New Zealand Prepared by: Nancy Bertler
email:nancy.bertler@vuw.ac.nz
Objectives
The New Zealand ITASE group at the Antarctic Research Centre, Victoria University, investigates in collaboration with the US ITASE group climate gradients in the McMurdo Dry Valleys region.
The McMurdo Dry Valleys (MDV) are located within the Transantarctic Mountains of South Victoria Land, just off the northern tip of the Ross Ice Shelf. Wedged between the Ross Sea, the East Antarctic Ice Sheet and the Transantarctic Mountains, the MDV combine some of the greatest contrasts found in Antarctica, which are responsible for the climatic extremes of the Region [Keys, 1980].
The MDV mainly consist of three major east-west valley systems: Taylor, Wright and Victoria Valley. The mean annual amplitudes of the air temperature in the MDV region is one of the highest compared to all records from the continent [Keys, 1980]. The large seasonal temperature amplitude of the Dry Valleys is due to higher energy absorption of the dark rocks during summer (which also prevents the development of atmospheric inversion) and increased upward radiation during winter than in comparison the ice and snow covered areas [King and Turner, 1997]. Meteorological data from the former Vanda Station showed that the valley floors are up to 8K warmer in summer and 10K colder in winter than areas of equivalent elevation elsewhere in the Transantarctic Mountains [Chinn, 1978]. During our 2000/2001 season, surface measurements showed that the rock surface in Victoria Valley reached +17?C on a clear, sunny day, while ambient air temperature reached only -8?C. Between mid December and late January, the temperatures are high enough, that some of the alpine glaciers discharge melt streams. All of these streams are located below 1500m altitude [Chinn, 1981], the present-day boundary of all year frost. The largest outflow, the Onyx River, flows during a few days per year for 28km before entering Lake Vanda.
Wind patterns of the MDV are controlled by valley topography, resulting in mainly easterlies and westerlies. In summer, the Dry Valleys display a diurnal regime causing easterlies of 8-10m/s to develop during afternoons and evenings when ground temperatures are highest and westerlies of 0-10m/s during early morning, when solar radiation flux is at its minimum [Hendrikx, 2001]. Sites of higher altitude or which are exposed to the south, such as the Wilson Piedmont Glacier, experience southerly and southwesterly winds, which are part of the larger McMurdo Sound weather system [Keys, 1980].
Victoria Valley not only displays a diurnal but also a seasonal wind pattern. While easterly winds (of the Ross Sea) are dominant during summer and warm periods of the day, westerly winds (of the East Antarctic Ice Sheet) are stronger and common during winter and at night hours. Gusty southerly and southwesterly cyclones are also passing through frequently. A study of the traverse sand dunes and the orientation of ventifacs at Victoria Valley has shown that the dominant wind direction is from the west and suggests that the wind regime was probably unchanged throughout the Quaternary [Keys, 1980].
The NZ ITASE sites have been chosen to capture and quantify the steep climate gradients from the Scott Coast to the Polar Plateau, the local climate system of the McMurdo Dry Valleys, and the effect of altitude within the Transantarctic Mountains. The sites are indicated below.