Organic signatures from modern and ancient seagrass in coarse-grained sediments near Poel Island, Baltic Sea

Marginal marine environments of the Skagerrak and Kattegat: a baseline study of living (stained) benthic foraminiferal ecology

Surface sediments, suspended particulate matter and fluffy-layer material, collected in the Arkona Basin and the Pomeranian Bay during 1995–1997, as well as air particulate matter, collected on the island of Rugen during August 1995, were analysed for total organic carbon content, saturated and polycyclic aromatic hydrocarbons (PAH). The resulting concentrations and distributions of these compounds and molecular PAH ratios are discussed in terms of matrix, origin of the organic matter and seasonal variations. The data show that the Oder river can be identified as a major source for PAH transported into the southern part of the Arkona Basin. A strong atmospheric input of PAH is noted for the central and northern part of the basin. In general, anthropogenic and bacterially degraded hydrocarbons bound to organic carbon-rich and small particles are mainly deposited in the basin center, whereas their natural counterparts accumulate mainly on the basin flanks covered by coarser grained sediments.

<p>Sea level rise along with the changing climate leads to severe enhancement of hydrodynamic impact to coastlines worldwide. Along the Baltic Sea coast of Schleswig-Holstein (Germany), this leads to the erosion of exposed glacial cliffs (up to 30 % of the coastline) and abrasion platforms (unknown extend). Irreversible land loss and seafloor deepening are the consequences, causing socio-economic and environmental concerns in affected areas. However, the adjacent coastal sections benefit from the development as the mobilized material constitutes the main sediment source to the nearshore bar and beach systems. Here, temporal built up of nearshore bars and the deposition at sandspits and beaches functions as natural shore protection.</p><p>The heterogenous and dynamic morphology, exposition and geology of the cliff sections and their offshore continuation complicates system understanding and management of the Schleswig-Holstein coastline. The availability of coarse-grained sediments (sand, gravel, stones) from the poorly sorted glacial till, forming the cliffs, is comparatively low. This lack of obtained material suitable to build up a coastal morphology attributes a central role to the source areas and the quantification of the sediment budget regarding coastal preservation.</p><p>On this account we attempt to develop a strategy towards a classified coastal sediment budget, which is based on a comprehensive field and literature data base, addressing the highly variable character of the observed coastline described in morphological, morphodynamic, geological, sedimentological, hydrodynamic and anthropogenic parameters.</p><p>The coastline of Schleswig-Holstein is structured into 58 active cliff sections for individual description via categorized cliff profiles. Furthermore, 22 abrasion platforms are defined in the offshore region and characterized by descriptive summaries. The data summary reveals well investigated zones (e.g. Schönhagen, Stohl, Heiligenhafen, Brodten), serving as potential pilot areas for complementary studies, but also identifies study areas which require further research.</p><p>The literature values for past cliff retreat and eroded sediment volumes bear high uncertainties. This is due to the fact that former studies are based on unequal spatial extend of cliff sections, variable time intervals and differing methods. Further, computation of eroded material volumes is lacking important input parameters, e.g. the degree of compaction and the grain size distribution. This is considered for budget calculations and their confidence for individual coastal units in template form.</p><p>The current study compiles and visualizes the heterogenous data for further scientific applications. The project aims to support future studies on the sediment availability and transport in the near-shore system using hydrodynamic modelling and thus creates a sound scientific base for system understanding and new governmental regulations concerning coastal protection measures at the Schleswig-Holstein Baltic Sea.</p>

