Influence of atmospheric modes of variability on a deep lake south of the Alps

Abstract

Limnological measurements and winter air temperatures recorded in a deep lake south of the Alps (Lake Garda) have been analysed and related to temporal variations in 5 teleconnection patterns, i.e. the East Atlantic pattern (EA), the Eastern Mediterranean Pattern (EMP), the North Atlantic Oscillation (NAO), the Scandinavia pattern (SCAND) and the East Atlantic/West Russia Pattern (EA/WR). The EA and EMP played a significant role in winter in the large-scale atmospheric circulation over the Mediterranean region. Positive and negative EA, and negative and positive EMP phases were closely connected with the development of mild and harsh winters, respectively. In turn, harsh winters had a strong positive impact on the development of diatoms in spring and cyanobacteria in summer and autumn. These modifications were controlled through a linked chain of factors, which included lower winter lake water temperatures, deep lake circulation episodes, and higher replenishment of epilimnetic phosphorus at spring overturn. This work demonstrates the existence of a strong connection between large-scale climatic fluctuations over the Mediterranean area and the temporal variations in the limnological characteristics of the large lakes located between the Alps and the northern border of the Mediterranean region. Conversely, the NAO, SCAND and EA/WR did not show any relationship with the winter climate and the limnological characteristics of Lake Garda.

Inter-annual climate variability and zooplankton: applying teleconnection indices to two deep subalpine lakes in Italy

“…In the considered period, Lake Maggiore was fully recovered from eutrophication, with well balanced, stable plankton communities. As for Lake Garda, the between-year fluctuations in the availability of nutrients in the same period were far more important compared with the long-term decadal changes (Salmaso, 2012). In addition, as shown in previous works (Salmaso et al, 2013) which analyzed more extended periods and a larger number of lakes, the comparison of the regressions obtained with the de-trended and non de-trended series provide equivalent results.…”

“…While being able to predict changes in plankton seasonality also in response to duration of the ice cover and melting timing (George et al, 2004), these indices resulted fully inappropriate when applied to the deep lakes in the southern slide of the subalpine region (Salmaso, 2005(Salmaso, , 2012Salmaso et al, 2013). The lower impact of NAO is likely a consequence of a sheltering effect of the Alps on the climate patterns prevailing in Northern and Central Europe.…”

“…In Lake Maggiore, over the longterm (1978-present), Daphnia year maximum clutch size has been detected after spring phytoplankton Standing Stock Biomass (SSB) peak (Manca et al, 2000a), as also suggested by the so-called PEG (Plankton Ecology Group) model of plankton seasonal succession (Sommer et al, 1986;Manca et al, 2008b). This hypothesis is further based on recent observations carried out in Lake Garda and in the other deep lakes south of the Alps which demonstrated a strong impact of the winter EA and EMP on the winter air and spring lake temperatures, spring deep mixing dynamics, replenishment of phosphorus in the epilimnetic layers, and development of phytoplankton during spring and summer (Salmaso, 2012;Salmaso et al, 2013).…”

“…The impact of atmospheric modes of circulation on the limnological variables and the populations of Daphnia in the two lakes were tested using 3 indices relevant or potentially relevant for the southern subalpine region N o n -c o m m e r c i a l u s e o n l y (Salmaso, 2012). The winter (December-February) North Atlantic Oscillation (NAO DJF ) and the winter East Atlantic pattern (EA DJF ) were computed by the NOAA-CPC (www.cpc.ncep.noaa.gov).…”

“…Because of this barrier, lakes located in the southern flank of the Alps are likely somewhat shaded against influences of climatic indices to which lakes in Northern and Central Europe respond. In an attempt to find reliable drivers able to explain changes in phytoplankton taxa composition and nutrient dynamics of Lake Garda, Salmaso (2012) applied two other-than-NAO DJF winter teleconnection indices of climate change, the Eastern Mediterranean Pattern (EMP DJF ) and the East Atlantic (EA DJF ) pattern for the winter (DecemberFebruary) period.…”