Monday, May 4, 2015

April snow [updated]

After modest snow accumulation during February and March, April 2015 snowfall at Quelccaya was more typical of the core wet season months. For our 11-year period of record, the median height change during April is 12 cm. However, this year's April snowfall was 460 percent of the median, at 55 cm. This is nearly three times that of the next "snowiest" April (2007) and in 2 of the 11 years there was net ablation during April.

Change in surface height only equate with accumulation in water equivalent if densities are equal, yet our experience indicates that snow density is quite consistent at Quelccaya. Next month we will be on the ice cap to measure density profiles, among other tasks, and will have a more accurate measure of accumulation.

The Landsat image above (23 April) illustrates widespread snowcover on the landscape around Quelccaya above ~4,700 m. Our fieldwork beginning later this month will focus on the area within the red ellipse shown on the image, primarily above 5,200 m. Credit:  USGS EROS data center

[UPDATE 5/20:  Accumulation continues! As of 18 May, a mid-month snowy interval was underway, bringing total accumulation for 2014-15 to exactly the median for the date, at 2.05 meters. One-third of the wet-season snowfall has occurred since the end of March, which is unusually late to have so much snow. We will be on the glacier at the end of the month, and will provide an update towards the end of June.]

Tuesday, January 20, 2015

Margin retreat

Looking through images of "North Lake" recently, this one caught my eye. It was taken on 7 July 2013 while climbing up to the ice cap margin. The view is towards the NW, with ice from the north side of Qori Kalis valley visible in the upper right-hand corner. Note that much of the lake surface is frozen, which is typical during the dry season when air temperature is lower and clear sky at night allows radiational cooling. In the portion of the lake barely visible to the right, blocks of ice were strong enough (for Carsten) to walk out onto.

Prior to ~1985 this lake did not exist, having been buried beneath ice cover for 4,700 years (Thompson et al., 2013). As the margin retreated, meltwater was impounded by bedrock which is out of view to the left, and lake formation almost certainly hastened ice retreat. Now note the section of ice within the blue ellipse above, and try to find it here:

This image is a different perspective, a wider field of view (81°) from the peninsula of bedrock just beneath the blue ellipse. It was taken only 15 months later, on 13 October 2014, and a large volume of ice is gone entirely! Here is part of this section in 2012, with a person for scale. This lower image can be explored in greater detail here, and the GigaPan below provides yet another perspective on the lake, also from October 2014.

Retreat of the glacier will likely continue this year, and soon, the margin will no longer be in contact with the lake. Within the past few decades, a series of proglacial lakes have similarly formed in the area due to ice retreat, including the well-documented Qori Kalis, and several others. Efforts continue to understand the rate of ice-volume change underway, as well as the implications for natural and human systems.

Monday, November 24, 2014

October panoramas

Above is one of three recently-posted GigaPan images from October fieldwork at Quelccaya, with different depictions of the ice cap's western margin (available here for browsers w/o Flash plug-in).

The image above is a 92° field of view with a relatively short focal length (42 mm), looking to the south. Virtually the entire landscape visible in the panorama was covered by ice during the late Holocene (e.g., 500 years ago or less), and most of the scene was buried only ~40 years ago. For example, the lake at 5,200 m elevation on the left-hand side began forming in ~1985 (Thompson et al., 2013). Along upper portions of the margin seen here (i.e., center of image) we have measured a retreat rate of ~10 m/yr over the past decade, in addition to thinning.

This panorama illustrates the extent to which the glacier controls local hydrology, which is also the case on a regional scale. Areas of bedrock scoured by ice often contain lakes, and areas of sediment deposition (i.e., moraines) are often responsible for development of wetlands upstream. Lakes, streams, and wetlands (bofedales) are all sustained by glacier meltwater, especially through the dry season months of June-August. Without water the landscape is dry and barren, as in this image. Throughout the Cordillera Vilcanota today, runoff from glaciers supports a tremendous biodiversity - of mammals, birds, reptiles, amphibians, insects and more.

Despite lower air temperature, the transient snowline elevation at Quelccaya progressively increases during the dry season, occasionally depressed by snowfall events. These panoramas were taken during the dry-to-wet season transition, as 2014-15 accumulation was getting underway (as shown here). By late October, the transient snowline had reached approximately 5,400 m, as can be seen above or more clearly in this image. Consequently, all portions of the glacier below this elevation lost mass during 2013-14, despite above-average accumulation at the summit.

Friday, November 14, 2014

AWS moonshadow

The image above isn't likely to win any contests; the beauty of this shot is that it captures a night-time moment at the automated weather station, when we were thousands of kilometers away. This is one of over 7,000 images acquired during a 15 month interval at the Quelccaya AWS by a Pentax K100D Super camera, in an early version of a Harbortronics Time-Lapse system. It nicely demonstrates one of the ways that modern automated stations can include more than sensors making basic weather measurements.

