Minutes of 6th 36°N consortium meeting

NOCS , 13-14 September 2007

Present: Ric Williams, Rhiannon Mather (Liv), Kay Thorne (BODC), Ute Schuster, Andy Watson (UEA), Elaine McDonagh, Brian King, Richard Sanders, Harry Bryden, Stuart Cunningham (NOCS).
Apologies: Tim Jickells, Pete Brown, Marie-Jo Messias, Sinhue Torres, Sarah Reynolds, Carol Robinson.


1. Introduction
2. State of data return and access of data - Kay Thorne

Concern about lack of bottle data being returned to BODC. Timetable discussed of likely return. Key investigators identified for each variable and Kay will approach them directly.

3. Report on western boundary solutions - Elaine McDonagh

Transport of Gulf Stream through Southern Section is consistent with Halkin and Rossby estimate when downstream strengthening is taken into account.

4. Report on initial flux estimates for the 26N, 36N and Gulf of Cadiz sections - Elaine McDonagh
  • Plausible variations of heat and freshwater flux between 26N and 36N.
  • Exchange with Mediterranean needs to be further reviewed (in the same way that the Gulf Stream estimate has been compared with historical data).
  • Breakdown of fluxes into individual layers leads to some large residual fluxes.
  • Silica fluxes are to be reviewed and probably used within the inverse solution to adjust the reference velocity.
  • Large eddy contributions along the section, providing locally reversing direction of fluxes, but much weaker cumulative contribution. Discussion of eddy contributions, but experience from Agulhas Rings suggests this aspect may not be crucial.

Nutrient fluxes are so far only for inorganic components and need to include organic versions.

Atmospheric inputs of N and P have been provided by Tim Lesworth & Tim Jickells, which will aid interpretation of the residual changes in N and P from the inverse model. Range in estimates provided, as well as the mean, which aids the inversion.

Aim to combine the data into an inverse solution for late December 2007.

5. Report on historical analyses and model studies - Ric Williams/Susan Leadbetter

Comparison of 1959, 1981 and 2005 sections reveal reversing water-mass changes: cooling of upper waters from 1959 to 1981, warming from 1981 to 2005. These changes diagnosed to be controlled by the vertical displacement of isopycnals. The changes are consistent with the change in wind forcing over the two periods: weaker pumping from 1959 to 1981, increased pumping from 1981 to 2005. Paper appeared in GRL, 2007.

6. Progress for inorganic and organic nutrients - Ric Williams/Rhiannon Mather/Richard Sanders

Distributions of DON & DOP obtained for the whole domain by combining AMT, 26N and 36N sections. Modeling of N & P pathways reveals recycling of DOP to be particularly important over the eastern North Atlantic, accounting for most of the P export. Measurements of enzyme activity reveal enhanced utilization of the DOP pool in the North Atlantic subtropical gyre.

7. Report of anthropogenic carbon changes based on three sections along 24N: 1992, 1998 and 2004 - Ute Schuster/Pete Brown/Andy Watson

Diagnostics of implied uptake over whole water column between 1992 and 1998, but uptake restricted to upper 800m for 1998 to 2004. Study reveals limitations in the anthropogenic carbon method.

8. Transient tracer estimates - Andy Watson/Marie-Jo Messias

SF6 and CFC-11 uptake compared with Green function model from Haine, Hall and Waugh. CFC-11 age seems to be high in the surface waters.


Proposed conference submissions to Ocean Sciences
  • Elaine McDonagh - inverse model applied to circulation and water-mass changes.
  • Ric Williams - divergence of inorganic nutrients in the subtropical gyre and the role of dissolved organic nutrients.
  • Pete Brown - anthropogenic carbon estimates for the subtropical North Atlantic.
  • Rhiannon Mather - phosphorus limitation in the North Atlantic.

Next meeting

Proposed to be at NOCS on 19-20 December 2007 (date will be reviewed).