- : Ms Word, Ms Word Format
- : 100 Pages
- : ₦5000
- : 1-5 Chapters
- Click to DOWNLOAD Materials
ARE THE DRY VALLEYS GETTING WETTER? A PRELIMINARY ASSESSMENT OF WETNESS ACROSS THE MCMURDO DRY VALLEYS LANDSCAPE
ABSTRACT
Liquid water is scarce across the landscape of the McMurdo Dry Valleys (MDV), Antarctica and is associated with soils that are adjacent to streams and lakes, during the annual thaw season. However, seeps, water tracks, and wet patches have been observed at several other locations as well. The source of water for these is likely generated by a combination of infiltration from melting snowpacks, melting of pore ice at the ice table beneath the water tracks, and melting of buried segregation ice formed during winter freezing. We are using high resolution (<1m pixel) remote sensing data gathered several times per week in the MDV region to determine the spatial and temporal distribution of wet soils. We assess the spatial consistency with which these wet soils occur for the 2008-2009 to 2011-2012 austral summers with complete coverage and partial coverage for 2003-2004 and 2006-2007 austral summers using a land cover classification. We also quantify the soil moisture of wetted soils using an artificial neural network (ANN). The ANN utilizes field radiometer data to retrieve estimates of surface moisture based on the spectral measurements and soil moisture samples collected during the 2010-2011 field season. The remote sensing based analyses of the wetted soils have shown the magnitude to vary greatly and how topography and regional microclimates influence the wetted soils in the
MDV. The 2010-2011 austral summer provided the most wetted soil area, 10.21 km2, and 20082009 covered the least, 5.38 km2. The ANN soil moisture distribution in the MDV shows values ranging from 0.36 % to over 19 %. We suggest that wet soils are a significant component of this cold desert land system and ecosystem.
TABLE OF CONTENTS
LIST OF FIGURES ………………………………………………………………………………………… vi
LIST OF TABLES ………………………………………………………………………………………….. vii
ACKNOWLEDGEMENTS ……………………………………………………………………………… viii
Chapter 1 Introduction to Study ………………………………………………………………………. 1
1.1 McMurdo Dry Valley Background ………………………………………………………… 1
1.2 McMurdo Dry Valley Hydrology ………………………………………………………….. 5
1.3 Water Tracks, Seeps, and Wet Patches ………………………………………………….. 8
1.4 Thesis Approach…………………………………………………………………………………. 11
Chapter 2 Characterizing Spatiotemporal Dynamics of Wetted Soils Across a Polar Desert Landscape, McMurdo Dry Valleys Antarctica……………………………………. 12
2.1 Introduction ………………………………………………………………………………………. 12
2.2 Methods …………………………………………………………………………………………….. 15
2.2.1 Site Selection …………………………………………………………………………….. 15
2.2.2 Satellite Image Processing …………………………………………………………… 16
2.2.3 Topographic Analyses ………………………………………………………………… 23
2.3 Results……………………………………………………………………………………………….. 25
2.3.1 Spatial and Temporal Distributions ………………………………………………. 25
2.3.2 Taylor Valley …………………………………………………………………………….. 28 2.3.3 Wright, Victoria, and Barwick Valley …………………………………………… 32
2.3.4 North Garwood, Marshall, and South Miers Valley………………………… 36
2.3.5 Possible Sources of Wetted Soils …………………………………………………. 40
2.4 Discussion ………………………………………………………………………………………….. 44
2.5 Conclusions ………………………………………………………………………………………… 47
Chapter 3 Satellite-Based Estimates of Soil Moisture using an Artificial Neural Network
Across a Polar Desert Landscape, McMurdo Dry Valleys Antarctica ……………… 49
3.1 Introduction ……………………………………………………………………………………….. 49 3.2 Data Collection and Image Processing ………………………………………………….. 53
3.3 Methodology ……………………………………………………………………………………… 61
3.4 Results………………………………………………………………………………………………. 66
3.4.1 Taylor Valley …………………………………………………………………………….. 69 3.4.2 Wright, Victoria, Barwick, and McKelvey Valley ………………………….. 71
3.4.3 Garwood, Marshall, and Miers Valley ………………………………………….. 75
3.4.4 Comparison of Soil Moisture Values ……………………………………………. 79
3.5 Discussion …………………………………………………………………………………………. 83
3.6 Conclusions ……………………………………………………………………………………….. 87 References ……………………………………………………………………………………………………… 89
Appendix A Taylor Valley Wetted Soil Land Cover Maps …………………………………. 99
Appendix B Wright, Victoria, Barwick, and McKelvey Valley Wetted Soil Land Cover Maps………………………………………………………………………………………………………. 105
Appendix C North Garwood, Garwood, Miers, Marshall and South Marhsall Valley
Wetted Soil Land Cover Maps…………………………………………………………………… 113
Chapter 1
Introduction to Study
1.1 McMurdo Dry Valley Background
The polar desert of the McMurdo Dry Valleys (MDV) (77°30’S 163°00’E), the largest ice-free region in Antarctica, is a matrix of deep permafrost, soils, glaciers, streams, and lakes that together form the geological context for the southernmost functioning terrestrial ecosystem (Kennedy, 1993; Lyons et al., 2000; Levy et al., 2011). The MDV encompass approximately
2000 km2 of ice-free terrain, situated between McMurdo Sound to the east and the Transantarctic
Mountains to the west and are separated by ridges that run perpendicular to the coast (Figure 1-1) (Wharton et al., 1993, Gooseff et al., 2011). The ridges can reach elevations of over 2000 m above sea level and the valley floors range in elevation from just above sea level to about 800 m above sea level.
