Trends in relevant environmental drivers
Winters were generally harsh, but more variable before the 1990s. The
winters 1990-1995 were relatively mild, and since then gradual cooling
has occurred (Fig. 5a). The winter air temperatures largely follow the
Baltic Sea index. Oxygen concentration was variable, yet slightly
declining during the entire period 1978-2012, and no hypoxic or anoxic
levels were estimated (Fig. 5b). Salinity peaked in the mid-1980s both
in spring and summer, and in open and coastal areas, whereafter it
declined until the mid-1990s and has fluctuated slightly since (Figs.
5c, d). In the spring, surface temperature fluctuated more until
mid-1990s in both open and coastal sea areas, whereafter it was slightly
increasing in the coastal area (Fig. 5e).