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A marked sedimentological change in subsurface sediments from the entire Baltic Proper, the Baltic Sea, has been previously noted. Our detailed work on a variety of multi‐cores from basin‐wide transects indicates that this sedimentological change was caused by a large shift in environmental conditions during the 1950s. Until the 1950s, the water column was rather weakly stratified and winter‐time convection – although weakened during the post Little Ice Age warming – was still able to ventilate the bottom waters of the Baltic Proper. Therefore, complete sediment sequences only accumulated in calm waters deeper than 150–160 m. High‐resolution benthic foraminiferal records of subsurface sediments obtained along the saline water inflow pathway in combination with historical data indicate that the depositional environment changed drastically owing to the giant saline water inflow in AD 1951. The accompanied sharpening of the halo(pycno)cline triggered a collapse in the ventilation of the basin, resulting in oxygen‐deficient bottom waters. This deficiency, in turn, caused the onset of phosphate release from the sediments, which accelerated primary production. The ventilation collapse also enabled the onset of deposition of organic carbon‐rich sediments also in shallower water areas as calm conditions prevailed up to the modern winter mixing depth (60–70 m). A slight return to Little Ice Age‐type conditions was observed during the late 1980s when temperatures decreased and stratification weakened. These conditions gave rise to a reduction in hypoxic areas and to a bottom‐water ventilation, most pronounced in the north of the so‐called Baltic Sea Klint, a hydrographic and topographic barrier. However, the general environmental conditions essentially have not changed since the 1950s. Remarkably, external (temperature and stratification) in combination with internal factors (e.g. ventilation collapse and phosphate release) were able to change the redox conditions of the Baltic Proper from oxic to hypoxic within less than 10 years. [ABSTRACT FROM AUTHOR]

The geomagnetic field behavior in polar regions remains poorly understood and documented. Although a number of Late Holocene paleomagnetic secular variation (PSV) records exist from marginal settings of the Amerasian Basin in the Arctic Ocean, their age control often relies on a handful of radiocarbon dates to constrain ages over the past 4,200 years. Here we present well‐dated Late Holocene PSV records from two sediment cores recovered from the Chukchi Sea, Arctic Ocean. The records are dated using 26 14C measurements, with local marine reservoir corrections calibrated using tephra layers from the 3.6 cal ka BP Aniakchak eruption in Northern Alaska. These 14C‐based chronologies are extended into the post‐bomb era using caesium‐137 dating, and mercury isochrons. Paleomagnetic measurements and rock magnetic analyses reveal stable characteristic remanent magnetization directions, and a magnetic mineralogy dominated by low‐coercivity minerals. The PSV records conform well to global spherical harmonic field model outputs. Centennial to millennial scale directional features are synchronous between the cores and other Western Arctic records from the area. Due to the robust chronology, these new high‐resolution PSV records provide a valuable contribution to the characterization of geomagnetic field behavior in the Arctic over the past few thousand years, and can aid in developing age models for suitable sediments found in this region. Plain Language Summary: Investigating past changes in Earth's magnetic field is important to understand how the field is generated and varies through time. Marine sediments can record geomagnetic field changes, and can be used to reconstruct past field behavior as long as they are well dated. There are few such records from the Arctic, particularly ones that have a robust chronology covering the past few thousand years. This study provides two new sedimentary paleomagnetic records from the Chukchi Sea of the Arctic Ocean, which were dated using radiocarbon and caesium‐137. Behavior of the geomagnetic field over the past 4,200 years as preserved in the studied sediments matches the predictions of geomagnetic field models, and is also similar to other regional sedimentary records. Features that current models do not capture provide new information on variations of the geomagnetic field, and can be used to improve the models, and to date sediments from the region. Key Points: Geomagnetic field directions are reconstructed for two sediment cores from the Chukchi Sea for the past 4,200 yearsThe geochronology is based on 26 radiocarbon dates, 137Cs and tephra from the Aniakchak CFE II eruptionThe records capture paleomagnetic features recognized in the western Arctic and could aid future geochronology [ABSTRACT FROM AUTHOR]

