Marine High Resolution Records of the Last Interglacial in Northwest Europe: A Review

The last Interglacial in Northwest Europe (the Eemian) corresponds to stable oxygen isotope substage 5e (ca. 130-115 ka BP). Foraminiferal studies from northern Denmark suggest that déglaciation after the Saalian Glacial (stage 6) occurred gradually over a period of about 3000 years. Data from borings on the island of Anholt show that the déglaciation was interrupted by a climatic fluctuation equivalent to the Allerod-Younger Dryas-Preboreal cycle at the Weichselian-Holocene transition (stage 2/1). The environmental interpretation of the foraminiferal data when compared to that of the deep sea stable isotope stratigraphy indicates that this climatic oscillation may have been a global event. An initial sea level rise of about 50-60 m occurred at the Saalian-Eemian transition (stage 6/5e at about 130 ka BP) and the assemblages indicate that the sea level rose further in the middle part of the Eemian prior to a gradual drop in sea level in the Late Eemian. The Eemian/ Weichselian boundary (stage 5e/5d at about 115 ka BP) was characterized by a major sea level drop and a temperature decrease from lusitanian to boreal conditions. The final change to fully glacial conditions did not occur until the Early-Middle Weichselian transition (stage 5/4 at about 74 ka BP).Le dernier interglaciaire dans le nord-ouest de l'Europe (l'Éémien) correspond au stade isotopique 5e (d'environ 130-115 ka BP). Les études sur les foramini-fères effectuées dans le nord du Danemark indiquent que la déglaciation s'est réalisée graduellement sur environ 3000 ans après le Saalien (stade 6). Les données obtenues des forages dans l'île de Anholt démontrent que la déglaciation a été interrompue par une fluctuation climatique correspondant au cycle Allerod-Dryas inférieur-Préboréal à la transition Wechselien-Holocène. L'interprétation environnementale des données sur les foraminifères comparée à la stratigraphie isotopique marine démontre que cette oscillation climatique était à l'échelle mondiale. La hausse initiale du niveau marin de 50 à 60 m a eu lieu à la transition entre le Saalien et l'Éémien (stade 6/5e vers 130 ka BP) et les assemblages montrent que la hausse s'est poursuivie à l'Éémien moyen avant une baisse graduelle à l'Éémien supérieur. Aux confins de l'Éémien-Weichselien (stade 5e/5d vers 115 ka BP), il y eut une importante baisse du niveau marin accompagnée d'une diminution des températures, passant ainsi de conditions climatiques lusitaniennes à des conditions boréales. L'établissement des conditions glaciaires ne s'est fait qu'à la transition entre le Weichselien inférieur et le Weichselien moyen (stade 5/4 vers 74 ka BP).Die letzte Interglazialzeit in Europa (Eem) ent-spricht dem stabilen Sauerstoff-lsotopen-Unterstadium 5e (vor rund 130,000-115,000 Jahren). Foraminiferen-Untersuchungen von Nord-Danemark deuten darauf hin, dass das Abschmelzen nach der Saale-Eiszeit (Stadium 6) allmàhlich ùber eine Période von ungefâhr 3000 Jahren erfolgte. Bohrdaten von der Insel Anholt zeigen, dass das Abschmelzen durch Klimaschwankungen àhnlich denen des Allerôd-Jungere Dryas-Prâboreal Zykluses zur Zeit des Weichsel-Holozân Ùberganges (Stadium 2/1) unter-brochen wurde. Korreliert man Foramini-feren-Befunde von Bohrungen auf Anholt mit isotopenstratigraphischen Daten aus der Tiefsee, ergibt sich, dass dièse Klimaschwankungen vermutlich von globalem Ausmass waren. Wàhrend des Saale-Eem Ùberganges (Stadium 6/5e vor rund 130,000 J.) stieg der Meeresspiegel zunàchst um 50-60 m. In der mittleren Eem-Zeit hob er sich môglicherweise erneut, bevor er im spâ-ten Eem allmàhlich zurùckging. Der Ùber-gang vom Eem zur Weichsel (Unterstadium 5e/5d vor rund 115,000 J.) war gekenn-zeichnet durch eine starke Senkung des Meeresspiegels bei einem gleichzeitigen Rùckgang der Temperatur von lusitanischen zu borealen Verhâltnissen. Der endgùltige Wechsel zu vollstândig eiszeitlichen Bedingungen erfolgte erst am Ùbergang von der Frùhen zur Mittleren Weichselôiszeit (Stadium 5/4 vor rund 74,000 J.)

