Showing papers by "Eberhard Fahrbach published in 2014"

Impact of recirculation on the East Greenland Current in Fram Strait: Results from moored current meter measurements between 1997 and 2009

Abstract: Transports of total volume and water masses obtained from a mooring array in the East Greenland Current (EGC) in Fram Strait are presented for the period 1997–2009 The array in the EGC was moved along isobaths from 79°N to 78 ° 50 ′ N in 2002 to line up with moorings in the eastern Fram Strait Analysis of the time series at the two latitudes shows that associated with the southward move, the annual mean volume transport of the EGC increased from 58±18 Sv to 87±25 Sv, mostly related with an increase in barotropic flow This suggests a recirculation of close to 3 Sv at 78 ° 50 ′ N as a consequence of the large-scale wind-driven cyclonic gyre in the Nordic Seas In addition, the volume transport at 78 ° 50 ′ N showed a clear seasonal cycle which was absent at 79°N Estimates of the wind-driven Sverdrup transport at two different latitudes show that the difference in total volume transport and seasonality can largely be explained by the wind-stress curl However, weak transport in 2003 was only partially related with weak Sverdrup transport and coincided also with anomalously weak northerly winds The stronger recirculation at 78 ° 50 ′ N has also consequences for the observed Atlantic Water: there is significantly more Atlantic derived water present at the southerly latitude In addition, the warm anomaly in Fram Strait between 2005 and 2007 doubled the amount of Recirculated Atlantic Water temporarily Finally, we estimate that close to 27 Sv, or 50%, of Atlantic derived water recirculates in Fram Strait

The contribution of the Weddell Gyre to the lower limb of the Global Overturning Circulation

Abstract: The horizontal and vertical circulation of the Weddell Gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports. The gyre is found to convey 42 ± 8 Sv (1 Sv = 106 m3 s-1) across the central Weddell Sea and to intensify to 54±15 Sv further offshore. This circulation injects 36±13 TW of heat from the Antarctic Circumpolar Current to the gyre, and exports 51 ± 23 mSv of freshwater, including 13 ± 1 mSv as sea ice to the mid-latitude Southern Ocean. The gyre's overturning circulation has an asymmetric double-cell structure, in which 13 ± 4 Sv of Circumpolar Deep Water (CDW) and relatively light Antarctic Bottom Water (AABW) are transformed into upper-ocean water masses by mid-gyre upwelling (at a rate of 2 ± 2 Sv) and into denser AABW by downwelling focussed at the western boundary (8 ± 2 Sv). The gyre circulation exhibits a substantial throughflow component, by which CDW and AABW enter the gyre from the Indian sector, undergo ventilation and densification within the gyre, and are exported to the South Atlantic across the gyre's northern rim. The relatively modest net production of AABW in the Weddell Gyre (6±2 Sv) suggests that the gyre's prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of Indian-sourced AABW.