The enclosure is installed looking toward the west, with a fixed field of view. About half of each scene shows the sky (i.e., clouds and all the information they convey about the atmospheric state), while the lower half illustrates the glacier surface, providing information such as snowfall timing, magnitude, subsequent wind re-distribution, and surface texture (see above). In addition, the foreground - only 75 cm from the camera - depicts sections of the tower, a guy cable, the GOES antenna, and a solar panel. Rime ice is easily observed here, during conditions when it develops. Remarkably, both distant and nearby elements of the image are almost always in focus!

This particular photo from 19:05 on 11 July is noteworthy because the only source of light was from a nearly-full moon, rising through clear sky to the east behind the camera. Faintly visible in the western background is a band of clouds; on the right-hand side a mountain in the Cordillera Vilcanota can be seen, ~50 km distant. On the foreground snow is a shadow of the AWS, clearly showing (left to right) an ultrasonic snow sensor, the big Met One T/RH radiation shield, and the RM Young Wind Monitor. EXIF data indicate the shutter speed was 6 seconds, with the aperture at f/4.

Our initial use for this set of hourly images is in aiding quality-control of snowfall measurements. Thanks to two different ultrasonic sensors on this station, raw measurements are usually unambiguous after adjusting for air-path temperature. But sometimes, it can be difficult to assess whether measurements recording a surface height increase are due to a snowfall event, re-distribution of previously-fallen snow, or something rare and unrelated to climate (e.g., jiggling of the tower as accumulation settles).

Getting the time-lapse system to this point hasn't been without frustration, but the result is proving both useful and interesting!

Tuesday, October 28, 2014

October Fieldwork

This year we had an opportunity to conduct fieldwork twice:  as the 2013-14 wet season was concluding last April, and then this month just before accumulation began again. In addition to collecting data and working at the AWS, our visits bracketing the dry season were designed to investigate seasonal changes in the stable isotope composition of accumulation, as well as the extent and effects of meltwater percolation through the snowpack (i.e., mass redistribution).

Collaborating this month with Margit Schwikowski's group from PSI (Switzerland), we also drilled an ice core which will hopefully extend the 2003 ice core record of Lonnie Thompson up to the present. The team of Dr. Theo Jenk, Jogy Schindler & Reto Schild discovered that their lightweight drill was ideally suited for Quelccaya, and they established a new depth record for the equipment! Ironically, drilling was the easy part in some respects, for getting the gear in and out of Perú has required a full 2 weeks of effort by our logistics guru Benjamin Vicencio, Theo, and several diplomats. The ice is currently in a Lima freezer, but we anticipate shipment to PSI this week.

The new drilling is in support of collaboration with Mathias Vuille and John Hurley at the University at Albany, as part NSF-sponsored research examining the climatological history of the South American summer monsoon. An overview of this project is available here.

The image above was taken late in the afternoon by Reto Schild near our main camp at 5,200 m. It nicely depicts Cordillera Vilcanota weather and environment during late October this year - aspects of which will be discussed and illustrated here in greater detail. Note, for example, dramatic convection caused by increasing atmospheric instability at this time of year. The Vilcanota landscape is a mosaic of starkly contrasting environments, whose attributes were especially apparent this October; extreme 2013-14 accumulation remained on glaciers at the highest elevations, yet with longer days and higher temperatures at this time of year, considerable low-albedo ice was exposed below the transient snowline. As a result, meltwater runoff from glaciers was much greater than that of the core dry season, flooding bofedales and lakes (see image). Where present, water in this landscape supports a fascinating biodiversity, as demonstrated to us nightly by a chorus of frogs outside our tents... in sub-freezing temperatures at 5,200 meters! 

Quelccaya Ice Cap and Vilcanota glaciers are receding rapidly. With their shrinkage, water resources will decline, and lead inexorably to environmental and ecological change. Without meltwater runoff from glaciers during the dry season, the landscape will be very different, as sparse vegetation in the foreground and middle distance suggest. But while the glaciers remain, we are attempting to learn as much as possible about them, the paleoclimate archive they record, and the ecosystems they support.

Wednesday, May 14, 2014

April in the Cordillera Vilcanota

The dry season is an ideal time for fieldwork on Quelccaya Ice Cap, when humidity is low, the atmosphere is stable, and intense solar radiation compensates for annual air temperature minima. Since installing the summit AWS, this is the time of year when we have serviced the station and made snowpit measurements (i.e., June or July). Although weather during our fieldwork has varied considerably from year to year, visiting exclusively during the dry season has provided an incomplete - even biased - perspective on Quelccaya climate.  AWS measurements, of course, demonstrate all the seasonal cycles and patterns, yet cannot substitute for the subjective impressions one gains by actually observing and experiencing weather; both are essential in advancing the understanding of a location's climate.

