ALBERT

Description: Two major water masses dominate the deep layers in the Mariana and Caroline Basins: the Lower Circumpolar Water (LCPW), arriving from the Southern Ocean along the slopes north of the Marshall Islands, and the North Pacific Deep Water (NPDW) reaching the region from the northeastern Pacific Ocean. Hydrographic and moored observations and multibeam echosounding were performed in the East Mariana and the East Caroline Basins to detail watermass distributions and flow paths in the area. The LCPW enters the East Mariana Basin from the east. At about 13°N, however, in the southern part of the basin, a part of this water mass arrives in a southward western boundary flow along the Izu–Ogasawara–Mariana Ridge. Both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the West Mariana Basin as suggested before, but also provides bottom water to the East Caroline Basin. The critical throughflow regions were identified by multibeam echosounding at the Yap Mariana Junction between the East and West Mariana Basins and at the Caroline Ridge between the East Mariana and East Caroline Basins. The throughflow is steady between the East and West Mariana Basins, whereas more variability is found at the Caroline Ridge. At both locations, throughflow fluctuations are correlated with watermass property variations suggesting layer-thickness changes. The total transport to the two neighboring basins is only about 1 Sverdrup (1Sv ≡ 106 m3 s−1) but has considerable impact on the watermass structure in these basins. Estimates are given for the diapycnal mixing that is required to balance the inflow into the East Caroline Basin. Farther above in the water column, the high-silica tongue of NPDW extends from the east to the far southwestern corner of the East Mariana Basin, with transports being mostly southward across the basin.

Description: Two major water masses dominate the deep layers in the Mariana and Caroline Basins: the Lower Circumpolar Water (LCPW), arriving from the Southern Ocean along the slopes north of the Marshall Islands, and the North Pacific Deep Water (NPDW) reaching the region from the northeastern Pacific Ocean. Hydrographic and moored observations and multibeam echosounding were performed in the East Mariana and the East Caroline Basins to detail watermass distributions and flow paths in the area. The LCPW enters the East Mariana Basin from the east. At about 13°N, however, in the southern part of the basin, a part of this water mass arrives in a southward western boundary flow along the Izu–Ogasawara–Mariana Ridge. Both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the West Mariana Basin as suggested before, but also provides bottom water to the East Caroline Basin. The critical throughflow regions were identified by multibeam echosounding at the Yap Mariana Junction between the East and West Mariana Basins and at the Caroline Ridge between the East Mariana and East Caroline Basins. The throughflow is steady between the East and West Mariana Basins, whereas more variability is found at the Caroline Ridge. At both locations, throughflow fluctuations are correlated with watermass property variations suggesting layer-thickness changes. The total transport to the two neighboring basins is only about 1 Sverdrup (1Sv ≡ 106 m3 s−1) but has considerable impact on the watermass structure in these basins. Estimates are given for the diapycnal mixing that is required to balance the inflow into the East Caroline Basin. Farther above in the water column, the high-silica tongue of NPDW extends from the east to the far southwestern corner of the East Mariana Basin, with transports being mostly southward across the basin.

Description: The overall objective of the subproject A3 of SFB 460* (1996 - 2003) was to observe the water mass transformation in the eastern basin of the subpolar gyre with direct methods including RAFOS floats. Our floats populated the 1500 m depth range of the Iceland Basin occupied by low salinity Labrador Sea Water and higher salinity Overflow Water. The first water mass reaches the Basin through the Charlie-Gibbs Fracture Zone. Its source region is in the Labrador Sea where it is generated on a yearly basis by deep reaching winter time convection. The second intermediate water mass of the eastern basin enters the region as Iceland Scotland Overflow Water with its perpetual source in the Norwegian Seas. At the southeastern margin of our region of interest remainders of Mediterranean Water mix with the other two characteristic water masses. A smaller number of floats was deployed in the lower deep water of the Iceland Basin at nominally 2600m depth. Data for the presented gallery of intermediate float trajectories were collected between summer 1997 and summer 2003. We have tracked 57 RAFOS floats. These neutrally buoyant in-situ drifters were launched during six research cruises. Their average underwater missions exceeded one year. The Lagrangian experiment lasted until 2003 when all four sound sources were completely recovered. The data set comprises also trajectories from float parks. These ensembles of floats enable repeated Lagrangian time series with identical initial conditions allowing estimates of the representativeness of individual trajectories. *SFB (Sonderforschungsbereich) stands for an accelerated research initiative comprising intensive observations and modelling efforts of fluctuations in the thermohaline circulation in the subpolar gyre of the North Atlantic.