Modeling the Nd isotopic composition in the North Atlantic basin using an eddy-permitting model
Résumé
Boundary Exchange (BE – exchange of elements
between continental margins and the open ocean) has
been emphasized as a key process in the oceanic cycle of
neodymium (Nd) (Lacan and Jeandel, 2005a). Here, we use
a regional eddy-permitting resolution Ocean General Circulation
Model (1/4) of the North Atlantic basin to simulate
the distribution of the Nd isotopic composition, considering
BE as the only source. Results show good agreement
with the data, confirming previous results obtained using the
same parameterization of the source in a coarse resolution
global model (Arsouze et al., 2007), and therefore the major
control played by the BE processes in the Nd cycle on
the regional scale. We quantified the exchange rate of the
BE, and found that the time needed for the continental margins
to significantly imprint the chemical composition of the
surrounding seawater (further referred as characteristic exchange
time) is of the order of 0.2 years. However, the
timescale of the BE may be subject to large variations as a
very short exchange time (a few days) is needed to reproduce
the highly negative values of surface waters in the Labrador
Sea, whereas a longer one (up to 0.5 years) is required to
simulate the radiogenic influence of basaltic margins and distinguish
the negative isotopic signatures of North Atlantic
Deep Water from the more radiogenic southern origin water
masses. This likely represents geographical variations in
erosion fluxes and the subsequent particle load onto the continental
margins. Although the parameterization of the BE
is the same in both configurations of the model, the characteristic
exchange time in the eddy-permitting configuration is
significantly lower than the previous evaluations using a low
resolution configuration (6 months to 10 years), but however
in agreement with the available seawater Nd isotope data.
This results highlights the importance of the model dynamics
in simulating the BE process
Origine : Publication financée par une institution
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