c. Soil moisture
In the Ross Sea region, a lack of soil moisture is often the
major limitation to biological activity. Annual precipitation
is generally very low and usually falls as snow. However,
occasionally a small amount of rain has been observed in
summer when air temperatures are above zero. The precipitation is higher in the coastal areas where usually there is
enough snowfall over winter to cover the ground surface,
leading to a spring meltwater event. Occasional summer
snowfalls may cover the ground near the coast for a week or
two before melting and evaporating.
In some coastal areas, runoff from snow or glacier melt
occurs for several weeks over summer, saturating the soil and
forming ephemeral streams. For example, the soil on the foot
slope on the edge of Granite Harbour at, and near, Botany
Bay, has water flowing through it for a large portion of the
summer. The water conducts heat into the soil providing an
unusually deep (>90 cm) active layer. The moisture also
supports an area of exceptional moss growth at Botany Bay.
In the McMurdo Dry Valleys, there is minimal snow-fall.
Annual precipitation of 45 mm was recorded at Vanda
Station in the Wright Valley in the 1970s. On the valley
floors, an occasional summer snow shower occurs where
snow settles on the ground surface. The snow is usually lost
to sublimation within a few hours with very little moisture
penetrating the soil surface. However, snow may accumulate
on the adjacent higher altitude mountain tops for extended
periods over summer. Some of the meltwater from higher
altitude areas moves down through the soils of the valley
walls to evaporate on the valley floor, sometimes leaving
accumulations of salt behind, such as at Don Juan Pond in
the Wright Valley. The areas of subsurface flow down valley
walls are sometimes called ‘water tracks’ and have been
described as ‘solute superhighways’ as they move both salt
and water downslope relatively rapidly.
In moister coastal areas, and soils with ice-cemented permafrost, the soil moisture content near the soil surface can
vary greatly through the summer, ranging from saturation
during snow-melt to less than 5% gravimetric moisture content as the surface soil becomes effectively ‘air dry’. Ten years
of monitoring at Marble Point showed sites generally had
three or four moistening (snow-melt) events per summer
where water extended to at least 20 cm depth and lasted for up
to 2 weeks before drying back to ‘air dry’. Moisture accumulates at the top of the permafrost where the temperature
remains at or below zero and moisture condenses from the air
and freezes, often forming ice lenses (which give a volumetric
moisture content of 100%). Within the permafrost, the soil
moisture (ice) content can be highly variable, with volumetric
moisture contents ranging from less than 10% in soil and rock
materials, to 100% in ice wedges and lenses.
Within the dry valleys, where there is dry permafrost, the
soils have moisture contents of less than 5% by weight, and
often as low as 1%, throughout the soil profile. In 10 years
of soil moisture monitoring on a dry permafrost site in the
Wright Valley, there were no soil moistening events that
extended to 20 cm deep in the soil. Once every few years,
there may be surface soil moistening for a few hours if a
snow patch forms and some snow melts before evaporating.
Some soils adjacent to lakes or ephemeral streams may be
moistened for extended periods during summer as capillary
rise can draw moisture through the soil for several metres
from the lake or stream. The outer margins of such areas are
often marked by the accumulation of salts left behind where
the water evaporates.
The soil moisture holding capacity is low because of the
coarse gravelly sand texture of most Antarctic soils. However, even at low soil moisture contents, much of the water
may not be strongly held due to the generally low (<1%)
clay and organic matter content, so it may be possible for
microbes to operate at lower moisture contents than would
generally be expected.
The first Antarctic soil science expedition
Norman Taylor, the Director of New Zealand Soil
Bureau from 1952 to 1962, planned to attend the 1960
International Soil Science Society meeting in Madison, Wisconsin, and wanted to impress the world by
showing that New Zealand soil survey reached from
the equator to the pole. Accordingly, he sent John
McCraw and Graeme Claridge to Antarctica during
the 1959–60 austral summer to investigate the soils, “if
any could be found”, and produce a soil map.
McCraw and Claridge set off without any
pre-planned programme, armed only with a spade,
cameras, and notebooks. Their first venture was to visit
the site of the 1907–09 Shackleton expedition hut at
Cape Royds, inhabited at that time by Norman Taylor’s
son who was studying penguins. They travelled to Cape
Royds, via sea ice, by Massey Fergusson tractor and
sledge. It was early in October, and very cold, but they
managed to explore the surroundings and dug their first
soil profile pits (albeit very shallow ones as the active
layer was not yet thawed, so was ice-cemented). They
were somewhat mystified by what they saw.