Quick‐clay landslides are important geohazards in Sweden, Norway and Canada. While they have been studied using various geotechnical and geophysical methods, only a handful of seismic surveys have been reported for their studies. Here, we reprocess active‐source seismic data from a quick‐clay landslide site in southwest Sweden to complement earlier studies of reflection imaging and first‐break traveltime tomography with surface‐wave dispersion analysis. Results suggest extremely low shear‐wave velocities, even as low as 60–100 m/s. From a geotechnical perspective, this implies that the region classifies as a high‐risk zone for landslides and construction purposes. High or anomalous values of Poisson's ratio (or similarly P‐ and S‐wave velocity ratio) depict a zone within the normally consolidated sediments that likely represents a coarse‐grained layer, thus confirming earlier results from a number of boreholes drilled in the study area. Overall, the results presented further support to the previous hypothesis that the coarse‐grained layer plays a major role in the formation and creation of quick‐clay landslides in the study area. Additionally, an attempt to model the distribution of potential quick clays along one of the seismic profiles is performed through a combination of the modelled geophysical properties and soil textures. This study illustrates the potential of seismic methods, and how the integration of multiple geophysical properties and different data handling strategies can help to accurately characterize regions susceptible to quick‐clay landslides. [ABSTRACT FROM AUTHOR]

The late Quaternary development of the Lower Volga region of Russia is characterized by an alternating influence of marine and continental environments resulting from fluctuations in Caspian Sea level during the last glaciation. However, sediments deposited under continental conditions have received very little research attention compared to the under- and overlying marine deposits, such that even their origin is still in debate. Detailed magnetic mineralogical analyses presented here show clear similarities to loess. The results suggest that climate during the time of loess deposition, the Atelian regression (27–80 ka, MIS 4–3), was dry and cool, similar to the modern-day Northern Caspian lowland. The magnetic properties recorded in the loess-paleosol sequences of the Lower Volga also point to short episodes of potentially more humid and warmer climate during the late Atelian. The new findings in regard to the local Caspian climate and environmental evolution support decreased river discharge from the Russian Plain and Siberian Plain as the dominant factor causing the low Caspian sea level stand during the Atelian, although local-regional climate changes might have had an additional influence. [ABSTRACT FROM AUTHOR]

This paper presents an age–depth model based on an ultra‐high‐resolution, 80‐m‐thick sedimentary succession from a marine continental shelf basin, the Kattegat. This is an area of dynamic deglaciation of the Fennoscandian Ice Sheet during the Late Pleistocene. The Kattegat is also a transitional area between the saline North Sea and the brackish Baltic Sea. As such, it records general development of currents and exchange between these two systems. Data for the succession were provided through the Integrated Ocean Drilling Program Site M0060. The site indicates onset of deglaciation at c. 18 ka BP and relatively continuous sedimentation until 13 ka BP. At this point, sediments record a hiatus until c. 9–7 ka BP. The uppermost sedimentary unit contains redeposited material, but it is estimated to represent only the last c. 9–7 ka BP. The age–depth model is based on 17 select, radiocarbon‐dated samples and is integrated with a set of physical and chemical proxies. The integrated records provide novel constraints on the timing of major palaeoenvironmental changes, such as the transition from glaciomarine proximal to glaciomarine distal and marine conditions, and their connections to known major events and processes in the region and the North Atlantic. Depositional evidence specifically documents connections between the Fennoscandian Ice Sheet behaviour and atmospheric and oceanic warming. Glacial retreat may have also depended on topographic factors such as changes in basin width and depth, linked to relative sea level changes and land uplift. The results indicate an early response of the Fennoscandian Ice Sheet to changing climate, and the ice sheet's possible influence on oceanic circulation during the Late Pleistocene deglaciation. [ABSTRACT FROM AUTHOR]

The Yermak Plateau is one of several regions in the Arctic Ocean where paleomagnetism yields controversial results. Despite low sedimentation rates, late Pleistocene paleomagnetic excursions have been reconstructed from many cores in the region, but they are characterized by considerably longer durations when compared to established ones. Self‐reversal during maghemitization of (titano)magnetite has been proposed as one explanation. Rock magnetic, 14C dating, sedimentological and stable isotope (δ18O) methods were employed to three new sediment cores to put paleomagnetic results in the context of the regional stratigraphy and chronology. Coherence of lithological parameters and δ18O variations validated the ratio of anhysteretic remanent susceptibility to bulk magnetic susceptibility (κARM/κ) as a parameter for cross‐core correlation. As established by earlier studies, we use the link between glacial/interglacial cycles and κARM/κ to tune our records to a global δ18O stack, which provides age models that are independent of radicarbon ages and paleomagnetic data. Our results show that zones of negative magnetic inclination are asynchronous across the plateau. Alternating field demagnetization data revealed that negative inclinations are contained in a medium‐high‐coercivity (>25–35 mT) magnetic phase that may be the result of postdepositional alteration of (titano)magnetite. We note a positive relationship between water depth and excursion duration, which may be driven by changes in water mass circulation on glacial/interglacial timescales. Key Points: New paleomagnetic and rock magnetic data from the Yermak Plateau (Arctic Ocean) are presentedWe link variations in magnetic grain size to changes in global oxygen isotope stratigraphy to construct independent age modelsBased on our age model approach, reconstructed paleomagnetic excursions are asynchronous [ABSTRACT FROM AUTHOR]

