A uniquely comprehensive set of four decades of ice breakup data from 196 Swedish lakes covering 13degrees of latitude (55.7degrees N to 68.4degrees N) shows the relationship between the timing of lake ice breakup and air temperature to be an arc cosine function. The nonlinearity inherent in this relationship results in marked differences in the response of the timing of lake ice breakup to changes in air temperature between colder and warmer geographical regions, and between colder and warmer time periods. The spatial and temporal patterns are mutually consistent, suggesting that climate change impacts on the timing of lake ice breakup will vary along a temperature gradient. This has potentially important ramifications for the employment of lake ice phenologies as climate indicators and for the future behavior of lacustrine ecosystem

Livingstone, David M.

Meili, Markus

Weyhenmeyer, Gesa

Epsilon Open Archive

  This is an author produced version of a paper published in Geophysical Research Letters. This paper has been peer-reviewed and includes the final publisher proof-corrections and journal pagination. Citation for the published paper: Weyhenmeyer, Gesa; Meili, Markus; Livingstone, David. (2004) Nonlinear temperature response of lake ice breakup. Geophysical Research Letters. Volume: 31, Number: 7. http://dx.doi.org/10.1029/2004GL019530. Access to the published version may require journal subscription. Published with permission from: American Geophysical Union.  Epsilon Open Archive http://epsilon.slu.se Nonlinear temperature response of lake ice breakupGesa A. Weyhenmeyer,1 Markus Meili,2 and David M. Livingstone3Received 20 January 2004; revised 3 March 2004; accepted 12 March 2004; published 6 April 2004.[1] A uniquely comprehensive set of four decades of icebreakup data from 196 Swedish lakes covering 13 oflatitude (55.7N to 68.4N) shows the relationship betweenthe timing of lake ice breakup and air temperature to be anarc cosine function. The nonlinearity inherent in thisrelationship results in marked differences in the responseof the timing of lake ice breakup to changes in airtemperature between colder and warmer geographicalregions, and between colder and warmer time periods.The spatial and temporal patterns are mutually consistent,suggesting that climate change impacts on the timing of lakeice breakup will vary along a temperature gradient. This haspotentially important ramifications for the employment oflake ice phenologies as climate indicators and for the futurebehavior of lacustrine ecosystems. INDEX TERMS: 1630Global Change: Impact phenomena; 1833 Hydrology:Hydroclimatology; 1845 Hydrology: Limnology; 1863Hydrology: Snow and ice. Citation: Weyhenmeyer, G. A.,M. Meili, and D. M. Livingstone (2004), Nonlinear temperatureresponse of lake ice breakup, Geophys. Res. Lett., 31, L07203,doi:10.1029/2004GL019530.1. Introduction[2] The timing of lake ice breakup has been of interestfor centuries because of its importance for transportationand fishing [Adams, 1981]. It is of critical ecologicalimportance for lakes because the disappearance ofthe ice cover has a drastic effect on the underwater lightclimate [Leppa¨ranta et al., 2003], nutrient recycling[Ja¨rvinen et al., 2002] and oxygen conditions [Stewart,1976; Livingstone, 1993], influencing for instancethe production and biodiversity of phytoplankton[Rodhe, 1955; Phillips and Fawley, 2002; Weyhenmeyeret al., 1999] and the occurrence of winter fishkills[Greenbank, 1945; Barica and Mathias, 1979]. Air tem-perature is the key variable determining the timing of icebreakup [Ruosteenoja, 1986; Vavrus et al., 1996]. Bothlong-term trends and short-term variability in air temper-ature are therefore reflected in the timing of ice breakup[Palecki and Barry, 1986; Robertson et al., 1992; Asseland Robertson, 1995; Livingstone, 1997, 1999; Magnusonet al., 2000; Sagarin and Micheli, 2001]. Here we examineregional and temporal differences in the response of lakeice breakup dates to air temperature, based on over 40 yrof data (1961–2002) from 196 lakes in Sweden.2. Data and Methods[3] The 196 Swedish lakes (Figure 1) vary widely in size,from 0.1 to 5,650 km2. The lakes are situated along a north-south gradient in annual mean surface air temperatureranging from 3C at about 68N to 7C at about 56N(1961–90). Riverine stations with a characteristic flowvelocity of >0.1 m s1 during ice breakup and hydroelectricreservoirs with a regulation amplitude of >3 m wereexcluded from the lake ice breakup dataset. An overviewof the ice data, including methods of observation, has beengiven by Eklund [1999].