Transports between Iceland and Scotland: Results from the Extended Ellett Line Clare Johnson (1), Stuart Cunningham (1), N. Penny Holliday (2) and Stefan Gary (1) (1) Scottish Association of Marine Science., Oban. (2) National Oceanography Centre, Southampton.

1948: surface sampling (weather ships) 1975: CTD sections Scotland to Rockall 1996: CTD sections Scotland to Iceland (typically occupied in late spring / summer) 2011, 2014: glider sections Scotland to Iceland (upper 1000 m) Holliday, N. P. and S. A. Cunningham (2013), The Extended Ellett Line: Discoveries from 65 years of marine observations west of the UK, Oceanography. The Extended Ellett Line – an annual hydrographic section 0°25 W20 W 15 W10 W5 W 60 N 63 N 57 N 54 N 51 N UK Iceland Rockall Trough Iceland Basin

Calculation of transports – geostrophic method Level of no motion chosen to: 1. minimise difference between sea surface dynamic height relative to an isoypycnal, and absolute sea surface height derived from altimeter data 2. make sense water mass wise Iceland Basin Rockall-Hatton Plateau Rockall Trough Mean σ t kg m -3 Iceland Basin and Rockall-Hatton Plateau: kg m -3 Rockall Trough: kg m -3

Results – upper waters ( kg m -3 ) Net flux Iceland Basin: 4.0 ± 1.2 Sv (~4.8 Sv – Chafik et al., 2014) Net flux Rockall Trough: 2.3 ± 3.0 Sv (2-3 Sv - Ellett et al., 1986; 3.7 ± 2.4 Sv - Holliday et al., 2000; ~ 3.5 Sv - Chafik et al., 2014) Net flux Iceland to Scotland: 6.2 ± 3.2 Sv (7.6 ± 0.9 Sv – Sarafanov et al., 2012; 8.0 ± 1.6 Sv – Chafik et al., 2014; 6.1 ± 0.3 Sv – Childers et al., accepted)

Results – upper waters ( kg m -3 )

Results – upper waters ( kg m -3 ) Rockall TroughIceland Basin Overturning stream function:

Results – ISOW (> kg m -3 in N / W Iceland Basin) Defined as: Water > kg m -3 in N / W Iceland Basin. Eastern boundary defined for each cruise. Where the zonally cumulatively summed transport of water > kg m -3 starts to remain constant or increase. Net flux Iceland Basin: ± 1.2 Sv (- 1.2 to Sv – previous work, summarised Kanzow and Zenk, 2014).

Results – Total transports Iceland Basin Rockall Trough Iceland to Scotland

First look geostrophic transport relative to an isopycnal in the thermocline: Upper waters: Iceland Basin 4.0 ± 1.2 Sv (no trend) Rockall Trough 2.3 ± 3.0 Sv (increasing 2001 to 2011, v low 2013) ISOW: -4.5 ± 1.2 Sv (no trend) Net overturning: Iceland to Scotland 6.3 ± 3.2 Sv (trend similar to upper waters in Rockall Trough) Summary – first look geostrophic analysis Next steps: Use of altimeter data Error analysis Heat and salt / fresh water fluxes

The research leading to these results has received funding from the European Union 7th Framework Programme (FP ), under grant agreement n NACLIM