Soluble Salts in Taylor Valley, Antarctica: Implications for Paleolakes and the Ross Sea Ice Sheet Jonathan D. Toner 1 ; Ronald S. Sletten 1 ; Michael L. Prentice 2 1. Earth and Space Sciences Department, University of Washington; 2. Environmental Geology Department, Indiana University Introduction Study Sites - Taylor Valley, Antarctica The Chemical Composition of Salt Accumulations Paleolakes in Western Taylor Valley Paleolakes in Eastern Taylor Valley Conclusions References This material is based upon work supported by the National science Foundation under Grant Nos. 0541054 and 0636998. Support was also provided by the department of Earth and Space Sciences at the University of Washington. During the Last Glacial Maximum (LGM), the Ross Sea Ice Sheet (RSIS) expanded across McMurdo Sound and entered the mouth of Taylor Valley. It is speculated that this ice dammed large, valley-wide proglacial paleolakes, which were over 300 m deep in places (Stuiver et al. 1981, Hall et al. 2000). These paleolakes have important implications for paleoclimate during and after the LGM, the sensitivity of the RSIS to deglacial sea level rise and warming trends, and past hydrologic and climatic regimes in Taylor Valley. To study these paleolake systems, we investigated soluble salt accumulations in Taylor Valley soils. Soluble salts accumulate in soils from marine sea-spray aerosols and atmospheric aerosols and are preserved from leaching due to prevailing cold-dry conditions. Soluble salts are by nature sensitive to inundation by lake water and should reflect the extensive paleolake systems believed to have filled Taylor Valley. Lake water is thought to influence soluble salt accumulations in Dry Valley soils by leaching inundated soils during lake high stands and accumulating soluble salts along wetted lake margins as lake levels lower. Salts accumulate near wetted lake margins as lake water moves along water potential gradients towards an evaporation zone near the soil surface. This process has been termed, ‘evapoconcentration’. We infer the extent of paleolake systems in Taylor Valley by examining the distribution of soils influenced by leaching and evapoconcentration processes. Methods: 89 soils were sampled throughout Taylor Valley and analyzed for soluble salts using a 1:25 soil:water extraction, with the goal of removing as much soluble salt as possible from soils. This study also incorporated soluble salt contents determined by other researchers. Samples were collected from soils at level sites on local topographic highs, such as paleoshorelines, moraine tops, and terrace apexes. Measured salt concentrations were converted to total salt contents per aerial surface area using the equations: Acknowledgements Hall, B. L., Denton, G. H., Hendy, C. H., Denton, G. H., & Hall, B. L. (2000). Evidence from Taylor Valley for a grounded ice sheet in the Ross Sea, Antarctica. Geografiska Annaler. Series A: Physical Geography, 82(2-3), 275-303. Stuiver, M., Denton, G. H., Hughes, T. J., & Fastook, J. L. (1981). History of the marine ice sheet in West Antarctica during the last glaciation; a working hypothesis. Barrett, J. E., M. A. Poage, et al. (2010). The legacy of aqueous environments on soils of the McMurdo Dry Valleys: contexts for future exploration of Martian soils. Life in Antarctic Deserts and other Cold Dry Environments. P. T. Doran, B. W. Lyons and D. M. McKnight. New York, Cambridge Astrobiology. Salt contents shown here are all influenced by paleolakes, but are higher at lower elevations indicating more stable paleolakes. Maps showing a reconstruction of maximum paleolake extents in Taylor Valley, after Hall et al. 2000 (left panel), compared to current lake levels (right panel). Salt Content eq m −2 = BD hor. ×t hor. ×C hor. × horizon % <2 100 ℎ. BD (g cm −3 )= 100 %w <2 mm ρ <2mm + 100 − %w <2 mm ρ g Soluble salt distributions in Bonney Basin indicate paleolake levels up to approximately 300 m elevation, which is consistent with the elevation of lacustrine strandlines and terraces. Soluble salts below 300 m elevation are lower than in higher elevation soils due to leaching by paleolakes. Salt contents in soils affected by paleolakes (below 300 m elevation) are a function of paleolake level stability. Above 116 m elevation, paleolakes would have been dammed by the RSIS (relatively unstable), while below 116 m elevation, paleolakes would have been closed basin lakes (relatively stable). The character of paleoshorelines in Bonney Basin provides additional evidence for paleolake stabilities. Shorelines above 116 m elevation are faint, while shorelines below 116 m elevation are broad and well defined. Graph showing lower salt contents in soils below 300 m elevation, due to leaching by paleolakes. Salts in eastern Taylor Valley have been modified by leaching and paleolakes. Salt distributions indicate paleolake levels up to approximately 120 m elevation, but no higher. Paleolakes filling eastern Taylor Valley may have been controlled by the height of the RSIS grounding line, which was presumably located near the Coral Ridge moraine complex in the valley mouth. • Salt contents in soils are influenced by a variety of factors including, soil age, distance from McMurdo Sound, leaching, soil texture, calcite/gypsum