Recent fieldwork has provided a new perspective on seasonal variability, as a component of NSF-sponsored research with Mathias Vuille & John Hurley (University at Albany, SUNY) examining the South American Summer Monsoon. Our new study is combining onsite measurements, the high-resolution ice-core record, and isotope-enabled model simulations to reconstruct monsoon variations upstream over the Amazon basin for the past millennium.

The images below provide an overview of our most-recent fieldwork, conducted during the transition from a particularly moist wet season to the 2014 dry season.  After two days acclimatizing at ~4,900 meters elevation, we moved up to a camp near the ice cap margin at 5,200 m for a week. Three days were spent at the summit (5,680 m), collecting AWS measurements, servicing the station, measuring and sampling snow for stable isotope and black carbon analysis, and collecting air samples for stable isotope analysis of water vapor (deuterium). Assisting in every aspect of the effort were Felix Benjamín Vicencio and Koky Casteñeda, both among the most-experienced Peruvian mountain guides (AGMP-UIAGM).

In a word, "moisture" was the most-different aspect of the Quelccaya environment in April compared to the dry season. Most obvious were more-numerous streams draining down into flooded, verdant bofedales (wetlands) which were alive with birds and insects, yet the difference in atmospheric humidity was so pronounced that it could be both felt and seen. During the day, visibility (transmissivity) was reduced, towering convection resulting from instability led to near-daily snowfall (esp. graupel), and intervals of solar radiation provided welcome warmth. At night, higher humidity and cloud cover kept the net longwave radiation balance much higher, with notably higher overnight air temperature than during the dry season.

Relative to mid-latitudes, the seasonal air temperature difference at Quelccaya is minor (1-2° C range in mean monthly values), yet at these high-elevations close to the freezing point, the biotic impact appears to be amplified. For example, we observed that the breeding season was underway for many resident bird species during this transitional time. We previously speculated that this might be the case (see here for link to paper) and on this trip we documented breeding by several species. Among our most-exciting discoveries in this realm was the first-ever documentation of an active Diuca speculifera nest, the only bird species known to successfully nest on glaciers (see photo below).

Other results from Quelccaya fieldwork in April will emerge in the months ahead. However, our initial measurements and observations raise concerns about the continually increasing atmospheric freezing level, as well as future changes in monsoon characteristics - both associated with enhanced greenhouse gas concentrations.

Figure 1 (above). Snow-covered landscape of the Cordillera Vilcanota at ~5100 m, slightly below our camp. Note lake, and bofedale in foreground.

Figure 2 (above).  Fresh snow and a small stream in the area around camp at 5200 m, burying all but seed heads of the grass Calamagrostis chrysanth.

Figure 3 (above).  Horses and the Condori family helping to transport equipment down from the glacier (visible in background). In these difficult conditions, we were humbled by their mental and physical toughness, ascending to our camp at dawn - during a snowstorm - wearing rudimentary open-toed sandals. One of the women is carrying her one-year-old (yellow hat) in addition to an even-larger bundle of other items.

Figure 4 (above).   Quelccaya AWS after ~3 m of snow accumulation during the 2013-14 wet season, with our snowpit in background. Note convection to the northeast over Amazonia.

Figure 5 (above).   Snow accumulation for 2013-14 amounted to 2.92 m on 28 April, with 5-10 cm additional early on the 30th. A continuous, 10-cm interval density profile was measured with a 1000 cm^3 Snowmetrics cutter (shown), and 2 sets of snow samples (50 mL tubes at left) were collected and kept frozen during transport.

Figure 6 (above).   One of two active bird nests discovered during fieldwork, the first conclusive evidence of nest building on a glacier by Diuca speculifera (White-winged diuca-finch). Two nestlings were present in this nest, which was completely protected from precipitation and longwave energy loss. Within a crevasse 6-8 m above the ground and accessible only with modern ice-climbing equipment, it was also safe from predators.

 Figure 7 (above).   Evening light on polished bedrock (ignimbrite) at the margin of Quelccaya Ice Cap, 5300 m.

Friday, February 28, 2014

Mean daily air temperature [updated]

Here is the annual cycle of air temperature at Quelccaya (5,680 m), based upon the best dataset available. Each mean daily value is based upon ~4 years of measurements, which are not contiguous due to a power problem in 2010-12; the record has been smoothed slightly for clarity. A previous post (available here) provides some background, and the data will be available here shortly.

Analyses of these and other Quelccaya data are gearing up, working towards publication of a Quelccaya climatology. As illustrated by this graph, some interesting patterns are emerging.

[UPDATE 3/25:  A complete record of quality-controlled hourly air temperatures for July 2007-June 2009 are available here, as well as the accompanying metadata.]