Present: Ric Wiliams, Elaine McDonagh, Sinhue Torres, Paula Mcleod, Ute Schuster, Richard Sanders, Brian King, Harry Bryden, Susan Leadbetter, Rhiannon Mather, Clare, Tim Lesworth, Hannah Longworth
Apologies: Alex Gardiner, Marie-Jose Messias, Andy Watson, Tim Jickells, Helen Beadman (NERC), George Wolff, Carol Robinson, Eric Achterberg, Clare Postlethwaite
A series of cruise reports were provided for the hydrography (Elaine), nutrients (Sinhue), carbon/CFCs/SF6/anthropogenic C (Ute/Pete), atmospheric inputs (Tim), tritium-helium measurements (Susan).
Each of the presentations will be made available on the web: http://www.bodc.ac.uk/36n/restricted/ where the presentations and any preliminary data analyses will be put on a password protected site for members of the Consortium. Consequently, only key points will be presented here:
Elaine: described the details of the cruise and emphasized how the stations in the Gulf of Cadiz will allow the influx of Mediterranean waters and associated property fluxes to be constrained. This constraint is a welcome addition to the programme.
Ute: described the difficulties in calibrating the C measurements, but how the combination of 2 instruments for pCO2 and TALK provided additional constraints.
Pete: provided a first preliminary estimate for anthropogenic C. Suggestion that this analysis could be separated for the west and eastern basins given the different ages of the waters.
Marie-Jo: the combination of the CFC and SF6 measurements appeared revealing where the CFC/SF6 ratio suggested possible mode water ventilation in the western Atlantic, as well as deep exchange at 2-3km with the eastern basin.
Sinhue: provided a description of the inorganic nutrient calibrations, which appeared promising with a good linear fit for Si.
Tim: described the atmospheric fluxes and highlighted how small the P flux was in the interior of the Atlantic. Isotopic signals used to separate the natural (depleted) and anthropogenic (enriched) signals.
Susan: described the tritium-helium analyses with 234 complete samples taken.
Stuart reported on the transport estimates along the 26.5N/24N section where the boundary current, Ekman and geostrophic fluxes have been identified. Harry, Hannah and Stuart have analysed historical data to diagnose a recent decrease in the overturning by 30% from 1981 to 2004.
Ric provided an overview of the programme for the new members of the Consortium, as well as described model studies for the decadal change in heat content (with Susan Leadbetter) and for the nutrient pathways in the North Atlantic (with Vassil Roussenov). The nutrient studies highlighted how the boundary flux at 36N is important in determining the downstream N distributions over the high latitudes of the North Atlantic.
Given the limited length of postdoc support provided, the inverse analyses have to be completed by the end of 2006. Thus, it is imperative that the inputs to the model inversion are provided early in 2006 otherwise the inversions will not be completed for all model fields. Given this constraint, the following timetable was agreed.
a) timing of subsequent workshops
A data gathering workshop will occur in late January 2006, probably in the
week of 26th. Possibly at UEA or Liverpool.
Action: Ric to liase with UEA to discuss when and where the next meeting is.
A synthesis workshop in June/July 2006 at NOC.
b) workplan
August to December 2005: provide first basic analyses of properties
January 2006: the first workshop will provide a target for the first basic data analyses to be completed: first physics estimate of the flow along the section, inorganic nutrients and carbon along 36N.
January to June 2006: Develop an inverse estimate of the transport and fluxes through both 36N and 26N, and the Mediterranean outflow. Meld the physics estimates of the circulation with the measured property distributions of inorganic nutrients and carbon.
Include analyses of dissolved organic nutrients and atmospheric deposition of nutrients.
July to December 2006: Complete and submit manuscripts addressing the themes of property changes, transports of heat, nutrients and carbon, as well as implied budget changes.
Unclear at this stage, as to when the tritium-helium data, anthropogenic carbon and transient tracer data will be available. However, they should be melded in when appropriate or lead to later papers.
Action: hydrography, inorganic nutrient and carbon teams to provide data estimates to Elaine for January 2006. Everyone else to identify when they can provide their analyses.
c) Inversion approach
The inversion will be developed using both 26N and 36N lines together, rather
than repeat them separately. However, the inversion will be repeated several
times with selective incorporation of data (by adjusting the weights) to identify
the sensitivity of the solutions. For example, we expect that the initial
physics guess of the circulation crossing 36N and conservation of mass will
be crucial constraints, but this information will be augmented by the estimate
of the deep western boundary current from 26N, and possibly including the
silica data.
It will be useful to include weaker constraints for all the tracers, but that will require external sources to be estimated with a priori estimates of errors and the likely storage between the two sections. In practice, suspect that T, S and Si will be used, but instead will wish to provide low weights for the N, P and C closures.
d) Achieving a viable budget
In order to complete this inverse estimate, further support for Elaine and
Paula will be needed in order to answer targeted questions:
e.g. silica inputs into the subtropical N. Atlantic, nitrogen fixation estimates,
river inputs, likely ranges for the air-sea fluxes and storage of properties
over the subtropical N. Atlantic. The additional requirements will be discussed
at the January 2006 data-gathering workshop.
Action: Elaine to provide list of requirements before January. All to contribute to targeted tasks.
a) related grant applications
Tritium-helium and adjoint model application into the responsive mode NERC
round by Ric Williams, Clare Postlethwaite, Chris Ballentine and Vassil Roussenov.
Need to discuss whether any follow up studies to 36N and AMT will map into the new core science plan to ensure personnel or infrastructure support is available to complement any further responsive mode/Consortium bids on relevant themes.
Action: leading investigators to discuss with institutional representatives writing Science plan, e.g. Andreas Oschlies at NOC.
b) links to other international programmes (Station W, US Climode,
Kiel, Meteor survey, RAPID, AMT)
Links made on web site. Need to contact US Carbon plan.
Action: Ric.
c) use of the web
Advocate the use of the web to raise profile of the study and on protected
pages make available preliminary data analyses, and display talks and submitted
manuscripts.
Action: Alex to put on the web, All to provide material to Alex.
d) final scientific meeting
Like AMT, it would be useful to have a scientific meeting providing the outcomes
of the programme, say in 2007. Perhaps could be linked to a Royal Society,
for assessing climate change in the North Atlantic. Would need to seek funding
for external speakers.
Action: Ric to discuss with our two FRS members, Harry and Andy, as to the procedure.
Action: Ric to liase with UEA to discuss when and where the next meeting is
Action: hydrography, inorganic nutrient and carbon teams to provide data estimates to Elaine for January 2006. Everyone else to identify when they can provide their analyses
Action: Elaine to provide list of requirements before January. All to contribute to targeted tasks
Action: leading investigators to discuss with institutional representatives writing Science plan, e.g. Andreas Oschlies at NOC
Action: Ric contact US Carbon plan
Action: Alex to put talks on the web, All to provide material to Alex
Action: Ric to discuss with our two FRS members, Harry and Andy, as to the procedure
© 2015 NERC.
Last updated: June 8, 2015