dissolution, cation exchange, and paleolakes. • The absence of paleolakes above 120 m in eastern Taylor Valley suggests that paleolakes in Bonney Basin were dammed by a lobe of the RSIS that filled eastern Taylor Valley to at least 300 m elevation. This contrasts with previous hypotheses that valley-wide paleolakes filled Taylor Valley during the LGM. Instead, we suggests that high paleolakes were restricted to Bonney Basin and that smaller paleolakes formed during the retreat of the RSIS in eastern Taylor Valley. A reconstruction of glacial and lacustrine events in Taylor Valley; (upper panel) LGM RSIS extent, (mid panel) 120 m high paleolakes following RSIS retreat, and (lower panel) present day lacustrine systems. Soils sampled in western Taylor Valley for salt contents. These soils typically did not contain ice-cemented soil and could be excavated to ~1 m depth. Only glacial tills were sampled. A map showing the location of the study and the soils sampled. A total of 89 soils were sampled. Soils were primarily sampled in eastern Taylor Valley, and only a few were sampled in western Taylor Valley. Soils sampled in eastern Taylor Valley. These soils all contained ice-cemented soil at about 30 cm depth. Glacial tills were sampled, as well as about 20 fluvial terraces, which have been interpreted as lacustrine deltas. Soluble Salt Distributions in Taylor Valley The dominant characteristic of soluble salt distributions in Taylor Valley is the occurrence of low salt contents in eastern Taylor Valley and high salt contents in western Taylor Valley. In general, salt distributions are consistent with differences in soil age between eastern and western Taylor Valley. In western Taylor Valley, soils are from older advances of Taylor Glacier and alpine glaciations, while in eastern Taylor Valley, soils are primarily from the LGM advance of the RSIS. There are a number of exceptions to this overall trend in salt content; some older soils have relatively low salt contents and some younger soils developing on RSIS sediments have relatively high salt contents. In western Taylor Valley, older soils having low salt contents are typically ice-cemented near the surface, which suggests a higher local moisture regime that may have leached soluble salts from these soils. In eastern Taylor Valley, ice-cemented soil is ubiquitous and salts have likely been leached from older soils due to the wetter climate. Relatively high salt contents in young RSIS sediments are primarily found below approximately 120 m elevation in eastern Taylor Valley. Barrett et al. [2010] found similar high salt accumulations near Lake Fryxell and Lake Hoare and concluded that these salt accumulations were deposited at the margins of paleolakes. Region n pH Ca 2+ Mg 2+ Na + K + Cl - SO 4 2- NO 3 - HCO 3 - Total moles m -2 eq m -2 Valley Mouth 15 9.7 1.09 1.06 12.05 1.10 5.88 0.61 0.16 8.72 34.88 Fryxell Basin 68 9.6 2.22 0.97 5.30 1.06 2.38 0.86 0.05 7.77 25.49 Bonney Basin 7 8.5 18.96 13.98 65.76 3.86 88.44 15.05 1.28 10.64 271.00 Graph of ion concentrations (the sum of all sequential extractions) measured at different soil water ratios. Extracted salts increase at higher extraction ratios, particularly Ca 2+ . Average soluble salt compositions measured in 1:25 soil:water extractions. The composition of salts and soil pH varies with distance from McMurdo Sound. Valley Mouth soils are composed almost entirely of Na + and HCO 3 - ions and the average soil pH is 9.7. Further inland, in Fryxell Basin, Na + and HCO 3 - are still the dominant ions and the average soil pH is 9.6, but soils contain higher proportions of Ca 2+ and Mg 2+ . In Bonney Basin, located furthest from McMurdo Sound, soils have high proportions of Cl - and SO 4 2- relative to HCO 3 - and the average soil pH decreases to 8.5. Tests performed at different soil:water ratios show that extracted soluble salts are strongly dependent on the number of sequential extractions and the soil:water ratio. This is consistent with a well known effect caused by cation exchange reactions and calcite dissolution. These reactions can be described by the following generalized equation: CaCO 3 +H 2 CO 3 + 2Na, 2K, Mg X 2 ↔ 2Na + , 2K + , Mg 2+ + 2HCO 3 − + CaX 2 The Na-HCO 3 composition of soils in eastern Taylor Valley is likely due to cation exchange and calcite dissolution, and reflects a high exchangeable Na component in these soils. It is important to interpret measured salts in light of the effects of exchange reactions and calcite dissolution. C13A-0606
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Soluble Salts in Taylor Valley, Antarctica: Implications for Paleolakes and the Ross Sea Ice Sheet
Jonathan D. Toner1; Ronald S. Sletten1; Michael L. Prentice2 1. Earth and Space Sciences Department, University of Washington; 2. Environmental Geology Department, Indiana University
Introduction
Study Sites - Taylor Valley, Antarctica
The Chemical Composition of Salt Accumulations
Paleolakes in Western Taylor Valley
Paleolakes in Eastern Taylor Valley
Conclusions
References This material is based upon work supported by the National science
Foundation under Grant Nos. 0541054 and 0636998. Support was also
provided by the department of Earth and Space Sciences at the
University of Washington.
