Zirkulation und Ökosysteme im subpolaren und polaren Nordatlantik : 23.5. - 17.9.2006 = Circulation and ecosystems in the subpolar and polar North Atlantic

Die zweite Reise des FS MARIA S. MERIAN setzt sich aus physikalisch-ozeanographischen und biologischen Programmen zusammen. Der erste Fahrtabschnitt (Leitung Lherminier) führt ein französisches Langzeitprogramm zur Erfassung der atlantischen Umwälzbewegung (OVIDE) fort, bei dem ein hydrographischer Schnitt mit einem umfangreichen Tracerprogramm zwischen Portugal und dem südlichen Grönland aufgenommen wird. Der zweite Abschnitt (Leitung Meincke) ist ein Beitrag zum Hamburger Sonder-forschungsbereich 512, Teilprojekt „Der Ostgrönlandstrom – Indikator niederfrequenter Veränderlichkeit des Ausstroms aus dem System Arktischer Ozean/Europäisches Nordmeer“ und zum Grundprogramm des Alfred-Wegener-Institutes zum Thema „Langzeit-variabilität von Konvektion und Transporten in der Grönlandsee“. Auf dem dritten Abschnitt (Leitung Freiwald) werden neben einer polarforschungshistorischen Studie auf Spitsbergen biosedimentäre Systeme polarer Karbonatvorkommen auf den Schelfen Svalbards im Zusammenhang mit rezenter Klimavariabilität analysiert. Im letzten Abschnitt (Leitung Schauer) werden Langzeitmessungen zum Wassermassenaustausch zwischen Nordatlantik und dem Nordpolarmeer durch die Framstraße und zur Ökologie der polaren Tiefsee fortgeführt. MSM02/1 Im Rahmen eines 2002 begonnenen Langzeitprogramms OVIDE zur Erfassung der atlantischen Umwälzbewegung wird alle 2 Jahre ein hydrographischer Schnitt zwischen Portugal und dem südlichen Grönland aufgenommen. Der Schnitt besteht aus 95 CTD-Stationen und einem umfangreichen Tracer-Programm Begleitet werden die Messungen durch direkte Strömungsmessungen mit ADCPs, - einem im Schiff verankerten sowie einem mit der Rosette gefierten Gerät. Das Programm ist Teil des französischen Programms PNEDC und des inter-nationalen Programms CLIVAR. MSM02/2 Der Fahrtabschnitt MSM02 dient der Fortführung von zwei längerfristigen physikalisch-ozeanographischen Beobachtungsprogrammen der Universität Hamburg und des Alfred-Wegener-Institutes für Polar- und Meeresforschung. Mit Hilfe von in situ Messungen und realitätsnaher Model-lierung soll die saisonale bis zwischenjährliche Veränderlichkeit der Wassermassenzusammensetzung und –transporte sowohl des oberflächennahen und tiefen Ostgrönlandstromes als auch des Grönlandsee-Wirbels untersucht werden. Sie liefern die Daten zur Rolle der Prozesse im Europäischen Nordmeer, die den Eintrag von oberflächennahem Süßwasser und tiefen Overflows in den Nordatlantischen Ozean kontrollieren und damit die für das europäische Klima wichtige atlantische thermohaline Umwälzzirkulation steuern. MSM02/3 Die wissenschaftliche Zielsetzung der Reise MSM02/3 widmet sich der postglazialen Entwicklung benthischer Lebensgemeinschaften auf den Schelfen um Spitzbergen. Die Integration geologischer, biologischer, meeres-chemischer und ozeanographischer Fragestellungen ist durch die Expertise der Fahrtteilnehmer gesichert. Zusätzlich wird das Schicksal der gescheiterten Deutschen Arktis Expedition und ihrer Rettungsexpedition in den Jahren 1912 und 1913 erforscht und ein wichtiges, wenngleich tragisches Kapitel in der deutschen Polarforschung geschlossen. MSM02/4 Das Programm dient ozeanographischen und biologischen Langzeitstudien in der Framstraße. Im Rahmen des EU-geförderten Programms „DAMOCLES“ wird der ozeanische Austausch zwischen dem Nordatlantik und dem Nord-polarmeer bestimmt. Dazu wird seit 1997 auf 79°N ein Verankerungsarray betrieben, das jährlich ausgetauscht wird. Um die räumlichen Skalen besser aufzulösen, werden parallel dazu CTD-Messungen durchgeführt. Über den gleichen Zeitraum währen multidisziplinäre Untersuchungen im Bereich der Tiefsee-Langzeitstation AWI-„Hausgarten“. Neben einem zentralen Experimentierfeld in 2500 m Wassertiefe werden Stationen entlang zweier Transekte in 1000 - 5500 m Wassertiefe aufgesucht, um in biologischen, geochemischen und sedimentologischen Untersuchungen saisonale und mehrjährige Veränderungen identifizieren zu können. Dabei werden neben schiffsgebundenen Proben-nahmegeräten Lander und Verankerungen eingesetzt. Im Rahmen des DFG-Projekts “Biodiversity and ecology of deepsea copepods in