Abstract
Abstract. The paper investigates the wintertime dynamics of the coastal northeastern Adriatic Sea and is based on numerical modelling and in situ data collected through field campaigns executed during the winter and spring of 2015. The data were collected with a variety of instruments and platforms (acoustic Doppler current profilers, conductivity–temperature–depth probes, glider, profiling float) and are accompanied by the atmosphere–ocean ALADIN/ROMS modelling system. The research focused on the dense-water formation (DWF), thermal changes, circulation, and water exchange between the coastal and open Adriatic. According to both observations and modelling results, dense waters are formed in the northeastern coastal Adriatic during cold bora outbreaks. However, the dense water formed in this coastal region has lower densities than the dense water formed in the open Adriatic due to lower salinities. Since the coastal area is deeper than the open Adriatic, the observations indicate (i) balanced inward–outward exchange at the deep connecting channels of denser waters coming from the open Adriatic DWF site and less-dense waters coming from the coastal region and (ii) outward flow of less-dense waters dominating in the intermediate and surface layers. The latter phenomenon was confirmed by the model, even if it significantly underestimates the currents and transports in the connecting channels. The median residence time of the coastal area is estimated to be approximately 20 days, indicating that the coastal area may be renewed relatively quickly by the open Adriatic waters. The data that were obtained represent a comprehensive marine dataset that can be used to calibrate atmospheric and oceanic numerical models and point to several interesting phenomena to be investigated in the future.
Highlights
Due to its geographical position and surrounding orography, the Adriatic Sea – a semi-enclosed 800 × 200 km basin located north of the Mediterranean (Fig. 1) – can be considered a unique test bed where a number of processes important for driving the circulation of the eastern Mediterranean Sea occur (Malanotte-Rizzoli et al, 2014)
As it is topographically separated from the open Adriatic by a number of islands (Fig. 1), the northeastern coastal area was not considered to be eligible for wintertime processes such as dense-water formation before the winter of 2012, at least not at rates that may impact the overall dynamics of the northern Adriatic
There are several reasons for this: (i) it is considered to not have a substantial influence on the overall dynamics of the Adriatic, as it is separated from the open Adriatic by several long islands that physically restrict water exchange, (ii) the area is positioned far away from research institutes, whose monitoring activities have not encompassed the area, and (iii) satellite remote sensing does not perform well in the region, as numerous channels and complex topography impair the quality of the data (Klemas, 2011)
Summary
Due to its geographical position and surrounding orography, the Adriatic Sea – a semi-enclosed 800 × 200 km basin located north of the Mediterranean (Fig. 1) – can be considered a unique test bed where a number of processes important for driving the circulation of the eastern Mediterranean Sea occur (Malanotte-Rizzoli et al, 2014). This concept has been supported by a number of numerical modelling studies (e.g. Beg-Paklar et al, 2001; Chiggiato and Oddo, 2008) This classical northern Adriatic DWF picture has been substantially changed following the exceptional DWF that occurred in the winter of 2012, when the formation of dense waters was observed in the northeastern coastal area (Fig. 1) (Mihanovicet al., 2013). It has been identified that a strong northern Adriatic thermohaline front (Lee et al, 2005; Poulain et al, 2011) has its starting point in the northeastern coastal Adriatic, in Kvarner Bay, with coastal waters advected towards the open sea, during strong bora events (Pullen et al, 2003; Lee et al, 2005; Beg Paklar et al, 2008) As it is topographically separated from the open Adriatic by a number of islands (Fig. 1), the northeastern coastal area was not considered to be eligible for wintertime processes such as dense-water formation before the winter of 2012, at least not at rates that may impact the overall dynamics of the northern Adriatic.
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