1. The Arctic–Atlantic Thermohaline Circulation ELDEVIK, T. & J.EVEN.Ø. NILSEN, J. CLIM. 26, 2013 OS14 HONOLULU 28.02.2014 U ≈ 9 Sv ∆T ≈ 8 ºC ∆S ≈ 1 heat loss ≈ 300 TW freshwater input ≈ 0.15 Sv IBCAO; Jakobsson et al. 2008

2. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project The estuarine circulation & the overturning circulation 3. Compensating inflow 1. Fresh water outflow 2. Mixing Estuarine circulation bottom surface river Arctic–Atlantic THC = two branch system A circulation of heat and salt => two degrees of freedom Courtesy of Bogi Hansen

3. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Our system: The Arctic–Atlantic THC constrained at GSR GSR OW PW AW GSR Circulation Salinity Pot. temperature Thermohaline heat loss freshwater Input

4. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Our model: Conservation equations at GSR GSR OW PW AW U 1 + U 2 + U 3 = 0 S 1 U 1 +S 2 U 2 +S 3 U 3 = q S T 1 U 1 +T 2 U 2 +T 3 U 3 = q T

5. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Our model: Solved for the circulation (i.e., THC) GSR OW PW AW U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 2 = (q S (T 3 -T 1 )-q T (S 3 -S 1 ))  U 3 = (q S (T 1 -T 2 )-q T (S 1 -S 2 )) 

6. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Sensitivity to northern heat and FW forcing anomalies GSR OW PW AW U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 1 = 0  q T /q S = (T 2 -T 3 )/(S 2 -S 3 ) q S =0, q T >0 => U 1 > 0 qSqS qTqT = COOLING

7. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Sensitivity to northern heat and FW forcing anomalies GSR OW PW AW U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 2 = (q S (T 3 -T 1 )-q T (S 3 -S 1 ))  qSqS qTqT

8. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Sensitivity to northern heat and FW forcing anomalies GSR OW PW AW U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 2 = (q S (T 3 -T 1 )-q T (S 3 -S 1 ))  U 3 = (q S (T 1 -T 2 )-q T (S 1 -S 2 ))  qSqS qTqT

9. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Sensitivity to northern heat and FW forcing anomalies GSR OW PW AW U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 2 = (q S (T 3 -T 1 )-q T (S 3 -S 1 ))  U 3 = (q S (T 1 -T 2 )-q T (S 1 -S 2 )) 

10. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Quantifying volume fluxes w.r.t. AW hydrography U 1 = (q S (T 2 -T 3 )-q T (S 2 -S 3 ))  U 2 = (q S (T 3 -T 1 )-q T (S 3 -S 1 ))  U 3 = (q S (T 1 -T 2 )-q T (S 1 -S 2 )) 

11. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project GSR +1Sv+1.5 Sv +0.5Sv Jan 1979Jan 2009 GSR Overflow Polar outflow Atlantic inflow Strengthening of the Atlantic Inflow with a blue Arctic? FW: +0.03 Sv [ ref. 1965; Peterson et al 2006 ] weakening of THC COOL: +50 TW, 40 yr of sea ice retreat [ - 0.4 mill km 2 ; 1967–present; Kvingedal 2005 ; +138 W/m 2 ; Årthun et al 2012 ] strengthening of THC FW + COOL strengthening of THC ++ Peterson et al. 2006 0.03 Sv

12. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Summary and implications ›Consistent framework to diagnose Arctic– Atlantic THC and -change ›THC is not overflow ›FW increase does not imply weaker THC ›The relative strength of estuarine vs overturning circulation reflects FW input ›Present changes in the Arctic contributes to increased THC ›Observed increasing TH-contrasts implies a more robust THC U 1 + U 2 + U 3 = 0 S 1 U 1 +S 2 U 2 +S 3 U 3 = q S T 1 U 1 +T 2 U 2 +T 3 U 3 = q T

13. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project

14. Explaining climate model Arctic–Atlantic THC Bergen Climate Model BCM time series courtesy of Iselin Medhaug and Helene R. Langehaug

15. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project Explaining climate model Arctic–Atlantic THC 15 Bergen Climate Model BCM time series courtesy of Iselin Medhaug and Helene R. Langehaug Also accounting for changing salt (and heat) storage

16. Eldevik & Nilsen, J. Clim. 26 (2013) + The NORTH project 16