Atlantic circulation changes across a stadial-interstadial transition

We combine consistently dated benthic carbon isotopic records distributed over the entire Atlantic Ocean with numerical simulations performed by a glacial configuration of the Norwegian Earth System Model with active ocean biogeochemistry, in order to interpret the observed Cibicides &delta;13C changes at the stadial-interstadial transition corresponding to the end of Heinrich Stadial 4 (HS4) in terms of ocean circulation and remineralization changes. We show that the marked increase in Cibicides &delta;13C observed at the end of HS4 between ~2000 and 4200 m in the Atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high latitude glacial North Atlantic. Our model results show that this Cibicides &delta;13C signal is associated with changes in the ratio of southern-sourced (SSW) versus northern-sourced (NSW) water masses at the core sites, whereby SSW is replaced by NSW as a consequence of the resumption of deep water formation in the northern North Atlantic and Nordic Seas after the freshwater input is halted. Our results further suggest that the contribution of ocean circulation changes to this signal increases from ~40 % at 2000 m to ~80 % at 4000 m. Below ~4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of HS4. The simulated lower remineralization during stadials than interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep Southern Ocean during stadials found in previous studies.</p

Late Holocene paleoceanographic evidence of the influence of the Aleutian Low and North Pacific High on circulation in the Seymour-Belize Inlet Complex, British Columbia, Canada

Foraminiferal and thecamoebian faunas from the Seymour-Belize Inlet Complex (SBIC), a fjord network situated on the mainland coast of British Columbia, were studied to assess climatic cycles and trends impacting the area through the ∼ AD 850–AD 2002 interval. Ocean circulation patterns prevalent in the SBIC are strongly linked to precipitation, which is closely linked to the relative strength and position (center of action; COA) of the seasonally developed Aleutian Low (AL) and North Pacific High (NPH) atmospheric circulation gyres. Through interpretation of cluster analysis and ordination methods, a period of weak estuarine circulation was recognized to have impacted the SBIC area between ∼ AD 850 and AD 1500. During this time waters in the SBIC were dysoxic to anoxic and the sediment–water interface was comprised of a depauperate foraminiferal fauna consisting of low diversity agglutinated forms. These reduced oxygen conditions came about as a result of diminished precipitation in the SBIC catchment as the COA of the AL progressively migrated westward over time, resulting in greatly reduced estuarine circulation and only infrequent and feeble incursions of well oxygenated open ocean water into the SBIC basin. By ∼AD 1575, following a gradual transition period of ∼75 years when circulation patterns in the inlet were unstable, very strong estuarine circulation developed in the SBIC, concomitant with the onset of the Little Ice Age (LIA) in western Canada. In the SBIC this interval was characterized by higher levels of precipitation, which greatly enhanced estuarine circulation resulting in frequent incursions of cold, well oxygenated ocean currents into the bottom waters of the SBIC and the development of a diverse calcareous foraminiferal fauna. This circulation pattern began to break down in the late 19th century AD and by ∼AD 1940 conditions similar to those that existed in the inlet prior to ∼AD 1500 had redeveloped, a process that continues at present

Age and duration of Laschamp and Iceland Basin geomagnetic excursions in the South Atlantic Ocean

International audienc

Ice volume and sea-level changes during Last Glacial Cycle: evidence from marine records

This chapter summarises the environmental changes that accompanied the rapid growth of the Northern Hemisphere ice sheets c. 35–30 cal ka BP and their maximum extent c. 29–19 cal ka BP, with a special focus on the European continent and its surrounding margins

A Simplified Palaeoceanography Archiving System (PARIS) and GUI for Storage and Visualisation of Marine Sediment Core Proxy Data vs Age and Depth

