New Direct Estimates of Iceland-Scotland Overflow Water Transport Through the Charlie-Gibbs Fracture Zone

Thursday, 18 December 2014: 8:15 AM
Amy S Bower1, Heather H Furey1 and Xiaobiao Xu2, (1)WHOI, Woods Hole, MA, United States, (2)Florida State University, Tallahassee, FL, United States
Detailed observations of the pathways, transports and water properties of dense overflows associated with the AMOC provide critical benchmarks for climate models and mixing parameterizations. A recent two-year time series from eight moorings provides the first long-term simultaneous observations of the hydrographic properties and transport of Iceland-Scotland Overflow Water (ISOW) flowing westward through the Charlie-Gibbs Fracture Zone. Using the isohaline 34.94 to define the ISOW layer, the two year mean and standard deviation of ISOW transport was -1.7 ± 1.5 Sv, compared to -2.4 ± 3.0 Sv reported by Saunders for a 13-month period in 1988-1989 using the same isohaline. Differences in the two estimates could reflect the difficulty of defining the long-term mean in the presence of strong transport variability on multiple time scales: ten 13-month mean transport estimates from the new two-year record range from -2.0 to -1.4 Sv. Furthermore, the temperature/salinity time series indicate large fluctuations in ISOW layer thickness: for example, thickness over the northern rift valley had a mean value of about 1400 m and ranged from 400 to 2100 m (compared to Saunders’ fixed value of 2200 m at this site). A time series of ISOW transport through CGFZ estimated from a multi-decadal run of the Hybrid Coordinate Ocean Model (HYCOM) shows a similar level of interannual variability as the observations.