Search

The Brown Bank Formation (BB Fm) is a clay‐rich sedimentary unit that is distributed over a large areain the southern North Sea. It is easily recognisable in 2D acoustic reflection profiles, forming sets of subparallel high‐amplitude reflections. Previous studies have provided only fragmentary information on the facies, and a variety ofinterpretations on the depositional environment and age of the BB Fm. In this study we combine high‐resolution 2Dacoustic reflection profiles and multiproxy sedimentological, geochemical and geochronological analyses of threevibrocores, to provide a detailed description and a new age assessment for the BB Fm at its type locality, adjacent tothe Brown Bank ridge. At the study site, the BB Fm shows morphologically well‐preserved submarine sand dunes,deposited in a high‐energy shelf setting, overlain by organic‐rich silty clays that were deposited under lower‐energyconditions in an increasingly compartmentalised marginal marine environment. Elevated terrestrial organic inputshows that the Rhine–Meuse delta was situated relatively close‐by. Luminescence ages indicate that the sediments ofthe BB Fm in our cores were deposited during the Weichselian Odderade interstadial (MIS5a, ca. 80 ka) and earliestparts of the Early Pleniglacial (MIS4, ca. 70 ka), which is later than previously reported in the literature.

The Late Pleistocene Marine Isotope Stage (MIS) 5 – MIS 4 transition (at ca. 75 ka) is globally known to correspond to a period of strong cooling and sea-level lowering. Terrestrial records indicate the transition had a large impact on terrestrial environments, but the impact on coastal and shallow-marine areas is poorly documented due to a lack of well-dated, continuous archives caused by erosion during succeeding glacial lowstands. The extensive offshore deposits of the Brown Bank Formation in the southern North Sea yield a valuable record of this transition in a shallow-marine environment. We show that the southern North Sea experienced subarctic marine conditions with a high input of terrestrial material during the MIS 5–4 transition. These continued marine conditions, which have not been described earlier for northwestern Europe, show that sea level remained relatively high, and lagged cooling on land inferred from lipid-biomarker palaeothermometry. The time-lag between terrestrial cooling and sea-level fall created a sediment preservation window during the onset of MIS 4 in a shallow-marine environment. Our record captures changes in both the terrestrial and shallow-marine environments, and allows for linking terrestrial and marine records of the MIS 5–4 transition in NW Europe.

The Brown Bank Formation (BB Fm) is a clay-rich sedimentary unit that is distributed over a large area in the southern North Sea. It is easily recognisable in 2D acoustic reflection profiles, forming sets of subparallel high-amplitude reflections. Previous studies have provided only fragmentary information on the facies, and a variety of interpretations on the depositional environment and age of the BB Fm. In this study we combine high-resolution 2D acoustic reflection profiles and multiproxy sedimentological, geochemical and geochronological analyses of three vibrocores, to provide a detailed description and a new age assessment for the BB Fm at its type locality, adjacent to the Brown Bank ridge. At the study site, the BB Fm shows morphologically well-preserved submarine sand dunes, deposited in a high-energy shelf setting, overlain by organic-rich silty clays that were deposited under lower-energy conditions in an increasingly compartmentalised marginal marine environment. Elevated terrestrial organic input shows that the Rhine–Meuse delta was situated relatively close-by. Luminescence ages indicate that the sediments of the BB Fm in our cores were deposited during the Weichselian Odderade interstadial (MIS5a, ca. 80 ka) and earliest parts of the Early Pleniglacial (MIS4, ca. 70 ka), which is later than previously reported in the literature.

Both marine dinoflagellate cysts and terrestrially derived pollen and spores are abundant in coastal sediments close to river mouths, making sediment records from such settings ideal to simultaneously study land– ocean climate interactions, marine productivity patterns and freshwater input over time. However, few studies consider the combined calibration of these palynological proxies in modern coastal sediments offshore from rivers, which is needed to strengthen the interpretation of paleoreconstructions. Here, we analyze the palynological content of marine surface sediments along land–sea transects off the Mississippi and Atchafalaya river mouths in the northern Gulf of Mexico (GoM) and test three palynological indices which are often employed in the paleo-domain: (i) the abundance of cysts of heterotrophic and autotrophic dinoflagellates (dinocysts) as a tracer for primary productivity (H /A ratio) and (ii) the ratio between non-bisaccate pollen and bisaccates (P /B) as well as (iii) the ratio between pollen (excluding bisaccates) and dinocysts (P /D), which are both tracers for river input and distance to the coast. Our results show that dinoflagellate cysts are most abundant on the shelf, where heterotrophic dinocyst species dominate coastal assemblages in reach of the river plume, while autotrophic taxa are more present in the oligotrophic open ocean. This is clearly reflected in decreasing H/A values further offshore. Individual dinocyst taxa also seem to inhabit specific niches along an onshore–offshore transect, linked to nutrient availability and proximity to the turbid river plume. The highest pollen concentrations are found close to the Mississippi river mouth and mostly represent a mixture of local coastal and upstream vegetation, whereas bisaccate pollen was most abundant further offshore of the Mississippi river. Multivariate redundancy analysis (RDA) performed on both pollen and dinocyst ass

