Impact of the Atlantic Multidecadal Oscillation on Baltic Sea Variability

Abstract

The Atlantic Multidecadal Oscillation (AMO) is a natural mode of variability of the North Atlantic sea surface temperature. The AMO can be used to describe the complex interaction of the coupled atmosphere-ocean system of the North Atlantic. By analyzing a preindustrial period of 850 years with a regional climate model, we show that the AMO influences the Baltic Sea. AMO-related changes of the atmospheric circulation affect precipitation over the Baltic Sea region, which leads to altered river runoff influencing the salinity of the Baltic Sea. A wavelet coherence analysis reveals a persistent coherence between AMO and salinity for the whole period of 850 years. This suggests that the Baltic Sea is under the constant influence of the AMO. Our results provide strong evidence for long-term changes in the Baltic Sea as a result of changing AMO phases. Plain Language SummaryCoastal seas are of great importance to society. A prominent example of such a coastal sea is the Baltic Sea, since it is strongly impacted by human activities. However, besides the human footprint there are also natural phenomena, that influence the Baltic Sea. Especially climate phenomena over the North Atlantic can have a strong impact on the Baltic Sea. One such phenomenon is the so-called Atlantic Multidecadal Oscillation (AMO), a seesaw between warm and cold sea surface temperatures in the North Atlantic with a period of 60-90 years. Reliable observations only exist for a period of about 150 years, which is too short to study multidecadal time scales. Therefore, we use an 850 years long model simulation. Our results show that changes in North Atlantic sea surface temperature associated with the AMO influence the atmospheric circulation, which impacts the rain and snowfall over the Baltic Sea region. This in turn enhances or decreases the river runoff into the Baltic Sea and thus impacts the Baltic Sea salinity. Thus, the AMO has a strong influence on the Baltic Sea.

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

“…Hence, multidecadal variations of the large‐scale atmospheric circulation would explain the multidecadal variations in salinity (cf. Börgel et al, ). However, neither the Atlantic Multidecadal Oscillation (periods of 60–90 years) nor the North Atlantic Oscillation (subdecadal variability) show a periodicity of about 30 years.…”

Baltic Sea Operational Oceanography—A Stimulant for Regional Earth System Research

“…With the help of Baltic Sea models, the impact of increasing nutrient loads and climate change on the marine ecosystem was detected and attributed to the various drivers of the system. We have now a better understanding of the natural variability in the Baltic Sea region and how large-scale atmospheric circulation affects the Baltic Sea climate variability (e.g., Börgel et al, 2018). During recent decades, changes in largescale atmospheric circulation have caused a north-eastward shift in low-pressure tracks consistent with a more zonal circulation over the Baltic Sea basin (e.g., Trenberth et al, 2007).…”

Assessment of Uncertainties in Scenario Simulations of Biogeochemical Cycles in the Baltic Sea

“…The Baltic Sea is affected by internal modes of variability of atmospheric large-scale circulation such as the North Atlantic Oscillation (NAO, e.g., Tinz, 1996;Omstedt and Chen, 2001;Andersson, 2002;Meier and Kauker, 2002;Chen and Omstedt, 2005;Löptien et al, 2013) or decadal and centennial variations related to ocean-atmosphere interactions in the adjacent Atlantic (e.g., Kauker and Meier, 2003;Meier and Kauker, 2003a,b;Hansson and Omstedt, 2008;Schimanke and Meier, 2016;Börgel et al, 2018). Therefore, in order to distinguish natural variations from anthropogenic induced changes, it is crucial to determine the magnitude of natural variability of physical and ecosystem characteristics undisturbed of anthropogenic influence, even though the projected impact of climate change at the end of the century can be expected to be substantially larger than the variability that has been recorded during the historical period.…”