Abstract
Winter sea-level pressure fields in the northern hemisphere were analysed with respect to regimes and regime shifts (RS). Classification of the North Atlantic Oscillation (NAO) patterns resulted in the identification of two longer lasting climate regimes: a persistent NAO− period from 1976 to 1988 followed by a persistent NAO+ period from 1989 to 2000. A further persistent NAO− period from 1956 to 1966 cannot be related to climate regime shifts. After 2000, the NAO lost its persistence and the autocorrelation disappeared, while the variance in the benthic data increased. The consequence was a decrease in potential predictability. The impact of the 1988/89 and 2000/2001 RS on the dominant species and taxonomic groups of benthic macrofauna as well as on benthic community structure was evaluated using an AMOEBA model, a quantitative method used in water management to represent the status of the ecosystem. The model confirmed the effects of the smooth RS in 1988/1989 and the abrupt RS in 2000/2001 on the macrofauna communities provided by earlier data analyses.
Highlights
Biological regime shifts (RS) in marine ecosystems often occur in connection with climate RS as documented in the North Pacific (Bond et al, 2003; Mantua, 2004), the North Atlantic (Drinkwater, 2006; Harris et al, 2013), the North Sea (Beaugrand, 2004; Schlüter et al, 2008), or the Baltic Sea (Möllmann et al, 2009) and result in reduction in species diversity
The climate system becomes unstable and moves into a new state, as observed during 1910– 1920, 1938–1945, 1976–1981, and 2001–2002 (Swanson and Tsonis, 2009). These periods were related to the turning points of the Atlantic Multidecadal Oscillation (AMO), (Sutton and Hodson, 2005), called the Atlantic Multidecadal Variability, which is driven by variations in the Atlantic meridional overturning circulation (Gulev et al, 2013)
The regime means for each variable are computed and the differences between the climate regimes are plotted in a polar plot with respect to the long-term climatic means and the ±1 standard deviation (STD)
Summary
Biological RS in marine ecosystems often occur in connection with climate RS as documented in the North Pacific (Bond et al, 2003; Mantua, 2004), the North Atlantic (Drinkwater, 2006; Harris et al, 2013), the North Sea (Beaugrand, 2004; Schlüter et al, 2008), or the Baltic Sea (Möllmann et al, 2009) and result in reduction in species diversity. E.g., Carpenter and Brock (2006) have documented that a rising variance is an indicator for an abrupt RS Those RS strongly influences the potential predictability of the biological system as documented for benthic community structure in the southern North Sea (Dippner et al, 2010). A climate RS can occur when modes of climate variability are synchronized and the coupling strength between those modes simultaneously increases In this case, the climate system becomes unstable and moves into a new state, as observed during 1910– 1920, 1938–1945, 1976–1981, and 2001–2002 (Swanson and Tsonis, 2009). A relatively cold period at the beginning of the Twentieth century was followed by a warm period in the 1940s and 1950s, another cold period in the 1970s and 1980s and a warm period in the 1990s (Ting et al, 2013)
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