During the Last Glacial Maximum (LGM), the Ross Sea Ice Sheet (RSIS) expanded across McMurdo Sound
and entered the mouth of Taylor Valley. It is speculated that this ice dammed large, valley-wide proglacial
paleolakes, which were over 300 m deep in places (Stuiver et al. 1981, Hall et al. 2000). These paleolakes
have important implications for paleoclimate during and after the LGM, the sensitivity of the RSIS to deglacial
sea level rise and warming trends, and past hydrologic and climatic regimes in Taylor Valley.
To study these paleolake systems, we investigated soluble salt accumulations in Taylor Valley soils. Soluble
salts accumulate in soils from marine sea-spray aerosols and atmospheric aerosols and are preserved from
leaching due to prevailing cold-dry conditions. Soluble salts are by nature sensitive to inundation by lake
water and should reflect the extensive paleolake systems believed to have filled Taylor Valley. Lake water is
thought to influence soluble salt accumulations in Dry Valley soils by leaching inundated soils during lake
high stands and accumulating soluble salts along wetted lake margins as lake levels lower. Salts
accumulate near wetted lake margins as lake water moves along water potential gradients towards an
evaporation zone near the soil surface. This process has been termed, ‘evapoconcentration’. We infer the
extent of paleolake systems in Taylor Valley by examining the distribution of soils influenced by leaching and
evapoconcentration processes.
Methods: 89 soils were sampled throughout Taylor Valley and analyzed for soluble salts using a 1:25
soil:water extraction, with the goal of removing as much soluble salt as possible from soils. This study also
incorporated soluble salt contents determined by other researchers. Samples were collected from soils at
level sites on local topographic highs, such as paleoshorelines, moraine tops, and terrace apexes. Measured
salt concentrations were converted to total salt contents per aerial surface area using the equations:
Acknowledgements Hall, B. L., Denton, G. H., Hendy, C. H., Denton, G. H., & Hall, B. L. (2000). Evidence from Taylor Valley for a grounded ice
sheet in the Ross Sea, Antarctica. Geografiska Annaler. Series A: Physical Geography, 82(2-3), 275-303.
Stuiver, M., Denton, G. H., Hughes, T. J., & Fastook, J. L. (1981). History of the marine ice sheet in West Antarctica during
the last glaciation; a working hypothesis.
Barrett, J. E., M. A. Poage, et al. (2010). The legacy of aqueous environments on soils of the McMurdo Dry Valleys:
contexts for future exploration of Martian soils. Life in Antarctic Deserts and other Cold Dry Environments. P. T. Doran, B.
W. Lyons and D. M. McKnight. New York, Cambridge Astrobiology.
Salt contents shown here are all influenced by paleolakes, but are
higher at lower elevations indicating more stable paleolakes.
Maps showing a reconstruction of maximum paleolake extents in Taylor Valley, after Hall et al. 2000 (left panel), compared to
current lake levels (right panel).
Salt Content eq m−2 = BD hor. × thor. × Chor.×
horizon
%𝑤<2 𝑚𝑚100
ℎ𝑜𝑟.
BD (g cm−3) =
100
%w<2 mmρ<2mm
+100 −%w<2 mm
ρg
Soluble salt distributions in Bonney Basin indicate paleolake levels up to approximately 300
m elevation, which is consistent with the elevation of lacustrine strandlines and terraces.
Soluble salts below 300 m elevation are lower than in higher elevation soils due to leaching
by paleolakes. Salt contents in soils affected by paleolakes (below 300 m elevation) are a
function of paleolake level stability. Above 116 m elevation, paleolakes would have been
dammed by the RSIS (relatively unstable), while below 116 m elevation, paleolakes would
have been closed basin lakes (relatively stable). The character of paleoshorelines in Bonney
Basin provides additional evidence for paleolake stabilities. Shorelines above 116 m
elevation are faint, while shorelines below 116 m elevation are broad and well defined.
Graph showing lower salt contents in soils below 300
m elevation, due to leaching by paleolakes.
Salts in eastern Taylor Valley have
been modified by leaching and
paleolakes. Salt distributions indicate
paleolake levels up to approximately
120 m elevation, but no higher.
