Synoptic and Seasonal Variability of Small River Plumes in the Northeastern Part of the Black Sea

Abstract

Small river plumes are typical features at many coastal regions in the World Ocean. These water masses have relatively small areas and volumes; however, due to their energetic dynamics localized in a thin surface layer, they strongly affect coastal circulation, water quality, and ocean-atmosphere interaction. In this study, we investigate external factors, which govern synoptic and seasonal variability of small river plumes, and, therefore, affect land-ocean fluxes of fluvial water and biogeochemically important material. We use numerical modeling to simulate small river plumes at the northeastern part of the Black Sea. We describe the response time of small river plumes to changes in river discharge and wind forcing conditions, which determines variability of river plumes at different time scales. We reveal that the influence of river plumes on coastal processes depends not only on total annual river discharge volume, but also on temporal distribution of high-discharge and low-discharge periods. Seasonal and synoptic features of local atmospheric circulation could strongly modify the relation between river plume characteristics and river discharge rate. The results obtained in this study are important for better assessment of delivery and fate of river-borne suspended and dissolved matter, as well as floating litter in coastal areas.

Detecting turbid plumes from satellite remote sensing: State-of-art thresholds and the novel PLUMES algorithm

“…The Patos Lagoon exhibits a microtidal regime, with a mean range of 0.5 m and diurnal dominance (Moller et al, 2001), having negligible influence on the lagoon's circulation (Moller et al, 2001;Fernandes et al, 2004). As the tidal amplitude is small, the dynamics of the lagoon and turbid plume is controlled by the combined effect Mean, standard deviation and covariance of spectral parameters for each trained class (Lihan et al, 2008), (Thomas and Weatherbee, 2006) Threshold SPM trial-and-error maximum autocorrelation (Constantin et al, 2018), (Zhang et al, 2016), (Petus et al, 2014) percentile 95 th (Longitude, Latitude, time) (Gangloff et al, 2017), (Ody et al, 2022) SPM and Digital Number* trial-and-error and region growing (Teodoro et al, 2008), (Teodoro and Goncalves, 2011) TOA Salinity and R rs (645)* maximum correlation with river discharge (Guo et al, 2017) Salinity** K-means cluster with manual adjustments (when needed) (Korshenko et al, 2023) Stratification salinity index** trial-and-error (Toublanc et al, 2023) Chlorophyll-a trial-and-error of gradient contour (Dzwonkowski and Yan, 2005) PLUMES Turbidity/SPM Similarity of pixels from control points and region growing check this study of wind and river discharge: high river discharge (Q > 2,000 m³s -1 ) overrules the dynamics promoted by winds, whereas, in dry periods, the wind effect becomes the most important forcing mechanism (Fernandes et al, 2002). Marques et al (2010a) verified the importance of the river discharge intensity to its formation and Zavialov et al (2018) identified the importance of the local wind action promoting the plume's stratification (Zavialov et al, 2018).…”

“…As we have shown in this work (e.g., Figure 8) these approaches are prone to ignore less intense plumes or smaller highly turbid coastal plumes. This drawback has been addressed by other authors with the aid of additional site-specific adjustments to achieve higher accuracy and precision; e.g., shallow-water masks (Gangloff et al, 2017); noiseremoval and region growing (Teodoro et al, 2008); manual adjustment of plume boundary (Korshenko et al, 2023).…”

“…In that case, maximum likelihood approaches need to be re-trained (e.g., Thomas and Weatherbee, 2006) and thresholds must be adjusted not only for a specific site but case-by-case (e.g., Maciel et al, 2021), otherwise plumes may be overestimated, underestimated, or missed. To avoid overestimation, a few studies have further applied shallow water masks (typically< 20 m depth; e.g., Gangloff et al, 2017;Ody et al, 2022), manual adjustments (e.g., Korshenko et al, 2023), or region growing technique (e.g., Teodoro et al, 2008;Teodoro and Goncalves, 2011); although the latter is less known for coastal applications but widely applied in the medical (e.g., Tariq et al, 2019;Kroon, 2022) and in spatial planning/cartography (e.g., Goncalves, 2006). Application of shallow-water masks is intended to prevent the recurring issue that the thresholding method cannot distinguish between causes of turbid zones (i.e., turbid wakes, wave-driven coastal resuspension from the plume itself) like the human eye.…”

Response of the Coastal Phytoplankton Community to the Runoff from Small Rivers in the Northeastern Black Sea

“…Interaction between fresh and seawaters forms local desalinated areas called plumes with a salinity up to 16 on the surface [18]. Despite the small annual river discharge in the NE sector, there is a significant seasonal and synoptic variability in the area and distribution of plumes on the surface of the Black Sea [19,20]. Seasonal variability is associated with the type of power supply of NE rivers, i.e., rain and seasonal snow.…”