Berx et al., Ocean Sci., 9, 639-654 , 2013

1. Integrating altimetry into the estimates of Atlatnic water transport in the Faroe Shetland Channel Bee Berx1, Bogi Hansen2, Svein Østerhus3, Karin Margaretha Larsen2, Toby Sherwin4 and Kerstin Jochumsen5 1 Marine Scotland Science (b.berx@marlab.ac.uk); 2 Faroe Marine Research Institute; 3 University of Bergen; 4 Scottish Association for Marine Science; 5 Universität Hamburg Berx et al., Ocean Sci., 9, 639-654, 2013

2. Why are we interested in the Faroe Shetland Channel (FSC)?

3. Oceanographic observations in the FSC

4. Observing Circulation in the FSC

5. Temperature and Salinity in the FSC

6. Incorporating altimetry in transport estimates The assumption of geostrophy allows us to convert sea level height measurements into current speeds. http://www.seos-project.eu/modules/oceancurrents/oceancurrents-c06-s02-p01.html SEOS Project

7. Estimating average transport of AW • Define the AW velocity in the ADCP data as “surface 325m” • Correlate monthly ADCP velocities with SSH difference • Calculate mean AW velocities from altimetry in all available months • Adjust geostrophic profiles from mean temperature & salinity in surface 325m equals altimetry-adjusted AW velocities

8. Mean velocity cross-section in the FSC

9. Average volume, relative heat and salt transports in the FSC Compared to the total transport of AtlatnicWater across the GSR = 7.0 Sv

10. Obtaining monthly estimates of AW Transport: 1. ADCP-based • ADCP sites given “associated widths” • Define AW layer as mean depth of 5°C isotherm • Use average altimetry-adjusted velocities at the boundaries • Depending on period, either 4 or 7 ADCPs across ~150km wide section

11. Obtaining monthly estimates of AW Transport: 2. altimetry-based Builds on two assumptions: • Vertical-average AW-velocity is proportional to the surface • The product of (1) with the depth of AW is approx. constant throughout the section. • Investigated these assumptions with ADCP data • Adjusted the altimetry-based estimate so the time series mean equals the long-term average calculated previously

12. Transport of Atlantic water in the FSC

13. Seasonal cycle in volume transport Seasonal amplitude of Atlantic water transport in FSC ~ 0.7-0.9 Sv This is ~ 25% of the average transport Maximum transport in winter-time, lowest transport in summer. Different amplitude based on calculation method

14. Transport of Atlantic Water in the FSC 1992-2012 No long term trend !

15. Conclusions • Combined water property observations (Temperature and Salinity) with current meter and sea elevation observations to estimate transport of Atlantic water through the FSC. • On average 2.7±0.5 Sv is transported into the Nordic Seas • Net volume transport shows consistent seasonality: maximum Dec-Jan, and amplitude of 0.7 Sv. • No significant trend in volume transport between 1992 and 2011. • We have observed increases in temperature and salinity, and may therefore expect trends in relative heat and salt transports (but difficult to verify statistically based on this time series). • Currently studying whether less variable observations can be made in an area to the south-west of the FIM section

16. 2014 Initiatives close to NACLIM in the FSC Brahan HF Radar Demonstration and end-user partners UK Ocean-Shelf Exchange Study

17. Thank you. The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu