Interannual Variability of Lake Superior’s Temperature: Consequences for cold-water fishes Elise A. Ralph, Large Lakes Observatory & Physics-Duluth Thomas Hrabik, Biology-Duluth Thomas Hrabik, Biology-Duluth University of Minnesota

Outline Data Collection Data Collection Temperature Variability Temperature Variability Implications for Cold-water fishes Implications for Cold-water fishes

Two Harbors Port Wing Duluth Two Harbors, MN Port Wing, WI Western Lake Superior: N

Current measurements : 60 minutes 60 minutes Temperature measurements : 15 minutes 15 minutes May 1998-May 2000 KITES and WLS

Weather causes rapid temperature changes at depths as deep as 50 meters

Wind-Driven Variability Wind-Driven Variability

Interannual Variability

Long-term Global-wide changes

Predicted change in temperature with double CO 2

Predicted changes within the lakes What has happened so far?

Annual Temperature Anomalies Trend is 0.87 degrees over 90 years of record

10-14 degree range: Thermal Niche for cold-water fish (Lake Trout and Herring)

Thickness of thermal niche thickness for cold-water fish (10-14 degrees C)

Lake Superior undergoes temperature changes over time scales ranging from days to decades. By observing these changes and their consequences, we can begin to understand what may happen to the Lake during climate change.Lake Superior undergoes temperature changes over time scales ranging from days to decades. By observing these changes and their consequences, we can begin to understand what may happen to the Lake during climate change. Lake Superior temperatures have risen by approximately 1 degree over the past century. The summer stratified season has gotten 20 days longer. past century. 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: