Climate change impacts on river discharge to the Sea of Marmara

The Sea of Marmara, located in Northwestern Türkiye, is under multiple stressors, including climate change and industrial, agricultural, and domestic pollution, that cause deoxygenation in coastal waters, with multiregional consequences affecting the surface and deep-water masses transported to the Mediterranean and Black Seas, respectively, via its straits. With climate-change driven changes in the intensity of extreme precipitation events, the marine environment becomes more vulnerable to increasing terrestrial pollutants. Evaluating the spatial and temporal variation of river runoff is crucial to understanding the interaction between the geophysical and hydrogeochemical processes that affects the nutrient balance of the sea. This study aims to (i) explore the historical (for the period 1960-2021) and spatial changes of monthly-averaged coastal discharges along the coastline of the Sea of Marmara for the first time, based on observations from the national hydrological service; (ii) analyze the change in long-term and seasonal trends of runoff and net-precipitation rate and derive a regional relation between the two parameters. Single Spectrum Analysis (SSA) is used to obtain the trends. Gaps in the time series are filled in using a non-parametric spectral estimation method. Discharges from the northern, eastern, and southern basins are, respectively, 3%, 17%, and 80% of the total discharge, which has varied between 1.5 and 15 km3 per year in the last decade, with short-lived extremes occurring in early spring. Total runoff rate shows a declining long-term trend that is accelerating with increasing evaporation. The intensity of the terrestrial precipitation extremes shows a temporal increase; there is a quadratic relation between the long-term trends of net precipitation and total runoff. Quantification of nutrient load distribution along the coastline associated with the spatial-temporal changes in coastal fluxes is urgent because the cumulative stressors (warming, nutrient overenrichment, pollutants) pose a threat of triggering extreme events and eutrophication in the Sea of Marmara with multiregional impact

Salinity inversions in the thermocline under upwelling favorable winds

This paper discusses and explains the phenomenon of salinity inversions in the thermocline offshore from an upwelling region during upwelling favorable winds. Using the nontidal central Baltic Sea as an easily accessible natural laboratory, high-resolution transect and station observations in the upper layers are analyzed. The data show local salinity minima in the strongly stratified seasonal thermocline during summer conditions under the influence of upwelling favorable wind. A simple analytical box model using parameters (including variation by means of a Monte Carlo method) estimated from a hindcast model for the Baltic Sea is constructed to explain the observations. As a result, upwelled water with high salinity and low temperature is warmed up due to downward surface heat fluxes while it is transported offshore by the Ekman transport. The warming of upwelled surface water allows maintenance of stable stratification despite the destabilizing salinity stratification, such that local salinity minima in the thermocline can be generated. Inspection of published observations from the Benguela, Peruvian, and eastern tropical North Atlantic upwelling systems shows that also there salinity inversions occur in the thermocline, but in these cases thermocline salinity shows local maxima, since upwelled water has a lower salinity than the surface water. It is hypothesized that thermocline salinity inversions should generally occur offshore from upwelling regions whenever winds are steady enough and surface warming is sufficiently strong.DFG/CRC/TRR 18

The soundscape of Islamic populism

Focusing on the failed coup attempt organized by a faction within the Turkish Armed Forces on July 15, 2016, this paper examines the soundscape of Islamic populism (Hadiz, 2016) as embraced by Turkey’s ruling Justice and Development Party (AKP) and its affective-auditory publics. Drawing on Althusser’s theories of ideology and interpellation concerning the Islamic call (Spadola, 2014), I explore AKP’s strategic use of Islamic sound as affect in governmentalizing urban space in order to understand the role that sound played in galvanizing support against the attempted coup. During the first twenty-four hours of the coup attempt, systematically regenerating discursive modes of Islamic rhetoric and sounds, utilizing the narratives of democracy, nationalism, and treachery to mobilize its publics, AKP re-cultivated the already existing polarized identity politics and recreated the sectarian spaces of belonging and otherness. I argue that AKP’s appropriation of sonic and aural qualities of Islam – particularly the public recitation of Sala (a form of Islamic call) – purposefully rechannelled the “ethical listening” (Hirschkind, 2006) of pious selves into a politically (re)functionalized listening in the populist reproduction of an Islamic soundscape. Such reproduction of the urban soundscape was responded to in a variety of ways by the mobilized auditory publics in service of the party while creating silenced private spaces of opposition.   NB: The article contains sound examples. In order to listen to embedded audio files, you must first download the pdf file and then open it with Adobe Acrobat

