Quaternary evolution of the northern North Sea (original) (raw)
Related papers
Sedimentation history of the northern North Sea Margin during the last 150 ka
Quaternary Science Reviews, 2009
The Norwegian Channel Ice Stream (NCIS) is one the defining features of the Fennoscandian icesheet. Still little is known of the detailed dynamics of this ice stream in relation to regional changes in ice cover, paleoceanographic and climatic changes. Sedimentological data from core MD99-2283 in combination with seismic data allow a detailed chronological reconstruction of the outbuilding of the margin and the ice extent in southern Scandinavia through the last 150 ka. An integrated stratigraphy of the margin is presented and compared to the glacial history. Changes in the regional ice cover are reflected in the accumulation rates, the clay mineralogy, the coarse chalk fraction and the number of IRD >2 mm in core MD99-2283, while the sedimentation on the North Sea Fan as derived from seismic data provides direct evidence for the glacial activity at the shelf edge. Tentative evidence was found for two Early Weichselian glacial advances in southern Scandinavia and possibly Scotland at around 110 and 80 ka BP. From 42 cal ka BP the ice cover expanded in southern Fennoscandia and led to increased deposition on the margin and the occurrence of local melt water outbursts. Significantly increased accumulation rates, coarse chalk, local meltwater output and smectite occur during the ice expansion in the North Sea from around 34 cal ka BP. The main outbuilding phase of the NSF during the last glacial cycle occurred after 30 cal ka BP. From around 24 cal ka BP the NCIS became highly active and advanced at least three times prior to the final retreat from the shelf edge around 19.0 cal ka BP.
The Quaternary succession in the northern North Sea
Marine Geology, 1991
Sejrup, H.P., Aarseth, I. and Haflidason, H., 1991. The Quaternary succession in the northern North Sea. In: T.O. Vorren, H. Sejrup and J. Thiede (Editors), Cenozoic Geology of the Northwest European Continental Margin and Adjacent Deep Sea Areas. Mar. Geol., 101: 103-111.
Earth and Planetary Science Letters, 2021
The thick sequence of Quaternary sediments preserved within the northern North Sea contains important information about the glacial history, palaeo-oceanographic conditions and slope stability of this region during the last 2.6 million years. The interplay between glacial, fluvial and contouritic processes can be determined from seismic stratigraphic studies. Here, seismic horizon, attribute and geomorphological interpretations of an extensive 2D seismic dataset (∼100,000 km 2) and two 3D seismic cubes (∼18,400 km 2) are integrated with lithological data from eight exploration wells to map sandy sedimentary units. Mapping of seismic horizons and facies reveals that, in addition to prograding glacial sediments derived from the Norwegian mainland, the Quaternary succession includes wedge-shaped units with prograding internal clinoforms building out from the East Shetland Platform, relatively flatlying units of acoustically stratified sediments within the central northern North Sea, and aggrading to prograding units with low-amplitude internal reflections on the continental slope. The lowermost unit of Quaternary sediment is interpreted as an ∼800 km 3 earliest Pleistocene (∼2.6 Ma) turbidite-contourite deposit, in which turbidites derived from a fluvial delta building out from the East Shetland Platform transition seaward into aggrading to prograding sediments of the Shetland Drift. The wedge-shaped units are intercalated with glacigenic sediments in the central northern North Sea, showing that the East Shetland Platform was a major source area for the delivery of coarse-grained sediments during the Early Pleistocene (∼2.6-0.8 Ma). The distribution of units of aggrading to prograding geometries suggests that contourites continued to develop on the continental slope, including on the North Sea trough-mouth fan, throughout the Quaternary. These interpretations constrain a new model for the Quaternary evolution of the northern North Sea that reconciles the development of the eastern and western sides of this margin, and shows the importance of fluvial-deltaic and contouritic sedimentation during periods of reduced glacigenic sediment input. Our model also provides a high-resolution analogue for the sedimentary architectures and seismic facies that can be produced by the interplay of down-slope and along-slope processes on other continental margins.
