Description: A sediment core from the West Spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last ~9 ka in the eastern Fram Strait (FS). Our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern FS occurred stepwise, in response to the postglacial sea-level rise and the related onset of modern sea-ice production on the shallow Siberian shelves. The late Early and Mid-Holocene interval (9 to 5 ka) was generally characterized by relatively unstable conditions. High abundance of the subpolar planktic foraminifer species Turborotalita quinqueloba implies strong intensity of Atlantic Water (AW) inflow with high productivity and/or high AW temperatures, resulting in a strong heat flux to the Arctic. A series of short-lived cooling events (8.2, 6.9, and 6.1 ka) occurred superimposed on the warm late Early to Mid-Holocene conditions. Our proxy data imply that simultaneous to the complete postglacial flooding of Arctic shallow shelves and the initiation of modern sea-ice production, strong advance of polar waters initiated modern oceanographic conditions in the eastern FS at ~5.2 ka. The Late Holocene was marked by the dominance of the polar planktic foraminifer species Neogloboquadrina pachyderma, a significant expansion of sea ice/icebergs, and strong stratification of the water column. Although planktic foraminiferal assemblages as well as sea subsurface temperatures suggest a return of slightly strengthened advection of subsurface AW after 3 ka, a relatively stable cold-water layer prevailed at the sea surface, and the study site was probably located within the seasonally fluctuating marginal ice zone during the Neoglacial period.

Description: Seabed environments reveal important insights into marine ecosystems and hydrodynamics. However, the knowledge regarding their distribution in the North Sea is still fragmentary since data interpretation and mapping is very time consuming. Hydroacoustic devices are able to provide rapid and reliable information on the acoustic characteristics of the seafloor that are instrumental for seafloor discrimination. In this study we compare data of two different hydroacoustic devices: Sidescan sonar data provide acoustic images of the seafloor including bedforms and grain-size distribution. The acoustic ground discrimination system RoxAnn (200 kHz) was used to measure backscatter intensities which indicate roughness (first echo return) and hardness (second echo return) parameters of the seafloor. The data were acquired in an exclusively sandy and relatively shallow investigation area in the Sylt-Rømø Basin (SE North Sea) which is typical for the European Wadden Sea. For ground-truthing surface-sediment samples were taken. The results reveal surficial sediments ranging from fine to coarse sand. Finer material is rather restricted to the shallow areas while coarser sediments characterize the deeper tidal channels. The determined roughness and hardness parameters also strongly increase within these inlets following the change in grain size. The sidescan sonar imagery shows flow-transverse subaqueous dunes of different sizes (0.7 to 35 m from crest to crest). Both, ebb- and flood-dominated structures occur. Altogether six physically different environmental units were defined using grain-size data of the grab samples as well as bedform and backscatter data provided by the sidescan sonar. Not all of these units can be discriminated by the RoxAnn. In particular those showing similar grain sizes or superimposed bedforms yield no clear signature in the hardness vs. roughness scatter plots. However, there are some areas characterized by fine sand that reveal completely different roughness and hardness properties than other places with granumlometrically identical fine sand. This is caused by varying amounts of shell fragments on the seafloor which do not become visible in the sidescan records. Both hydroacoustic methods are suitable to identify seafloor properties even in difficult shallow and sandy environments but a combination of the methods yields more information at higher precision especially about shell content and grain-size distribution. Both hydroacoustic methods in combination with occasional grab samples and/or underwater video provide a sound data base for large-scale mapping activities as demanded by the EU government.

Description: Kelp forests represent a major habitat type in coastal waters worldwide and their structure and distribution is predicted to change due to global warming. Despite their ecological and economical importance, there is still a lack of reliable spatial information on their abundance and distribution. In recent years, various hydroacoustic mapping techniques for sublittoral environments evolved. However, in turbid coastal waters, such as off the island of Helgoland (Germany, North Sea), the kelp vegetation is present in shallow water depths normally excluded from hydroacoustic surveys. In this study, single beam survey data consisting of the two seafloor parameters roughness and hardness were obtained with RoxAnn from water depth between 2 and 18 m. Our primary aim was to reliably detect the kelp forest habitat with different densities and distinguish it from other vegetated zones. Five habitat classes were identified using underwater-video and were applied for classification of acoustic signatures. Subsequently, spatial prediction maps were produced via two classification approaches: Linear discriminant analysis (LDA) and manual classification routine (MC). LDA was able to distinguish dense kelp forest from other habitats (i.e. mixed seaweed vegetation, sand, and barren bedrock), but no variances in kelp density. In contrast, MC also provided information on medium dense kelp distribution which is characterized by intermediate roughness and hardness values evoked by reduced kelp abundances. The prediction maps reach accordance levels of 62% (LDA) and 68% (MC). The presence of vegetation (kelp and mixed seaweed vegetation) was determined with higher prediction abilities of 75% (LDA) and 76% (MC). Since the different habitat classes reveal acoustic signatures that strongly overlap, the manual classification method was more appropriate for separating different kelp forest densities and low-lying vegetation. It became evident that the occurrence of kelp in this area is not simply linked to water depth. Moreover, this study shows that the two seafloor parameters collected with RoxAnn are suitable indicators for the discrimination of different densely vegetated seafloor habitats in shallow environments.