Scientific discovery can be aided when data are shared following the principles of findability, accessibility, interoperability, reusability (FAIR) data (Wilkinson et al., 2016). Recent discussions in the palaeoclimate literature have focussed on defining the ideal database format for storing data and associated metadata. Here, we highlight an often overlooked primary process in widespread adoption of FAIR data, namely the systematic creation of machine readable data at source (i.e. at the field and laboratory level). We detail a file naming and structuring method that was used at LSCE to store data in text file format in a way that is machine-readable, and also human-friendly to persons of all levels of computer proficiency, thus encouraging the adoption of a machine-readable ethos at the very start of a project. Thanks to the relative simplicity of downcore palaeoclimate data, we demonstrate the power of this simple but powerful file format to function as a basic database in itself: we provide a Matlab-based GUI tool that allows users to search and visualise isotope data by sediment core location and species type, against either depth or age. We share the database format here so that other laboratories might consider developing a similar approach depending on their own needs and requirements

Refonte du systeme de carottage de l’Atalante. Mission ATA-ESSTECH-2023. Essai du nouveau système de carottage

Faits saillants : • Le système de carottage est opérationnel jusqu'à 24 m avec une qualité de prélèvement satisfaisante mais perfectible • Le carottage 30 m n'est pas opérationnel en conditions standards (3 matelots) et par condition météo difficile • La récupération des tubes flambés et des tubes instrumentés en flux de chaleur n'est pas opérationnelle • Les temps de carottage (hors filage et virage) restent à préciser, ils sont de 5.5 h (tube 15 m), 6.5 h (tube 24 m), et 8.5 h (tube 30 m), incluant le temps de découpe ne pouvant s'effectuer en temps masqué • Les bers sont fragiles et encombrants. Ils limitent le déploiement à un maximum de 24 m • L'ensemble du système reste lourd avec un coût opérationnel élevé (transport et installation) Objectifs à atteindre : • L'objectif de carottage 30 m en conditions opérationnelles standards n'est pas atteint, or c'était l'objectif affiché de la refonte du carottage sur l'Atalante • Réduire le temps opérationnel • Réduire la dangerosité des manoeuvres de récupération sur la plateforme de carottage • Réduire la lourdeur de mise en oeuvre et le coût opérationnel du système de carottage. Recommandations : • Remplacer les 4 bers par 4-5 tangons, ce que permettra : 1. le déploiement d'un tube de 30 m en conditions opérationnelles standard et par météo difficile, 2. la récupération des tubes flambés et des tubes instrumentés pour le flux de chaleur, 3. la libération du pavois et autorisera le déploiement d'outils (CTD, carottier multi-tubes) du labo humide en alternance avec le carottage, 4. la libération de l’espace de circulation et de travail dans la coursive, 5. la réduction de l'encombrement du système, peut-être son stockage à bord du navire et réduira ainsi les coûts opérationnels élevés du transport et des jours de montage à quai • Réduire le temps d'opération en facilitant l'insertion de la chemise par arrière (haut du carottier) à travers la plateforme --> modifier/déplacer l'extraction de ventilation du local tube • Ajouter un treuil sur le bordé pour la récupération du câble pilote pour éviter une chute à la mer du personne

Abrupt (or millennial or suborbital) climatic variability: Heinrich events/stadials

The causes and consequences of the episodic iceberg-discharge events from the Hudson Strait Ice Stream of the Laurentide Ice Sheet, or Heinrich events (HE), are one of the most explored topics in Pleistocene palaeoclimatology. In this chapter, we summarise three decades of intense research while introducing recent results from both the European and Cordilleran Ice Sheets that could call for a paradigm shift in our understanding of the HE

Chapter 7 - The Younger Dryas Stadial

The Younger Dryas (YD) stadial is the last extreme cold event detected in the northern hemisphere during the last deglaciation. Many theories have been proposed to explain the causes of this event. Currently, the most accepted one is that the increased meltwater discharges into the North Atlantic or Arctic Sea produced a series of changes in ocean circulation and sea ice cover that triggered substantial shifts in the atmospheric circulation patterns. The impact of these changes is marked by a series of climate shifts within the YD stadial with a complex spatial distribution of hydroclimate in Europe in each phase