Distribution of modern benthic foraminiferal assemblages across the Northeast Greenland continental shelf

Analysis of benthic foraminifera in surface samples from 23 sites on the Northeast Greenland continental shelf reveal key assemblage differences between sites. Cluster analysis creates two clear geographical faunal assemblage zones: the 1) inner shelf, and 2) mid and outer shelf sites. These assemblages differ significantly, with the inner shelf sites being characterised by a high percentage and concentration of calcareous species, whilst the mid and outer shelf sites are dominated by agglutinated taxa. At almost all sites, the calcareous assemblages are dominated by Cassidulina neoteretis and Cassidulina reniforme, suggesting that they thrive across the shelf. Stetsonia horvathi, Oridorsalis tener, as well as Glomulina oculus and other miliolid species are found to be key calcareous species at many sites in the inner shelf zone, but they are rare-to-absent on the mid and outer shelf. Canonical correspondence analysis shows that September sea-ice cover and bottom water oxygen content are positively correlated with benthic foraminiferal assemblages at inner shelf sites, whereas organic carbon content is correlated with those in the mid and outer shelf. The formation of seasonal sea-ice and the Northeast Water polynya rejects brine into surrounding waters and transports CO2 to the seafloor, creating a highly corrosive environment for calcium carbonate. These environments are also highly productive, as indicated by the high organic carbon content and low bottom water oxygen content. The oxidation of this organic material creates CO2. We propose that these processes are key drivers in the dissolution of calcareous tests. In contrast, extensive sea-ice, high bottom water oxygen content and low primary productivity in the glacier-proximal region facilitates carbonate preservation

Evidence for influx of Atlantic water masses to the Labrador Sea during the Last Glacial Maximum

The Last Glacial Maximum (LGM, 23–19,000 year BP) designates a period of extensive glacial extent and very cold conditions on the Northern Hemisphere. The strength of ocean circulation during this period has been highly debated. Based on investigations of two marine sediment cores from the Davis Strait (1033 m water depth) and the northern Labrador Sea (2381 m), we demonstrate a significant influx of Atlantic-sourced water at both subsurface and intermediate depths during the LGM. Although surface-water conditions were cold and sea-ice loaded, the lower strata of the (proto) West Greenland Current carried a significant Atlantic (Irminger Sea-derived) Water signal, while at the deeper site the sea floor was swept by a water mass comparable with present Northeast Atlantic Deep Water. The persistent influx of these Atlantic-sourced waters entrained by boundary currents off SW Greenland demonstrates an active Atlantic Meridional Overturning Circulation during the LGM. Immediately after the LGM, deglaciation was characterized by a prominent deep-water ventilation event and potentially Labrador Sea Water formation, presumably related to brine formation and/or hyperpycnal meltwater flows. This was followed by a major re-arrangement of deep-water masses most likely linked to increased overflow at the Greenland-Scotland Ridge after ca 15 kyr BP

Middle to Late Holocene Variations in Salinity and Primary Productivity in the Central Baltic Sea: A Multiproxy Study From the Landsort Deep