Claridge and McCraw next set off to cross
McMurdo Sound, again by tractor and sledge. They
were dropped off in the Taylor Valley with no radio
contact and a vague arrangement that they would be
picked up by people from Scott Base a month later. To
keep warm on the sledge they converted a large
packing case into a shelter. At the mouth of the Taylor
282
17 Soils in the Ross Sea Region of Antarctica
In the Ross Sea region, a lack of soil moisture is often the
major limitation to biological activity. Annual precipitation
is generally very low and usually falls as snow. However,
occasionally a small amount of rain has been observed in
summer when air temperatures are above zero. The precipitation is higher in the coastal areas where usually there is
enough snowfall over winter to cover the ground surface,
leading to a spring meltwater event. Occasional summer
snowfalls may cover the ground near the coast for a week or
two before melting and evaporating.
In some coastal areas, runoff from snow or glacier melt
occurs for several weeks over summer, saturating the soil and
forming ephemeral streams. For example, the soil on the foot
slope on the edge of Granite Harbour at, and near, Botany
Bay, has water flowing through it for a large portion of the
summer. The water conducts heat into the soil providing an
unusually deep (>90 cm) active layer. The moisture also
supports an area of exceptional moss growth at Botany Bay.
In the McMurdo Dry Valleys, there is minimal snow-fall.
Annual precipitation of 45 mm was recorded at Vanda
Station in the Wright Valley in the 1970s. On the valley
floors, an occasional summer snow shower occurs where
snow settles on the ground surface. The snow is usually lost
to sublimation within a few hours with very little moisture
penetrating the soil surface. However, snow may accumulate
on the adjacent higher altitude mountain tops for extended
periods over summer. Some of the meltwater from higher
altitude areas moves down through the soils of the valley
walls to evaporate on the valley floor, sometimes leaving
accumulations of salt behind, such as at Don Juan Pond in
the Wright Valley. The areas of subsurface flow down valley
walls are sometimes called ‘water tracks’ and have been
described as ‘solute superhighways’ as they move both salt
and water downslope relatively rapidly.
In moister coastal areas, and soils with ice-cemented permafrost, the soil moisture content near the soil surface can
vary greatly through the summer, ranging from saturation
during snow-melt to less than 5% gravimetric moisture content as the surface soil becomes effectively ‘air dry’. Ten years
of monitoring at Marble Point showed sites generally had
three or four moistening (snow-melt) events per summer
where water extended to at least 20 cm depth and lasted for up
to 2 weeks before drying back to ‘air dry’. Moisture accumulates at the top of the permafrost where the temperature
remains at or below zero and moisture condenses from the air
and freezes, often forming ice lenses (which give a volumetric
moisture content of 100%). Within the permafrost, the soil
moisture (ice) content can be highly variable, with volumetric
moisture contents ranging from less than 10% in soil and rock
materials, to 100% in ice wedges and lenses.
Within the dry valleys, where there is dry permafrost, the
soils have moisture contents of less than 5% by weight, and
often as low as 1%, throughout the soil profile. In 10 years
of soil moisture monitoring on a dry permafrost site in the
Wright Valley, there were no soil moistening events that
extended to 20 cm deep in the soil. Once every few years,
there may be surface soil moistening for a few hours if a
snow patch forms and some snow melts before evaporating.
Some soils adjacent to lakes or ephemeral streams may be
moistened for extended periods during summer as capillary
rise can draw moisture through the soil for several metres
from the lake or stream. The outer margins of such areas are
often marked by the accumulation of salts left behind where
the water evaporates.
The soil moisture holding capacity is low because of the
coarse gravelly sand texture of most Antarctic soils. However, even at low soil moisture contents, much of the water
may not be strongly held due to the generally low (<1%)
clay and organic matter content, so it may be possible for
microbes to operate at lower moisture contents than would
generally be expected.
The first Antarctic soil science expedition
Norman Taylor, the Director of New Zealand Soil
Bureau from 1952 to 1962, planned to attend the 1960
International Soil Science Society meeting in Madison, Wisconsin, and wanted to impress the world by
showing that New Zealand soil survey reached from
the equator to the pole. Accordingly, he sent John
McCraw and Graeme Claridge to Antarctica during
the 1959–60 austral summer to investigate the soils, “if
any could be found”, and produce a soil map.
McCraw and Claridge set off without any
pre-planned programme, armed only with a spade,
cameras, and notebooks. Their first venture was to visit
the site of the 1907–09 Shackleton expedition hut at
Cape Royds, inhabited at that time by Norman Taylor’s
son who was studying penguins. They travelled to Cape
Royds, via sea ice, by Massey Fergusson tractor and
sledge. It was early in October, and very cold, but they
managed to explore the surroundings and dug their first
soil profile pits (albeit very shallow ones as the active
layer was not yet thawed, so was ice-cemented). They
were somewhat mystified by what they saw.
Claridge and McCraw next set off to cross
McMurdo Sound, again by tractor and sledge. They
were dropped off in the Taylor Valley with no radio
contact and a vague arrangement that they would be
picked up by people from Scott Base a month later. To
keep warm on the sledge they converted a large
packing case into a shelter. At the mouth of the Taylor
282
17 Soils in the Ross Sea Region of Antarctica