The MDV are the focus of the McMurdo Long Term Ecological Research (MCM-LTER)
program, an interdisciplinary and multidisciplinary study of the aquatic and terrestrial ecosystems in an ice-free region of Antarctica. MCM joined the National Science Foundation’s LTER Network in 1993 and is funded through the Office of Polar Programs. The MDV ecosystem is vastly different than most ecosystems of the world, with both aquatic and terrestrial ecosystems survive in one of the planets harshest environments. The perennially ice-covered lakes, ephemeral streams and extensive areas of exposed soil within the MDV are subject to low temperatures, limited precipitation and salt accumulation.
Figure 1-1: USGS topographic map of the McMurdo Dry Valleys, Antarctica and surrounding areas.
The climate is very cold with mean annual air temperature of -18 °C and dry with <10 cm water equivalent of precipitation per year. During the austral summer, October to February, there is continuous sunlight which can generate temperatures up to 10.7°C (Doran et al., 2008). The winter months experience continuous darkness where the temperatures can reach -65 °C. The MDV polar desert receives little precipitation due to the strong precipitation shadow cast locally by the Transantarctic Mountains (Monaghan et al., 2005; Gooseff et al., 2011). The MDV has an annual water equivalent precipitation, which is dominated by snow, in the valley bottoms of 2– 50 mm (Fountain et al., 2010; Gooseff et al., 2011). Due to the extremely arid and frigid conditions, most of the snowfall sublimates within days of falling (Chinn 1993). Katabatic winds (i.e. drainage winds) occur in the MDV, which flow from the polar plateau at the western edge of the MDV to the coast at the eastern end of the MDV (Gooseff et al., 2011). These winds reach speeds of 37 m⁄ s and play an important factor in the valley morphology and biology and warm the valleys due to compressional heating as the winds descend to lower elevations (Gooseff et al., 2011). The air temperature can increase 30 °C in a few hours and for every 1% increase in the average frequency of katabatic wind events, summer air temperatures increase by 0.4 °C and winter air temperatures increase by 1.0 °C (Nylen et al., 2004, Gooseff et al., 2011).
Katabatic winds can transport snow from the valley walls and glaciers, and occasionally from the Antarctic Plateau (just west of the MDV), and account for about half of the measured snow accumulation (Gooseff et al., 2011). Snow presence is greater in the winter than the summer and is spatially variable (Gooseff et al., 2003). Winter snow can persist nearly all winter at Lake Vida but can last a few weeks at Lake Bonney (Gooseff et al., 2011). This difference is possibly due to the mass of snow accumulated at each site and the frequency of wind events that erode and sublimate the snow cover (Gooseff et al., 2011).
A majority of the ice-free MDV landscape below 1000 m elevation is underlain by dry permafrost (Bockheim et al., 2007). The active layer soils at the surface thaw during the austral summer to depths of 60–70 cm, harboring vibrant microbial and invertebrate communities (Treonis et al., 1999; Gooseff et al., 2011). The MDV soils consist of composed of glacial drift, valley-wall colluvium, marine sediments, and paleo–lake beds (Bockheim et al., 2008; Levy et al., 2011). The soil thermal regime is driven by strong surface energy variability annually, with greatest thaw depths typically observed in early January (Gooseff et al., 2011). Soils across the MDV are generally dry, except where sustained sources of liquid water are present, such soils that border streams and lakes are locations of consistent wetness during the austral summer (Gooseff et al., 2011).