Thermocline Salinity Minima Due To Wind‐Driven Differential Advection

Observations from the global ocean have long confirmed the ubiquity of thermohaline inversions in the upper ocean, often accompanied by a clear signal in biogeochemical properties. Their emergence has been linked to different processes such as double diffusion, mesoscale stirring, frontal subduction, and the recently discussed submesoscale features. This study uses the central Baltic Sea as a natural laboratory to explore the formation of salinity inversions in the thermocline region during summer. We use realistic high‐resolution simulations complemented by field observations to identify the dominant generation mechanism and potential hotspots of their emergence. We propose that the strongly stratified thermocline can host distinct salinity minima during summer conditions resulting primarily from the interaction between lateral surface salinity gradients and wind‐induced differential advection. Since this is a generic mechanism, such salinity inversions can likely constitute a typical feature of the upper ocean in regions with distinct thermoclines and shallow mixed layers.Plain Language Summary: The upper ocean is characterized by a well‐mixed surface layer, below which temperature decreases rapidly with depth, forming the so‐called thermocline region. A corresponding salinity increase with depth is typically anticipated for stable density stratification to occur. Temperature and salinity inversions can, however, emerge in the upper ocean. Such thermohaline inversions have been observed in different regions of the world's oceans, and various mechanisms have been proposed to explain their generation. Here, the central basin of the Baltic Sea is used as a natural laboratory to explore the formation of distinct salinity minima in the thermocline region during summer conditions. Using high‐resolution numerical simulations and measurements from a field campaign, we show that inversions are abundant and can emerge throughout the entire basin. They increase with increasing wind speeds and concentrate mainly in regions with strong lateral salinity differences. We propose that thermocline salinity minima can occur during summer when the wind transports saltier water over less saline surface waters. This is a generic mechanism that can therefore be responsible for the formation of the salinity inversions observed worldwide in areas with distinct thermoclines and shallow mixed layers.Key Points: Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline region. Realistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesis. Lateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions.German Research Foundationhttp://doi.io-warnemuende.de/10.12754/data-2022-000

Wind Effects on Small‐Scale River and Creek Plumes

In contrast to large river plumes, Coriolis effects are weak, and inertia is quickly depleted so that the fate and structure of small‐scale plumes are more sensitive to tide and wind. Advected alongshore by reversing tidal currents in absence of wind forcing, small buoyant plumes are persistently deflected downwind in presence of alongshore winds and exhibit little tidal variability. The effect of different upwelling/downwelling winds on buoyant outflows ∼10 m3 s−1 is explored. With increasing wind, tidal variability decreases, as does asymmetry in plume characteristics—for strong winds upwelling/downwelling plume structure is similar as the plume is retained closer to the shore. Wind forcing is exerted directly by wind stress on the surface of the plume and indirectly by wind‐driven currents that deflect the upwind boundary of the plume. While inertia and buoyancy dominate the inner plume, and wind dominates the outer plume, the mid‐plume responds to an interaction of wind and buoyancy forcing that can be indexed by a Plume Wedderburn Number Wpl (wind stress vs. density gradients): for weaker winds (Wpl 1) surface stress mixes the plume vertically, shortening the reach of low‐salinity waters. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind. Shoreline exposure to outflow transitions from a quasi‐symmetrical tide‐averaged zone of impact under zero‐wind to a heavily skewed zone with persistent weak wind and a one‐sided zone for strong wind.Plain Language Summary: Compared to large river plumes, outflow from small rivers and mountainous streams is more sensitive to tides and winds because of the weak Coriolis effect and quickly reduced inertia. Alongshore (upwelling/downwelling) winds carry these small plumes in their direction. We use a numerical model to study the effect of these upwelling/downwelling winds on plumes spreading from small rivers with discharge rates of 10 m3 s−1 or less. Increasing wind reduces tidal fluctuations in plume patterns such that with strong winds the plume spreads similarly for upwelling and downwelling winds as it remains close to the shore. Wind affects the plume surface directly and the upwind‐plume boundary indirectly via wind‐driven currents. Inertia and buoyancy control the inner plume while wind and buoyancy control the mid‐plume and wind controls the outer plume. Weaker winds increase the plume length and layering by horizontally tilting the density gradients. Stronger winds shorten the plume by vertically mixing it. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind.Key Points: Plume bends downwind, with upstream boundary deflected by ambient current and downstream boundary deflected by surface wind stress. Asymmetry in plume shape between weak upwelling versus downwelling winds vanishes with strong winds that retain the plume nearshore where Ekman transport negligible. Inertia & buoyancy control the near‐field; wind forcing & buoyancy control the mid‐field; wind mixing & passive advection control the far‐field.National Science Foundation http://dx.doi.org/10.13039/100000001Leibniz Institute für Ostseeforschung Warnemündehttp://doi.io-warnemuende.de/10.12754/data-2022-000

A local eddy viscosity parameterization for wind-driven estuarine exchange flow, Part II: Entrainment

Structure and intensity of estuarine exchange flow depend significantly on the eddy viscosity Av profile which is dynamically linked to various forces (e.g., gravitational, tidal, wind-driven). The impact of winds on the exchange flow is complex due to its direct (local and remote changes in shear and density stratification) and indirect (modifications to Av profiles) contributions. This study aims (i) to include wind entrainment effects in the tidally averaged Av parameterization; (ii) to develop an analytical one-dimensional model for the wind driven exchange flow by using this novel parameterization and assess the tidally averaged dynamics over a relevant physical parameter-space, subdomains of which have not yet been explored numerically. This one-dimensional model is based on a balance between frictional forces and pressure gradient, calibrated with a tidally-resolving one-dimensional water-column model with second-moment closure. Structure and intensity of the resulting exchange flow profiles are analyzed with respect to three dimensionless parameters (the unsteadiness of boundary layer mixing Un, scaled-directional wind stress W, and horizontal stratification Si). While down-estuarine winds enhance the gravitational circulation, up-estuarine winds result in either a two-layer inverted circulation opposing the gravitational circulation, or a three-layer flow (favored by relatively strong Si, weak W, and moderate Un) that is up-estuarine at the surface with classical two-layer circulation underneath. Relative thickness of surface and bottom boundary layers affect both the intensity and the inflection depth of the exchange flow layers. Up-estuarine winds with W≳0.5 yield unstable stratification and reduce the exchange flow intensity with increasing W.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Mathematical Physic