Particle Fluxes at the Edge of the Ross Ice Shelf: the Rôle of Physical Forcing
185
145-147) clearly appears as a strong event of supercold water outflowing from
below the RIS. Analysis of the vertical profile évolution of the physical parameters
considered in Figs. 3 and 4 shows evidence of the pulsing dynamics existing at the
edge of the RIS. Not only is 5.02 days frequency the most characteristic Fourier
component but also the puise events only last a few days. Microscopie observation
of the sédiment trap samples corresponding to the collection intervals, including
the above-mentioned short-term puise events, does not show any différences that
may be specifically correlated to them. This may be due to the discrepancy existing between the duration of the puise events (2-4 days) and that of the collection
interval (15 days): even if the material brought by the short-term puise exhibits
its own specificity, this does not appear évident because it is "diluted" in the bulk
of the material collected during the rest of the 15-day collection period.
On the basis of the potential density anomaly évolution, picnoclyne depth variations were calculated and vertical displacement was computed for every isopyenal surface ranging from 27.69 to 27.77. Figure 5 shows the average vertical displacement of these isopycnal surfaces, expressed in métrés per day, during the
first 240 days of mooring records. We can recognize a seasonal signal, with peaks
corresponding to strong movements of the isopycnal surfaces during puises.
During the first 120 Julian days the vertical displacement never exceeds 20 m day1.
Afterwards, during autumn and winter seasons, it rises to a maximum of 100 m
day'1: this is a value comparable with the intrinsic settling velocity of the particles
collected by the trap and can thus affect the measured flux.
3.2 Particle Fluxes
Particle fluxes (average of the 15-day collecting period), expressed as total mass,
organic matter, carbonate and biogenic silica, are shown in Fig. 6. The material
collected by each cup was not always sufficient to produce subsamples for the
détermination of the different biogenic components and thus a complété data set
is not available for the period May - early December.
Total mass flux shows a clear seasonal trend, with relatively high values in
February (52.7 - 61 mg m'2 day'1) that nearly halve in March (27.5-35.9 mg m'2
day1) and drastically diminish in April (9.4 - 4.5 mg m'2 day1). Downward flux
appears to be extremely depleted in winter and through mid-spring and is
restored again in early December, with values comparable with the previous
February, which are maintained and increased through late January 1996, when
total mass flux is the highest of the whole deployment period (83.3 mg m'2 day'1).
The annual particle flux is estimated to be equal to 6.18 g m ", with an average
daily value of 16.9 mg m'2. The seasonal variation of total mass flux well matches
with the trend of its biogenic components. Most of the biogenic silica flux occurs
during the same period of increased total mass flux, with a maximum percentage
value registered in the period mid-February/mid-March. Opal fluxes range from
16 to 39.9 mg m'2 day'1 in February and March, drop to very low values (down to
0.01 mg m'2 day1) in the period April-November and reach the highest value
(59.8 mg m'2 day'1) in January 1996. A similar trend can be observed for organic
matter and carbonate, which show fluxes ranging respectively from 4 to 13.3 mg
m'2 d-1 and from 6.4 to 9.9 mg m'2 day'1 in February and March, that decrease in
185
145-147) clearly appears as a strong event of supercold water outflowing from
below the RIS. Analysis of the vertical profile évolution of the physical parameters
considered in Figs. 3 and 4 shows evidence of the pulsing dynamics existing at the
edge of the RIS. Not only is 5.02 days frequency the most characteristic Fourier
component but also the puise events only last a few days. Microscopie observation
of the sédiment trap samples corresponding to the collection intervals, including
the above-mentioned short-term puise events, does not show any différences that
may be specifically correlated to them. This may be due to the discrepancy existing between the duration of the puise events (2-4 days) and that of the collection
interval (15 days): even if the material brought by the short-term puise exhibits
its own specificity, this does not appear évident because it is "diluted" in the bulk
of the material collected during the rest of the 15-day collection period.
On the basis of the potential density anomaly évolution, picnoclyne depth variations were calculated and vertical displacement was computed for every isopyenal surface ranging from 27.69 to 27.77. Figure 5 shows the average vertical displacement of these isopycnal surfaces, expressed in métrés per day, during the
first 240 days of mooring records. We can recognize a seasonal signal, with peaks
corresponding to strong movements of the isopycnal surfaces during puises.
During the first 120 Julian days the vertical displacement never exceeds 20 m day1.
Afterwards, during autumn and winter seasons, it rises to a maximum of 100 m
day'1: this is a value comparable with the intrinsic settling velocity of the particles
collected by the trap and can thus affect the measured flux.
3.2 Particle Fluxes
Particle fluxes (average of the 15-day collecting period), expressed as total mass,
organic matter, carbonate and biogenic silica, are shown in Fig. 6. The material
collected by each cup was not always sufficient to produce subsamples for the
détermination of the different biogenic components and thus a complété data set
is not available for the period May - early December.
Total mass flux shows a clear seasonal trend, with relatively high values in
February (52.7 - 61 mg m'2 day'1) that nearly halve in March (27.5-35.9 mg m'2
day1) and drastically diminish in April (9.4 - 4.5 mg m'2 day1). Downward flux
appears to be extremely depleted in winter and through mid-spring and is
restored again in early December, with values comparable with the previous
February, which are maintained and increased through late January 1996, when
total mass flux is the highest of the whole deployment period (83.3 mg m'2 day'1).
The annual particle flux is estimated to be equal to 6.18 g m ", with an average
daily value of 16.9 mg m'2. The seasonal variation of total mass flux well matches
with the trend of its biogenic components. Most of the biogenic silica flux occurs
during the same period of increased total mass flux, with a maximum percentage
value registered in the period mid-February/mid-March. Opal fluxes range from
16 to 39.9 mg m'2 day'1 in February and March, drop to very low values (down to
0.01 mg m'2 day1) in the period April-November and reach the highest value
(59.8 mg m'2 day'1) in January 1996. A similar trend can be observed for organic
matter and carbonate, which show fluxes ranging respectively from 4 to 13.3 mg
m'2 d-1 and from 6.4 to 9.9 mg m'2 day'1 in February and March, that decrease in