Anthropogenic forcing has led to an increased extent of hypoxic bottom areas in the Baltic Sea during recent decades. The Baltic Sea ecosystem is naturally prone to the development of hypoxic conditions due to its geographical, hydrographical, geological, and climate features. Besides the current spreading of hypoxia, the Baltic Sea has experienced two extensive periods of hypoxic conditions during the Holocene, caused by changing climate conditions during the Holocene Thermal Maximum (HTM; 8–4.8 cal ka BP) and the Medieval Climate Anomaly (MCA; 1–0.7 cal ka BP). We studied the variations in surface and bottom water salinity and primary productivity and their relative importance for the development and termination of hypoxia by using microfossil and geochemical data from a sediment core retrieved from the Landsort Deep during IODP Expedition 347 (Site M0063). Our findings demonstrate that increased salinity was of major importance for the development of hypoxic conditions during the HTM. In contrast, we could not clearly relate the termination of this hypoxic period to salinity changes. The reconstructed high primary productivity associated with the hypoxic period during the MCA is not accompanied by considerable increases in salinity. Our proxies for salinity show a decreasing trend before, during and after the MCA. Therefore, we suggest that this period of hypoxia is primarily driven by increasing temperatures due to the warmer climate. These results highlight the importance of natural climate driven changes in salinity and primary productivity for the development of hypoxia during a warming climate

The Lower–Middle Jurassic of the Anholt borehole: implications for the geological evolution of the eastern margin of the Danish Basin

This study of Upper Pliensbachian – Bajocian/Bathonian deposits in a borehole drilled on the island of Anholt, Denmark incorporates sedimentology, biostratigraphy (palynomorphs and foraminifera), palaeomagnetism and coal petrology. The studied succession records a gradual change from marine inner shelf storm-influenced clays to mainly terrestrial sands, clays, and lignite containing a flora of mainly freshwater algae and pollen. The regression was initiated at the Pliensbachian–Toarcian boundary and marine influence ceased during Bajocian–Bathonian times; the regression thus took place earlier at Anholt than in the centre of the Danish Basin. The sediments in the Anholt borehole are referred to the Fjerritslev and Haldager Sand Formations. Although the Lower–Middle Jurassic boundary is commonly placed at the boundary between the two formations, our data indicate that at Anholt the upper Fjerritslev Formation (member F-IV) is of Aalenian age. The Lower–Middle Jurassic boundary occurs close to the boundary between members F-III and F-IV of the Fjerritslev Formation. In contrast to other Lower–Middle Jurassic successions in the North Sea region, smectites of inferred volcanic origin are preserved in the Anholt section, suggesting limited burial and hence less intense diagenetic illitisation or chloritisation of smectites. A down-hole increase in diagenetic influence is reflected by the increase down-section both in the thermal stability of kaolinite and in the vitrinite reflectance. Kaolinite of inferred authigenic origin forms a white powder in the quartz-dominated sands of the Haldager Sand Formation; this kaolinite is thermally very unstable and is interpreted to be of late diagenetic, post-uplift origin. The vitrinite reflectance data indicate that the Jurassic formations have been exposed to thermal maturation corresponding to burial to a depth of 1000–1200 m below their present depth. Post-maturation uplift of the order of 1 km probably occurred partly during Late Cretaceous – Paleocene inversion in the Kattegat area and partly during Oligocene–Recent regional uplift, the latter being the most important of the two uplift phases. Palaeomagnetic data indicate that the main carrier of magnetic remanence is fine-grained magnetite. The stable remanence shows a pronounced inclination shallowing, which is attributed to post-depositional compaction

Learning from the past : Impact of the Arctic Oscillation on sea ice and marine productivity off northwest Greenland over the last 9,000 years

Climate warming is rapidly reshaping the Arctic cryosphere and ocean conditions, with consequences for sea ice and pelagic productivity patterns affecting the entire marine food web. To predict how ongoing changes will impact Arctic marine ecosystems, concerted effort from various disciplines is required. Here, we contribute multi-decadal reconstructions of changes in diatom production and sea-ice conditions in relation to Holocene climate and ocean conditions off northwest Greenland. Our multiproxy study includes diatoms, sea-ice biomarkers (IP(25)and HBI III) and geochemical tracers (TOC [total organic carbon], TOC:TN [total nitrogen], delta C-13, delta N-15) from a sediment core record spanning the last c. 9,000 years. Our results suggest that the balance between the outflow of polar water from the Arctic, and input of Atlantic water from the Irminger Current into the West Greenland Current is a key factor in controlling sea-ice conditions, and both diatom phenology and production in northeastern Baffin Bay. Our proxy record notably shows that changes in sea-surface conditions initially forced by Neoglacial cooling were dynamically amplified by the shift in the dominant phase of the Arctic Oscillation (AO) mode that occurred at c. 3,000 yr BP, and caused drastic changes in community composition and a decline in diatom production at the study site. In the future, with projected dominant-positive AO conditions favored by Arctic warming, increased water column stratification may counteract the positive effect of a longer open-water growth season and negatively impact diatom production.Peer reviewe