polar seas – speciation processes and ecological niches in the homogeneous environment of the pelagic realm” werden die Biodiversität und die Ernährungsökologie dominanter Cope-podenarten der arktischen Tiefsee untersucht.The second cruise of RV MARIA S. MERIAN serves long-term studies of the variability of physical and biological systems of the North Atlantic. The first leg (chief scientist: Lherminier) aims at continuation of a French long-term observation of the North-Atlantic circulation and meridional overturning (OVIDE). It repeats a hydrographic section including a comprehensive tracer programme between Portugal and southern Greenland and exchanges moorings array. The second leg (chief scientist: Meincke) is a contribution to the Hamburg Special Research programme 512, work package ”The east Greenland Current - indicator of low frequency variability of the outflow from the system Arctic Ocean/Nordic Seas” and to the research topic “Convection and transports in the Greenland Sea” of the Alfred Wegener Institute. During the third leg (chief scientist: Freiwald) biosedimentary systems of polar carbon deposits will be investigated with respect to recent climate variability. This will be combined with a study of polar research history on Spitsbergen. The last leg (chief scientist: Schauer) addresses the interannual variability of water mass exchange between North Atlantic and Arctic Ocean through Fram Strait and of the ecology of the polar deep sea. MSM02/1 The OVIDE survey of 2006 is the third of this kind after 2002 and 2004. The core of the project is a hydrographic line crossing the North Atlantic from Greenland to Portugal, measuring tracers and anthropogenic carbon in addition to temperature, salinity and currents at full depth stations every 30 nm at most. The OVIDE hydrographic line is proposed within the framework of CLIVAR and CARBOCEAN (section A25). This project is part of a joint proposal to the PNEDC (a French programme which supports climate research) in collaboration with the SURATLANTE (G. Reverdin). It is also related to the ARGO programme. MSM02/2 The cruise leg MSM02/2 continues ongoing physical oceanographic field measurements carried out by the University of Hamburg and by the Alfred Wegener Institute for Polar and Marine Research. The programme is aimed at measuring and modelling the seasonal to interannual variability of the watermass composition and the transports within the Eastgreenland Current and of the convective activity in the Greenland Sea gyre. We will quantify those processes of the Nordic Seas which provide the Arctic input of freshwater and dense overflow to the North Atlantic and thereby control the Atlantic thermohaline overturning circulation. MSM02/3 The major objective of MSM02/3 is to improve our understanding of the post-glacial evolution of benthic communities on the shelves around Svalbard. The integration of geology, biology, marine chemistry and oceanography is reflected in the expertise of the scientific crew. In addition, the investigation of the fate of the Deutsche Arktis Expedition and the failed rescue expedition in the suceeding year will close an important chapter of Germany’s polar history. MSM02/4 This leg serves to investigate the long-term variability of oceanic fluxes through Fram Strait and of marine polar ecosystems. In the framework of the EU-funded programme DAMOCLES the oceanic exchange between the North Atlantic and the Arctic Ocean will be determined. To that end, since 1997 a mooring array has been maintained at 79°N that is exchanged each year. Along the line, a CTD survey provides temperature, salinity and velocity at a high spatial resolution. The multidisciplinary study of polar deep-sea ecosystems in the AWI-“Hausgarten” lasts for a similar time period. Here, stations between 1000 and 5500 m water depth are sampled each year for biological, geochemical and sedimentological parameters in order to identify interannual changes. Lander and moorings allow seasonal resolution. The biodiversity and feeding strategy of dominant polar deep-sea copepods is studied in the framework of the national project “Biodiversity and ecology of deep-sea copepods in polar seas – speciation processes and ecological niches in the homogeneous environment of the pelagic realm

