Drifter trajectories through a current meter array at Drake Passage

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247

164

The two principal fronts within the Antarctic Circumpolar Current (ACC), the Subantarctic Front (SAF) and the Polar Front (PF), are investigated with respect to their spatial patterns and relations to deep water masses from the northern Drake Passage to the western and southern Argentine Basin. Observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters. East of Drake Passage, the width of the Polar Frontal Zone (PFZ) increases rapidly when the SAF turns sharply northward as a part of the Falkland (Malvinas) Current, while the PF remains oriented mainly toward the northeast. Found within this region of the PFZ are mesoscale eddies, the upper layers of which consist of Subantarctic Mode Water from the Pacific. The contrasts in upper layer water properties that identify the SAF can be traced the entire length of the Falkland Current to the Brazil‐Falkland confluence zone and then southward to the southern Argentine Basin. There the SAF turns eastward and later, but perhaps not always, merges with the PF north of Ewing Bank to form a single, intense current core strongly influenced by bottom topography. At times this eastward current loops southward through a gap in the Falkland Ridge into the Georgia Basin, thereby supplying relatively warm and salty Subantarctic water to the Antarctic Zone. East of the gap, the two fronts become separated and are once again distinct features in the vicinity of the Islas Orcadas Rise. At depth, within Drake Passage and the western Scotia Sea, the SAF and PF are not lateral boundaries between distinct water masses, but are instead identified by enhanced vertical displacements of property isopleths. With the northward turn of the SAF east of Drake Passage, a thick layer of Circumpolar Deep Water (CDW) is advected over the Falkland Plateau into the Argentine Basin. There it is joined by waters entering the Argentine Basin via a deep spreading route through the Georgia Basin: denser CDW, deep water from the Weddell Sea, and episodically, deep water from the southeastern Pacific Ocean. Together, these waters form a northward flow off the Patagonian shelf that extends from the sea surface to the bottom, most of which turns back toward the south with the Falkland Current return. Also flowing south, along the seaward side of the Falkland Current return well away from the western boundary, is the main core of North Atlantic Deep Water (NADW). Detatched masses of NADW are observed within the CDW at the western boundary as well as within the ACC south of the SAF in the south central Argentine Basin.

Section: Drifter Trajectories In the Abcs Study Areasupporting

confidence: 70%

The subantarctic and polar fronts in relation to deep water masses through the southwestern Atlantic

Peterson¹,

Whitworth²

1989

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247

164

“…The difference in drift speed between drogued and undrogued buoys as well as the correlation between drift and wind speed could be verified. Undrogued buoys drifted with about 2.5% of the wind speed, a figure that agrees well with the 3.4 -+ 1.4% given by Peterson [1985]. Furthermore, it was found that drifter acceleration as well as the variance of the mean drift speed are also larger for undrogued buoys.…”

Section: General Differences In Drift Behaviorsupporting

confidence: 84%

Differences in drift behavior between drogued and undrogued satellite‐tracked drifting buoys

Brügge¹,

Dengg²

1991

Drift behavior of drogued and undrogued Hermes‐type buoys is studied. After drogue loss, an increase in drift speed and acceleration is observed as well as improved correlations between drift and wind in both speed and direction. With these criteria, a method for the separation of large data sets into a drogued and an undrogued part has been developed. In most areas of the North Atlantic this works very well; problems arise in regions with strong surface currents and/or light winds. A statistical analysis is performed in a selected area to demonstrate the errors that can be caused by indiscriminate use of drogued and undrogued drifters. Mean and rms velocities as well as kinetic energies change significantly when undrogued buoys are considered. Therefore caution is essential when using surface drifters without drogues.

“…A potentially useful tool for high-latitude studies is the coastal zone color scanner (CZCS). Peterson [1985] demonstrated that there is a high degree of correlation between surface drifter trajectories and near-surface flow observed in CZCS imagery. Satellite altimetry also may prove useful for tracking features in the ACC.…”

Section: Discussionmentioning

confidence: 88%

A synoptic description of the flow at Drake Passage from year‐long measurements

Hofmann¹,

Whitworth²

1985

The fronts and water mass zones comprising the Antarctic Circumpolar Current at Drake Passage have associated with them characteristic temperature structures. This property is used to construct maps that depict changes in the location of the fronts at 500 m. The zonation maps are based on temperature and velocity data obtained from 15 moorings deployed in the northern and central Drake Passage as part of the International Southern Ocean Studies experiment DRAKE 79. They provide a description of the flow of the Antarctic Circumpolar Current through Drake Passage at weekly intervals for a period of 1 year: January 1979 to January 1980. Mesoscale activity in central Drake Passage was dominated by the migration of three cold‐core rings and one warm‐core ring. The cold‐core rings formed from northward extending meanders of the Polar Front; the warm‐core ring from a southward extending meander of the Subantarctic Front. All four rings appeared to form within Drake Passage and to follow similar trajectories, which were influenced by local bathymetry. Variations in the location of the Subantarctic and Polar fronts were caused by meanders. In the narrowest portion of Drake Passage, when rings are present in the Polar Frontal Zone, the Polar Front is found farther south than when rings are absent.