Spatial Distribution of Energy of Subinertial Baroclinic Motions in the Baltic Sea

Andrey Kurkin,Oxana Kurkina,Ekaterina Rouvinskaya,Artem Rybin,Tarmo Soomere

doi:10.3389/feart.2020.00184

Abstract

We explore the basic properties of the “climate” of the field of subinertial motions with periods of 2–12 days in the Baltic Sea. The calculations are performed using the output of the Rossby Center Ocean Model RCO with a spatial resolution of 2 nautical miles for 1961–2005. The field of such motions in the Baltic Sea is strongly asymmetric, with much more energy present in the eastern regions of the sea. Spatial distributions of 5-yr average amplitudes of fluctuations of the main and seasonal pycnocline, near-bottom velocity and kinetic and potential energy reflect this asymmetry and also exhibit extensive variability on scales of a few tens of kilometers. The majority of potential energy of such motions is concentrated in a narrow nearshore strip of the sea with a typical width of <20 km. The largest values of kinetic energy occur along the gently sloping seabed at intermediate depths. The areas of maximum of absolute nearbed velocities only partially match similar areas hosting very large kinetic energy or strong fluctuations of the location of the pycnocline. Both the major properties and spatial details of the discussed distributions exhibit almost no difference for the years 1961–1965 and 2000–2005, except for the maximum seabed velocities that are somewhat larger in 2000–2005 apparently because of exceptional storms in 2001 and 2005.

Highlights

The well-being of the Baltic sea called Baltic (Sea) ecosystem and many details of the functioning of the entire sea (Leppäranta and Myrberg, 2009) substantially rely on the mechanisms that support strong vertical stratification in this water body
About 30% of the energy needed for Baroclinic Oscillations in the Baltic Sea deep water mixing below the halocline in the Baltic Sea may be provided by the breaking of internal waves (Meier et al, 2006)
Both distributions suggest that the intensity of nearbed processes driven by baroclinic motions and internal waves is relatively low in the Gulf of Riga, Gulf of Finland and Bay of Bothnia compared to the open Baltic proper and the vicinity of Danish straits

Summary

INTRODUCTION

The well-being of the Baltic Sea ecosystem (e.g., in terms of eutrophication, Reissmann et al, 2009) and many details of the functioning of the entire sea (Leppäranta and Myrberg, 2009) substantially rely on the mechanisms that support strong vertical stratification in this water body. The largest difference (up to 15–20%) occurs at the lower margins of pycnoclines; the vertical structure of density and FIGURE 2 | Temperature (T), salinity (S) and density (ρ) profiles from the World Ocean Database and from the RCO model, and the associated relative error (ε) at the location with coordinates 20.583◦E, 57.525◦N on August 28, 1994. The time series and extremes of sea surface heights generally follow the measured values in the eastern Baltic Sea (except for a few locations that are affected by strong wave set-up, Eelsalu et al, 2014) This feature suggests that the model is suitable for the replication of processes with time scales of a few days. Given the demonstrated quality of the output of the RCO model (see the relevant references above), it is likely that the established qualitative patterns and areas that host high and low levels of different quantities are reliable

RESULTS

CONCLUSIONS AND DISCUSSION

DATA AVAILABILITY STATEMENT