Ecological Regime Shifts in Lake Kälksjön, Sweden, in Response to Abrupt Climate Change Around the 8.2 ka Cooling Event

Linda Randsalu-Wendrup,Ian Snowball,Sherilyn C Fritz,Jacob Carstensen,Catherine Jessen,Daniel J Conley

doi:10.1007/s10021-012-9588-1

Linda Randsalu-Wendrup, Ian Snowball + Show 4 more

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https://doi.org/10.1007/s10021-012-9588-1

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Abstract

A detailed diatom record from Lake Kalksjon, west- central Sweden, reveals two periods of abrupt ecological change correlative with the 8.2 ka cool- ing event. Using a combination of abrupt step changes and piece-wise linear regressions, the diatom data were analyzed for change points over time, and two sudden and large events that are described as regime shifts were detected. During the first event at c. 8040 cal. y BP, a doubling in diatom biomass took place over 5-10 years. This increase in primary productivity can be connected to an erosion event in the catchment that resulted in an abrupt increase in nutrient supply to the lake. The second event was characterized by a sub- stantial shift within the planktonic diatom com- munity from taxa indicative of colder conditions to those indicating warm over 5-10 years at c. 7850 cal. y BP. This event was superimposed on a successive change from periphytic to planktonic diatom dominance over a 250-year period and a gradual diversification of the periphytic community that spanned c. 150 years. Rapid climate warming following the 8.2 ka event likely caused these changes and both regime shifts are examples of externally driven abrupt ecological change. This study demonstrates that it is possible to detect, quantify and test for regime shifts in paleoecologi- cal data, and it highlights the need for high sam- pling resolution and precise chronological control. High-resolution paleoecological reconstructions of ecological regime shifts in response to climate change can provide useful analogues of future changes in ecosystem structure and functioning.

Highlights

IntroductionAbrupt climate change and associated or independent abrupt ecological change has been observed in various ecosystems, including marine environments (for example, Beaugrand 2004; Collie and others 2004; Spencer and others 2011), Arctic lakes (Smol and others 2005; Ruhland and others 2008), brackish lagoons (Jeppesen and others 2007), terrestrial ecosystems (Dearing 2008), coastal areas (Conley and others 2009; Duarte and others 2009) and shallow lakes (for example, Scheffer and van Nes 2007; Scheffer and Jeppesen 2007; Zimmer and others 2009)
Abrupt climate change and associated or independent abrupt ecological change has been observed in various ecosystems, including marine environments, Arctic lakes (Smol and others 2005; Ruhland and others 2008), brackish lagoons (Jeppesen and others 2007), terrestrial ecosystems (Dearing 2008), coastal areas (Conley and others 2009; Duarte and others 2009) and shallow lakes
The second event was characterized by a substantial shift within the planktonic diatom community from taxa indicative of colder conditions to those indicating warm over 5–10 years at c. 7850 cal. y BP

Summary

Introduction

Abrupt climate change and associated or independent abrupt ecological change has been observed in various ecosystems, including marine environments (for example, Beaugrand 2004; Collie and others 2004; Spencer and others 2011), Arctic lakes (Smol and others 2005; Ruhland and others 2008), brackish lagoons (Jeppesen and others 2007), terrestrial ecosystems (Dearing 2008), coastal areas (Conley and others 2009; Duarte and others 2009) and shallow lakes (for example, Scheffer and van Nes 2007; Scheffer and Jeppesen 2007; Zimmer and others 2009). Analysis of Greenland ice-core records indicates that an abrupt cooling event began around 8175 ± 30 cal. Y BP has been described in several proxy records in the Northern Hemisphere (for example, Alley and others 1997; Tinner and Lotter 2001; Veski and others 2004; Hammarlund and others 2005; Ojala and others 2008; Panizzo and others 2008; Snowball and others 2010) but due to the natural smoothing of palaeoclimate records, relatively low sampling resolution, chronological uncertainties, possible delays in ocean–atmospheric coupling and inconsistent responses of different proxy records to the assumed climate excursion, the records are difficult to compare and the total impact of the event has been difficult to study (Ojala and others 2008; Snowball and others 2010) A cooling episode around 8200 cal. y BP has been described in several proxy records in the Northern Hemisphere (for example, Alley and others 1997; Tinner and Lotter 2001; Veski and others 2004; Hammarlund and others 2005; Ojala and others 2008; Panizzo and others 2008; Snowball and others 2010) but due to the natural smoothing of palaeoclimate records, relatively low sampling resolution, chronological uncertainties, possible delays in ocean–atmospheric coupling and inconsistent responses of different proxy records to the assumed climate excursion, the records are difficult to compare and the total impact of the event has been difficult to study (Ojala and others 2008; Snowball and others 2010)

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