Sedimentary records of benthic processes

Werner, Friedrich; Erlenkeuser, H.; Grafenstein, Ulrich von; McLean, S. R.; Sarnthein, Michael; Schauer, Ursula; Unsöld, G.; Walger, Eckart; Wittstock, R.-R.

doi:10.1029/ln013p0162

Cited by 9 publications

(7 citation statements)

References 182 publications

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“…The mouth of Eckernförde Bay is divided into a deeper northern entrance and a shallower southern channel by a morainal sill called Mittelgrund (Figure 1). Sediment grain size distribution in Eckernförde Bay gradually decreases with increasing water depth (Seibold et al, 1971; Werner et al, 1987). The sediments are mainly derived from the retreating till cliffs surrounding the bay with a minor amount contributed by the abrasion of Mittelgrund (Healy & Wefer, 1980; Healy & Werner, 1987).…”

Section: Geological Settingmentioning

confidence: 99%

Complex Eyed Pockmarks and Submarine Groundwater Discharge Revealed by Acoustic Data and Sediment Cores in Eckernförde Bay, SW Baltic Sea

Hoffmann

Deimling²,

Schröder³

et al. 2020

Geochem Geophys Geosyst

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Submarine groundwater discharge into coastal areas is a common global phenomenon and is rapidly gaining scientific interest due to its influence on marine ecology, the coastal sedimentary environment, and its potential as a future freshwater resource. We conducted an integrated study of hydroacoustic surveys combined with geochemical pore water and water column investigations at a well-known groundwater seep site in Eckernförde Bay (Germany). We aim to better constrain the effects of shallow gas and submarine groundwater discharge on high-frequency multibeam backscatter data and to present acoustic indications for submarine groundwater discharge. Our high-quality hydroacoustic data reveal hitherto unknown internal structures within the pockmarks in Eckernförde Bay. Using precisely positioned sediment core samples, our hydroacoustic-geochemical approach can differentiate intrapockmark regimes that were formerly assigned to pockmarks of a different nature. We demonstrate that high-frequency multibeam data, in particular the backscatter signals, can be used to detect shallow free gas in areas of enhanced groundwater advection in muddy sediments. Intriguingly, our data reveal relatively small (typically <15 m across) pockmarks within the much larger, previously mapped pockmarks. The small pockmarks, which we refer to as "intrapockmarks," have formed due to the localized ascent of gas and groundwater; they manifest themselves as a new type of "eyed" pockmarks, revealed by their acoustic backscatter pattern. Our data suggest that, in organic-rich muddy sediments, morphological lows combined with a strong multibeam backscatter signal can be indicative of free shallow gas and subsequent advective groundwater flow.Plain Language Summary Groundwater that seeps out of the ocean floor is a common global phenomenon. Marine ecosystems are highly dependent on nutrient supply from land, and recent studies have suggested that groundwater seeping out of the seafloor supplies even more nutrients to the world's oceans than rivers do. Also, nearshore freshwater springs have been used as a source of drinking water for decades and large offshore groundwater reserves in continental shelves can potentially prevent future freshwater shortages. We use echo sounding methods to search for indications for submarine groundwater. The methods enable us to carry out detailed investigations of intriguing seafloor depressions (i.e., "pockmarks"). Our accurate measurements give new insights into the morphology and characterization of the Eckernförde Bay pockmarks and reveal a new type of pockmark that is related to seeping groundwater. In the muddy sediment of Eckernförde Bay, methane gas forms in the sediments due to microbial decomposition of biomass. In areas of enhanced groundwater advection, this methane gas is brought closer to the seafloor, where pockmarks form and where we can detect the gas with our sonar system. Given the abundant global distribution of muddy gaseous sediments, our findings have important implications for the future detect...

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Section: Geological Settingmentioning

confidence: 99%

Complex Eyed Pockmarks and Submarine Groundwater Discharge Revealed by Acoustic Data and Sediment Cores in Eckernförde Bay, SW Baltic Sea

Hoffmann

Deimling²,

Schröder³

et al. 2020

Geochem Geophys Geosyst

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“…The movement may lead to a liquefaction of the furrow walls, resulting in a gravitative grain size differentiation and settling, producing a thin, graded layer with a sharp base. Subsequent hydrodynamic events may result in the rapid passive filling of the furrow (Werner et al, 1987;Werner, 2002).…”