[4] In this study we relate both spatial and temporalvariations in the timing of lake ice breakup in Sweden toair temperature. The air temperature data utilized in thespatial comparison were atlas reference normals computedfrom 30 yr of data (1961–90) measured at 510 meteoro-logical stations [Raab and Vedin, 1995]. The data for thetemporal comparison were obtained from 12 of thesestations.3. Regional Patterns of Lake Ice Breakup[5] Latitude has been viewed as a simple proxy for airtemperature, and linear relationships of lake ice breakupdates to latitude have been reported [Palecki and Barry,1986; Assel and Herche, 2000]. However, our data suggestthat the latitudinal dependence of the timing of ice breakupmight not be simply linear: both the gradient of the curve ofice breakup date versus latitude and the magnitude of theyear-to-year variations in ice breakup dates decline atlatitudes higher than 62N (Figure 2). In contrast, lake-to-lake variability in the median date of ice breakup is highestnorth of 62N (Figure 2), where isotherms tend to followlongitude rather than latitude [Raab and Vedin, 1995].Because of the influence of the sea and local topography,latitude can be considered a valid proxy for air temperatureonly on large scales. We therefore carried out a more directcomparison of the ice data with lake-specific mean airtemperatures (1961–90 normals [Raab and Vedin, 1995]).The data suggest that the timing of lake ice breakupresponds in a nonlinear fashion to air temperature(Figure 3a). The response is much stronger in the warmestsouthern region of Sweden (14 d per 1C), wherethe duration of ice cover usually varies between 0 and125 d [Eklund, 1999], than in the coldest northern region(4 d per 1C), where it is substantially longer (200–250 d[Eklund, 1999]). We explored whether such regional differ-ences in the climatic sensitivity of the timing of ice breakupcan be linked to differences in the annual air temperaturecycle. To a first approximation the annual cycle can beGEOPHYSICAL RESEARCH LETTERS, VOL. 31, L07203, doi:10.1029/2004GL019530, 20041Department of Environmental Assessment, Swedish University ofAgricultural Sciences, Uppsala, Sweden.2Institute of Applied Environmental Research (ITM), StockholmUniversity, Stockholm, Sweden.3Water Resources Department, Swiss Federal Institute of EnvironmentalScience and Technology (EAWAG), Du¨bendorf, Switzerland.Copyright 2004 by the American Geophysical Union.0094-8276/04/2004GL019530$05.00L07203 1 of 4expressed as a sinusoid, characterized by a site-specifictemperature mean (Tm) and amplitude (Ta). The duration ofthe period with air temperatures below 0C, D  (1/p)arccos(Tm/Ta), responds to changes in Tm approximatelylinearly if D is between 3 and 9 months, but deviatesincreasingly from linearity as D approaches 0 or 12 months.Employing the above equation for D, the median calendardate of ice breakup (tB) can be expressed as a nonlinearfunction of mean air temperature by taking advantage ofregional relationships between the means, amplitudes andphase shifts of temperature cycles in air and lake surfacewater. Based on regional temperature patterns in Sweden[Raab and Vedin, 1995], Ta and Tm are related such thatTm/Ta in the above expression for D can be approximatedby 2  Tm/(24C  Tm), thus allowing the slope andcurvature of D to be predetermined independently of theice data. Adding the median deviation of the observedbreakup dates (55 d) as a phase parameter reflecting theoverall timing of breakup in the region then yields thefollowing equation to predict the median Julian day (tB, ind) of lake ice breakup in our Swedish lakes based solely onlake-specific annual mean air temperatures:tB ¼ 365d2p arccos2Tm24C Tm þ 55dThe timing of breakup of individual lakes is usually relatedmost strongly to air temperatures integrated over periods of1–3 months previous to the mean date of breakup [e.g.,Palecki and Barry, 1986; Robertson et al., 1992;Livingstone, 1997, 1999]. In our model we used annualFigure 1. Map of Sweden showing the even geographicaldistribution of the 196 lakes with available ice data uponwhich the spatial and temporal comparisons of Figures 2and 3 were based. The 54 lakes with complete 30-yr time-series (1961–1990) are represented by black dots and theremaining 142 lakes by gray dots. The 14 lakes representedby black dots within each of the geographical regions I andII are those used in the temporal comparison of Figure 3b.Figure 2. Relationship between the timing of ice breakupin Swedish lakes and latitude. The black symbols representthe median breakup dates during 1961–90 for 54 lakes withcomplete 30-yr series of ice observations; the gray symbolsrepresent all available breakup dates from 196 lakes during1961–2002. See Figure 1 for the locations of the lakes.Figure 3. (a) Spatial variation in the relationship betweenmedian ice breakup dates during 1961–90 and lake-specificmean air temperatures (1961–90 normals [Raab and Vedin,1995]) for the 54 lakes with complete data series illustratedin Figure 2, and for 16 southern lakes for which at least 28 yrof ice data were available (open symbols; missing data wereinterpolated from neighboring lakes, which influencedmedians by only 0–1 d). The curve illustrated is based onregional patterns in the annual temperature cycle (see text).