Horizontal dispersion in shelf seas: High resolution modelling as an aid to sparse sampling

Abstract

a b s t r a c tThe ability of a hydrodynamic model to reproduce the results of a dye release experiment conducted in a wide shelf sea environment was investigated with the help of the Massachusetts Institute of Technology general circulation model (MITgcm). In the field experiment a fluorescent tracer, Rhodamine WT, was injected into the seasonal pycnocline, and its evolution was tracked for two days using a towed undulating vehicle equipped with a fluorometer and a CTD. With a 50 m horizontal resolution grid, and with three different forcings initialized in the model (viz: tides, stationary current, and wind stress on the free surface), it was possible to replicate the dye patch evolution quite accurately. The mechanisms responsible for the enhancement of horizontal dispersion were investigated on the basis of the model results. It was found that enhancement of the dye dispersion was controlled by vertically sheared currents that, in combination with vertical diapycnal mixing, led to a substantial increase in the ''effective'' horizontal mixing. The values of ''effective'' horizontal mixing found from the model runs were in good agreement with those obtained from in-situ data, and the probable degree to which the observational techniques undersampled the dye patch was revealed.

High-resolution under-water laser spectrometer sensing provides new insights to methane distribution at an Arctic seepage site

“…The 2D model was run to steady state with different diffusion coefficients, ∈ [0.3 − 4.9 m 2 s −1 ], adopted from dyeexperiments offshore Rhode Island (Sundermeyer and Ledwell, 2001). These coefficients are in agreement with the ones obtained from the Celtic Sea ( ∈ [0.8 − 4.4 m 2 s −1 ]) (Stashchuk et al, 2014), but much higher than the coefficient applied by Graves et al (2015) ( = 0.07 m 2 s −1 ). The best fit between the 2D model and the MILS data (R = 0.68) was achieved 285 during a simulation with k = 1.5 m 2 s -1 .…”

“…The best fit between the 2D model and the MILS data (R = 0.68) was achieved 285 during a simulation with k = 1.5 m 2 s -1 . Because the high-end coefficients of Sundermeyer and Ledwell (2001) and Stashchuk et al (2014) were derived during wavy conditions, and because our model mainly resolves the near-bottom region, away from wave action, we interpret that our best-fit diffusion coefficient is relatively high. The resulting range of model outputs and the best fit-model simulation are visualized and compared with high-resolution measurements in Fig.…”

Impact of remotely generated eddies on plume dispersion at abyssal mining sites in the Pacific

“…Dissolved tracer plume modelling is now considered in the context of existing prototype mining scenarios assuming potential leaks of fluids from: (a) the pipes connecting a mining device on the seabed to a floating platform on sea-surface; (b) the mining vehicle (nodule collector) it self; and (c) spreading of the liquid fraction of re-suspended sediments during collection and de-watering processes. A neutrally buoyant tracer plume model was configured in a standard manner 48 . In numerical Experiment I a plume of a dissolved tracer was continuously pumped (at a rate of 1 unit·s −1 ) from the near-bottom model cell in the centre of the mooring triangle.…”

Modelling tidally induced larval dispersal over Anton Dohrn Seamount

“…The model was forced by the principal tidal harmonic M 2 added to the right-hand side of the momentum balance equations as a tidal potential. Stashchuk et al (2014) presents the details of the procedure of tidal implementation into the MITgcm.…”

“…The MITgcm has such an option, and we applied this method for modelling of the in situ experiment conducted in the Jones Bank area (Celtic Sea) (Stashchuk et al 2014). It was found there that after 4 days of the in situ and model experiments, the Rhodamine concentration fell down below the threshold of its detection both in observation and in the numerical fields.…”