Cyclonic Eddies in the Cape Basin

• Main Author: Hall, C
• Other Authors: Lutjeharms, Johann R E
• Format: Dissertation
• Language: English
• Published: University of Cape Town 2014
• Subjects: Physical Oceanography
• Online Access: http://hdl.handle.net/11427/6586

A great deal of attention has been paid to the inter-ocean exchange of thermohalineproperties in the Agulhas Retroflection region. Recent observations have shown thatthe highly energetic field of the southern half of the Cape Basin consists of bothcyclonic and anticyclonic eddies. These eddies interact with each other, resulting inthe vigorous stirring of these water mass. Investigations have shown that the cycloniceddies tend to be smaller and outnumber the anticyclonic rings. Nonetheless, verylittle is known of their characteristics and the nature in which they are formed. Usingremote sensing data, confirmed with hydrographic data, this study determines thelocation, frequency and seasonality of cyclonic eddy formation; their size, trajectoriesand lifespan; physical components and associations with Agulhas Rings.Cyclonic eddies were seen to split, merge and link with other cyclonic eddies, withsplitting events creating child cyclonic eddies. The 105 parent and 157 child cycloniceddies identified during this study show that an average of II parent and 17 childcyclonic eddies were formed annually. 31.58 % follow an overall west-southwestdirection, with 27.37 % translocating west north-westward. Poleward translocationspeeds average at 0.3 kIn/day, whereas translocation speeds obtained from alldirectional components averages at 2.153 kIn/day for parent and 2.975 km/day forchild cyclonic eddies. Parent cyclonic eddies lived for approximately 254 days,whereas child cyclonic eddies survived for a mean of 188 days. Of note was asignificant variation of lifespan between parent and child cyclonic eddies formed inboth the north and south of the study area. 77 % of northern and 93 % of southerncyclonic eddies were formed directly adjacent to positive sea level anomalies orAgulhas Rings, resulting in an total overall association of 82.93 % parent and 89.63 %child cyclonic eddies. Cyclonic eddy groups were seen to merge at a rate of 16.38parent and 14 child cyclonic eddies per year, whereas topography appeared to affectthe demise of 17.00 % of the investigated cyclonic eddies.Therefore this study may form a basis for further investigations into the influenceCape Basin cyclonic eddies have on the meridional transfer of heat, salt, nutrients,oxygen and carbon concentrations in the South-East Atlantic Ocean. A more in-depthstudy using model outputs and targeted in situ hydrographical data would againenhance cyclonic eddy knowledge.