Description: The North Sea Basin is shaped by multiple glacial advances and retreats that left complex sequences of glacio-fluvial and sub-glacial deposits, cut by sub-glacial tunnel valleys. Today, the submerged valley of the Elbe forms one of the most prominent structures of the southern North Sea. Flanked by huge moraine deposits of older glacials, the valley developed to its present form during the Weichselian sea-level lowstand (-130 m below present). Melt waters that discharged in north-westerly directions along the Scandinavian Ice Sheet fed the paleo Elbe at that time. During the Holocene the valley drowned in the rising sea. Here we present an area-wide high-resolution map of the seafloor and high-resolution shallow seismic data covering 1,600 km2 of the paleo Elbe valley (PEV) including its eastern levee. The data allow to shed new light on the PEV development including the historical process of sedimentary infill with the successive Holocene sea level rise in detail. Shallow seismic data with transect distances of 400 m and several cross sections allow 3-D visualization. The eastern flank of the valley is characterized by a relatively steep slope with one or more terraces. At its levee a significant sediment change is present on the modern sea floor, representing moraine and marine deposits. High resolution sidescan sonar data of this area show a much higher heterogeneity and complexity in sediment and habitat distribution as assumed before. Holocene marine sediments form a patchy and thin drape east of the valley floor. The western slip-off slope of the valley slope is much smoother than the eastern undercut slope. As yet, significant sedimentological changes at the present seafloor are not known for the western side of the PEV. Shallow seismic data show the base of the PEV. There are conspicuous internal seismic reflectors above the base, inclined in northeastern direction. They indicate a sedimentary infill of the valley from the southwest when the southern part of the Dogger Bank was flooded during the early Holocene sea-level rise. In this process the steeper eastern slope acted as a natural barrier towards the northeast and averted sediment transport beyond the eastern boundary of the PEV.

Description: Marine habitats worldwide are increasingly pressurized by climate change, especially along the Antarctic Peninsula. Well-studied areas in front of rapidly retreating tidewater glaciers like Potter Cove are representative for similar coastal environments and, therefore, shed light on habitat formation and development on not only a local but also regional scale. The objective of this study was to provide insights into habitat distribution in Potter Cove, King George Island, Antarctica, and to evaluate the associated environmental processes. Furthermore, an assessment concerning the future development of the habitats is provided. To describe the seafloor habitats in Potter Cove, an acoustic seabed discrimination system (RoxAnn) was used in combination with underwater video images and sediment samples. Due to the absence of wave and current measurements in the study area, bed shear stress estimates served to delineate zones prone to sediment erosion. On the basis of the investigations, two habitat classes were identified in Potter Cove, namely soft-sediment and stone habitats that, besides influences from sediment supply and coastal morphology, are controlled by sediment erosion. A future expansion of the stone habitat is predicted if recent environmental change trends continue. Possible implications for the Potter Cove environment, and other coastal ecosystems under similar pressure, include changes in biomass and species composition.

Description: The knowledge regarding the distribution of seabed environments in the North Sea is still fragmentary. Hydroacoustic devices can provide rapid and reliable information on the acoustic characteristics of the seafloor. Data of a typical, exclusively sandy and shallow investigation area located in the German Wadden Sea are here presented. The study area includes shallow sublittoral areas and deep channels. The acoustic ground discrimination system RoxAnn was used to measures backscatter intensities, which indicate roughness and hardness parameters of seafloor. Sidescan-sonar data provide acoustic images that are instrumental in seafloor characterization. For ground truthing, surface-sediment samples were collected. The results reveal surficial sediments that range from fine to coarse sand. Finer material is rather restricted to the shallow patches, while coarser sediments characterize the deeper tidal channels. The determined roughness and hardness parameters also strongly increase within these inlets following the change in grain size. The sidescan-sonar imagery shows flow-transverse subaqueous dunes of different sizes. Both ebb- and flood-dominated structures are present. RoxAnn reflects these zones of subaqueous dunes basically through the formation of distinct clusters of data points in hardness vs. roughness scatter plots. Further, the results show that areas characterized by similar grain-size spectra and sonar imagery occasionally reveal completely different roughness and hardness properties. This is caused by varying amounts of shell fragments on the seafloor. Both in situ and hydroacoustic methods are suitable for identifying seafloor properties, but the combination of methods yields more information at higher precision, especially about shell content and grain-size distribution.

