High Arctic lakes as sentinel ecosystems: Cascading regime shifts in climate, ice cover, and mixing

Abstract

Climate and cryospheric observations have shown that the high Arctic has experienced several decades of rapid environmental change, with warming rates well above the global average. In this study, we address the hypothesis that this climatic warming affects deep, ice-covered lakes in the region by causing abrupt, threshold-dependent shifts rather than slow, continuous responses. Synthetic aperture radar (SAR) data show that lakes (one freshwater and four permanently stratified) on Ellesmere Island at the far northern coastline of Canada have experienced significant reductions in summer ice cover over the last decade. The stratified lakes were characterized by strong biogeochemical gradients, yet temperature and salinity profiles of their upper water columns (5-20 m) indicated recent mixing, consistent with loss of their perennial ice and exposure to wind. Although subject to six decades of warming at a rate of 0.5uC decade 21 , these lakes were largely unaffected until a regime shift in air temperature in the 1980s and 1990s, when warming crossed a critical threshold forcing the loss of ice cover. This transition from perennial to annual ice cover caused another regime shift whereby previously stable upper water columns were subjected to mixing. Far northern lakes are responding discontinuously to climate-driven change via a cascade of regime shifts and have an indicator value beyond the regional scale.There is a broad consensus that the world is entering a period of accelerated climate change (Solomon et al. 2007). Anthropogenic emissions of greenhouse gases and the resultant increase in net radiative forcing are widely accepted as the cause of this rapidly changing climate (Hansen et al. 2006). We are now faced with the challenge of evaluating the extent and pace of this change and its effect on the biosphere.Computer models and direct observations (Serreze and Francis 2006) indicate that the highest amplitude and most rapid climate changes are occurring in the Arctic. Although there is considerable variability among regions, the annual average air temperature in the North American continental Arctic increased by 1.06uC decade 21 during the last two decades (Comiso 2003), well above the global average of 0.2uC decade 21 during the same period (Hansen et al. 2006). The thinning and decrease in extent of Arctic sea ice cover (Maslanik et al. 2007) will lead to even more pronounced changes through an albedo-driven positive feedback that would cause Arctic Ocean warming, a further decrease in sea ice extent, and more amplification of high latitude warming.Many reports have shown significant climate change and associated ecosystem effects in the Arctic since the beginning of the short observational period in this region (Serreze et al. 2000). Long-term trends, however, have been difficult to resolve in the Arctic, in part because of the lack of site-specific data and substantial interannual variability in climate, which is exacerbated by the Northern Annular Mode. These factors act to obscure underlying tre...

Exceptional summer warming leads to contrasting outcomes for methane cycling in small Arctic lakes of Greenland

“…Projected climate change is expected to change ice cover characteristics in lakes (Fang and Stefan, 2009;Mueller et al, 2009). Ice coverage duration has already decreased for many lakes as ground-level air temperatures have increased (Bertilsson et al, 2013;Weyhenmeyer et al, 2011).…”

Lakes and reservoirs as sentinels, integrators, and regulators of climate change

“…Sophisticated scaling and modeling approaches are required to integrate these disparate levels of response of lakes to climate change at local, regional, and global scales (MacKay et al 2009). To really understand the role of lakes as sentinels, integrators, and regulators of climate change, broader-scale assessment of key regulating variables such as ice cover (Mueller et al 2009) and DOM (Kutser et al 2005) is necessary, and techniques such as remote sensing are being successfully developed to do this.…”

“…Climate-induced regime shifts have also been recognized in lakes where changes in phenology, and more specifically the timing of the CWP events, are altered by climate change (Scheffer et al 2001). Arctic lakes are currently undergoing important regime shifts as warmer temperatures are leading them to transition from perennially ice-covered to annually ice-covered systems (Mueller et al 2009). …”

“…Polar and alpine lakes are undergoing particularly rapid climate change (Bradley et al 2006;Veillette et al 2008;Mueller et al 2009), and as such may be some of the most sensitive sentinels of climate change. Optical changes in UV and fluorescence in an alpine lake in the Sierra Nevada of Spain are effective sentinels of dust blown from the Sahara Desert (Mladenov et al 2009).…”

“…Several papers examine climatic control of the physical structure (MacIntyre et al 2009;Mueller et al 2009;Verburg and Hecky 2009) and carbon chemistry (Catalan et al 2009;Finlay et al 2009;Weyhenmeyer and Karlsson 2009) of lake ecosystems. Climatic forcing of biological responses in lake ecosystems (Castañ eda et al 2009;Drö scher et al 2009;Graham and Vinebrooke 2009;Wagner and Adrian 2009a;Winder et al Fig.…”