Section: Nicholson 1872mentioning

confidence: 99%

Natural and Anthropogenic Sediment Mixing Processes in the South-Western Baltic Sea

et al. 2019

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Natural and anthropogenic sediment mixing can significantly impact the fidelity of sedimentary records of climate and environmental variability and human impact. This can lead to incorrect interpretations of the previous state(s) of a given ecosystem, its forcing mechanisms, and its future development. Here, natural and anthropogenic sediment mixing processes (i.e., bioturbation, hydroturbation and direct anthropogenic impact) are investigated in the southwestern Baltic Sea by sedimentological, ichnological, geochemical, and radionuclide analyses to assess their impact on timemarker profiles and sediment deposition. Depth profiles of mercury and caesium-137 display a varyingly strong disturbance down to 5-25 cm. The deviations from undisturbed profiles can be used to estimate the relative degree of sediment mixing. Sedimentary fabric analysis of high-resolution X-radiographs provides further insight into bioturbation. Ichnofossils identified in short sediment cores suggest that the primary sedimentary structure is partly overprinted by burrowing organisms living in the upper 5-7 cm of sediment. Meteorological and hydrological data from automated measuring stations combined with results from resuspension experiments show that hydrodynamic events, such as storms and saline water inflows from the North Sea, have the potential to resuspend and laterally transport sediment particles in the southwestern Baltic Sea. Partially graded layers in the scale of mm to cm in the investigated cores are likely associated with such hydrodynamic events. Multiple generations of linear traces on the seafloor are made visible through sidescan-sonar mapping and document a strong anthroturbation in the muddy sediments of the Mecklenburg Bight and the Arkona Basin, e.g., by bottom trawling. Depending on the core location and assumed mixing depth, determined mean net linear sedimentation rates range between 0 and 3.5 mm/a and reconstructed net mass accumulation rates range between 0 and 1.86 kg/m 2 /a in the mud basins. The calculable inventory of anthropogenic contaminants in the sediments illustrates the important, at least temporary storage function of the mud basins and of the adjacent sandy areas over industrial times. The findings of this study help identify the

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“…This condition, together with detailed field and laboratory studies of bioturbation of important Baltic Sea burrowing macrofauna (Dold, 1980;Powilleit et al, 1994), allows certain identifiable biogenic sedimentary structures (trace fossils) to be linked to the activity of known burrowers with reasonable confidence. This approach has proved useful in studies carried out in Kiel Bay (Werner et al, 1987;Werner, 2002) and Great Belt (Winn, 2006) in the south-west Baltic Sea, and in the Archipelago Sea in the northern Baltic Sea proper (Virtasalo et al, 2006).…”

Section: Gotland Deep Benthosmentioning

confidence: 99%

Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep, Baltic Sea

et al. 2011

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Two ca 8000 year long sediment cores from the Gotland Deep, the central sub‐basin of the Baltic Sea, were studied by means of digital images, X‐radiographs and scanning electron microscopy–energy‐dispersive X‐ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary‐fabric formation in modern and ancient seas with a high flux of organic carbon, and associated oxygen stress and depauperate ichnofauna. Four lithofacies were recognized: (i) sharply laminated mud; (ii) biodeformed mud; (iii) burrow‐mottled mud; and (iv) sedimentation‐event bed. The sharply laminated and burrow‐mottled facies dominate the cores as alternating long intervals, whereas the biodeformed and sedimentation‐event facies occur as thin interbeds within the sharply laminated intervals. The sharply laminated mud comprises alternating diatom‐rich and lithic laminae, with occasional Mn‐carbonate laminae. Lamination discontinuity horizons within the laminites, where the regular lamination is overlain sharply by gently inclined lamination, challenge the traditional view of mud accumulation by settling from suspension, but indicate localized accumulation by particle‐trapping microbial mats and, potentially, by the rapid lateral accretion of mud from bedload transport. The biodeformed interbeds record brief (few years to few decades) oxic–dysoxic conditions that punctuated the anoxic background conditions and permitted sediment‐surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier. The likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents. The sedimentation‐event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas. The turbidite preservation was favoured by the anoxic background conditions. The long burrow‐mottled intervals are characterized by intensely bioturbated fabrics with discrete Planolites, rare Arenicolites/Polykladichnus and very rare Lockeia trace fossils, as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings. These burrowed intervals represent longer periods (several years to few centuries) of oxic–dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm‐like macrofauna and bivalves, resulting in the development of a transition tier. These observations imply more dynamic and oxic depositional conditions in Gotland Deep than previously thought. Comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics, and the identification of probable biodeforming and trace‐producing species. Implications for current biofacies and trace‐fossil models are discussed.

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Sedimentary records of benthic processes

Cited by 9 publications

References 182 publications

Complex Eyed Pockmarks and Submarine Groundwater Discharge Revealed by Acoustic Data and Sediment Cores in Eckernförde Bay, SW Baltic Sea

Complex Eyed Pockmarks and Submarine Groundwater Discharge Revealed by Acoustic Data and Sediment Cores in Eckernförde Bay, SW Baltic Sea

Natural and Anthropogenic Sediment Mixing Processes in the South-Western Baltic Sea

Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep, Baltic Sea

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