Use of principal component analysis to extract environmental information from lake water isotopic compositions

Abstract

Lake water hydrogen (δD) and oxygen (δ18O) isotopic ratios have been widely used to study the hydrologic cycle. In a given region, δD and δ18O values from multiple lakes are often correlated and define a local evaporation line (LEL). The slope of and extension of each lake along this line contain information of many variables with entangled effects of important lake fluxes (e.g., evaporation). We present a new method to extract regional and local (a particular lake) environmental information based on principal component analyses (PCAs) of the δD‐δ18O relationships. Water of up to 30 lakes in West Greenland was sampled every summer for 5 yr, and measured for δD and δ18O values. For a given year, PCA yields values of the first (Enrichment) and second (Deviance) principal components for each lake. In addition, we obtain the slope of the line along the first eigenvector, which is similar, but not identical, to the LEL. We refer to this line as the regional isotopic enrichment line (RIEL), and demonstrate that the RIEL slope changes interannually with the dominant atmospheric circulation patterns affecting regional humidity, specifically the North Atlantic Oscillation and frequency of sea breezes. The Deviance of a lake correlates strongly with its longitude and surface area, both of which influence local humidity and isotopic ratios of vapor. Conversely, Enrichment carries little extractable environmental information because it is controlled by many variables of competing effects. This method can be widely applied to both modern hydrological studies and paleoclimate reconstructions using lake sediments.

Reconstructing Arctic Precipitation Seasonality Using Aquatic Leaf Wax δ2H in Lakes With Contrasting Residence Times

“…Evaporative enrichment of terrestrial plant leaf water controls leaf wax δ 2 H values (Kahmen, Hoffmann, et al, 2013;. In the same set of lake water studies near Kangerlussuaq, 261 lakes near the ice sheet experience similar degrees of evaporative enrichment, with evaporation line slopes of 3.5 to 5 (Cluett & Thomas, 2020;Kopec et al, 2018;Leng & Anderson, 2003) and deuterium excess values of -24±15‰ (1 SD; n = 75) (Cluett & Thomas, 2020). Plants in this same region experience 264 dramatically more evaporative enrichment, with evaporation line slopes around 2.5 and leaf water 265 deuterium excess values of -115±50‰ (1 SD; n = 21) (Bush et al, 2017).…”

“…We are aware of one site in the Arctic, near Sisimiut and Kangerlussuaq, Greenland, with isotopic measurements of both terrestrial plant leaf water (Bush et al, 2017) and lake water (Cluett & Thomas, 2020;Kopec et al, 2018;Leng & Anderson, 2003). This region spans a climatic gradient from maritime near the coast (Sisimiut) to continental (evaporation > precipitation) near the ice sheet (Kangerlussuaq) (Hasholt & Søgaard, 1978).…”

“…This region spans a climatic gradient from maritime near the coast (Sisimiut) to continental (evaporation > precipitation) near the ice sheet (Kangerlussuaq) (Hasholt & Søgaard, 1978). The inferred isotopic composition of source water for lakes and terrestrial 241 plants near the ice sheet is similar, falling between mean annual and winter precipitation isotope values 242 (Bush et al, 2017;Cluett & Thomas, 2020;Kopec et al, 2018;Leng & Anderson, 2003). In contrast, source waters for lakes closer to the coast tend to be summer-biased.…”

Changing Lake Dynamics Indicate a Drier Arctic in Western Greenland

“…Additionally, potential evaporation hydrological losses to the atmosphere in the summer months of June, July, and August (Figure ) are likely an important factor to west Greenland lake declines. Increasing summertime water deficits have also been observed in other regions of the circumpolar north (Hinzman et al, ; Riordan et al, ), meaning increasing evapotranspiration could be an Arctic‐wide occurrence (Bring et al, ; Kopec et al, ). At a global scale, model predictions estimate lake evaporation to increase by as much as 16% by the end of the century, despite little changes due to incoming solar radiation at the surface (Wang et al, ).…”

Modern Eastern Canadian Arctic Lake Water Isotopes Exhibit Latitudinal Patterns in Inflow Seasonality and Minimal Evaporative Enrichment

“…Another mechanism that may cause the observed isotopic differences between the lakes is the “lake size effect” (Feng et al., 2016; Kopec et al., 2018). Apex Road Lake has a relatively small lake surface area, and therefore a small fetch, meaning that air blowing across the lake surface may be less saturated than that over other lakes.…”