Constraining the North Atlantic circulation with transient tracer observations
Location4.5°S - 39.5°N
KeywordOcean circulation; Trace elements in water; Chlorofluorocarbons; Tritium content; Radioactive tracers in oceanography; Chemical oceanography; Oceanus (Ship : 1975-) Cruise OC202; Oceanus (Ship : 1975-) Cruise OC134; Endeavor (Ship: 1976-) Cruise EN214; Endeavor (Ship: 1976-) Cruise EN223; Charles Darwin (Ship) Cruise CD62; Meteor (Ship) Cruise M393
The capability of transient tracers to constrain the ocean circulation in the North Atlantic is explored. Study of an idealized tracer shows that inferences of circulation properties from transient state distributions are impacted by uncertainties in the time-varying boundary conditions and sparse data coverage. Comparison of CFC, tritium, temperature and salinity (T-S) observations with model results in the North Atlantic shows that regions of important model-data disagreements in the transient tracer fields can also be readily identified in the T-S distributions. In the model, excessive vertical penetration of convective adjustment, leads to problematic production and outflow of the NADW, again appearing in both transient tracer and T-S fields. Sensitivities of the model fields are determined using the adjoint model. In the dual solutions, CFC-ll, CFC-ll/CFC-12 ratio age, and T - (ß/α)S (α and ß are thermal and haline expansion coefficients, respectively) exhibit the major ventilation pathways and the associated timescales, in the model. High sensitivity fields are candidates for providing the most powerful constraints in the corresponding inverse problems. Assimilation of both CFC and tritium data, with different input histories, sampling distributions, and radioactive decay constants, shows that by adjusting only initial-boundary conditions of CFCs and tritium, a 1° x 1° offline model and the transient tracer data can be brought into near-consistency, in the domain between 4.5°S and 39.5°N of the North Atlantic. Constraining a GCM with transient tracers is thus fully practical. However, the large uncertainties in the time-varying boundary conditions of transient tracer concentrations, and in their interior distributions, renders the transient tracers less-effective in determining the circulation than are more conventional steady tracers, and known oceanic dynamics.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2003
Showing items related by title, author, creator and subject.
Rasmussen, Linda L. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2003-06)Pathways of exchange between the shelf and slope in the Mid-Atlantic Bight were investigated using a combination of radiochemical tracer and hydrographic measurements. The motivation was to provide evidence of transport ...
Variability in the North Atlantic Deep Western Boundary Current : upstream causes and downstream effects as observed at Line W Pena-Molino, Beatriz (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-09)The variability in the DWBC, its connection to the forcing in the northern North Atlantic and interaction with the Gulf Stream were explored from a combination of remote sensing and in-situ measurements in the western ...
Irish, James D.; Kerry, S.; Fucile, Paul D.; Beardsley, Robert C.; Lord, Jeffrey; Brink, Kenneth H. (Woods Hole Oceanographic Institution, 2005-12)As part of the U.S. GLOBEC Northwest Atlantic/Georges Bank program, moorings were deployed on Georges Bank as part of the broad-scale survey component to help measure the temporal variability of both physical and biological ...