Interannual Interannual Variability of Lake Variability of Lake Superior’s Superior’s Temperature: Temperature: Consequences for cold- Consequences for cold- water fishes water fishes Elise A. Ralph, Large Lakes Observatory & Elise A. Ralph, Large Lakes Observatory & Physics-Duluth Physics-Duluth Thomas Hrabik, Biology-Duluth Thomas Hrabik, Biology-Duluth University of Minnesota University of Minnesota
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Interannual Variability of Lake Superior’s Temperature: Consequences for cold-water fishes Elise A. Ralph, Large Lakes Observatory & Physics-Duluth Thomas.
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Interannual Variability of Interannual Variability of Lake Superior’s Lake Superior’s Temperature: Temperature:
Consequences for cold-Consequences for cold-water fisheswater fishesElise A. Ralph, Large Lakes Observatory & Physics-Elise A. Ralph, Large Lakes Observatory & Physics-
DuluthDuluth
Thomas Hrabik, Biology-DuluthThomas Hrabik, Biology-Duluth
University of MinnesotaUniversity of Minnesota
OutlineOutline
Data CollectionData Collection Temperature VariabilityTemperature Variability Implications for Cold-water fishesImplications for Cold-water fishes
Two Harbors
Port Wing
Duluth
Two Harbors, MN
Port Wing, WI
Western Lake Superior: 1995-2002
N
Current measurements :Current measurements :
60 minutes60 minutes
Temperature measurements : Temperature measurements :
15 minutes15 minutes
May 1998-May 2000
KITES and WLS
Weather causes rapid temperature Weather causes rapid temperature changes at depths as deep as 50 changes at depths as deep as 50
10-14 degree range: Thermal Niche for cold-water fish(Lake Trout and Herring)
07/01 10/01 01/010
10
20
30
40
50
60
70
thic
kne
ss (
me
ters
)
701
843
19981999
Thickness of thermal niche thickness for cold-water fish (10-14 degrees C)
2.3
4.6
6.9
9.2
0 5 10 15
July (Linear Fit)August
Leptodiaptomus
y = 4.0 + 0.33 xr = 0.90
2.3
4.6
6.9
9.2
ln (
N / c
ubic
m )
0 5 10 15
Diacyclops
y = 1.6 + 0.54 xr = 0.84
2.3
4.6
6.9
9.2
0 5 10 15 Temperature (Celsius)
Limnocalanus
y = 6.4 - 0.06 xr = 0.34,where x > 5
• Lake Superior undergoes temperature changes over time Lake Superior undergoes temperature changes over time scales ranging from days to decades. By observing scales ranging from days to decades. By observing these changes and their consequences, we can begin to these changes and their consequences, we can begin to understand what may happen to the Lake during climate understand what may happen to the Lake during climate change.change.
Lake Superior temperatures have risen by approximately 1 degree over theLake Superior temperatures have risen by approximately 1 degree over the past century.past century.
The summer stratified season has gotten 20 days longer.The summer stratified season has gotten 20 days longer.
Winter mixing (“turn-over”) is an important source of oxygen to deep lake waters. If the temperature increase is consistent with model predictions, winter-mixing will shut off.
Changes in stratification, as well as mean temperature, affect the thickness and duration of thermal niches.