North Atlantic western boundary currents are intense dissolved organic carbon streams

In the North Atlantic, there are two main western boundary currents related to the Atlantic Meridional Overturning Circulation (AMOC): the Gulf Stream flowing northward and the Deep Western Boundary Current (DWBC) flowing southward. Here we analyze data from the OVIDE section (GO-SHIP A25 Portugal-Greenland 40-60 degrees N) that crosses the DWBC and the northward extension of the Gulf Stream, the North Atlantic Current. We show that North Atlantic western boundary currents play a key role in the transport of dissolved organic matter, specifically dissolved organic carbon (DOC). Revisited transports and budgets of DOC with new available data identify the eastern Subpolar North Atlantic (eSPNA) as an important source of locally produced organic matter for the North Atlantic and a key region in the supply of bioavailable DOC to the deep ocean. The East Greenland Current, and its upstream source the East Reykjanes Ridge Current on the eastern flank of the mid-Atlantic ridge, are export pathways of bioavailable DOC toward subtropical latitudes. The fast overturning and subsequent remineralization of DOC produced in the autotrophic eSPNA explains up to 38% of the total oxygen consumption in the deep North Atlantic between the OVIDE section and 24 degrees N. Carbon budgets that do not take into account this organic remineralization process overestimates the natural uptake of carbon dioxide (CO2) from the atmosphere by one third. The inclusion of DOC transports in regional carbon budgets reconciles the estimates of CO2 uptake in the North Atlantic between model and observations.FCT: UID/Multi/04326/2019/ CEECINST/00114/2018.info:eu-repo/semantics/publishedVersio

Observatoire de la variabilité interannuelle à décennale en Atlantique Nord

41 páginas, 19 figuras.-- Pascale Lherminier ... et al.-- Merian Cruise N. 2, Leg. 1, Lisbon (Portugal) - Thorshavn (Faroes), May 21 to June 28, 2006Cruise MSM02/1 is the third occurrence of the Ovide hydrological section that was performed in 2002 and 2004, as part of the CLIVAR programme under the name of A25. The Ovide Principal Investigator is Herlé Mercier. A Greenland-Portugal section was previously performed in 1997 under the leadership of S. Bacon (NOCS), slightly south of the Ovide path. The Ovide route crosses Reykjanes Ridge 300 miles north of Charlie-Gibbs Fracture Zone and runs through the West European Basin without having to sample on top of the complex Mid-Atlantic Ridge. The objective of this repeated hydrological section is to monitor the variability of water mass properties and main current transports in the basin, complementing the international observation array relevant for climate studies. The western part of the Ovide section is redundant with AR7E (called also A1) which was done on the odd years and will allow a better analysis of the inter annual variability. The hydrological section includes a hundred surface-bottom stations from coast to coast, collecting profiles of temperature, salinity, oxygen and currents. From the 28 bottles closed at various depth at each stations, samples of sea water are used for salinity and oxygen calibration, and for measurements of biogeochemical components, including tracers, isotopes, nutrients and carbon. From the thermal wind equations, geostrophic transports are deduced from temperature and salinity. Then, direct current observations, preferentially those measured by the ship ADCP, are used to constrain the velocity at the chosen reference level. This is particularly important in the Irminger Sea, where bottom currents are very energetic. This way, the contribution in heat and fresh water of the major currents crossed (mostly perpendicularly) by the Ovide line can be estimated. From north to south, the major currents are the East Greenland/Irminger Current (about 20 Sv southward, 1 Sv = 106 m3s-1), the Deep Western Boundary Current (about 10 Sv southward), the Irminger Current (about 10 Sv northward), and the North Atlantic Current (about 20 Sv northward). Between 1997 and 2004, we already observed a significative variability of these transports (about 30%)The Meridional Overturning Circulation reflects the equilibrium between the warm and salty waters flowing poleward near surface and the cold and relatively fresh water flowing equatorward near the bottom. Measured across Ovide, it is mainly the balance between the North Atlantic Current and the Deep Western Boundary Current. The simple sketch is however complicated by the export into the Labrador Sea and around the Subpolar Gyre of part of the highly variable East Greenland Current. This is why an array of four currentmeter moorings and one ADCP lander was deployed on the East Greenland slope and shelf in 2004, for two year. While temperature and salinity are often the basic parameters to identify water masses, it is useful to use tracers like CFCs to determine when they were ventilated. Oxygen is also a good indicator near the sources, but not conservative. Combining oxygen with nutrients gives useful information on the biological activity and on the remineralization processes. CFCs and nutrients are analysed by the Roscoff team led by Pascal Morin (LCM). The measurements and analyses of pH, alkalinity and pCO2 are performed by a Fiz Perez and Aida Rios from Vigo (IIMV) at every Ovide cruise. In 2006, it was officially part of the CARBO-OCEAN international program, and the objective is to better quantify the role of the North Atlantic in the storage and transport of anthropogenic carbon accumulated in the atmosphere. In 2006, samples were taken to measure isotopes of oxygen (18) and carbon (13) after the cruise. Oxygen isotopes are very useful to determine the proportion of fresh water from different origin (rain/snow, runoff, sea ice).Peer reviewe

Report on Tracers, Carbon and ADCPs

Report on Tracers, Carbon and ADCPs: Report on transient tracer, carbonate system variables and ADCP data from hydrographic sections and a system to sustain these observations past AtlantOS on key hydrographic section

The GEOVIDE cruise in May-June 2014 reveals an intense Meridional Overturning Circulation over a cold and fresh subpolar North Atlantic

The GEOVIDE cruise was carried out in the subpolar North Atlantic (SPNA) along the OVIDE section and across the Labrador Sea in May-June 2014. It was planned to clarify the distribution of the trace elements and their isotopes in the SPNA as part of the GEOTRACES international program. This paper focuses on the state of the circulation and distribution of thermohaline properties during the cruise. In terms of circulation, the comparison with the 2002-2012 mean state shows a more intense Irminger Current and also a weaker North Atlantic Current, with a transfer of volume transport from its northern to its central branch. However, those anomalies are compatible with the variability already observed along the OVIDE section in the 2000s. In terms of properties, the surface waters of the eastern SPNA were much colder and fresher than the averages over 2002-2012. In spite of negative temperature anomalies in the surface waters, the heat transport across the OVIDE section estimated at 0.56±0.06PW was the largest measured since 2002. This relatively large value is related to the relatively strong Meridional Overturning Circulation measured across the OVIDE section during GEOVIDE (18.7±3.0Sv). By analyzing the air-sea heat and freshwater fluxes over the eastern SPNA in relation to the heat and freshwater content changes observed during 2013 and 2014, we concluded that on a short timescale these changes were mainly driven by air-sea heat and freshwater fluxes rather than by ocean circulation

The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities

The oceanic uptake of atmospheric carbon dioxide (CO2) emitted by human activities alters the seawater carbonate system. Here, the chemical status of the Northeast Atlantic is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). The increase of atmospheric CO2 leads to an increase in ocean anthropogenic carbon (Cant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate undersaturation. In this study we show a progression to undersaturation with respect to aragonite that could compromise the conservation of the habitats and ecosystem services developed by benthic marine calcifiers inhabiting that depth-range, such as the cold-water corals (CWC) communities. For each additional ppm in atmospheric pCO2 the waters surrounding CWC communities lose carbonate at a rate of − 0.17 ± 0.02 μmol kg−1 ppm−1. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ will avoid the exhaustion of excess carbonate in the Northeast Atlantic

Observations of Irminger Sea Anticyclonic Eddies

Mesoscale anticyclonic eddies in the Irminger Sea are observed using a mooring and a glider. Between 2002 and 2009, the mooring observed 53 anticyclones. Using a kinematic model, objective estimates of eddy length scales and velocity structure are made for 16 eddies. Anticyclones had a mean core diameter of 12 km, and their mean peak observed azimuthal speed was 0.1 m s(-1). They had core salinities and potential temperatures of 34.91-34.98 and 4.488-5.34 degrees C, respectively, making them warm and salty features. These properties represent a typical salinity anomaly of 0.03 and a temperature anomaly of 0.28 degrees C from noneddy values. All eddies had small (<< 1) Rossby numbers. In 2006, the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0.3 m s(-1). Similar salinity anomalies were detected throughout the Irminger Sea by floats profiling in anticyclones. Two formation regions for the eddies are identified: one to the west of the Reykjanes Ridge and the other off the East Greenland Irminger Current near Cape Farewell close to the mooring. Observations indicate that eddies formed in the former region are larger than eddies observed at the mooring. A clear increase in eddy salinity is observed between 2002 and 2009. The observed breakup of these eddies in winter implies that they are a source of salt for the central gyre. The anticyclones are similar to those found in both the Labrador Sea and Norwegian Sea, making them a ubiquitous feature of the subpolar North Atlantic basins

Freshwater exports from Arctic to the Labrador and Greenland shelf andslope.

Publisher's version (útgefin grein)We investigate whether one can detect changes in the freshwater contributions to the North Atlantic subpolar gyre(SPG), in light of the observed recent decrease of salinity in the region. We focus on two important conduits offreshwater from the Arctic to the interior North Atlantic subpolar gyre: the Coastal Labrador Current and thesouthern Greenland shelf, and use a dataset of different freshwater tracers from a set of cruises over the period2010-2014.Icelandic research institute (RANNÍS no. 152229)Peer reviewe

North Atlantic CO2 sink variability revealed by the Go-Ship A25-OVIDE section

EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022.-- This work is distributed under the Creative Commons Attribution 4.0 LicenseAbout 30% of the carbon dioxide derived from human activities (CANTH) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Friedlingstein et al., 2021), with the North Atlantic (NA) being one of the largest CANTH sinks per unit area (Khatiwala et al., 2013; Sabine et al., 2004). In the NA, oceanic CANTH uptake strongly relies on the meridional overturning circulation and the associated regional winter deep convection. In fact, the formation and deep spreading of Labrador Sea Water stands as a critical CANTH gateway to intermediate and abyssal depths. The NA CANTH uptake has fluctuated over the years according to changes in the North Atlantic Oscillation. Biennial observation of the marine carbonate system along the Go-Ship A25-OVIDE section has allowed us assessing the decadal and interannual variability of the CANTH storage in the subpolarNA from 2002 to 2021. In this study, we investigate 1) the trend of CANTH and 2) the relationship between the CANTH saturation, the apparent oxygen utilization, and the ventilation of the water masses between the A25-OVIDE section and the Greenland-Iceland-Scotland sills during 2002-2021. We divided the A25-OVIDE section into three main basins (Irminger, Iceland, and Eastern NA). Our results show that the Irminger Basin presents a more homogenous CANTH profile and higher CANTH saturation values at depth than the other two basins, which is related to the pronounced convective activity in the Irminger Basin. In contrast, the Eastern NA Basin has higher CANTH values at the surface due to its higher surface temperature, but its deep water masses show the lowest CANTH values since they are the less ventilated in the section. Our analysis also reveals that, overall, the NA CANTH storage has increased during 2002-2021, but varied according to the ventilation changes. While the Eastern NA water masses experienced a relatively constant, although shallower, average ventilation, the Irminger and Iceland Basins underwent a less steady CANTH uptake pattern characterized by alternating periods of strong and weak CANTH storageN