Description: IMCOAST among a number of other initiatives investigates the modern and the late Holocene environmental de- velopment of south King George Island with a strong emphasis on Maxwell Bay and its tributary fjord Potter Cove (maximum water depth: about 200 m). In this part of the project we aim at reconstructing the modern sediment distribution in the inner part of Potter Cove using an acoustic ground discrimination system (RoxAnn) and more than136 ground-truth samples. Over the past 20 years the air temperatures in the immediate working area increased by more than 0.6 K (Schloss et al. 2012) which is less than in other parts of the West Antarctic Peninsula (WAP) but it is still in the range of the recovery of temperatures from the Little Ice Age maximum to the beginning of the 20th century. Potter Cove is a small fjord characterized by a series of moraine ridges produced by a tidewater glacier (Fourcade Glacier). Presumably, the farthest moraine is not much older than about 500 years (LIA maxi- mum), hence the sediment cover is rather thin as evidenced by high resolution seismic data. Since a few years at least the better part of the tidewater glacier retreated onto the island’s mainland. It is suggested that such a fun- damental change in the fjord’s physiography has also changed sedimentation patterns in the area. Potter Cove is characterized by silty-clayey sediments in the deeper inner parts of the cove. Sediments are coarser (fine to coarse sands and boulders) in the shallower areas; they also coarsen from the innermost basin to the mouth of the fjord. Textural structures follow the seabed morphology, i.e. small v-shaped passages through the moraine ridges. The glacier still produces large amounts of turbid melt waters that enter the cove at various places. We presume that very fine-grained sediments fall out from the meltwater plumes and are distributed by mid-depth or even bottom currents, thus suggesting an anti-estuarine circulation pattern. Older sediments that are more distal to the glacier front and sediments in shallower places (e.g. on top of the moraine ridges) become increasingly overprinted by coarser sediments from the shallow areas of the fjord. These areas are prone to wave induced winnowing effects as well as disturbances by ploughing icebergs. It can be concluded that coarsening of the fjord sediments will continue while the supply of fine-grained meltwater sediments might cease due to exhaustion of the reservoirs.

Description: During the past decades Mg/Ca ratios have been increasingly used in order to calculate past temperature variations independent from faunal assemblages. Especially in the Fram Strait, the main pathway of heat flux to the Arctic, new temperature estimation tools are urgently needed to better understand past complex interaction of different water masses and the extent of Atlantic Water advection to the Arctic Ocean. The Holocene section of a sediment core from the western Svalbard margin has been studied at high-resolution for benthic proxy indicators to reconstruct deepwater sources and mixing in the Arctic Gateway since the last ca 10,000 years. Benthic stable isotope values and sortable silt mean grain size data are compared to a first, preliminary data set of Mg/Ca paleotemperatures established from the benthic foraminifer species Cibicidoides wuellerstorfi in the eastern Fram Strait. When compared to planktic proxy indicators, this reconstruction of past bottom water temperatures at a northernmost site allows to estimate the linkage between deepwater inflow and AW advection within the West Spitsbergen Current. Furthermore, benthic Mg/Ca temperatures can help unravelling the local impact (e.g., by brine-enriched waters) from general trends in bottom water circulation. Short-lived decreases in benthic carbon isotope values seem to correlate to cold surface water events in the area such as the 8.2 ka event. Similarly, decreases in benthic carbon isotope values in the Nordic Seas around 8 ka have been assigned to decreased bottom water ventilation possibly due to an entrainment of relatively fresh water into the thermohaline system (Bauch et al., 2001). While sluggish bottom current speeds have been found for the 8.2 ka event north of our site on the Yermak Plateau (Hass, 2002), during colder events on the Western Svalbard margin sediment data seem to anticorrelate to benthic carbon isotope data either suggesting a rather unexpected increase in bottom current velocity or an impact of brine-enriched winter waters from the fjord/trough system which might have generated increased lateral coarser-grained sediment injections (Sarnthein et al., 2003). A Late Holocene trend towards significantly higher benthic oxygen isotopes may be either related to a cooling or increasing salinity in bottom waters. Higher salinity of bottom waters may be again caused by dense water formation during winter sea-ice formation in southern and western Svalbard fjords (e.g., Quadfasel et al., 1988; Rudels et al., 2005). Bauch, H. A., H. Erlenkeuser, R. F. Spielhagen, U. Struck, J. Matthiessen, J. Thiede, and J. Heinemeier (2001a), A multiproxy reconstruction of the evolution of deep and surface waters in the subarctic Nordic seas over the last 30,000 yr, Quaternary Science Reviews, 20(4), 659-678. Hass, H. C. (2002), A method to reduce the influence of ice-rafted debris on a grain size record from northern Fram Strait, Polar Research, 21(2), 299-306. Quadfasel, D., B. Rudels, and K. Kurz (1988), Outflow of dense water from a Svalbard fjord into the Fram Strait, Deep Sea Research Part A. Oceanographic Research Papers, 35(7), 1143-1150. Rudels, B., G. Bjork, J. Nilsson, P. Winsor, I. Lake, and C. Nohr (2005), The interaction between waters from the Arctic Ocean and the Nordic Seas north of Fram Strait and along the East Greenland Current: results from the Arctic Ocean-02 Oden expedition, Journal of Marine Systems, 55(1-2), 1-30. Sarnthein, M., S. van Krefeldt, H. Erlenkeuser, P. M. Grootes, M. Kucera, U. Pflaumann, and M. Schulz (2003), Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75◦N, Boreas, 32, 447-461.