The harsh environment and low availability of carbon and water support a simplified ecosystem of rotifers, tardigrades, nematodes, and microarthropods near lakes and ephemeral streams, and even simpler communities in the arid soils that occupy the majority of the landscape (Wall and Virginia, 1999; Wall, 2005; Adams et al., 2006; Simmons et al., 2009). Scottnema lindsayae, the most abundant and widely distributed metazoan invertebrate, often occurs in the arid soils and all other invertebrate species are more abundant in moist or saturated soils where algae and moss are more abundant (Powers et al., 1998; Treonis et al., 1999; Wall and Virginia,
1999; Bamforth et al., 2005; Wall, 2005; Adams et al., 2006; Ayres et al., 2007; Simmons et al., 2009). In addition to the available water content, soil chemistry is an important control on the terrestrial ecosystem of the MDV. MDV soils contain less than 1% organic carbon (0.01-0.03% organic matter by weight) and typically have high salinity (Campbell and Claridge, 1987). This high salinity is a product of marine aerosol deposition, large evaporation rates, and the matric potential. The salt crusts can be visibly present at the surface (Figure 1-2).
Figure 1-2: Salt crusts forming on wetted soils near Lake Fryxell in Taylor Valley. Image provided by Dr. Michael Gooseff during the 2011-2012 austral summer.
1.2 McMurdo Dry Valley Hydrology
The hydrologic cycle of the MDV is strongly driven by climate and the surface energy balance (i.e. net radiation, sensible and latent heat exchanges) has a stronger control on the hydrologic cycle than precipitation (Gooseff et al., 2011). The hydrologic activity is controlled by the daily, seasonal, and annual cycles of surface energy balance across the landscape. A strong positive surface energy balance in the austral summer, driven by warm temperatures and 24 hours of solar radiation, allows for liquid water to be present on glaciers, in streams, at the edges of ice-covered lake surfaces and in some soils (Gooseff et al., 2011). However, the energy available for glacier and snow melt can vary considerably over the diurnal timescale due to variations in solar aspect and topographic shading (Gooseff et al., 2011).
The MDV are closed systems with no outflow to the ocean due to the presence of a coastal ridge and the hydrology can be divided into three parts: glaciers and snowfields, streams, and lakes. The hydrologic system of the MDV is described by each reservoir, its fluxes and connections to other reservoirs, and then the sensitivity of the system to changing climate (Figure
1-3). The MDV hydrologic reservoirs include: the atmosphere, glaciers, soils ⁄ permafrost, streams and their hyporheic zones, and lakes (Gooseff et al., 2011). Neither infiltration of snowmelt nor groundwater movement (shallow or deep) has been considered to be a major hydrological process (Cartwright and Harris, 1981; Chinn, 1993; Hunt et al., 2010).Soil moisture generation (snow or glacier melt), movement, and evaporation in the MDV are obvious at the surface and the role in the hydrologic system is unknown. These soils with high soil moisture profiles include water tracks, wet patches, and seeps and will be further discussed in this chapter.
Figure 1-3: Conceptual models of hydrologic connections in the MDV.
Three large, ice-covered, closed-basin lakes are located in Taylor Valley that includes
Lake Bonney, Hoare, and Fryxell. These lakes are primarily fed from glacier melt (Lyons et al., 1998; Levy et al., 2011). Thirty named streams route glacier meltwater to the lakes and more than 60 channels wider than ~6 m across are present along the valley walls (McKnight et al., 1999; Levy et al., 2011). Wright and Victoria Valley consists of eighty four streams, the Onyx
River (the longest and largest monitored Antarctic river), and two lakes (Lake Vida and Vanda). Barwick and McKelvey Valley only have nine streams and one lake (Lake Vashka), primarily due to low concentrations of snow and glacier activity. Garwood, Miers, and Marshall Valley have three lakes and seven streams running to the McMurdo Ice Shelf and McMurdo Sound. Below Miers Valley there are six streams running into Walcott Bay. Above Garwood Valley there are four streams running into McMurdo Sound.