Anisotropy of magnetic susceptibility data obtained from discrete subsamples recovered from two Integrated Ocean Drilling Program sites (Expedition 347 sites M0061 and M0062 in the Baltic Sea) by an Advanced Piston Corer are compared to results obtained on subsamples recovered by replicate 6-m-long Kullenberg piston cores. Characteristic natural remanence directions were obtained from the total of 1097 subsamples using principal component analyses. The three principal anisotropy axes of subsamples taken from Advanced Piston Core liners align to the subsample axes, with the maximum axis (K1) parallel to the split core surfaces, possibly caused by outwards relaxation of the core-liners after splitting. A second anomalous anisotropy fabric is characterized by steep values of the angular difference between the inclination of the minimum anisotropy axes (K3) and that expected for horizontal bedding (90°). This fabric is confined to the upper 1–2 m of the Kullenberg cores and specific sections of the advanced piston cores, and we attribute it to conical deformation caused by either excessive penetration speeds and downwards dragging of sediment along the edge of the liner or stretching caused by undersampling. By using our data in an example, we present a protocol to accept palaeomagnetic secular variation data that uses (i) a threshold 90-K3 value of 15°, combined with a modelled, locally applicable minimum inclination of 65° and (ii) an A95 cone of confidence based on Fisher statistics applied to virtual geomagnetic pole distributions. [ABSTRACT FROM AUTHOR]

Abstract Industrial emissions can impact aquatic environments and unregulated discharges from pulp and paper factories have resulted in deposits of cellulose fiber along the Swedish coast. These deposits are contaminated by metals, but due to their unique fibrous character the extent of sorption and dispersal of the metals is unclear. Fibrous sediments were sampled at two sites in the Ångermanälven river estuary, Sweden. The partitioning of metals between the sediment, pore water and bottom water was investigated and the degree of bioavailability was evaluated. The levels of metals in the sediment were high in fibrous or offshore samples, depending on the metal, whereas the levels of dissolved metals in pore water were low or below the limit of quantification. Partition coefficients (K D) showed that sorption to the sediment was stronger at one of the fibrous sites, possibly related to the type and size of organic matter. Undisturbed bottom water samples contained low levels of both dissolved and particle bound metals, but when comparing measured metal concentrations to threshold values of ecological status and ecotoxicological assessment criteria, both sediments and bottom water may be detrimental to living organisms. In-situ re-suspension experiments showed that the concentrations of particle bound metals increased whereas the dissolved concentrations decreased. The analyzed metals are probably retained by the solid phases of the fibrous sediment or adsorbed to particles in the water, reducing their bioavailability. Highlights • Old pulp industry waste contaminated by metals is present in coastal sediments. • Levels of some metals are harmful (exceed thresholds) in sediment and bottom water. • Pore/bottom water levels of metals do not visibly reflect sediment levels. • Geochemical conditions in the sediment, e.g. hypoxia, is likely to affect sorption. • Dissolved metal levels in bottom water did not increase after sediment resuspension. [ABSTRACT FROM AUTHOR]

We present here radiocarbon dating results from two boreal lakes In Finland, which are permanently (meromictic) or seasonally stratified and contain continuous sequences of annually laminated sediments that started to form In the early Holocene. The radiocarbon dating results of different organic components were compared with the varve-based sediment chronologies. The deviation between the Lake Valkiajarvi varve chronology (8400 varve years ±2-3% error estimate) and 33 14C dates taken from insoluble and soluble organic phases vary inconsistently throughout the Holocene. In extreme cases mean calibrated radiocarbon dates with 95.4% confidence levels (2σ) are -2350 and +2040 years offset when compared with the varve chronology. On average, the radiocarbon dates are offset by ca. +550 years. The deviation between the Lake Nautajarvl varve chronology (9898 varve years ±1% error estimate) and 26 14C dates analyzed with conventional and AMS methods indicates that radiocarbon dates are systematically older by 500-1300 years (about 900 years on average). This significant offset mean that radiocarbon dates obtained from organic bulk sediment of meromictic and seasonally hypoxic lakes must be cautiously interpreted because of the reservoir effect and carbon cycling at the sediment-water Interface. Direct evidence was obtained from the dating of soluble fraction and insoluble organic matter from near bottom water In the monimolimnion of Lake Valkiajarvi, which yielded 14C ages of 560 ±80 BP and 2070 ±140 BP, respectively. Our study reinforces previous results that age-depth models based on bulk sediment radiocarbon dates obtained on sediments of stratified lakes are of limited value for accurate dating of changes in land use and especially the commence of agriculture. [ABSTRACT FROM AUTHOR]