interannual variability of lake superior’s temperature: consequences for cold-water fishes elise...
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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
metersmeters
05/25 06/14 07/04 07/24 08/13 09/02 09/220
2
4
6
8
10
12
14
16
18
20Eagle Harbor mooring
19 m39 m87 m
Wind-Driven VariabilityWind-Driven Variability
Interannual VariabilityInterannual Variability
0 5 10 15 20 25 30
-200
-150
-100
-50
0
distance from shore (km)
TH 07-Jul-1997 Temperature (C)
dep
th (
m)
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20 25 30
-200
-150
-100
-50
0TH 06-Jul-1998 Temperature (C)
dep
th (
m)
distance from shore (km)
Interannual VariabilityInterannual Variability
May98 Jun98 Jul98 Aug98 Sep98 Oct98 Nov98 Dec98 Jan99 Feb99 Mar99 Apr99 May99
0
2
4
6
8
10
12
14
16
18
20
May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00
0
2
4
6
8
10
12
14
16
18
20
Long-term Global-wide Long-term Global-wide changeschanges
Predicted change in Predicted change in temperature with double temperature with double
COCO22
Predicted changes within Predicted changes within the lakesthe lakes
What has happened so far?
Annual Temperature Annual Temperature AnomaliesAnomalies
Trend is 0.87 degrees over 90 years of record
1900 1920 1940 1960 1980 2000-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5T
emp
erat
ure
o C
Anomalies
1900 1920 1940 1960 1980 2000160
170
180
190
200
210
220
230
240
250Length of Stratified Period
May98 Jun98 Jul98 Aug98 Sep98 Oct98 Nov98 Dec98 Jan99 Feb99 Mar99 Apr99 May99
0
2
4
6
8
10
12
14
16
18
20
May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00
0
2
4
6
8
10
12
14
16
18
20
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.
CONCLUSIONS and CONSEQUENCES:
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