Temporal Variability of Currents in the Ross Sea (Antarctica)
109
Currents observed at mooring A are characterised by a high variability with
frequent inversions and rotations; daily mean velocities are generally less than 10
cm/s except during a few events in May and July when they reach more than 20
cm/s and are directed southeast at both levels. Daily mean data of direction show
a clear bimodal distribution more accentuated at 780 m with 32% in the range 4690°N and 25% in the range 180-225 °N. Currents are directed west during the
period February-July; after then they turn southeast, indicating cold and salty
waters (température below -1.9°C and salinity around 34.72) probably coming
from the polynya région entering the Ross Ice Shelf or recirculating in the shelf at
a depth of around 250 m. Resulting annual mean values, which account for the
water masses transport, are extremely small: less than 1 cm/s directed southeast.
Corrélation between correspondent velocity components at the intermediate and
near-bottom levels is around 0.75. Warming at the depth of 220 m occurs from
March to late April with maximum température (-1.54°C) followed by a long
period (from June to January) with température below -1.9 °C.
Flow at 220 m at mooring B is characterised by meandering, frequent and rapid
complété rotations both clockwise and anticlockwise and slow speeds with 65% of
daily mean values below 5 cm/s (Fig. 3b). Main direction is Southwest until mid
March; then it inverts, going northeast for about 6 months. From November it
turns southeast with a more regular pattern. Thirty five percent of daily mean currents is directed in the range 45-135 °N while the remaining is almost uniformly
distributed. Température in this level is generally warmer than in the inner shelf,
ranging from about -0.4 °C at the end of March to -1.84°C in mid December. An
épisode of rapid warming with température higher than -0.7 °C and a peak of
-0.5°C,lasting about 20 days is observed in March; after decreasing to 1.4 °C, température still increases, remaining higher than -1.2 °C until early August. This discrepancy from the expected seasonal cycle, associated with the high variability of
the currents, could be ascribed to intrusions into the shelf of warmer waters from
the open sea. Deeper current (550 m) patterns differ from the upper: flow is mainly directed east (55% of daily mean direction being in the range 45-135°N), with
some north-south oscillations of about 2 month periods clearly évident during
austral summer months; velocities are extremely low (75% of values less than 5
cm/s), especially during the period April-August.
Currents in the northwestern edge of the Ross Sea Shelf (mooring C) are
rather constant in direction, due to the topographie effects such as the narrowing of the shelf. Daily mean direction is concentrated in the range 315-45°N
(80%) at 230 m and 270-360°N (88%) at 425 m (Fig. 4). Forty percent of velocities are higher than 10 cm/s with peaks of 25 and hourly mean intensity reaching more than 90 cm/s. Resulting annual mean velocities are respectively 8 and
8.4 cm/s directed 343 and 316°N. Température is higher than elsewhere in the
shelf, being around 0.5 °C at 22 m and -0.7 °C at 425 m probably owing to the
stronger interaction with the general open sea circulation.
Main feature and temporal variations of currents in Terra Nova Bay are
deduced by the analysis of data from mooring D. A more detailed description is
found in [4]. A two-layer System, persistent ail year long, çharacterises the circulation in this area. Currents at 55 and 140 m show strong northern alongshore
components; peaks of more than 50 cm/s are frequent at the upper level, partly
109
Currents observed at mooring A are characterised by a high variability with
frequent inversions and rotations; daily mean velocities are generally less than 10
cm/s except during a few events in May and July when they reach more than 20
cm/s and are directed southeast at both levels. Daily mean data of direction show
a clear bimodal distribution more accentuated at 780 m with 32% in the range 4690°N and 25% in the range 180-225 °N. Currents are directed west during the
period February-July; after then they turn southeast, indicating cold and salty
waters (température below -1.9°C and salinity around 34.72) probably coming
from the polynya région entering the Ross Ice Shelf or recirculating in the shelf at
a depth of around 250 m. Resulting annual mean values, which account for the
water masses transport, are extremely small: less than 1 cm/s directed southeast.
Corrélation between correspondent velocity components at the intermediate and
near-bottom levels is around 0.75. Warming at the depth of 220 m occurs from
March to late April with maximum température (-1.54°C) followed by a long
period (from June to January) with température below -1.9 °C.
Flow at 220 m at mooring B is characterised by meandering, frequent and rapid
complété rotations both clockwise and anticlockwise and slow speeds with 65% of
daily mean values below 5 cm/s (Fig. 3b). Main direction is Southwest until mid
March; then it inverts, going northeast for about 6 months. From November it
turns southeast with a more regular pattern. Thirty five percent of daily mean currents is directed in the range 45-135 °N while the remaining is almost uniformly
distributed. Température in this level is generally warmer than in the inner shelf,
ranging from about -0.4 °C at the end of March to -1.84°C in mid December. An
épisode of rapid warming with température higher than -0.7 °C and a peak of
-0.5°C,lasting about 20 days is observed in March; after decreasing to 1.4 °C, température still increases, remaining higher than -1.2 °C until early August. This discrepancy from the expected seasonal cycle, associated with the high variability of
the currents, could be ascribed to intrusions into the shelf of warmer waters from
the open sea. Deeper current (550 m) patterns differ from the upper: flow is mainly directed east (55% of daily mean direction being in the range 45-135°N), with
some north-south oscillations of about 2 month periods clearly évident during
austral summer months; velocities are extremely low (75% of values less than 5
cm/s), especially during the period April-August.
Currents in the northwestern edge of the Ross Sea Shelf (mooring C) are
rather constant in direction, due to the topographie effects such as the narrowing of the shelf. Daily mean direction is concentrated in the range 315-45°N
(80%) at 230 m and 270-360°N (88%) at 425 m (Fig. 4). Forty percent of velocities are higher than 10 cm/s with peaks of 25 and hourly mean intensity reaching more than 90 cm/s. Resulting annual mean velocities are respectively 8 and
8.4 cm/s directed 343 and 316°N. Température is higher than elsewhere in the
shelf, being around 0.5 °C at 22 m and -0.7 °C at 425 m probably owing to the
stronger interaction with the general open sea circulation.
Main feature and temporal variations of currents in Terra Nova Bay are
deduced by the analysis of data from mooring D. A more detailed description is
found in [4]. A two-layer System, persistent ail year long, çharacterises the circulation in this area. Currents at 55 and 140 m show strong northern alongshore
components; peaks of more than 50 cm/s are frequent at the upper level, partly