The Mediterranean Sea Regime Shift at the End of the 1980s, and Intriguing Parallelisms with Other European Basins

Abstract

BackgroundRegime shifts are abrupt changes encompassing a multitude of physical properties and ecosystem variables, which lead to new regime conditions. Recent investigations focus on the changes in ecosystem diversity and functioning associated to such shifts. Of particular interest, because of the implication on climate drivers, are shifts that occur synchronously in separated basins.Principal FindingsIn this work we analyze and review long-term records of Mediterranean ecological and hydro-climate variables and find that all point to a synchronous change in the late 1980s. A quantitative synthesis of the literature (including observed oceanic data, models and satellite analyses) shows that these years mark a major change in Mediterranean hydrographic properties, surface circulation, and deep water convection (the Eastern Mediterranean Transient). We provide novel analyses that link local, regional and basin scale hydrological properties with two major indicators of large scale climate, the North Atlantic Oscillation index and the Northern Hemisphere Temperature index, suggesting that the Mediterranean shift is part of a large scale change in the Northern Hemisphere. We provide a simplified scheme of the different effects of climate vs. temperature on pelagic ecosystems.ConclusionsOur results show that the Mediterranean Sea underwent a major change at the end of the 1980s that encompassed atmospheric, hydrological, and ecological systems, for which it can be considered a regime shift. We further provide evidence that the local hydrography is linked to the larger scale, northern hemisphere climate. These results suggest that the shifts that affected the North, Baltic, Black and Mediterranean (this work) Seas at the end of the 1980s, that have been so far only partly associated, are likely linked as part a northern hemisphere change. These findings bear wide implications for the development of climate change scenarios, as synchronous shifts may provide the key for distinguishing local (i.e., basin) anthropogenic drivers, such as eutrophication or fishing, from larger scale (hemispheric) climate drivers.

Synchronous marine pelagic regime shifts in the Northern Hemisphere

“…esrl.noaa.gov/psd/data/timeseries/AMO/). Each of these indices track phenomena that have been assumed to play a role in some of the reported regime shifts [6,8,19,43,65].…”

“…Regime shifts have been reported for the North Pacific (1976/1977 and 1989) [6,[26][27][28][29], specifically the northeast Pacific (1976/1977) [30,31], (1998/1999) [32,33] and the northwest Pacific (1976/1977, 1988/1989 and 1998) [34][35][36]; the Humboldt Current in the southern Pacific (1968/1970 and 1984/1986) [37,38]; and the northwest Atlantic (1989Atlantic ( /1990 [39][40][41][42][43]. In addition, regime shifts were observed in the late 1980s around all European seas [8]: the North Sea [44,45], the Baltic Sea [9,46], the northwest European shelf seas (1987/1990) [47,48], the western [49] and eastern (Adriatic) Mediterranean Sea [8,50,51] and the Black Sea [52,53]. Other shifts have been observed in the late 1990s in the northeast Atlantic and its adjacent seas, in the Black Sea, and in San Francisco Bay [54][55][56][57] at the time of a global shift in temperature [19].…”

“…of appropriate length for our multi-decadal investigation. Even if the data used in this investigation represent mostly one trophic level, it has to be noted that other studies have identified ecosystemwide regime shifts in most of these areas [6,8,9,11,36,43,44,47]. Second, we identified temporal shifts in all these systems, individually and in aggregate, and examined their relationships to (i) large-scale climatic indices (Northern Hemisphere temperature (NHT) anomalies, Arctic Oscillation (AO), Atlantic Multi-decadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)), and (ii) spatial patterns of change in sea surface temperature (SST) and sea-level pressure (SLP) over the NH.…”

Interannual variability of the Mediterranean trophic regimes from ocean color satellites

“…These important environmental modifications are supposed to strongly modify the dynamics of the Mediterranean marine ecosystems (The Mermex Group, 2011), by modifying the food web structure (Coll et al, 2008), triggering regime shifts (Conversi et al, 2010) or unexpected events (e.g., jellyfish blooms, Purcell, 2005), which should have strong consequences on human activities. In the context of climate change, phytoplankton plays a key role, because any perturbations on its dynamics would affect the rest of the marine food web (Edwards and Richarson, 2004).…”

Trends and regime shifts in climatic conditions and river runoff in Estonia during 1951–2015

“…For example, a regime shift on this period was reported from the Mediterranean Sea based on ecological, hydrological and climatic variables (Conversi et al, 2010). In a review article on regime shifts in marine ecosystems, many studies are referred to where the shift since 1989 in the North Atlantic was found (DeYoung et al, 2004).…”