Roy M. Koerner

Holocene climatic records from Agassiz Ice Cap, Ellesmere Island, NWT, Canada:

Four ice cores from the top of the Agassiz Ice Cap and down a flow line have been variously analysed for 8 (18O), ECM (solid conductivity) and ice-melt layer stratigraphy. Stratigraphic correlation of volcanic horizons is used to date the last 8000 years of the cores. The timescales at the Wisconsin/ Holocene transition are pinned at the new GRIP ice-core date. Both 8 and summer-melt records from cores A84 and A87 imply summer temperatures have decreased from 8000 BP to the present by about 2.0°C. Differences in the various 8 series are explained in terms of local drift noise, excessive summer melt and ice flow originating from higher up the local dome where winter snow is scoured away. The present accumulation pattern along the flow line allows one to explain the smoothed differences in the δ records from 8000 BP to the present, but the massive summer melting between 8000 BP and the transition seems to have significantly altered the site and possibly introduced discontinuities. The massive summer melting in the early Holocene alters the volcanic acid (ECM) record in all the cores.

Ice Core Evidence for Extensive Melting of the Greenland Ice Sheet in the Last Interglacial

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested.

Signal and noise in four ice-core records from the Agassiz Ice Cap, Ellesmere Island, Canada: details of the last millennium for stable isotopes, melt and solid conductivity

Four ice cores and two deep pit/auger sequences from the top of the Agassiz Ice Cap have been variously analysed for δ(O18), ECM (solid conductivity) and ice melt-layer stratigraphy. The high- resolution data are presented on time scales covering about the last 1000 years. The 8 time series are compared and the noise examined in terms of snow-drifting and wind-scouring of winter snow from the higher exposed parts of flow lines. The highly scoured 8 records reflect a mixture of summer-biased conditions and the amount of winter-scoured snow. Sites away from the ridges and domes are not scoured. The signal part of the scoured and unscoured sites is obtained by stacking (averaging normalized series). The stacked unscoured series of 8 and accumulation are compared to similar stacked series from central Greenland for the last century of annual averages. The comparison is surprisingly good suggesting that at these resolutions low-noise 8 series have some coherence over fairly large distances. The percentage melt series are presented and compared to those from the Devon Island Ice Cap.

Near-Surface Temperature Lapse Rates over Arctic Glaciers and Their Implications for Temperature Downscaling

Distributed glacier surface melt models are often forced using air temperature fields that are either downscaled from climate models or reanalysis, or extrapolated from station measurements. Typically, the downscaling and/or extrapolation are performed using a constanttemperaturelapserate, which is often taken to be the free-air moist adiabatic lapse rate (MALR: 68‐78 Ck m 21 ). To explore the validity of this approach, the authors examined altitudinal gradients in daily mean air temperature along six transects across four glaciers in the Canadian high Arctic. The dataset includes over 58 000 daily averaged temperature measurements from 69 sensors covering the period 1988‐2007. Temperature lapse rates near glacier surfaces vary on bothdailyandseasonaltimescales,areconsistentlylowerthan theMALR(ablation seasonmean:4.98Ckm 21 ), and exhibit strong regional covariance. A significant fraction of the daily variability in lapse rates is associated with changes in free-atmospheric temperatures (higher temperatures 5 lower lapse rates). The temperature fields generated by downscaling point location summit elevation temperatures to the glacier surface using temporally variable lapse rates are a substantial improvement over those generated using the static MALR. Thesefindingssuggestthatlowernear-surfacetemperaturelapseratescanbeexpectedunderawarmingclimate and that the air temperature near the glacier surface is less sensitive to changes in the temperature of the free atmosphere than is generally assumed.

