Santander 2011 Monitoring the Rockall Trough Toby Sherwin 1 Penny Holiday 2, Jane Read 2, Clare Johnson 1 and many others, including Bill Turrell 3 (with posthumous acknowledgement to David Ellett 1 ) 1 Scottish Association for Marine Science, Oban 2 National Oceanography Centre, Southampton 3 Marine Scotland, Aberdeen

AABW & LSW 0.9 Sv (0.3) NAW 0.6 Sv ~3 Sv Anton Dohrn The Rockall Trough Temperature / o C AABW ENAW LSW WTOW Salinity Anton Dohrn Rockall ENAW – Eastern North Atlantic Water WTOW – Wyville Thomson Ridge Overflow Water LSW – Labrador Sea Water AABW – Antarctic Bottom Water

Santander 2011 Three parts to talk: 1.Historical observation record 2.Future advances 3.Nutrients

Santander 2011 Three parts to talk: 1.Historical observation record 2.Future advances 3.Nutrients

Santander 2011 The Ellett Line Shared by SAMS and NOCS Regular sections since 1975 Initially 4 times a year More recently annually Nutrients since 1996 RRS Challenger David Ellett

Santander 2011 θ and S across the Rockall Trough Annual std dev indicated Averaged three times i)Across the RT ii)Between 30 and 800 m iii)By year (when >1 cruises) θ increase reversal S increase levelling out

Santander 2011 Labrador Sea Water east of Anton Dorhn For a definition of LSW see the IROC θ and S at ~ 1750 m

Santander 2011 Observations by Ocean Weather Ships UK Met Office 1948 to 1992 Various tracks S of Anton Dorhn Surface T and S Measurement technique changed over time Averaged across the trough by Ellett and Jones, MAFF Rpt 36, 1994 Look at winter months JFM

Santander 2011 OWS Surface θ and S across RT Great salinity anomaly JFM averages Annual averages

Santander 2011 OWS Surface Temperature and Salinity across RT Towed thermometer Mercury in board Autolab salinometer Guildline salinometer Thermistors In board sampling Titration

Santander 2011 Synthesis of Sea Surface Temperatures HadiSST - UK Met Office 1856 onward by vessels of opportunity Synthesis of sea surface temperature (SST) only Area average into 5 o by 5 o boxes

Santander 2011 HadiSST JFM averages HadiSST SSTs in the north-eastern North Atlantic

Santander 2011 Surface versus deep observations Ellett Line + top 4 m ● 30 to 800 m ?

Santander 2011 Part 1 conclusions: 1.OWS surface salinity seem good before HadiSST SSTs seem to be ‘reasonable’ proxy for RT winter water column temperatures The standard Ellett Line data are the ‘gold standard’ But will that always be the case?

Santander 2011 Three parts to talk: 1.Historical observation record 2.Future advances 3.Nutrients

Santander 2011 Argo tracks in the RT to March 2011

Santander 2011 Glider observations Operated SAMS Started winter 2009/2010 Continuous monitoring to 1000 m Latest mission started May 2011

Santander 2011 Glider temperature and salinity winter 09/10

Santander 2011

Gliders are adding to the annual cruise data

Santander 2011 Three parts to talk: 1.Historical observation record 2.Future advances 3.Nutrients

P314 July 2004 NO23 (μM) PO4 (μM) Si (μM) Rockall A ‘typical’ year July 2004

Temperature / o C AABW ENAW LSW WTOW Nutrient profiles East of Anton Dorhn NO23 PO4 Si West of Anton Dorhn NO23 PO4 Si

Nutrient time series east of Anton Dohrn Month of cruise indicated

D321 Nutrient time series west of Anton Dohrn Month of cruise indicated

Santander 2011 Nutrient observations since 1996

Santander 2011 Conclusions (wrt last decade) The rise in surface temperature since 1995 seems to be tailing off Salinities continue to rise and have returned to pre-GSA levels Neither θ nor S levels appear significantly higher than historical values, but … LSW signature continues to freshen and cool There are real trends in nutrient levels need to be explained by a nutrient chemist

Santander 2011 Chnbo Guo Svein Osterhus Detlef Quadfasel Bogi Hansen