Persistent Nordic deep-water overflow to the glacial North Atlantic
Geology, 2011
North Atlantic climate is very sensitive to overturning in the Greenland-Iceland-Norwegian (GIN) Seas, overflow of deep water into the North Atlantic via the Greenland-Iceland-Scotland Ridge, and compensating northward flow of warm surface water. Physical models suggest that, in the absence of such overturning, oceanic heat transport to the northern hemisphere is reduced by as much as 50%, open North Atlantic sea surface temperatures are up to 6°C lower, and the winter sea-ice limit migrates as far south as 45°N. Although simulations of the equilibrium climate state for the Last Glacial Maximum (LGM) suggest the absence of GIN Seas overflow, tests of these model results have been hampered by ambiguity in sedimentary proxies. Here we present a bottom water neodymium (Nd) isotope record from the Rockall Trough to investigate changes in the sources of circulating waters over the last 43 kyr. Today and throughout most of the Holocene, water from the GIN Seas, along with water from the North Atlantic Current (NAC) entrained during overflow, sets the bottom water Nd isotope composition of the Rockall Trough to around -10. Our results suggest the persistence of this scenario back into the LGM and beyond to mid-Marine Isotope Stage 3. Periodic radiogenic excursions punctuate the record at times of meltwater events, implying either continued GIN Seas overflow without NAC entrainment, or millennial-scale interruptions in the overflow and shoaling of Southern-Sourced Water (SSW). We conclude that overflow was at least intermittently present during the LGM, if not continuous, and that the GIN Seas has remained a source of deep water to the North Atlantic during the last glacial cycle.
Late Weichselian and Holocene sediment fluxes of the northern North Sea Margin
Marine Geology, 1998
An event chronology has been determined for temporal and lateral magnitudes of material fluxes across the northern North Sea Margin, including the Norwegian Channel and the North Sea Fan. This has allowed the governing factors for the sediment processes on the margin to be estimated. The chronological model of selected cores is based on 14 C AMS dates, regional tephra layers and planktonic foraminiferal stratigraphy. Based on this chronological framework the core sediments across the North Sea Margin have been divided into four main climatostratigraphic intervals: (a) Oldest Dryas (15-13 ka); (b) Bølling-Allerød (13-11 ka); (c) Younger Dryas (11-10 ka); and (d) Holocene (10-0 ka). Further, the Holocene period has also been divided into two subperiods, the Preboreal (10-9 ka) and the Holocene interglacial (9-0 ka), creating five well-defined lithological units (deposition phases), in all of which the deglaciation units (15-9 ka) usually constitute 90% of the sediment budget. The recognition of an almost identical lithological succession both in the records on the fan and in the high-resolution record of the channel suggests that sedimentation on the North Sea Margin must be governed dominantly by regional sedimentary processes. For each time interval the sedimentation rate in the Norwegian Channel is, on average, an order of magnitude higher than on the North Sea Fan diminishing distally from the shelf edge. Sedimentation under the Holocene interglacial period (9-0 ka) contrasts totally from the deglaciation pattern, controlled dominantly by pelagic productivity in the area. Close to 50% of the hemipelagic sediments on the North Sea Margin are of Bølling-Allerød age (15-13 ka). This extreme sedimentation resulted from a combination of a rapid sea-level rise, constantly exposing new areas for marine erosion=winnowing, and aggressive surface ocean current activity. Surface ocean currents and the associated bottom currents provide the dominant control on the pattern of deglacial sedimentation on the North Sea Margin (15-9 ka). This is especially apparent during the Oldest Dryas and the Bølling-Allerød periods where the distribution pattern across the margin is essentially hydrodynamically controlled. Only during the Younger Dryas period are the surface ocean processes overprinted by sedimentary processes from melting icebergs. The high-resolution records reveal that the shifts in the lithological style of sedimentation are directly linked to the rapid reorganisation of the surface ocean system frequently taking place during the deglacial and Holocene time period, suggesting a fairly regional type of sedimentation pattern. As the shift between the different lithological styles of sediments is both abrupt and regional, they should be detectable on the seismic high-frequency records.