A robust understanding of the impact of anthropogenic activities on high-altitude tropical aquatic ecosystems is key for the conservation and protection of the Tropical Andean biodiversity hot spot. We present the results of a multiproxy study of lake sediments from the high Andean páramo of El Cajas National Park, a UNESCO biosphere reserve in Ecuador. The main site, Laguna Pallcacocha, is well known for recording El Niño-driven clastic flood layers that are triggered by high-intensity rainfall anomalies from the eastern Pacific. The second site, Laguna El Ocho, does not contain clastic laminations, providing a control. The records show abrupt shifts in diatom assemblages ca. AD 1991 in both high-elevation Andean lakes accompanied by local changes in páramo composition that suggest a sudden nutrient enrichment of the environment. The diatom assemblages from Laguna Pallcacocha, in relation to the clastic input events, are remarkably stable and do not show evident El Niño signals at the analysed resolution. Based on comparison with the nonlaminated El Ocho record, we deduce the main source of this nutrient enrichment to be the construction of a heavily transited road that runs through the park, while climate warming played secondary role by amplifying its effects.

Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584-m-long DEEP sediment succession and a comparison to a 197-m-long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake.

The Nieuweveen pingo is one of the many pingos present in the Eastern part of the Netherlands. But it is unique thanks to the large and continuous sedimentary record. Preliminary research of the Nieuweveen core showed very little human impact present at this site. Therefore, the aim of this research is to determine how and when human influence impacted the natural vegetation around the site. 45 samples were taken from the Nieuweveen core and the pollen were extracted and analyzed. Based on the obtained pollen record it became clear that humans influenced the area since 5500 cal. yr. BP. However, clear human impact on the environment around the Nieuweveen site did not happen until around 3500 cal. yr BP, which is extremely late. Comparisons with other well-known pingo remnants such as the Hijkermeer pingo, Mekelermeer pingo and Uddelermeer pingo show that the human impact on the Nieuweveen site was also very limited compared to other parts of the Netherlands. As a result the vegetation around this site gives a clear picture of the natural vegetation during most of the Holocene. Small scale farming, deforestation and establishing of settlements all influenced the area. Although some had more impact than others. Furthermore, changes in temperature and precipitation between 4200 cal. yr BP and 3200 cal. yr BP were also important contributors to some of the changes in the natural vegetation, such as a rapid and sudden increase and later on a decline in Betula.

The sediment record from Lake Ohrid (Southwestern Balkans) represents the longest continuous lake archive in Europe, extending back to 1.36 Ma. We reconstruct the vegetation history based on pollen analysis of the DEEP core to reveal changes in vegetation cover and forest diversity during glacial–interglacial (G–IG) cycles and early basin development. The earliest lake phase saw a significantly different composition rich in relict tree taxa and few herbs. Subsequent establishment of a permanent steppic herb association around 1.2 Ma implies a threshold response to changes in moisture availability and temperature and gradual adjustment of the basin morphology. A change in the character of G–IG cycles during the Early–Middle Pleistocene Transition is reflected in the record by reorganization of the vegetation from obliquity- to eccentricity-paced cycles. Based on a quantitative analysis of tree taxa richness, the first large-scale decline in tree diversity occurred around 0.94 Ma. Subsequent variations in tree richness were largely driven by the amplitude and duration of G–IG cycles. Significant tree richness declines occurred in periods with abundant dry herb associations, pointing to aridity affecting tree population survival. Assessment of long-term legacy effects between global climate and regional vegetation change reveals a significant influence of cool interglacial conditions on subsequent glacial vegetation composition and diversity. This effect is contrary to observations at high latitudes, where glacial intensity is known to control subsequent interglacial vegetation, and the evidence demonstrates that the Lake Ohrid catchment functioned as a refugium for both thermophilous and temperate tree species.