Christophe Kinnard

Reconstructed changes in Arctic sea ice over the past 1,450 years

Arctic sea ice extent is now more than two million square kilometres less than it was in the late twentieth century, with important consequences for the climate, the ocean and traditional lifestyles in the Arctic. Although observations show a more or less continuous decline for the past four or five decades, there are few long-term records with which to assess natural sea ice variability. Until now, the question of whether or not current trends are potentially anomalous has therefore remained unanswerable. Here we use a network of high-resolution terrestrial proxies from the circum-Arctic region to reconstruct past extents of summer sea ice, and show that—although extensive uncertainties remain, especially before the sixteenth century—both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years. Enhanced advection of warm Atlantic water to the Arctic seems to be the main factor driving the decline of sea ice extent on multidecadal timescales, and may result from nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation. These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically forced warming.

Internal structure and composition of a rock glacier in the Andes (upper Choapa valley, Chile) using borehole information and ground-penetrating radar

Abstract This study uses boreholes, ground temperature monitoring and ground-penetrating radar (GPR) in order to understand the internal structure and composition of a rock glacier in the upper Choapa valley, northern Chile. The rock glacier is a small valley-side feature, 200 m long and ranging between 3710 and 3780 ma.s.l. Two boreholes were drilled down to depths of 20 and 25 m, respectively, using the diamond drillhole technique. An ice-rock mixture was encountered in the boreholes, with heterogeneous ice content averaging 15-30%. Data from common-midpoint (CMP) and constant-offset (CO) GPR surveys acquired, respectively, near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar-wave velocity. The GPR profiles depict a rock glacier constituted of stacked and generally concordant layers, with a thickness ranging from 10 m in its upper part to ∼30m towards its terminus. The CMP analysis highlights radar-wave velocities of 0.13-0.16 m ns–1 in the first 20 m of the structure. Larger vertical and lateral velocity variations are highlighted from CO data, reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure. Given the average air temperature registered at the site (+0.5°C), the near-melting-point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from GPR data, it is thought that the permafrost in the rock glacier is currently degrading.

Evidencing a large body of ice in a rock glacier, Vanoise Massif, Northern French Alps

Abstract The achette rock glacier is an active rock glacier located between 2660 and 2480 m a.s.l. in the anoise assif, orthern rench lps (45° 29′ , 6° 52′ E). In order to characterize its status as permafrost feature, shallow ground temperatures were monitored and the surface velocity measured by photogrammetry. The rock glacier exhibits near‐surface thermal regimes suggesting permafrost occurrence and also displays significant surface horizontal displacements (0.6–1.3 ± 0.6 m yr–1). In order to investigate its internal structure, a ground‐penetrating radar survey was performed. Four constant‐offset profiles were performed and analyzed to reconstruct the stratigraphy and model the radar wave velocity in two dimensions. Integration of the morphology, the velocity models and the stratigraphy revealed, in the upper half of the rock glacier, the good correspondence between widespread high radar wave velocities (>0.15–0.16 m ns–1) and strongly concave reflector structures. High radar wave velocity (0.165–0.170 m ns–1) is confirmed with the analysis of two punctual common mid‐point measurements in areas of exposed shallow pure ice. These evidences point towards the existence of a large buried body of ice in the upper part of the rock glacier. The rock glacier was interpreted to result from the former advance and decay of a glacier onto pre‐existing deposits, and from subsequent creep of the whole assemblage. Our study of the achette rock glacier thus highlights the rock glacier as a transitional landform involving the incorporation and preservation of glacier ice in permafrost environments with subsequent evolution arising from periglacial processes.

Pre-industrial and recent (1970-2010) atmospheric deposition of sulfate and mercury in snow on southern Baffin Island, Arctic Canada.

Sulfate (SO4(2-)) and mercury (Hg) are airborne pollutants transported to the Arctic where they can affect properties of the atmosphere and the health of marine or terrestrial ecosystems. Detecting trends in Arctic Hg pollution is challenging because of the short period of direct observations, particularly of actual deposition. Here, we present an updated proxy record of atmospheric SO4(2-) and a new 40-year record of total Hg (THg) and monomethyl Hg (MeHg) deposition developed from a firn core (P2010) drilled from Penny Ice Cap, Baffin Island, Canada. The updated P2010 record shows stable mean SO4(2-) levels over the past 40 years, which is inconsistent with observations of declining atmospheric SO4(2-) or snow acidity in the Arctic during the same period. A sharp THg enhancement in the P2010 core ca 1991 is tentatively attributed to the fallout from the eruption of the Icelandic volcano Hekla. Although MeHg accumulation on Penny Ice Cap had remained constant since 1970, THg accumulation increased after the 1980s. This increase is not easily explained by changes in snow accumulation, marine aerosol inputs or air mass trajectories; however, a causal link may exist with the declining sea-ice cover conditions in the Baffin Bay sector. The ratio of THg accumulation between pre-industrial times (reconstructed from archived ice cores) and the modern industrial era is estimated at between 4- and 16-fold, which is consistent with estimates from Arctic lake sediment cores. The new P2010 THg record is the first of its kind developed from the Baffin Island region of the eastern Canadian Arctic and one of very few such records presently available in the Arctic. As such, it may help to bridge the knowledge gap linking direct observation of gaseous Hg in the Arctic atmosphere and actual net deposition and accumulation in various terrestrial media.

