Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka. Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.publishedVersio

Late Quaternary paleoceanography of the northern continental margin of Svalbard

This study focuses on the reconstruction of the variability of Atlantic Water inflow to the Arctic Ocean and its influence on the Svalbard-Barents Sea Ice Sheet (SBIS), sea-ice cover, variations in the bottom current strength and the depositional environment in the past. For this reconstruction, the distribution patterns of planktic and benthic foraminiferal assemblages, oxygen and carbon stable isotopes in planktic and benthic foraminifera, ice-rafted debris, grain size of the sediment in particular sortable silt, and organic carbon content from two sediment cores were investigated. The results show that variable strength of the subsurface Atlantic Water together with insolation has influenced the extent of the sea-ice cover and the stability of the SBIS since 132,000 years before present (Termination II). Besides, distinct increase in freshwater flux from melting of glacier ice during deglaciation periods at around 60,000 years (MIS 4/3) and between 19,000 and 11,500 years (MIS 2/1) also had significant influence on the oceanography through stratification of the upper water column and weakening of the ocean circulation. This led to poor ventilation at the sea bottom and expansion of sea-ice cover at the surface. The influence of these ‘climate drivers’ on the local sedimentary and oceanographic environment varied significantly. This emphasizes the importance of considering regional environmental parameters and feedback mechanisms in reconstructions of the past climate

Palaeoceanography of the Barents Sea continental margin, north of Nordaustlandet, Svalbard, during the last 74 ka

We investigated gravity core HH11‐09GC from 488 m water depth at the northern Svalbard margin in order to reconstruct changes in Atlantic Water (AW) inflow to the Arctic Ocean. The study was based on the distribution patterns of benthic and planktic foraminifera, benthic and planktic oxygen and carbon isotopes, lithology and physical properties of the sediments. The core contains sediments from Marine Isotope Stages (MISs) 5a to 1. MIS 4 was characterized by glacial conditions and at c. 65 ka the Svalbard‐Barents Sea Ice Sheet (SBIS) advanced. Polynya was formed in front of the SBIS at c. 62 ka. During late MIS 3 (32–29 ka) and MIS 2 (22–20 ka), a strong influence of AW resulted in high productivity of both planktic and benthic foraminiferal faunas. During 23–22 ka, the SBIS advanced to the shelf edge. The last deglaciation began at 18.5 ka and at 16.9 ka ‘a peak’ influx of meltwater from the retreating SBIS caused a weakening of the ocean circulation. At the start of the Bølling‐Allerød interstadial at c. 15.5 ka, inflow of relatively warm AW probably intensified the release of meltwater at 14 and 12.8 ka. This probably led to expansion of sea ice cover during the Younger Dryas stadial. The late Holocene from 3.7 ka was characterized by the presence of seasonal to perennial sea ice cover and a slight warming of the bottom waters. The sea ice cover decreased for a short period at 1.5 ka owing to the advection of relatively warm AW. Correlation with results from the northwestern Svalbard margin shows that the patterns of ice retreat and advance correlate closely with changes in inflow of AW and were regulated by meltwater discharge, sea ice export and insolation

Coastal permafrost was massively eroded during the Bølling-Allerød warm period

Acknowledgements: We thank all the people working in the Marine Geochemistry group at the Alfred Wegener Institute in Bremerhaven for the help and support. The Master and crew of the R/V Helmer Hanssen are gratefully acknowledged for their help during the coring. This study was supported by Ca’ Foscari University of Venice as part of the PhD programme in Polar Sciences. T.T. acknowledges the Italian Research Program in the Arctic (PRA-2019) for financial support (PAST-HEAT project). A.N., T.T. and G.M. acknowledge the Italian-German partnership on “Chronologies for Polar Paleoclimate Archives (PAIGE)” and the funding from the Helmholtz European Partnering.The Bølling-Allerød interstadial (14,700–12,900 years before present), during the last deglaciation, was characterized by rapid warming and sea level rise. Yet, the response of the Arctic terrestrial cryosphere during this abrupt climate change remains thus far elusive. Here we present a multi-proxy analysis of a sediment record from the northern Svalbard continental margin, an area strongly influenced by sea ice export from the Arctic, to elucidate sea level - permafrost erosion connections. We show that permafrost-derived material rich in biospheric carbon became the dominant source of sediments at the onset of the Bølling-Allerød, despite the lack of direct connections with permafrost deposits. Our results suggest that the abrupt temperature and sea level rise triggered massive erosion of coastal ice-rich Yedoma permafrost, possibly from Siberian and Alaskan coasts, followed by long-range sea ice transport towards the Fram Strait and the Arctic Ocean gateway. Overall, we show how coastal permafrost is susceptible to large-scale remobilization in a scenario of rapid climate variability

Coastal permafrost was massively eroded during the Bølling-Allerød warm period

Acknowledgements: We thank all the people working in the Marine Geochemistry group at the Alfred Wegener Institute in Bremerhaven for the help and support. The Master and crew of the R/V Helmer Hanssen are gratefully acknowledged for their help during the coring. This study was supported by Ca’ Foscari University of Venice as part of the PhD programme in Polar Sciences. T.T. acknowledges the Italian Research Program in the Arctic (PRA-2019) for financial support (PAST-HEAT project). A.N., T.T. and G.M. acknowledge the Italian-German partnership on “Chronologies for Polar Paleoclimate Archives (PAIGE)” and the funding from the Helmholtz European Partnering.AbstractThe Bølling-Allerød interstadial (14,700–12,900 years before present), during the last deglaciation, was characterized by rapid warming and sea level rise. Yet, the response of the Arctic terrestrial cryosphere during this abrupt climate change remains thus far elusive. Here we present a multi-proxy analysis of a sediment record from the northern Svalbard continental margin, an area strongly influenced by sea ice export from the Arctic, to elucidate sea level - permafrost erosion connections. We show that permafrost-derived material rich in biospheric carbon became the dominant source of sediments at the onset of the Bølling-Allerød, despite the lack of direct connections with permafrost deposits. Our results suggest that the abrupt temperature and sea level rise triggered massive erosion of coastal ice-rich Yedoma permafrost, possibly from Siberian and Alaskan coasts, followed by long-range sea ice transport towards the Fram Strait and the Arctic Ocean gateway. Overall, we show how coastal permafrost is susceptible to large-scale remobilization in a scenario of rapid climate variability.</jats:p