Dynamics of the circulation in the Sea of Marmara: numerical modeling experiments and observations from the Turkish straits system experiment

Abstract

During September 2008 and February 2009, the NR/V Alliance extensively sampled the waters of the Sea of Marmara within the framework of the Turkish Straits System (TSS) experiment coordinated by the NATO Undersea Research Centre. The observational effort provided an opportunity to set up realistic numerical experiments for modeling the observed variability of the Marmara Sea upper layer circulation at mesoscale resolution over the entire basin during the trial period, complementing relevant features and forcing factors revealed by numerical model results with information acquired from in situ and remote sensing datasets. Numerical model solutions from realistic runs using the Regional Ocean Modeling System (ROMS) produce a general circulation in the Sea of Marmara that is consistent with previous knowledge of the circulation drawn from past hydrographic measurements, with a westward meandering current associated with a recurrent large anticyclone. Additional idealized numerical experiments illuminate the role various dynamics play in determining the Sea of Marmara circulation and pycnocline structure. Both the wind curl and the strait flows are found to strongly influence the strength and location of the main mesoscale features. Large displacements of the pycnocline depth were observed during the sea trials. These displacements can be interpreted as storm-driven upwelling/ downwelling dynamics associated with northeasterly winds; however, lateral advection associated with flow from the Straits also played a role in some displacements.

Circulation of the Turkish Straits System between 2008–2013 under complete atmospheric forcings

“…This circulation pattern in the western Marmara Sea is persistent throughout the simulation but with different intensities. This type of circulation structure has been reported in other studies (Chiggiato et al, 2012;Beşiktepe et al, 1994). In 2011 (Fig.…”

“…Chiggiato et al (2012) modelled the Marmara Sea using realistic atmospheric forcing and open boundaries at the junctions of the straits with the Sea, indicating surface circulation changes in 5 response to changes in the strength and directional pattern of the wind force.…”

Seasonal and interannual variability of the water exchange in the Turkish Straits System estimated by modelling

“…The Marmara Sea was described by one-dimensional area averaged model (Maderich, 1998;1999) and by three-dimensional numerical models (Demyshev & Dovgaya, 2007;Chiggiato et al, 2011). However, with the exception of the works of Maderich (1998;1999), Blain et al (2010), and Hüsrevoğlu et al (2010), the Marmara Sea has not yet been modelled as a component of the TSS.…”

“…However, hydraulic control is quasisteady (Gregg et al, 1999) and exchange is partly controlled by friction (Gregg & Özsoy, 2002). The observed thermohaline structure and circulation in the Marmara Sea as an intermediary basin filled by water from the Bosphorus and Dardanelles were considered by Beşiktepe (1993), Beşiktepe et al (1993) and Chiggiato et al (2011). Deep layer waters in Marmara Sea are renewed with incoming Dardanelles lower layer flow (Beşiktepe, 1993).…”

OSSE for a sustainable marine observing network in the Marmara Sea

“…In the region, in-situ observations are generally scarce and collected by dedicated projects [Beşiktepe et al, 1994;Chiggiato et al, 2012;Özsoy et al, 2001;Tugrul et al, 2002;Ünlüata et al, 1990] for a limited area and time. Moreover, the spatial resolution and frequency of satellite observations are still not sufficient to monitor the system continuously.…”