Marine aerosol source regions to Prince of Wales Icefield, Ellesmere Island, and influence from the tropical Pacific, 1979–2001

Using a coastal ice core collected from Prince of Wales (POW) Icefield on Ellesmere Island, we investigate source regions of sea ice-modulated chemical species (methanesulfonic acid (MSA) and chloride (Cl−)) to POW Icefield and the influence of large-scale atmospheric variability on the transport of these marine aerosols (1979–2001). Our key findings are (1) MSA in the POW Icefield core is derived primarily from productivity in the sea ice zone of Baffin Bay and the Labrador Sea, with influence from waters within the North Water (NOW) polynya, (2) sea ice formation processes within the NOW polynya may be a significant source of sea-salt aerosols to the POW core site, in addition to offshore open water source regions primarily in Hudson Bay, and (3) the tropical Pacific influences the source and transport of marine aerosols to POW Icefield through its remote control on regional winds and sea ice variability. Regression analyses during times of MSA deposition reveal sea level pressure (SLP) anomalies favorable for opening of the NOW polynya and subsequent oceanic dimethyl sulfide production. Regression analyses during times of Cl− deposition reveal SLP anomalies that indicate a broader oceanic region of sea-salt sources to the core site. These results are supported by Scanning Multichannel Microwave Radiometer- and Special Sensor Microwave/Imager-based sea ice reconstructions and air mass transport density analyses and suggest that the marine biogenic record may capture local polynya variability, while sea-salt transport to the site from larger offshore source regions in Baffin Bay is likely. Regression analyses show a link to tropical dynamics via an atmospheric Rossby wave.

Comparison of the Spatiotemporal Variability of Temperature, Precipitation, and Maximum Daily Spring Flows in Two Watersheds in Quebec Characterized by Different Land Use

We compared the spatiotemporal variability of temperatures and precipitation with that of the magnitude and timing of maximum daily spring flows in the geographically adjacent L’Assomption River (agricultural) and Matawin River (forested) watersheds during the period from 1932 to 2013. With regard to spatial variability, fall, winter, and spring temperatures as well as total precipitation are higher in the agricultural watershed than in the forested one. The magnitude of maximum daily spring flows is also higher in the first watershed as compared with the second, owing to substantial runoff, given that the amount of snow that gives rise to these flows is not significantly different in the two watersheds. These flows occur early in the season in the agricultural watershed because of the relatively high temperatures. With regard to temporal variability, minimum temperatures increased over time in both watersheds. Maximum temperatures in the fall only increased in the agricultural watershed. The amount of spring rain increased over time in both watersheds, whereas total precipitation increased significantly in the agricultural watershed only. However, the amount of snow decreased in the forested watershed. The magnitude of maximum daily spring flows increased over time in the forested watershed.

Historical black carbon deposition in the Canadian High Arctic: a 190-year long ice-core record from Devon Island

Black carbon aerosol (BC), which is emitted from natural and anthropogenic sources (e.g., wildfires, coal burning), can contribute to magnify climate warming at high latitudes by darkening snowand ice-covered surfaces, and subsequently lowering their albedo. Therefore, modeling the atmospheric transport and deposition of BC to the Arctic is important, and historical archives of BC accumulation in polar ice can help to validate such modeling efforts. Here we present a > 250-year ice-core record of refractory BC (rBC) deposition on Devon ice cap, Canada, spanning the years from 1735 to 1992. This is the first such record ever developed from the Canadian Arctic. The estimated mean deposition flux of rBC on Devon ice cap for 1963–1990 is 0.2 mg m−2 a−1, which is at the low end of estimates from Greenland ice cores obtained using the same analytical method (∼ 0.1–4 mg m−2 a−1). The Devon ice cap rBC record also differs from the Greenland records in that it shows only a modest increase in rBC deposition during the 20th century. In the Greenland records a pronounced rise in rBC is observed from the 1880s to the 1910s, which is largely attributed to midlatitude coal burning emissions. The deposition of contaminants such as sulfate and lead increased on Devon ice cap in the 20th century but no concomitant rise in rBC is recorded in the ice. Part of the difference with Greenland could be due to local factors such as melt– freeze cycles on Devon ice cap that may limit the detection sensitivity of rBC analyses in melt-impacted core samples, and wind scouring of winter snow at the coring site. Air back-trajectory analyses also suggest that Devon ice cap receives BC from more distant North American and Eurasian sources than Greenland, and aerosol mixing and removal during long-range transport over the Arctic Ocean likely masks some of the specific BC source–receptor relationships. Findings from this study suggest that there could be a large variability in BC aerosol deposition across the Arctic region arising from different transport patterns. This variability needs to be accounted for when estimating the large-scale albedo lowering effect of BC deposition on Arctic snow/ice.