A reconstruction of warm-water inflow to Upernavik Isstrøm since 1925 CE and its relation to glacier retreat

International audienceThe mass loss from the Greenland Ice Sheet has increased over the past 2 decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Periods of rapid retreat of these tidewater glaciers have been linked to the concurrent inflow of warm Atlantic-sourced waters. However, little is known about the variability of these Atlantic-derived waters within the fjords, due to a lack of multi-annual in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to the fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We conclude that the foraminiferal assemblage is predominantly controlled by changes in bottom water composition and provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water influx during the 1930s and again after 2000, a pattern that is comparable to the Atlantic Multidecadal Oscillation (AMO). The comparison of these results to historical observations of front positions of Upernavik Isstrøm reveals that inflow of warm Atlantic-derived waters likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s and 1970s, showing that glacier retreat continued despite a reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord, and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the coming decade, potentially minimizing or stabilizing the retreat of Upernavik Isstrøm during this time interval.climate chang

Microfaunal Recording of Recent Environmental Changes in the Herschel Basin, Western Arctic Ocean

Microfaunal assemblages of benthic foraminifera, ostracods, and tintinnids from two marine sediment cores retrieved from the Herschel Basin of the Canadian Beaufort Sea shelf document relationships with environmental parameters such as salinity, sea-ice cover, and turbulence. Cores YC18-HB-GC01 and PG2303-1 were collected at 18 and 32 m water depth, respectively. At these sites, sediment accumulation rates range between 0.6 and 1.7 cm yr–1 allowing a near-annual temporal resolution over the last 50 years. Multivariate analyses indicate that benthic foraminiferal assemblages respond primarily to food supply. Dissimilarities between the microfaunal assemblages of the two cores are mainly the result of bottom water salinity levels linked to water depth. High abundance of the benthic foraminiferal species Elphidium clavatum and occurrences of Elphidium bartletti point to varying, but relatively low, salinities at the shallow core site YC18-HB-GC01, which may be affected by variations in the summer halocline depth. Higher species diversity and more abundant Cassidulina reniforme and Stainforthia feylingi characterize the deeper core PG2303-1, which might reflect more stable conditions and higher bottom-water salinities throughout the studied time interval. The most important microfaunal shift of the last 50 years, observed in the shallower longer core YC18-HB-GC01, occurred at the turn of the 21st century. Prior to ∼2000 CE, the presence of Islandiella norcrossi indicates more stable and saline conditions. Since ∼2000 CE, increased abundances of Haynesina nivea and of the ciliate Tintinnopsis fimbriata suggest decreased salinity and increased turbidity. An increased abundance of Eoeponidella pulchella after ∼2000 CE suggests a concurrent increase in productivity in the last two decades. This shift is nearly synchronous with a decrease in mean summer sea-ice concentration, which can play an important role in bottom water stability on the shelf. Easterly winds can induce a reduction in the sea-ice cover, but also foster a westward spreading of the Mackenzie River plume and the upwelling of nutrient-rich Pacific waters onto the shelf. Both factors would explain the increased freshening and productivity of the Herschel Basin. The last two decades were also marked by a decrease in ostracod abundance that may relate to higher water turbidity. This study shows that combining information from benthic foraminifera, ostracods, and tintinnids provides a comprehensive insight into recent hydrographic/climatic changes in nearshore Arctic habitats, where productivity is critical for the food security of local communities