Beschreibung: Highlights: • Mooring observations show the East Greenland Spill Jet to be ubiquitous. • It is fed by classical DSOW in Denmark Strait, shelf water, and Irminger Sea water. • Its transport is similar to the classical DSOW plume. • It is the origin of a large fraction of the water in the Labrador Sea Water density range. Abstract: The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean׳s role in climate.

Beschreibung: The Mediterranean Sea has been investigated intensively since the early nineties, using modern techniques and collaborative approaches. This overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western Mediterranean. The water mass formation processes are now much better understood and have been quantified to a large extent. The boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy, thus enabling future investigation of interannual variability. The dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses. The deep circulation is being investigated with Lagrangian techniques (tracers and floats). First results show a large component of the deep water originating from the Tyrrhenian Sea and intense cyclonic and anticyclonic eddy flows.

Beschreibung: Hydrographic and tracer [chlorofluorocarbon (CFC), component F11] data in the tropical Atlantic off Brazil taken in spring 1994 are used to describe the development of the water mass characteristics of Antarctic Bottom Water (AABW) between 10 degrees S and 11 degrees N. To compute the AABW transports, geostrophic computations and directly measured velocity fields are combined. Velocity profiles were measured with the Pegasus profiling system and an ADCP attached to the CTD. The F11 increase from 10 degrees S to 11 degrees N, mainly in the upper part of the tracer-poor AABW, reveals the mixing of AABW along its path with the overlying North Atlantic Deep Water, which carries a significant F11 signal in the equatorial Atlantic. While propagating north of 5 degrees S, the AABW shifts to higher salinities at a given temperature. About one-third of the northward flowing AABW at 10 degrees S (4.8 Sv) and at 5 degrees S (4.7 Sv) west of about 31 degrees 30'W enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35 degrees W (1.5-1.8 Sv). The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40 degrees W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise (2.2 Sv). At 44 degrees W, north of the Ceara Rise, AABW flows west in the interior of the basin in a main core near 7 degrees 15'N (1.9 Sv). A net return how of about 0.5 Sv was found north of 8 degrees 43'N. A large fraction of the AABW (1.1 Sv) enters the eastern Atlantic through the Vema Fracture Zone, leaving only 0.3 Sv of AABW for the western Atlantic basins

Beschreibung: The tropical South East Pacific is characterized by strong coastal upwelling on the narrow continental shelf and an intense oxygen minimum zone (OMZ) in the intermediate water layer. These hydrographic properties are responsible for a permanent supply of intermediate water masses to the surface rich in nutrients and with a remarkably low inorganic N:P stoichiometry. To investigate the impact of OMZ-influenced upwelling waters on phytoplankton growth, elemental and taxonomical composition we measured hydrographic and biogeochemical parameters along an east–west transect at 10°S in the tropical South East Pacific, stretching from the upwelling region above the narrow continental shelf to the well-stratified oceanic section of the eastern boundary regime. New production in the area of coastal upwelling was driven by large-sized phytoplankton (e.g. diatoms) with generally low N:P ratios (〈16:1). While nitrate and phosphate concentrations were at levels not limiting phytoplankton growth along the entire transect, silicate depletion prohibited diatom growth further off-shore. A deep chlorophyll a maximum consisting of pico-/nano- (Synechococcus, flagellates) and microphytoplankton occurred within a pronounced thermocline in subsurface waters above the shelf break and showed intermediate N:P ratios close to Redfield proportions. High PON:POP (〉20:1) ratios were observed in the stratified open ocean section of the transect, coinciding with the abundance of two strains of the pico-cyanobacterium Prochlorococcus; a high-light adapted strain in the surface layer and a low-light adapted strain occurring along the oxic-anoxic transition zone below the thermocline. Excess phosphate present along the entire transect did not appear to stimulate growth of nitrogen-fixing phytoplankton, as pigment fingerprinting did not indicate the presence of diazotrophic cyanobacteria at any of our sampling stations. Instead, a large fraction of the excess phosphate generated within the oxygen minimum zone was consumed by non-Redfield production of large phytoplankton in shelf surface waters.