Paleolakes filling eastern Taylor Valley
may have been controlled by the
height of the RSIS grounding line,
which was presumably located near
the Coral Ridge moraine complex in
the valley mouth.
• Salt contents in soils are influenced by a variety
of factors including, soil age, distance from
McMurdo Sound, leaching, soil texture,
calcite/gypsum dissolution, cation exchange, and
paleolakes.
• The absence of paleolakes above 120 m in
eastern Taylor Valley suggests that paleolakes in
Bonney Basin were dammed by a lobe of the
RSIS that filled eastern Taylor Valley to at least
300 m elevation. This contrasts with previous
hypotheses that valley-wide paleolakes filled
Taylor Valley during the LGM. Instead, we
suggests that high paleolakes were restricted to
Bonney Basin and that smaller paleolakes
formed during the retreat of the RSIS in eastern
Taylor Valley.
A reconstruction of glacial and lacustrine events in Taylor
Valley; (upper panel) LGM RSIS extent, (mid panel) 120 m
high paleolakes following RSIS retreat, and (lower panel)
present day lacustrine systems.
Soils sampled in western Taylor Valley for salt contents. These
soils typically did not contain ice-cemented soil and could be
excavated to ~1 m depth. Only glacial tills were sampled.
A map showing the location of the study and the soils sampled. A total of 89 soils were
sampled. Soils were primarily sampled in eastern Taylor Valley, and only a few were
sampled in western Taylor Valley.
Soils sampled in eastern Taylor Valley. These soils all
contained ice-cemented soil at about 30 cm depth. Glacial tills
were sampled, as well as about 20 fluvial terraces, which have
been interpreted as lacustrine deltas.
Soluble Salt Distributions in Taylor Valley
The dominant characteristic of soluble salt distributions in Taylor Valley is the occurrence
of low salt contents in eastern Taylor Valley and high salt contents in western Taylor Valley.
In general, salt distributions are consistent with differences in soil age between eastern
and western Taylor Valley. In western Taylor Valley, soils are from older advances of
Taylor Glacier and alpine glaciations, while in eastern Taylor Valley, soils are primarily from
the LGM advance of the RSIS.
There are a number of exceptions to this overall trend in salt content; some older soils
have relatively low salt contents and some younger soils developing on RSIS sediments
have relatively high salt contents. In western Taylor Valley, older soils having low salt
contents are typically ice-cemented near the surface, which suggests a higher local
moisture regime that may have leached soluble salts from these soils. In eastern Taylor
Valley, ice-cemented soil is ubiquitous and salts have likely been leached from older soils
due to the wetter climate. Relatively high salt contents in young RSIS sediments are
primarily found below approximately 120 m elevation in eastern Taylor Valley. Barrett et al.
[2010] found similar high salt accumulations near Lake Fryxell and Lake Hoare and
concluded that these salt accumulations were deposited at the margins of paleolakes.
Region n pH Ca2+ Mg2+ Na+ K+ Cl- SO42- NO3
- HCO3- Total
moles m-2 eq m-2
Valley Mouth 15 9.7 1.09 1.06 12.05 1.10 5.88 0.61 0.16 8.72 34.88
Fryxell Basin 68 9.6 2.22 0.97 5.30 1.06 2.38 0.86 0.05 7.77 25.49
Bonney Basin 7 8.5 18.96 13.98 65.76 3.86 88.44 15.05 1.28 10.64 271.00
1
Graph of ion concentrations (the sum of all
sequential extractions) measured at different
soil water ratios. Extracted salts increase at
higher extraction ratios, particularly Ca2+.
Average soluble salt compositions measured in 1:25 soil:water extractions.
The composition of salts and soil pH varies with
distance from McMurdo Sound. Valley Mouth soils
are composed almost entirely of Na+ and HCO3- ions
and the average soil pH is 9.7. Further inland, in
Fryxell Basin, Na+ and HCO3- are still the dominant
ions and the average soil pH is 9.6, but soils contain
higher proportions of Ca2+ and Mg2+. In Bonney
Basin, located furthest from McMurdo Sound, soils
have high proportions of Cl- and SO42- relative to
HCO3- and the average soil pH decreases to 8.5.
Tests performed at different soil:water ratios show
that extracted soluble salts are strongly dependent
on the number of sequential extractions and the
soil:water ratio. This is consistent with a well known
effect caused by cation exchange reactions and
calcite dissolution. These reactions can be
described by the following generalized equation:
CaCO3 + H2CO3 + 2Na, 2K,Mg X2 ↔ 2Na+, 2K+, Mg2+ + 2HCO3
− + CaX2
The Na-HCO3 composition of soils in eastern Taylor Valley is likely due to cation exchange
and calcite dissolution, and reflects a high exchangeable Na component in these soils. It
is important to interpret measured salts in light of the effects of exchange reactions and
calcite dissolution.
C13A-0606
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