Quaternary Science Reviews, 2004
High-resolution seismic data and sediment cores show that an up to 280 m thick sedimentary sequence has been deposited on the south Vøring margin, off mid-Norway, the last ca 250 ka. The sedimentary succession has been divided into six seismic units, dominated by hemipelagic sediments. Five wedge-shaped massive sequences, of marine isotope stages 8, 6 and 2, interfinger the hemipelagic deposits on the upper slope. The wedge-shaped sequences represent glacigenic debris flows that have been fed by till transported to the shelf edge by grounded ice sheets during maximum glaciations. The hemipelagic units show well-defined depocentres, of various thicknesses, on the upper continental slope. Seismic facies interpretation indicates that the sediment distribution locally has been controlled by currents. Commonly, the hemipelagic units are characterised by parallel and continuous reflectors. However, the second youngest unit identified, deposited between 15.7 and 15.0 14 C ka BP, is acoustic transparent. We suggest that this unit has been sourced by along-slope transported meltwater plume deposits, released during the initial stage of the last deglaciation of the Norwegian Channel. The hemipelagic sedimentation rates have varied considerably throughout the studied time period. Until ca 21 14 C ka BP the rates did not exceed 1.4 m/kyr, whereas during the Last Glacial Maximum the rates increased and reached values of about 36 m/kyr before decreasing again at ca 15 14 C ka BP. Observation of iceberg scourings, of MIS 8 age, about 800 m below the present day sea level, suggest that the south Vøring margin has subsided by a rate of 1.2 m/kyr in the Late Quaternary. r
Active Nordic Seas deep-water formation during the last glacial maximum
Nature Geoscience
The Nordic Seas are the primary location where the warm waters of the North Atlantic Current densify to form North Atlantic Deep Water, which plays a key part in the modern Atlantic Meridional Overturning Circulation. The formation of dense water in the Nordic Seas and Arctic Ocean and resulting ocean circulation changes were likely driven by and contributed to the regional and global climate of the last glacial maximum (LGM). Here, we map the source and degree of mixing of deep-water in the Nordic Seas, and through the Arctic Gateway (Yermak Plateau) over the last 35 thousand years using neodymium isotopes (εNd) measured on authigenic phases in deep-sea sediments with a high spatial and temporal resolution. We find that a large-scale reorganisation of deep-water formation in the Nordic Seas took place between the LGM (23-18 thousand years ago) and the rapid climate shift that accompanied the subsequent deglaciation (18-10 thousand years ago). We show that homogeneous εNd signatures across a wide range of sites support LGM deepwater formation in the Nordic Seas. In contrast, during the deglaciation disparate and spatially variable εNd values are observed leading to the conclusion that deep-water formation may have been reduced during this time. Deep-water formation processes in the Nordic Seas regulate the global climate via the redistribution of heat by the surface ocean and the capacity of the deep ocean to store carbon 1. At present the Atlantic Meridional Overturning Circulation (AMOC) links polar and sub-polar climate with the formation of North Atlantic Deep Water (NADW), a major component of the global oceanic thermohaline circulation. The densest northern-sourced waters in the modern AMOC are formed in the Nordic Seas, primarily by deep convection and gradual transformation of North Atlantic surface waters 2. These dense waters formed in the modern Nordic Seas overflow the Greenland-Scotland Ridge (GSR), eventually contributing to NADW accumulating carbon and nutrients as it flows throughout the deep ocean 2 (Fig. 1). The extent, mechanism, and importance of deep-water formation in the Nordic Seas during glacial periods and periods of ice rafting during meltwater events (Heinrich Events/Heinrich Stadials) are still not adequately understood. The canonical view is that the glacial AMOC was displaced from the Nordic Seas to south of Iceland in the form of a fast and shallow overturning