(b) Temporal variation in the relationship between icebreakup dates (median values for 14 lakes in each ofRegions I and II) and annual mean air temperatures (July–June) from 1961 to 1990 (black; all data series complete)and from 1991 to 2002 (gray; a few missing data wereinterpolated as in Figure 3a). See Figure 1 for the locationsof Regions I and II.L07203 WEYHENMEYER ET AL.: PATTERNS OF LAKE ICE BREAKUP L072032 of 4mean air temperatures to determine ice breakup dates.Annual means have the advantage of being free of anarbitrary choice of time period, and are therefore particu-larly useful for studies along a latitudinal gradient with awide range of breakup dates (in Sweden, these extend fromJanuary to June). In addition, annual means are rarelylimited by data availability (readily accessible atlas data canbe used). For reasons of general applicability, therefore, amodel based on annual mean air temperatures is preferableto one based on air temperatures integrated over a shortertime period.[6] The observed ice breakup dates follow the predictedair temperature dependence surprisingly well across thewhole temperature range (Figure 3a). In addition, theresiduals are very small, although they include uncertaintiesin both the temperature and ice data, and although temper-atures here are represented exclusively by annual means,which indicates that the control of ice breakup by factorsother than the regional climate (e.g., local weather condi-tions or lake morphometry) is weak. Apart from areas understrong maritime influence and the warmest regions withirregular ice cover, residuals of the 30-yr medians from ourregional model are usually less than 5 d. This illustrates theaccuracy with which median ice breakup dates can bepredicted from air temperature normals by using simplealgorithms, even without accounting for local seasonality.4. Temporal Patterns of Lake Ice Breakup[7] The nonlinear temperature response of lake icebreakup on a spatial scale might possibly differ from thaton a temporal scale. We therefore investigated the sensitiv-ity of breakup dates to interannual variations in air temper-ature over 42 yr (1961–2002) within two climaticallydifferent geographical regions, one covering most of thenorth-east of Sweden (Region I in Figure 1; 61–67N, Tm 0–3C) and the other covering the south of Sweden(Region II; 56–60N, Tm  5–7C). Each of these regionswas represented by median dates from 14 evenly distributedlakes and by annual mean temperatures (July– June)derived from the anomalies observed at six evenly distrib-uted meteorological stations. Evaluations based on our datahad shown that both air temperature and breakup dates werehighly coherent within each of the regions, and that theinfluence of the selection and number of lakes and stationson the computed median values was negligible. We foundthat the dependence of the timing of ice breakup on airtemperature derived from the temporal comparison(Figure 3b) was virtually identical to that derived fromthe spatial comparison (Figure 3a). Moreover, the residualswere only about twice as large (as would be expectedbecause the number of observations included was fourtimes less), although neither local nor seasonal deviationsfrom the average regional temperature cycle had been takeninto account.5. Recent Patterns of Lake Ice Breakup[8] The observed nonlinearity of the relationship betweenbreakup dates and mean air temperature implies that long-term changes in air temperature will have a greater effect onthe timing of lake breakup in warmer regions (air temper-ature reference normals: 5 to 7C) than in colder regions(2 to 2C). This was tested with data from the period1991–2002, when mean air temperatures over the whole ofSweden were homogeneously 0.8C higher than during theperiod 1961–90. This recent temperature increase causedice breakup to occur on average 17 d earlier in the warmerRegion II but only 4 d earlier in the colder Region I (medianof the 14 lakes in each region; Figure 3b).6. Conclusions[9] We conclude that, whereas increasing air temper-atures may result in drastic shifts in the timing of lake icebreakup in temperate regions, such shifts are likely to bemuch less drastic in colder regions. As a consequence, anyfuture increase in air temperature might result not only ingenerally earlier ice breakup, but also in a heterogeneousshift in the timing of breakup along regional temperaturegradients. Since the timing of ice breakup determines thetiming of many physical, chemical and biological lakeprocesses, this may lead to an alteration in the diversity oflake types in many areas.