present characteristics of atmospheric circulation and also for helping in the development and interpretation of paleoenvironmental records in regions without vegetation, such as ice caps.

Pollen Analysis and Discussion of Time-Scales in Canadian Ice Cores

Previous pollen analyses of ice cores from Devon and Ellesmere islands have contributed considerably to our knowledge of past climate in the Canadian High Arctic. In this case, in 1979, bulk (35-83 litres) water samples were melted down a hole 139 m deep, drilled to bedrock, 1.2 km from the top of the flow line in Agassiz Ice Cap in northern Ellesmere Island. Analysis of ten of these samples, plus some taken in very dirty ice from the melt tank during drilling 7 years ago, has yielded pollen concentrations that, together with the oygen-isotope (6) signatures, suggest the Agassiz Ice Cap began its growth during the last interglacial period. A discrepancy between melt-tank and bulk-sample pollen concentrations is believed to be due to a loss of pollen from the melt-tank samples during the drilling process. INTRODUCTION Cores drilled from surface to bedrock at the tops of Devon Island ice cap and Agassiz Ice Cap (Table I) all show three major oxygen-isotope (6) stages. These are shown on the 6 profile from the A 79 core. We use this core for reference, as it is closer to the top of its flow line than the other three (Table I). Its ice has therefore suffered less deformation, so that its climatic record is the least disturbed of the four cores. The same general sequence also appears in the much deeper surface-to-bedrock cores from Camp Century and Dye 3 in Greenland (Dansgaard and others 1982). The upper two sections (A and B in Fig.l) have unequivocally been considered in all cases as Holocene (A) and Wisconsinan (B) in age. Identification of the OrIgm of section C is less certain. The upper boundary of the approximately equivalent section C in the Camp Century core was originally dated at 65 ka (Johnsen and others 1972) and, by alignment with the same core, Paterson and others (1977) assumed the same date for the upper boundary of the same section in the 072 and 073 cores from Devon Island ice cap (Table I). Comparison TABLE I. BORE-HOLE DATA Location Core no. Elevation Year Distance down ma.s.l. drilled flow line km Devon Island D72 180

High Arctic Holocene temperature record from the Agassiz ice cap and Greenland ice sheet evolution

Significance Reconstructions of past environmental changes are important for placing recent climate change in context and testing climate models. Periods of past climates warmer than today provide insight on how components of the climate system might respond in the future. Here, we report on an Arctic climate record from the Agassiz ice cap. Our results show that early Holocene air temperatures exceed present values by a few degrees Celsius, and that industrial era rates of temperature change are unprecedented over the Holocene period (∼12,000 y). We also demonstrate that the enhanced warming leads to a large response of the Greenland ice sheet; providing information on the ice sheets sensitivity to elevated temperatures and thus helping to better estimate its future evolution. We present a revised and extended high Arctic air temperature reconstruction from a single proxy that spans the past ∼12,000 y (up to 2009 CE). Our reconstruction from the Agassiz ice cap (Ellesmere Island, Canada) indicates an earlier and warmer Holocene thermal maximum with early Holocene temperatures that are 4–5 °C warmer compared with a previous reconstruction, and regularly exceed contemporary values for a period of ∼3,000 y. Our results show that air temperatures in this region are now at their warmest in the past 6,800–7,800 y, and that the recent rate of temperature change is unprecedented over the entire Holocene. The warmer early Holocene inferred from the Agassiz ice core leads to an estimated ∼1 km of ice thinning in northwest Greenland during the early Holocene using the Camp Century ice core. Ice modeling results show that this large thinning is consistent with our air temperature reconstruction. The modeling results also demonstrate the broader significance of the enhanced warming, with a retreat of the northern ice margin behind its present position in the mid Holocene and a ∼25% increase in total Greenland ice sheet mass loss (∼1.4 m sea-level equivalent) during the last deglaciation, both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern Greenland.

The effects of flowline length evolution on chemistry - δ18O profiles from Penny Ice Cap, Baffin Island, Canada

Abstract The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland, and Penny Ice Cap, Baffin Island, Canada, are compared. the usual pattern of low δ 18O, high Ca2+ and high Cl– is presented in the Summit records, but Penny Ice Cap has lower than present Cl– in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. the low ice-age Cl– from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit’s flowlines all start close to the present site. the Penny Ice Cap early-Holocene δ 18O’s had to be corrected to offset the Laurentide meltwater distortion. the analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about 500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity.