Showing papers by "Martin Visbeck published in 2017"

Decline in global oceanic oxygen content during the past five decades

Abstract: Ocean models predict a decline in the dissolved oxygen inventory of the global ocean of one to seven per cent by the year 2100, caused by a combination of a warming-induced decline in oxygen solubility and reduced ventilation of the deep ocean1, 2. It is thought that such a decline in the oceanic oxygen content could affect ocean nutrient cycles and the marine habitat, with potentially detrimental consequences for fisheries and coastal economies3, 4, 5, 6. Regional observational data indicate a continuous decrease in oceanic dissolved oxygen concentrations in most regions of the global ocean1, 7, 8, 9, 10, with an increase reported in a few limited areas, varying by study1, 10. Prior work attempting to resolve variations in dissolved oxygen concentrations at the global scale reported a global oxygen loss of 550 ± 130 teramoles (1012 mol) per decade between 100 and 1,000 metres depth based on a comparison of data from the 1970s and 1990s10. Here we provide a quantitative assessment of the entire ocean oxygen inventory by analysing dissolved oxygen and supporting data for the complete oceanic water column over the past 50 years. We find that the global oceanic oxygen content of 227.4 ± 1.1 petamoles (1015 mol) has decreased by more than two per cent (4.8 ± 2.1 petamoles) since 1960, with large variations in oxygen loss in different ocean basins and at different depths. We suggest that changes in the upper water column are mostly due to a warming-induced decrease in solubility and biological consumption. Changes in the deeper ocean may have their origin in basin-scale multi-decadal variability, oceanic overturning slow-down and a potential increase in biological consumption11, 12.

From interannual to decadal: 17 years of boundary current transports at the exit of the Labrador Sea

Abstract: Over the past 17 years, the western boundary current system of the Labrador Sea has been closely observed by maintaining the 53°N observatory (moorings and shipboard station data) measuring the top-to-bottom flow field offshore from the Labrador shelf break. Volume transports for the North Atlantic Deep Water (NADW) components were calculated using different methods, including gap filling procedures for deployment periods with suboptimal instrument coverage. On average the Deep Western Boundary Current (DWBC) carries 30.2 ± 6.6 Sv of NADW southward, which are almost equally partitioned between Labrador Sea Water (LSW, 14.9 ± 3.9 Sv) and Lower North Atlantic Deep Water (LNADW, 15.3 ± 3.8 Sv). The transport variability ranges from days to decades, with the most prominent multiyear fluctuations at interannual to near decadal time scales (±5 Sv) in the LNADW overflow water mass. These long-term fluctuations appear to be in phase with the NAO-modulated wind fluctuations. The boundary current system off Labrador occurs as a conglomerate of nearly independent components, namely, the shallow Labrador Current, the weakly sheared LSW range, and the deep baroclinic, bottom-intensified current core of the LNADW, all of which are part of the cyclonic Labrador Sea circulation. This structure is relatively stable over time, and the 120 km wide boundary current is constrained seaward by a weak counterflow which reduces the deep water export by 10–15%.

SDG14 Conserve and sustainably use the oceans, seas and marine resources for sustainable development

Abstract: TITLE-ABS-KEY((marine OR ocean* OR sea OR seas) AND ({water cycle} OR {water cycles} OR {biogeochemical cycle} OR {biogeochemical cycles} OR {biochemical cycle} OR {biochemical cycles} OR {glacier dynamics} OR {glacier mass} OR {glacier retreat} OR {global circulation model} OR {global circulation models} OR {global circulation modelling} OR {global circulation modeling} OR {iceocean} OR {submarine geophysics} OR eutrophicat* OR marine OR ocean* OR sea OR seas OR {coral bleach} OR {coral bleaching} OR {coastal management} OR paleoceanography OR paleooceanography OR paleo-oceanography OR {coastal habitat} OR {coastal habitats} OR {marine debris})) AND PUBYEAR BEF 2018 AND PUBYEAR AFT 2012

Meeresatlas: Daten und Fakten über unseren Umgang mit dem Ozean

Abstract: Ohne das Meer gabe es kein Leben auf unserem Planeten. Es regelt weitgehend das Klima, gibt uns Nahrung und liefert Energie. Daruber hinaus ist es ein wichtiger Verkehrsweg, ein Erholungsraum und ein Quell asthetischen Vergnugens. Aber das Meer steht unter Stress, denn das alte Prinzip von der „Freiheit der Meere“ hat zu Uberfischung, Artenverlust und einer immensen Verschmutzung der Ozeane gefuhrt. Deshalb muss der Umgang mit dem Meer auf nachhaltige und gerechte Grundlagen gestellt werden. Der Meeresatlas 2017 liefert dazu die Daten, Fakten und Zusammenhange. Er zeigt in zahlreichen Beitragen und uber 50 Grafiken, in welch schlechtem Zustand sich die Weltmeere befinden, warum das so ist und was man tun muss, um die Situation der Ozeane zu verbessern.

South Atlantic Crossing (SACROSS) - Cruise No. M133: 15.12.2016-13.01.2017, Cape Town (South Africa)-Stanley (Falklands)

Abstract: The cruise M133 SACROSS (South Atlantic Crossing) was a multidisciplinary ocean survey of the South Atlantic gyre roughly along 34.5° S. This transect is covered by the international SAMOC moored array and also the path of the internationally agreed AX18 XBT line. Most of the measurements were based on using underway methods including near-surface water sampling for the determination of SST, and SSS as well as shipboard ADCP current observations. Moreover, an underway CTD allowed to sample the upper 300-400 m every hour. Chemical analysis of surface waters as well as atmospheric parameter were of scientific interest to both compare different regions with each other but also to document long term trends. At the western and eastern boundary current regime full water column water mass properties were measured. Upper ocean 10-700m plankton assemblages allow improving the calibration of sediment proxies. Water samples for later lab-based biodiversity analysis were taken. A number of smaller student projects were carried out as part of a global ocean learning and capacity building effort. Finally, continuous swath bathymetry mapping was made, and a number of floats and drifters were launched in support of the global ocean observing system arrays. The cruise was very successful, all objectives were reached, and the measurements were carried out as planned.