Oceanic freshwater flux at 26°N in the Atlantic Brian King, Harry Bryden, Peggy Courtois, Stuart Cunningham, Zoltan Szuts, Chris Atkinson, Neil Wells, Joel Hirschi and Simon Josey Elaine McDonagh, National Oceanography Centre, Southampton MONACO (NERC funded RAPID WATCH project)

Oceanic freshwater flux at 26°N in the Atlantic What is it? Why do we care? How do we calculate it?

What is it?

Mean = Sv, σ = 0.23 Sv E>P Increase in freshwater storage E<P decrease in freshwater storage Mass flux across the section Based on salinity rather than mass conservation Difference between -0.8Sv and freshwater flux represents integrated surface freshwater fluxes and change in the oceanic freshwater storage between Bering Strait and 26°N. Mean (-1.13 Sv) standard deviation (0.23 Sv)

Mean flux Sv consistent with recent hydrography Wijffels, 2001

Why do we care? Monitoring integrated freshwater input and changes in oceanic freshwater storage over the climatically important Arctic and the deep water formation sites of the North Atlantic

How do we calculate it? We split the section into regions similar to that used for the overturning calculation for the rapid array and calculate a salinity flux. Gulf Stream Western Boundary Wedge Ekman Flux Interior deeper than 2000m Interior shallower than 2000m

How do we calculate it?

Constrain the salinity flux at each timestep to be -26 Svpsu (salinity flux at Bering Strait) by adding a volume flux at the section average salinity. The net volume flux across the section is the freshwater flux. How do we calculate it?

A couple of interesting things…. v = + (z) + v’(x,z) s = + (z) + s’(x,z) At each time step a salinity flux can be decomposed into components Mean Overturning (z) (z) Horizontal v’(x,z) s’(x,z)

A couple of interesting things…. At each time step the ekman salinity flux across the section is well approximated by mean Ekman transport * mean Ekman salinity, salinity transport associated with correlations of the residuals has a mean value of only 0.07 Sv psu (or Sv in freshwater)

A couple of interesting things…. Adding the Argo data in the interior shallower than 2000m reduces the southward freshwater flux by 0.11 Sv on average

Oceanic freshwater flux at 26°N in the Atlantic Brian King, Harry Bryden, Peggy Courtois, Stuart Cunningham, Zoltan Szuts, Chris Atkinson, Neil Wells, Joel Hirschi and Simon Josey Elaine McDonagh, National Oceanography Centre, Southampton MONACO (NERC funded RAPID WATCH project)