cell forming Glacial North Atlantic Intermediate Water and that there was Southern-sourced water in the deep (> 2.5 km) Atlantic e.g,3. Contrary to this several studies e.g.4,5 argue for the presence of glacial NADW and speculate that this dense water may have been sourced from the Nordic Seas. Keigwin and Swift 6 similarly suggest that a Northern-sourced water mass may have been present in the deep (~ 5000 m) Atlantic, which could plausibly have been sourced from the Nordic Seas 7. However, proposed scenarios of LGM deep-water formation in the Nordic Seas range from near-cessation to vigorous present-day-like deep-water formation 8-11. There is evidence supporting a continued or intermittent subsurface inflow of the North Atlantic Current (NAC) during the LGM 12,13 to the Norwegian Sea. Polynya formation proximal to ice-sheets has been inferred, ventilating parts of the LGM deep Nordic Seas 7,9,14. Several proxy studies indicate a persistent overflow from the Nordic Seas into the glacial Atlantic Ocean 8,15,16. However, warmer waters (~ 1 to 2 o C warmer than the modern) in the intermediate to deep Nordic Seas and Arctic 11,17,18 indicate a reduced heat release to the atmosphere and less net cooling of the NAC waters, which could be due to subsurface expansion and deepening of the NAC 13,19. This does not support widespread deep-water formation by brine rejection or modern-like open-ocean convection, which would produce cooler waters at depth. Nevertheless, periodic cooler bottom water temperatures have been observed in LGM-aged sediments near Svalbard and in the Lofoten Basin 18,20. Less efficient deep-water formation via convective processes, upwelling, slow modification and return of Atlantic waters, or small-scale brine formation at shelf edges could be consistent with studies to date. Ultimately, the question of Nordic Seas deep-water formation during the LGM and its geographical extent remains an open debate which has not yet been fully constrained by proxy studies. Resolving the location and extent of deep-water formation under glacial conditions is key to understanding the link between climate, the oceans, ice-sheets, heat transport and carbon cycling. In this study, therefore, we provide, at a high spatial and temporal resolution, a depiction of past Nordic Seas circulation under glacial conditions. Neodymium isotope tracing of ocean circulation Neodymium (Nd) isotopes measured on authigenic phases (authigenic εNd) are a powerful tool used to trace water mass circulation 21. εNd is a proxy of the source of the Nd in the water mass. Spatial records can be related to each other to trace the flow path of water masses, and deduce their mixing with other water masses, so long as new sources of Nd are not added. However, the local input of Nd to water masses 22,23 can also alter the dissolved seawater εNd composition. This is likely to be of greater relative importance in controlling spatial patterns of εNd during times of reduced advection. High resolution εNd We measured authigenic εNd in 17 core sites to map out the geographical extent and consistency, or inconsistency, of Nordic Sea water-mass compositions from the last glacial period (~ 35 ka) to the late Holocene (< 5 ka). Individual core records from selected high-resolution core sites are shown in Fig. 2. Data are compared to similar records from the NE Atlantic and central Arctic Ocean as records in Fig. 2 and are also presented as time-slice cross sections in Fig. 3. Due to the high resolution of this data set and to understand the larger scale pattern of εNd, the data are temporally averaged. The data group naturally into 3 equal sized (5 ka) time intervals (Fig. 4), comprising the late Holocene (5-0 ka), the deglaciation (18-13 ka) and the LGM (23-18 ka). This compilation is focused on the Nordic Seas and Arctic Gateway (Yermak Plateau). The data are shown as probability density plots and histograms (Fig. 4). We compare the late Holocene with seawater values from the same depth and latitudinal range (Fig. 4), as well as to the LGM and deglacial values. These datasets were also compared using statistical tests (details are given in the Methods and Extended Data Fig. 5 and Extended Data Tables 1 and 