Disentangling the impact of nutrient load and climate changes on Baltic Sea hypoxia and eutrophication since 1850

Changing Salinity Gradients in the Baltic Sea As a Consequence of Altered Freshwater Budgets

“…Since the 2000s, the salinity is increasing again. The low‐frequency variability with a period of about 30 years can also be seen in the freshwater supply of the model forcing (Meier et al, , their Figure ).…”

“…Sources of uncertainty mainly arise from the database of the river discharges. As a homogeneous data set for the entire period 1850–2008 does not exist, the model forcing is a combination of several different runoff data sets (Meier et al, ) leading to possible inhomogeneities. To narrow this uncertainty, only simulation results after 1921 are used (two data sets for river runoff) and results are compared to the period with a consistent observational data set (1950–2004).…”

“…The river runoff in the simulation consists of multiple observational data sets which were merged in order to get a homogeneous river runoff data set (Meier et al, ). Reconstructions for 1850–1900 by Hansson et al (), for 1901–1920 by Cyberski et al (), and for 1921–1949 by Mikulski () were used.…”

“…The model is forced for the period 1850-2008 with the high-resolution atmospheric forcing fields HiResAFF by Schenk and Zorita (2012) which were used before to address long-term climate variability of the Baltic Sea region (Gustafsson et al, 2012;Kniebusch et al, 2019;Meier et al, 2018).…”

“…On long-term, river runoff and net precipitation are considerably correlated (Meier & Kauker, 2003a). Hence, it is sufficient to examine runoff only to attribute long-term salinity changes since the total runoff (14,000 m 3 /s) is much higher than the total net precipitation (precipitation-evaporation = 1,000 … 2,000 m 3 /s) for the whole Baltic Sea area (Meier & Kauker, 2003a;Meier et al, 2018). The right column in Figure 2 shows the anomalies in SSS (b) and the gradient (d) for the simulations REF, WIND, constRUNOFF, and FRESH.…”