River‐induced particle distribution in the northwestern Black Sea (September 2002 and 2004)

Abstract

[1] Observations from two comprehensive oceanographic surveys on the northwestern Black Sea are analyzed to reveal the hydrological characteristics of the shelf area around the Danube delta in relation to particulate matter dynamics. These processes have broader implications on flows through the adjacent complex strait system. The surveys cover both a period of high (September 2002) and low (September 2004) discharge of the Danube River. The resulting low-salinity waters generally occupied the upper 10-15 m within the 20-30 m thick warm layer that was separated by deeper cooler waters through a sharp thermocline. The buoyant plume was influenced by the discharge conditions and the prevailing wind patterns. The plume structure was identified using in situ bottle data, continuous beam transmission and fluorescence profiles, and satellite remotely sensed data. Particulate matter concentration values correlated with low-salinity riverine waters and their maxima were recorded in the immediate vicinity of the Danube branches, decreasing rapidly toward the open sea. The preferred particle transport pathway in 2002 was along a narrow strip near the coast, with a south-southwest direction, favored by the strong northeasterlies which predominated prior to the cruise. Low-salinity waters and riverine particles in 2004 were characterized by mostly offshore removal, attributed to calmer northwesterlies prior to the survey. Changes in ambient stratification due to wind-driven vertical displacements of the seasonal thermocline appeared to also influence the plume dynamics. The downwelling (upwelling) conditions that prevailed in 2002 (2004) were revealed in both the in situ vertical profile temperature measurements and the satellite-derived sea surface temperature patterns.

The impact of ambient stratification on freshwater transport in a river plume

“…It consists of a well-pronounced anticyclonic bulge and a narrower coastal current with a fairly uniform structure alongshore. The Danube River plume is observed in June, when a very intense near-surface thermocline forms in the Black Sea (Yankovsky et al, 2004;Karageorgis et al, 2009). It comprises a number of mesoscale eddies but without a coherent structure of the river plume similar to the Columbia River and model examples with nonstratified ambient flow.…”

“…Coastal buoyancy-driven currents represent an important conduit for the freshwater transport both along-and offshore, and their dynamics determines the fate of freshwater discharge on the continental shelf. Freshwater transport by coastal currents can be further affected by wind forcing (e.g., Fong and Geyer, 2001;García Berdeal et al, 2002;Lentz, 2004;Hetland, 2005;Whitney and Garvine, 2005;Rogers-Cotrone et al, 2008), ambient circulation (e.g., Fong and Geyer, 2002;Yankovsky, 2000;2004), and tidal mixing (e.g., Kourafalou et al, 1996;Chen, 2000, Hetland andSignell, 2005;Whitney and Garvine, 2006). Under certain conditions, buoyancy-driven currents can develop strong mesoscale variability (e.g., Garvine, 1996;Williams et al, 2007;Pennel et al, 2012).…”

Influence of Mississippi River induced circulation on the Deepwater Horizon oil spill transport

“…Examples include those from estuaries/bays such as the Delaware [ Münchow and Garvine , ], the Chesapeake [ Boicourt , ], the Columbia [ Hickey et al ., ; Horner‐Devine et al ., ], and the Niagara [ Masse and Murthy , ; Horner‐Devine , ], and from low‐salinity bands that result from multirivers, such as in the Southeast U.S. Continental Shelf [ Blanton et al ., ; Kourafalou et al ., ]. In addition, an “upstream” coastal current also develops [ Kourafalou et al ., ; Matano and Palma , ], which is particularly pronounced in delta discharges [ Kourafalou , ; Tsiaras et al ., ; Karageorgis et al ., ]. The buoyant outflow is subject to a variety of factors that can change the “typical” circulation pattern.…”

Developments in Earth observation for the assessment and monitoring of inland, transitional, coastal and shelf-sea waters

“…(i) those studies focused on the Daunbe river and the dynamics of the sediment plume and its seasonal variability (e.g., Constantine et al, 2016;Guttler et al, 2011;Karageorgis et al, 2009); (ii) those studies that sought to map in-water optical properties and constituents and their distribution to assess environmental interactions in the wider northwest Black Sea and to use the observations to improve ecosystem models, including CDOM…”