Vincent Favier

One‐year measurements of surface heat budget on the ablation zone of Antizana Glacier 15, Ecuadorian Andes

tropical Andes of Ecuador (inner tropics). These variables were used to compute the annual cycle of the local surface energy balance (SEB). The four radiative fluxes were directly measured, and the turbulent fluxes were calculated using the bulk aerodynamic approach, calibrating the roughness length by direct sublimation measurements. The meteorological conditions are relatively homogeneous throughout the year (air temperature and air humidity). There is a slight seasonality in precipitation with a more humid period between February and June. During June-September, wind velocity shows high values and is responsible for intense turbulent fluxes that cause reduction of melting. Considering the SEB over the whole year, it is dominated by net radiation, and albedo variations govern melting. During the period under consideration the net short-wave

Irregular tropical glacier retreat over the Holocene epoch driven by progressive warming

The causes and timing of tropical glacier fluctuations during the Holocene epoch (10,000 years ago to present) are poorly understood. Yet constraining their sensitivity to changes in climate is important, as these glaciers are both sensitive indicators of climate change and serve as water reservoirs for highland regions. Studies have so far documented extra-tropical glacier fluctuations, but in the tropics, glacier–climate relationships are insufficiently understood. Here we present a 10Be chronology for the past 11,000 years (11 kyr), using 57 moraines from the Bolivian Telata glacier (in the Cordillera Real mountain range). This chronology indicates that Telata glacier retreated irregularly. A rapid and strong melting from the maximum extent occurred from 10.8 ± 0.9 to 8.5 ± 0.4 kyr ago, followed by a slower retreat until the Little Ice Age, about 200 years ago. A dramatic increase in the rate of retreat occurred over the twentieth century. A glacier–climate model indicates that, relative to modern climate, annual mean temperature for the Telata glacier region was −3.3 ± 0.8 °C cooler at 11 kyr ago and remained −2.1 ± 0.8 °C cooler until the end of the Little Ice Age. We suggest that long-term warming of the eastern tropical Pacific and increased atmospheric temperature in response to enhanced austral summer insolation were the main drivers for the long-term Holocene retreat of glaciers in the southern tropics.

Atmospheric Temperature Measurement Biases on the Antarctic Plateau

AbstractObservations of atmospheric temperature made on the Antarctic Plateau with thermistors housed in naturally (wind) ventilated radiation shields are shown to be significantly warm biased by solar radiation. High incoming solar flux and high surface albedo result in radiation biases in Gill (multiplate)-styled shields that can occasionally exceed 10°C in summer in cases with low wind speed. Although stronger and more frequent when incoming solar radiation is high, biases exceeding 8°C are found even when solar radiation is less than 200 W m−2. Compared with sonic thermometers, which are not affected by radiation but are too complex to be routinely used for mean temperature monitoring, commercially available aspirated shields are shown to efficiently protect thermistor measurements from solar radiation biases. Most of the available in situ reports of atmospheric temperature on the Antarctic Plateau are from automatic weather stations that use passive shields and are thus likely warm biased in the summ...

Mass balance of Glaciar Zongo, Bolivia, between 1956 and 2006, using glaciological, hydrological and geodetic methods

Abstract The longest continuous glaciological mass-balance time-series in the intertropical zone of South America goes back to 1991 on Glaciar Zongo, Bolivia. Photogrammetric and hydrological data have been used to (1) check the specific net balance over long periods and (2) extend the mass-balance time series over the last 50 years. These data reveal a bias in the glaciological mass balance which can be explained by the field-measurement sampling network. Our study shows a large temporal variability of the surface mass balances in the ablation area and reveals strong relationships between independent surface mass-balance data coming from selected ablation areas with numerous data. It demonstrates the very large contribution (80%) of low-elevation ranges (one-third of the surface) to the specific mass balance and, consequently, the importance of the reduction of the area of the tongue. With these new results, Glaciar Zongo offers the longest and most accurate mass-balance series in any Andean country. The dataset shows that Glaciar Zongo experienced a relatively steady state over the period 1956–75, with even a slight mass gain over 1963–75, and a rapid and continuous decrease since then.

Unstable ice stream in Greenland during the Younger Dryas cold event

Past, present, and future ice sheet stability is closely linked to the dynamic behavior of major draining ice streams and surrounding ice shelves. While short observational records document the recent variability and acceleration of ice streams, the long-term dynamics of ice streams remain poorly documented. Here, we date the Pjetursson’s Moraine on Disko Island, Greenland, to 12.2 ± 0.6 ka and demonstrate that the Jakobshavn Isbrae (JI) ice stream collapsed during the middle of the Younger Dryas (YD) cold interval. We suggest that this collapse was due to the incursion of warm subsurface water under the ice shelf fronting the JI ice stream, as well as increased surface-air temperature and sea-surface temperature seasonality starting at the beginning of the YD cold interval. The triggered acceleration of the land-based JI and the delivery of icebergs into Disko Bugt potentially contributed to Heinrich Event 0 at the end of the YD. The collapse of the JI ice stream 12.2 ± 0.6 ka ago demonstrates that calving marine-based ice margins can respond rapidly to environmental changes. It provides a new benchmark for marine-terminating ice stream models.