1.3 Water Tracks, Seeps, and Wet Patches
Recent observations in the MDV of shallow groundwater discharge referred to as seeps (Harris et al., 2007; Lyons et al., 2005), downslope water transport known as water tracks (Head et al., 2007; Levy et al., 2008; Levy et al. 2011), and wet patches sourced by the deliquescence of soil salts (Levy et al., 2012) generate a new interest in examining these features that route water through the Valleys (Figure 1-4). These features can be observed in aerial photographs extending back to 1959 and even Griffith Taylor’s photographs in 1910, suggesting that they are not a
“new” feature of the McMurdo Dry Valleys (Levy et al. 2011).
9
Figure 1-4:Wetted Soils in Taylor and Victoria Valley : A) south-facing slope near LaCroix Glacier, B) water tracks on the south-facing slopes above east lobe of Lake Bonney, C) north-facing slopes above west lobe of Lake Bonney, D) wet patch on the valley-bottom location south of Lake Hoare, E) wetted soils at base of outcrop, north-facing slope near Lake Vanda. All images taken by Dr. Michael Gooseff in 2009-10 field season.
Water tracks are zones of high soil moisture that route water downslope over the ice table in polar environments that occurs in the absence of well-defined channels (Hastings et al., 1989; McNamara et al., 1999, Levy et al., 2011). Most water tracks are clearly associated with surface ice in the form of snow and during the summer contribute water as snowmelt infiltrates into the soil (Levy et al., 2011). Water tracks in the MDV can also be present in association with landforms related to water transport, such as incised stream channels. The water tracks width ranges from ~1-3 m and lengths of ~200-1900 m, and is narrowest along steep slopes and widest where the water track is deflected around an ice-cored moraine (Levy et al. 2011). Water tracks may wick saline water (2–4 dS/m) into the MDV soil ecosystems and solute transport are two orders of magnitude faster than adjacent dry or damp soil, making water tracks “salt superhighways” (Levy et al., 2011).
The seeps in the MDV are not supplied by direct glacier melt, the primary source of liquid water in the polar desert of the McMurdo Dry Valleys, and appear to be supplied by melting of permafrost, snow patches, refrozen precipitation that has accumulated in the subsurface or buried glacier ice (Harris et al., 2007; Head et al., 2007; Levy et al., 2008). Seeps are typically discharged at points where boulders produce a local break in slope, resulting from upslope damming of colluvium (Putkonen et al., 2007; Levy et al., 2011). The presence of seeplike features can be observed in water tracks suggests that seeps are an emergent process associated with water track activity, and they are locations where saline solutions moving downslope through water tracks discharge at the surface due to abrupt changes in slope (Levy et al., 2011).
The wet patches in the MDV are not associated with snowbanks, shallow groundwater, or seasonal streams and are surrounded by dry soil suggesting a lack of hydrological connectivity with surface/near-surface waters (Levy et al., 2012). Wet patches are typically found on topographic highpoints or on isolated hillslopes and cover a small area in the MDV (<0.1%) (Levy et al., 2012). The wet patches in Taylor Valley were found to be approximately an order of magnitude more enriched in salts than typical Taylor Valley soils (Levy et al., 2012). In the absence of snowmelt, deliquescence of soil salts and fluid growth by vapor deposition is the most likely source for this moisture, which results in a flux of water vapor from the atmosphere into the salty soil (Levy et al., 2012).
1.4 Thesis Approach
The MDV streams, seeps, and water tracks represent a morphological continuum between overland flow in streams and shallow active-layer flow and represent a source of moisture and geochemistry to soil ecosystems. The thesis is broken up into two chapters; the first chapter’s objective is to characterize the distribution of water tracks, seeps, and wet patches within the MDV through the use of high-resolution satellite imagery. We quantify the spatial and temporal variation of wetted soils at the landscape scale and assess the controls topography and microclimates for specific austral summers. A digital elevation model (DEM) will be used for analyzing the topography and local meteorological stations for the microclimates. The second chapter’s objective is to quantify the soil moisture from water tracks, wet patches, and wet seeps. This study is based on a retrieval method for soil moisture from high resolution satellite data using an artificial neural network (ANN) over selected sites in MDV.
ARE THE DRY VALLEYS GETTING WETTER? A PRELIMINARY ASSESSMENT OF WETNESS ACROSS THE MCMURDO DRY VALLEYS LANDSCAPE