Mass balance of glaciers in the Queen Elizabeth Islands, Nunavut, Canada

Abstract Mass-balance measurements began in the Canadian High Arctic in 1959. This paper considers the >40 years of measurements made since then, principally on two stagnant ice caps (on Meighen and Melville Islands), parts of two ice caps (the northeast section of Agassiz Ice Cap on northern Ellesmere Island and the northwest part of Devon Ice Cap on Devon Island) and two glaciers (White and Baby Glaciers, Axel Heiberg Island). The results show continuing negative balances. All the glaciers and ice caps except Meighen Ice Cap show weak but significant trends with time towards increasingly negative balances. Meighen Ice Cap may owe its lack of a trend to a cooling feedback from the increasingly open Arctic Ocean nearby (Johannessen and others, 1995). Feedback from this ocean has been shown to be the main cause of this ice cap’s growth and persistence at such a low elevation of <300 ma.s.l. (Alt, 1979). There may be a similar feedback in the lower elevations on Sverdrup Glacier which drains the northwest sector of Devon Ice Cap. The ablation rates there have not increased to the same extent as they have at higher elevations on the same glacier. Although evidence from the meteorological stations in the area shows that the eastern Arctic has either been cooling or has shown no change on an annual basis between 1950 and 1998, the same records show that the summers are showing a slight warming (Zhang and others, 2000). The summer warming, although slight (<1.0˚C over 48 years), is the cause of the weak trend to increasingly negative balances. This is because the mass-balance variability is dominated by the year-to-year variations in the summer balance; there is a very low variability, and no trend over time even within sections of the time series, of the winter balance of the various ice caps and glaciers. Repeat laser altimetry of ice caps by NASA for the period 1995–2000 over most of the ice caps in the Canadian Arctic Archipelago (Abdalati and others, 2004) has shown that the ablation zones are thinning while the accumulation zones show either a slight thickening or very little elevation change. Laser altimetry is revealing similar patterns of change in Greenland (Krabill and others, 2000) and Svalbard (Bamber and others, 2004). The thickening of the accumulation zones in the Canadian case may be due to higher accumulation rates, not just between the two years of laser measurements, but over a period substantially longer than the >40 years of ground-based measurements.

Ice core studies of anthropogenic sulfate and nitrate trends in the Arctic

Ice core studies have shown that sulfate and nitrate concentrations in Arctic snow have increased significantly since the end of the 19th century due to the influx of anthropogenic pollutants transported from industrialized regions. Trends of increasing sulfate and nitrate concentrations in snow are evident in all the ice core data from Greenland, the Canadian Arctic, and Svalbard. Temporal patterns, however, show spatial variation. In the area around Dye 3, south Greenland, significant increases in sulfate are found beginning in the 1890s. Increases in nitrate began ∼50 years later. A similar pattern is seen at Penny Ice Cap, Baffin Island, in the Canadian low Arctic. In contrast, both sulfate and nitrate concentrations started to increase significantly in the 1940s on Agassiz Ice Cap, Ellesmere Island, in the Canadian high Arctic; and Snofjellafonna, Svalbard. At Summit, central Greenland, and sites in north Greenland, sharp sulfate increases occurred at about the turn of the 20th century and again about 1940 or 1950, where the latter increase is the greater of the two. At these central and north Greenland sites, significant increases in nitrate began about 1940 or 1950. The difference between the magnitude and timing of increasing trends of the sulfate ions at these sites can be attributed to their having different source regions and pathways for these pollutant ions. The pollutant sources appear to be North America for south Greenland and Baffin Island, Eurasia, for Ellesmere Island and Svalbard, and both North America and Eurasia for central and north Greenland.

Predominance of industrial Pb in recent snow (1994–2004) and ice (1842–1996) from Devon Island, Arctic Canada

Predominance of industrial Pb in recent snow (1994-2004) and ice (1842-1996) from Devon Island, Arctic Canada

Variability of Sea-Ice Extent in Baffin Bay over the Last Millennium

Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.

Inter-comparison of Ice Core δ(18O) and Precipitation Records from Sites in Canada and Greenland over the last 3500 years and over the last few Centuries in detail using EOF Techniques.

Oxygen -18 records for the Polar sites in Canada and Greenland are compared over the last 3500 years on a 50 yr average basis. The common spatial covariance is found using EOF (Empirical Orthogonal Functions) techniques that identify two main spatial modes that occur with nearly the same frequency. Together these two Eigenvectors explain 50% of the variance in the detrended O-18 records.

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.