Interannual Variability of Lake Superior’s Temperature: Consequences for cold-water fishes Elise A. Ralph, Large Lakes Observatory & Physics-Duluth Thomas Hrabik, Biology-Duluth University of Minnesota Outline Data Collection Temperature Variability Implications for Cold-water fishes Western Lake Superior: 1995-2002 N Two Harbors, MN Duluth Port Wing Port Wing, WI Two Harbors May 1998-May 2000 KITES and WLS Current measurements : 60 minutes Temperature measurements : 15 minutes Weather causes rapid temperature changes at depths as deep as 50 meters Eagle Harbor mooring 20 18 19 m 39 m 87 m 16 14 12 10 8 6 4 2 0 05/25 06/14 07/04 07/24 08/13 09/02 09/22 Wind-Driven Variability Interannual Variability 0 TH 07-Jul-1997 Temperature (C) 0 18 16 -50 depth (m) -50 depth (m) 20 TH 06-Jul-1998 Temperature (C) -100 -150 14 12 -100 10 -150 8 6 -200 0 -200 5 10 15 20 25 distance from shore (km) 30 0 4 5 10 15 20 distance from shore (km) 25 30 2 Interannual Variability 20 18 16 14 12 10 8 6 4 2 0 May98 Jun98 Jul98 Aug98 Sep98 Oct98 Nov98 Dec98 Jan99 Feb99 Mar99 Apr99 May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00 20 18 16 14 12 10 8 6 4 2 0 May99 Long-term Global-wide changes Predicted change in temperature with double CO2 Predicted changes within the lakes What has happened so far? Annual Temperature Anomalies 2.5 Anomalies 2 Temperature o C 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 1900 1920 1940 1960 1980 2000 Trend is 0.87 degrees over 90 years of record 250 Length of Stratified Period 240 230 220 210 200 190 180 170 160 1900 1920 1940 1960 1980 2000 10-14 degree range: Thermal Niche for cold-water fish (Lake Trout and Herring) 20 18 16 14 12 10 8 6 4 2 0 May98 Jun98 Jul98 Aug98 Sep98 Oct98 Nov98 Dec98 Jan99 Feb99 Mar99 Apr99 May99 Jun99 Jul99 Aug99 Sep99 Oct99 Nov99 Dec99 Jan00 Feb00 Mar00 Apr00 May00 20 18 16 14 12 10 8 6 4 2 0 May99 Thickness of thermal niche thickness for cold-water fish (10-14 degrees C) 70 1998 1999 701 60 843 thickness (meters) 50 40 30 20 10 0 07/01 10/01 01/01 Leptodiaptomus 9.2 y = 4.0 + 0.33 x r = 0.90 6.9 4.6 July (Linear Fit)Augus t 2.3 0 5 10 15 10 15 Diacyclops 9.2 ln (N / cubic m ) y = 1.6 + 0.54 x r = 0.84 6.9 4.6 2.3 5 9.2 0 Limnocalanus 6.9 4.6 y = 6.4 - 0.06 x r = 0.34, where x > 5 2.3 0 5 10 15 Temperature (Celsius) CONCLUSIONS and CONSEQUENCES: • 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. 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.
© Copyright 2024 Paperzz
