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
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
that this might be the case (see here for link to paper) and on this
trip we documented breeding by several species. Among our
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 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.