2). The late Holocene compositions (0-5 ka) observed in the Nordic Seas and Yermak Plateau show the same spatial patterns (Fig 3A,B) and variability (Fig 4) as the modern across a range of core sites from the shallowest (at 488 m water depth, today bathed in warm northward flowing Atlantic waters on the Yermak Plateau) to the deepest in the Greenland Sea (3050 m water depth). This demonstrates that for the late Holocene, a seawater-derived signature is recorded with εNd on authigenic phases. In addition, the similar spatial pattern to the modern implies a hydrographic link between the inflow and deeper regions in the Nordic Seas and the Yermak Plateau. The homogeneity of the modern and late Holocene dataset relative to the large Nd isotope range of potential sources (which span almost the entire crustal array of εNd, ~-40 on Greenland, to ~ 10 on Iceland) also indicates vigorous circulation acting to homogenize compositions in the Nordic Sea, with a value of ~-10 (Fig. 4). The Yermak Plateau provides the ideal locality to test for changes in the NAC composition over time, because this is where warm high salinity Atlantic-derived subsurface waters are in contact with the sediment-water interface 26,27. A shallow sediment core from the Yermak Plateau (Fig. 2c, at 488 m) is used to monitor past changes in this Atlantic-derived endmember. Many studies indicate the continued strong influence of warm Atlantic waters in this region at the LGM, including at this core site 12,26. We compare this shallow core site to two other cores at different water depths (798 m and 2531 m). These Yermak Plateau cores sites have differing sedimentation rates (4, 6 and 10 cm/kyr) and likely distinctive sediment provenances 28. All the sites show similar changes through time (Fig. 2c). The three core sites are hydrographically linked in the modern ocean by vigorous circulation and the influence of Atlantic-derived waters across the Arctic Ocean 27. The Holocene εNd at these three core sites are within error of modern compositions 29,30. During the LGM the Yermak Plateau εNd averages to-13.1±0.9 (2σ (standard deviation) with a similar homogeneity and stability to the late Holocene but systematically offset in composition. The strong co-variation between these sites and the homogeneous LGM and Holocene compositions (Fig. 2C) indicates that these sites are recording an advected seawater signature resulting from Atlantic inflow and deep-water mixing and not localised sediment inputs or pore fluid processes. While some mixing with fresh and intermediate waters and localized inputs of Nd from sediment may change the NAC εNd along its pathway, the homogeneity of the signature at the LGM supports deep-water mixing that dominates over any local process. The LGM εNd at the Yermak Plateau is within error of modern composition of the NAC as it enters the Nordic Seas (-12.9±1.1 (2σ (standard deviation) 31), suggesting that this signature might be derived entirely from Atlantic waters. However, the past NAC endmember composition is unknown, and it may well have changed. The similar standard deviation of LGM εNd (Fig 2c) as the modern, regardless of the absolute value, over several residence times of Nd in the ocean, implies that at least the shallow site records the LGM NAC composition entering the...
Marine and Petroleum Geology, 2005
High-resolution seismic data have been used to study the ice-stream-fed North Sea Fan, deposited from approximately Marine Isotope Stage (MIS) 12 and onwards. Located at the outlet of the Norwegian Channel on the SE Nordic Seas continental slope, the 110,000 km 2 fan is dominated by glacigenic debris flows and slide debrites. The fan is divided in two provinces by the volcanic Møre Marginal High. The proximal province has been characterised by alternation between deposition and erosion, while the distal province has been dominated by deposition. From wMIS 12 until the present the fan has received R32,000 km 3 of sediments. Age constraints on fan stratigraphy provided by core investigations indicate that the Fennoscandian ice sheet advanced to the shelf edge during MIS 2, 6, 8, 10 and probably 12. The fan experienced megaslides in late wMIS 6, 9 and during wMIS 11-12. q