[10] Acknowledgments. We thank the Swedish Meteorological andHydrological Institute for providing temperature and ice breakup data, andJakob Nisell for generating lake-specific mean air temperatures. This workwas partly funded by the European Union and by the Swiss Federal Officeof Education and Science within the framework of the European Commis-sion projects CLIME (‘Climate and Lake Impacts in Europe’, EVK1-CT-2002-00121) and Euro-limpacs (‘Integrated Project to Evaluate the Impactsof Global Change on European Freshwater Ecosystems’, GOCE-CT-2003-505540).ReferencesAdams, W. P. (1981), Snow and ice on lakes, in Handbook of Snow:Principles, Processes, Management and Use, edited by D. M. Grayand D. H. Male, pp. 437–474, Pergamon, New York.Assel, R. A., and L. H. Herche (2000), Coherence of long-term lake icerecords, Verh. Int. Ver. Limnol., 27, 2789–2792.Assel, R. A., and D. M. Robertson (1995), Changes in winter air tempera-tures near Lake Michigan, 1851–1993, as determined from regional lakeice-records, Limnol. Oceanogr., 40, 165–176.Barica, J., and J. A. Mathias (1979), Oxygen depletion and winterkill risk insmall prairie lakes under extended ice cover, J. Fish. Res. Board Can., 36,980–986.Eklund, A. (1999), Isla¨ggning och islossning i svenska sjo¨ar (Ice-on andice-off in Swedish lakes), SMHI-Rep. Hydrol. 81, Statens Meteorol. ochHydrol. Inst., Norrko¨ping, Sweden.Greenbank, J. (1945), Limnological conditions in ice-covered lakes, espe-cially related to winterkill of fish, Ecol. Monogr., 15, 343–392.Ja¨rvinen, M., M. Rask, J. Ruuhija¨rvi, and L. Arvola (2002), Temporalcoherence in water temperature and chemistry under the ice of boreallakes (Finland), Water Res., 36, 3949–3956.Leppa¨ranta, M., A. Reinart, A. Erm, H. Arst, M. Hussainov, and L. Sipelgas(2003), Investigation of ice and water properties and under-ice light fieldsin fresh and brackish water bodies, Nord. Hydrol., 34, 245–266.Livingstone, D. M. (1993), Lake oxygenation: Application of a one-boxmodel with ice cover, Int. Rev. Ges. Hydrobiol., 78, 465–480.Livingstone, D. M. (1997), Break-up dates of alpine lakes as proxy data forlocal and regional mean surface air temperatures, Clim. Change, 37,407–439.Livingstone, D. M. (1999), Ice break-up on southern Lake Baikal and itsrelationship to local and regional air temperatures in Siberia and to theNorth Atlantic oscillation, Limnol. Oceanogr., 44, 1486–1497.Magnuson, J. J., et al. (2000), Historical trends in lake and river ice cover inthe Northern Hemisphere, Science, 289, 1743–1746.Palecki, M. A., and R. G. Barry (1986), Freeze-up and break-up of lakes asan index of temperature changes during the transition seasons: A casestudy for Finland, J. Clim. Appl. Meteorol., 25, 893–902.Phillips, K. A., and M. W. Fawley (2002), Winter phytoplankton commu-nity structure in three shallow temperate lakes during ice cover, Hydro-biologia, 470, 97–113.Raab, B., and H. Vedin (Eds.) (1995), The National Atlas of Sweden:Climate, Lakes, and Rivers, Bokfo¨rlaget Bra Bo¨cker, Ho¨gana¨s, Sweden.L07203 WEYHENMEYER ET AL.: PATTERNS OF LAKE ICE BREAKUP L072033 of 4Robertson, D. M., R. A. Ragotzskie, and J. J. Magnuson (1992), Lake icerecords used to detect historical and future climate change, Clim. Change,21, 407–427.Rodhe, W. (1955), Can phytoplankton production proceed during winterdarkness in subarctic lakes?, Verh. Int. Ver. Limnol., 12, 117–122.Ruosteenoja, K. (1986), The date of break-up of lake ice as a climaticindex, Geophysica, 22, 89–99.Sagarin, R., and F. Micheli (2001), Climate change in nontraditional datasets, Science, 294, 811.Stewart, K. M. (1976), Oxygen deficits, clarity and eutrophication in someMadison lakes, Int. Rev. Ges. Hydrobiol., 61, 563–579.Vavrus, S. J., R. H. Wynne, and J. A. Foley (1996), Measuring the sensi-tivity of southern Wisconsin lake ice to climate variations and lake depthusing a numerical model, Limnol. Oceanogr., 41, 822–831.Weyhenmeyer, G. A., T. Blenckner, and K. Pettersson (1999), Changes ofthe plankton spring outburst related to the North Atlantic oscillation,Limnol. Oceanogr., 44, 1788–1792.G. A. Weyhenmeyer, Department of Environmental Assessment, SwedishUniversity of Agricultural Sciences, Box 7050, SE-750 07 Uppsala,Sweden. (gesa.weyhenmeyer@ma.slu.se)M. Meili, Institute of Applied Environmental Research (ITM), StockholmUniversity, Frescativa¨gen 50/54, SE-106 91 Stockholm, Sweden. (markus.meili@itm.su.se)D. M. Livingstone, Water Resources Department, Swiss Federal Instituteof Environmental Science and Technology (EAWAG), U¨berlandstrasse 133,CH-8600 Du¨bendorf, Switzerland. (living@eawag.ch)L07203 WEYHENMEYER ET AL.: PATTERNS OF LAKE ICE BREAKUP L072034 of 4

Nonlinear temperature response of lake ice breakup

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Nonlinear temperature response of lake ice breakup

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