Reconstructing Alpine Snowpacks Using
Diatom Inference Models and Long-Term
Records of Lake Hydrochemistry
Jim Sickman and Danuta Bennett Department of
Environmental Sciences, University of California
Riverside
Importance of seasonal snowpack
The need for alternative snowpack proxies
The influence of snowpack on lake chemistry
Sierra Nevada
Cascades
Rocky Mountains
Diatom reconstructions of lake ANC and
snowpack at Emerald Lake (1825-2010)
Future directions
Global Importance of Seasonal Snow Cover:
• The mean area of seasonal snowpack in the Northern Hemisphere
winter represents 61% of hemispheric land area (Armstrong and
Brodzik 2005)
• Seasonal snow cover comprises the largest component of the
cryosphere and it is highly important to the Earth’s energy balance
• The top of atmosphere radiative forcing for land-based snowpack is
of the same magnitude as the forcing caused by sea ice and
glaciers
• Recent satellite-based observations suggest that the area of
seasonal snow cover has declined since 1979 coincident with
warming of the Northern Hemisphere (Flanner et al. 2011).
MODIS
Pardee
Hetch
Hetchy
Reservoir
Shasta
Dam Reservoir
Oroville
Dam
CVP
Mokelumne River
Aqueduct
California
Aqueduct
Hetch
Hetchy
System
SWP
DWR
San
USGroundwater,
Bureau
Francisco
of Reclamation
Public
Utilities
East
Bay Municipal
Utility
CA
Department
ofLocal
Water
Commission
Central
Valley&Project
District
Resources
Resources
Conservation
Hetch
1940 Water
-Hetchy
1st water
System
delivered
Mokelumne
River
Aqueduct
State
Project
1913
(Contra
- Raker
CostaAct
Canal)
1960
Burns
Porter
Act
1929
1973 - 1st water to So.Cal.
Climate Change - Predicted
Changes in Inflows to Delta
higher winter peaks
 On-going shift in runoff
timing toward winter,
extending low-flow
periods – 1/3 loss of
snowpack by 2050
 Increase in intensity and
frequency of winter runoff
events
drier summer
Change in inflows to Delta by 2060 (Knowles and Cayan, 2004)
Pacific Maritime Snowpack is Also Sensitive to
Inter-decadal Climate Variability:
ENSO and PDO
• Warm ENSO events associated with
increased snowpack in the Southwest
• Cold ENSO events associated with
increased snowpack in the Northwest.
A set of 42 tree-ring chronologies from
California, Nevada, and Oregon were used to
develop a regression model to predict historical
flows in the Sacramento River.
Meko, D. M. 2001. Reconstructed Sacramento River System Runoff From Tree
Rings. Report prepared for the California Department of Water Resources, July
2001.



Ring characteristics are primarily set during the
growing season, so climate variability in the
winter has less influence (e.g., summer
monsoon vs. winter snowfall)
Trees near treeline may be more affected by
temperature variations than snowfall variations
Trees at mid-elevations may be more waterlimited, therefore ring characteristics may more
strongly reflect precipitation changes, but…
-18 µEq/L
-11 µEq/L
Snowpack Water Equivalence (mm)
April-1
EML ANC:Snowpack Relationship
1983-2011
3500
3000
1986 Avalanche
2500
2000
y = -106x + 4,329
R² = 0.85
1500
1000
500
0
0
10
20
30
September Lake ANC (µEq /L)
40
ANC:Snowpack Relationship
20 Sierra Nevada Lakes
All lakes show snowmelt dilution of ANC
Variation in ANC response to snowmelt dilution
= -8.1 to -270 mm/µEq/L
= 4.2 to 65 µEq/L change in ANC between wet and dry years
Select “snowpack sensitive” Lakes for
Paleo-reconstructions
Less
sensitive
More
sensitive
ANC:Snowpack Relationship
In Cascade Lake
ANC:Snowpack Relationship
In Rocky Mt. Lakes
Diatoms




High species diversity
Well-defined ecological requirements
Respond quickly to changes in lake chemistry
Cell walls composed of silica are well preserved in sediments
Psammothidium
subatomoides
Stauroneis construens
Diatom Inference Model for Lake ANC
ANC Time-series for Emerald Lake
2010
1930
1890
Field
Observations
1850
Diatom
Reconstruction
1.50
1.00
0.50
1810
0.00
ANC Anomaly (Relative to
Mean ANC 1983-2010 and 1982-1825)
Calendar Year (AD)
1970
Recall….
Snowpack Water Equivalence (mm)
April-1
3500
3000
1986 Avalanche
2500
2000
y = -106x + 4,329
R² = 0.85
1500
1000
500
0
0
10
20
30
September Lake ANC (µEq /L)
40
Snowpack Time-series for Emerald Lake
2010
1930
1890
1850
1810
4000
2000
0
April-1 SWE mm (1825-2010)
Based on EML ANC:Snowpack Relationship
Calendar Year (AD)
1970
Validation of SWE Reconstruction

Strengths:




Method relies on a hydrochemical proxy that is
highly sensitive to changes in snowpack
Method can be applied in regions where tree growth
is less sensitive to precipitation (e.g., Cascades)
Method can be applied in zones above the treeline
Method may be most useful for identifying periods
with above normal precipitation (e.g., Holocene
glacial studies)

Weaknesses:





Temporal resolution is coarser than tree-ring records
Method must be applied to lakes that exhibit strong
sensitivity to snowmelt
Method relies on lake-specific information regarding
ANC:snowpack relationships (long-term data
needed)
Method requires diatom inference model of ANC
Diatom species change substantially over century
time scales, perhaps limiting the diatom
reconstructions of SWE to hundreds rather than
thousands of years




The hydrochemistry of lakes is sensitive to the
maritime Pacific snowpack
Acid neutralizing capacity (ANC) strongly affects lake
diatom species and its concentration is primarily
controlled by:
 Rock weathering
 Snowmelt dilution of weathering products
Diatom inference models can be used with lake-specific
relationships between ANC & snowpack to reconstruct
SWE from sediment cores
Model is being applied to longer sediment cores and
reconstructions are being validated by comparisons to
dendroclimatic data
Q
U
E
S
T
I
O
N
S
?
ANC:Snowpack Relationship
In Rocky Mt. Lakes