Despite more than 100 years of research, a number of questions concerning the evolution of the post-glacial connection between Lake Ladoga, the largest European lake, and the Baltic Sea remain unanswered. In particular, the location and chronological frames of the paleo-outlet from Lake Ladoga in the Holocene remain debatable. Paleolimnological studies were performed in small lakes in the northern part of the Karelian Isthmus (NW Russia), where the outlet from Lake Ladoga, the Heinjoki Strait, is thought to have existed until the lake drained to the south due to the tilting of its basin. The presence of the indicative “Ladoga species” (e.g., Aulacoseira islandica, Achnanthes joursacense, Cymbella sinuata, Ellerbeckia arenaria, Navicula aboensis, N. jaernefeltii, N. jentzschii, etc.) in the diatom assemblages is used as evidence for the influence of Lake Ladoga during the accumulation of coarse-grained sediments at the bottom of the ancient channel. It also confirms the functioning of the hypothetical northern local branch of the strait. Decreased abundances of the “Ladoga species” and the onset of the accumulation of fine-grained sediments suggest that the water discharge via this paleo-outlet rapidly reduced starting from ca. 4100 cal BP. The termination of the functioning of the Heinjoki Strait is recorded as an abrupt disappearance of the indicative taxa from the diatom record. This was dated to ca. 3500–3200 cal BP, which corresponds to the estimated ages of the birth of the River Neva, the present outlet from Lake Ladoga.

Three-dimensional geological and groundwater flow models of a submarine groundwater discharge (SGD) site at Hanko (Finland), in the northern Baltic Sea, have been developed to provide a geological framework and a tool for the estimation of SGD rates into the coastal sea. The dataset used consists of gravimetric, ground-penetrating radar and shallow seismic surveys, drill logs, groundwater level monitoring data, field observations, and a LiDAR digital elevation model. The geological model is constrained by the local geometry of late Pleistocene and Holocene deposits, including till, glacial coarse-grained and fine-grained sediments, post-glacial mud, and coarse-grained littoral and aeolian deposits. The coarse-grained aquifer sediments form a shallow shore platform that extends approximately 100–250 m offshore, where the unit slopes steeply seawards and becomes covered by glacial and post-glacial muds. Groundwater flow preferentially takes place in channel-fill outwash coarse-grained sediments and sand and gravel interbeds that provide conduits of higher hydraulic conductivity, and have led to the formation of pockmarks on the seafloor in areas of thin or absent mud cover. The groundwater flow model estimated the average SGD rate per square meter of the seafloor at 0.22 cm day−1 in autumn 2017. The average SGD rate increased to 0.28 cm day−1 as a response to an approximately 30% increase in recharge in spring 2020. Sensitivity analysis shows that recharge has a larger influence on SGD rate compared with aquifer hydraulic conductivity and the seafloor conductance. An increase in recharge in this region will cause more SGD into the Baltic Sea.

The pre-Littorina section of a sediment core collected from the eastern slope of the Landsort Deep has been analysed with respect to diatoms and sedimentologic parameters. The occurrences of different Fe-sulphide phases are related to the depositional and diagenetic conditions that are reflected by Corg and S contents and the illite to quartz ratio. The later parameter is applied as a proxy for the sediment grain size. Diatom documentation allows the sub-division of the pre-Littorina stratigraphy into intervals corresponding to the Yoldia Sea and Ancylus Lake. The Yoldia Sea interval is additionally divided into three phases, with the middle phase corresponding to the period when the entire water column was brackish. During the first phase the bottom waters were brackish and surface waters fresh and during the last phase rapid freshening took place. The occurrence of distinct pockets and lenses with FeS in two portions of the pre-Littorina sediments is explained by the elevated Corg content in these intervals. The relatively high Corg favoured sulphide generation through sulphate reduction and fixation as FeS. However, the sulphidic precipitation itself is interpreted to be sulphide limited, consistent with FeS preservation. The upper portion of the pre-Littorina sequence is affected by an additional sulphide influx by downward diffusion from Littorina Sea sediments above, facilitating the transformation of FeS to pyrite in these sediments. The variable Corg content and the grain size are primarily controlled by the proportions of sediment contribution from two different sediment sources: locally supplied, relatively organic-rich and coarse-grained littoral and fluvial sediments, and fine-grained, organic-poor sediments supplied from the melting ice-sheet.

The structure and stratigraphy of the sedimentary succession in the Swedish sector of the Baltic Basin: New insights from vintage 2D marine seismic data