Evidence of groundwater flow on Antizana ice-covered volcano, Ecuador

Abstract Hydrological and glaciological data were gathered in the watershed (1.37 km2) of the Antizana Glacier 15 (0.7 km2) in the periods 1997–2002 and 1995–2005, respectively. In addition, tracer experiments were carried out to analyse the flow through permeable morainic deposits located between the glacier snout and the runoff gauging station. Over 11 years, the mean specific net balance of the glacier was negative (–627 mm w.e.), despite the occurrence of positive values in the La Niña years (1999–2000). From the glacier net mass balance between 1997 and 2002, it was found that the mean flow originating from ice melt was significantly higher than the mean discharge measured at the hydrological station. Analyses of tracer experiments and of the different components of the hydrological balance suggest groundwater flow that originates below the glacier accounts for the remaining water. This result is important for regional analyses of available water resources and for the relationship between hydro-cryospheric processes and volcanic activity.

Modeling the mass and surface heat budgets in a coastal blue ice area of Adelie Land, Antarctica

Meteorological data recorded from 12 December 2008 to 30 June 2010 were analyzed to assess the surface energy balance (SEB) in a blue ice area of Cap Prudhomme, Adelie Land (66°41′S, 139°55′E). The SEB was computed with a newly developed model forced by direct measurements and with a voluntarily limited number of parameters to better assess model sensitivity. Incoming short‐wave radiation was corrected for the slope and orientation of the local terrain assuming direct and diffuse radiation components. Turbulent heat fluxes were assessed using the bulk aerodynamic approach. Heat conduction in the ice was computed by solving the thermal diffusion equation. Snow accumulation was modeled using ERA interim total precipitation and a one‐dimensional erosion model. The surface heat budget and accumulation/erosion model accurately reproduced field observations. The occurrence of blue ice is linked with higher rates of erosion than in the surrounding snow covered areas, which may be caused by local flow divergence or snow not being redistributed from higher elevations. Melting occurs between December and February when incoming short‐wave radiation is high. However, the SEB was closely linked to air temperature through the incoming long‐wave radiation and the turbulent sensible heat flux. Several warm events caused by cyclones intruding into the continent led to significant warming of the ice and high melting rates. Intruding cyclones were also associated with high precipitation that led to significant accumulation. Except in blue ice areas, modeling suggests that expected higher precipitation in a warmer climate will result in more accumulation.

Paradoxical cold conditions during the medieval climate anomaly in the Western Arctic

In the Northern Hemisphere, most mountain glaciers experienced their largest extent in the last millennium during the Little Ice Age (1450 to 1850 CE, LIA), a period marked by colder hemispheric temperatures than the Medieval Climate Anomaly (950 to 1250 CE, MCA), a period which coincided with glacier retreat. Here, we present a new moraine chronology based on 36Cl surface exposure dating from Lyngmarksbræen glacier, West Greenland. Consistent with other glaciers in the western Arctic, Lyngmarksbræen glacier experienced several advances during the last millennium, the first one at the end of the MCA, in ~1200 CE, was of similar amplitude to two other advances during the LIA. In the absence of any significant changes in accumulation records from South Greenland ice cores, we attribute this expansion to multi-decadal summer cooling likely driven by volcanic and/or solar forcing, and associated regional sea-ice feedbacks. Such regional multi-decadal cold conditions at the end of the MCA are neither resolved in temperature reconstructions from other parts of the Northern Hemisphere, nor captured in last millennium climate simulations.

Atmospheric drying as the main driver of dramatic glacier wastage in the southern Indian Ocean

The ongoing retreat of glaciers at southern sub-polar latitudes is particularly rapid and widespread. Akin to northern sub-polar latitudes, this retreat is generally assumed to be linked to warming. However, no long-term and well-constrained glacier modeling has ever been performed to confirm this hypothesis. Here, we model the Cook Ice Cap mass balance on the Kerguelen Islands (Southern Indian Ocean, 49°S) since the 1850s. We show that glacier wastage during the 2000s in the Kerguelen was among the most dramatic on Earth. We attribute 77% of the increasingly negative mass balance since the 1960s to atmospheric drying associated with a poleward shift of the mid-latitude storm track. Because precipitation modeling is very challenging for the current generation of climate models over the study area, models incorrectly simulate the climate drivers behind the recent glacier wastage in the Kerguelen. This suggests that future glacier wastage projections should be considered cautiously where changes in atmospheric circulation are expected.

Recent glacier decline in the Kerguelen Islands (49°S, 69°E) derived from modeling, field observations, and satellite data

The retreat of glaciers in the Kerguelen Islands (49°S, 69°E) and their associated climatic causes have been analyzed using field data and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images to validate a positive degree-day (PDD) model forced by data from local meteorological stations. Mass balance measurements made during recent field campaigns on the largest glacier of the Cook Ice Cap were compared to data from the early 1970s, providing a 40 year view of the differences in the spatial distribution of surface mass balance (SMB). To obtain additional regional data for the validation of our models, we analyzed MODIS images (2000–2012) to determine if our model was capable of reproducing variations in the transient snow line. The PDD model correctly simulated the variations in the snow line, the spatial variations in the SMB, and its trend with elevation. Yet current SMB values diverge from their classic linear representation with elevation, and stake data at high altitudes now display more negative SMB values than expected. By analyzing MODIS albedo, we observed that these values are caused by the disappearance of snow and associated feedback on melt rates. In addition, certain parts of Ampere Glacier could not be reproduced by the surface energy balance model because of overaccumulation due to wind deposition. Finally, the MODIS data, field data, and our models suggest that the acceleration of glacier wastage in Kerguelen is due to reduced net accumulation and an associated rise in the snow line since the 1970s.