Project

Data Analysis:

Numerical Modeling:

 

 

Numerical Modeling: Experiments

Experiment E1: No Stratification

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Evolution of salinity near the seabed during the experiment E1 (idealized topography and no stratification) is illustrated in animation and figures 11-14. Early stages of cascading development are very similar to those described in model experiments with constant along-slope topography (e.g. Gawarkiewitz and Chapman, 1995). During the initial time interval (~8 days) the entire salt flux through the surface is spent on increase of salinity in the forcing region. By day 10, tongues of salty water start stretching downslope from the forcing region, distorting initially circular frontal interface. In 30 days, initially round-shaped salinity anomaly is completely deformed by meanders and eddies of opposite sign. However, the shape of the leading edge of cascade mainly retains circular geometry. The leading edge reaches the shelf break while some portion of dense water forms bottom current along the shore-line. Between 40 and 50 days massive intrusion of dense water in the deep zone through submarine canyon starts. From this point and up to the end of the experiment dense water propagates along and cross slope in a shape of a solitary tongue, filled with eddies.

 

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Fig. 11

Within ~20 days salinity in the forcing region reaches saturation.

Current speed levels up.

 

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Fig. 13

F17 & F18:

The speed of front propagation near the bottom is ~12 times higher than that at the surface.

 

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Fig. 12

The rate of salt accumulation in the forcing region steadily decreases.

Rates of salt accumulation on shelf and in the deep water highly and negatively correlate

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Fig. 14

The shape of the cross-isobaths flux curves at different depths is very similar: rapid growth, and then oscillations around some constant value.

Experiment E2: Stratified Ocean

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Fig. 15

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Fig. 16

According to experiment E2 (stratified ocean), a sharp pycnocline embedded right below the surface mixed layer influences cascading in several ways. First of all, it decelerates down-slope penetration of dense water. Cascade does not reach the base of the continental slope (Figs. 15 and 16). Slower removal of dense water from the forcing region causes a larger salinity (density) increase. The mean increase of salinity in the forcing region during this experiment is equal to 0.34 PSU versus 0.23 PSU in the unstratified ocean.
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Fig. 17

Cascading triggers an opposite-directed up-slope motion (upwelling) of lighter water from the deep (animation and Fig. 17). On the average, uplifted water moves above the near-bottom dense flow and eventually replenishes the upper layer in the production zone. Two oppositely-directed flows create a circulation loop with denser outflow near the bottom and lighter inflow near the surface. In stratified Arctic Ocean the water uplifted from the deep is warmer and saltier then the water on shelf.

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Fig. 18

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Fig. 19

We calculated cross-slope heat and salt fluxes associated with cascading for conventional water layers in the northwestern Laptev Sea from the surface to the depth of dense water penetration (Figs. 18 and 19) Down-slope motion of cold shelf water causes a considerable loss of heat from the Atlantic layer with an absolute maximum equal to 0.20x105 W/m2. This is relatively large value compared with heat transport associated with AW entering the Fram Strait (Schauer et al., 2004). Owing to cascading, AW also loses salt. Despite the fact that cascading is forced by salinification of shelf water, this water is still fresher than AW, thus causing a negative salt flux. According to our results, cold halocline layer acts as a sink for salt entering from the shelf (at depths less than 200 m), and additionally from the AW layer (at depths greater than 200 m). The latter is the result of the joint effect of upwelling and intensive eddy salt flux, The surface mixed layer receives both heat and salt, but in substantially smaller amounts than the amounts received by the deeper layers.