Mesoscale activity in the Comoros Basin from satellite altimetry and a high‐resolution ocean circulation model

Abstract

Recently it has been shown that anticyclonic eddies are generated in the Comoros Basin contesting the long-held notion of a single large anticyclonic cell, the Comoros Gyre. Limited knowledge exists about the mesoscale activity within the basin, a potential key source of variability for the Mozambique Channel and subsequently the Agulhas Current. In this paper an automated eddy tracking scheme, applied to satellite altimetry data and a high-resolution model simulation, is used to determine the characteristics of the anticyclonic eddies generated in the Comoros Basin. The generation and characteristics of cyclonic eddies are also investigated. The eddy tracking scheme revealed that anticyclonic eddies are primarily generated west of the tip of Madagascar due to barotropic instabilities whereas cyclonic eddies are mainly generated along the northwest coast of Madagascar as a result of baroclinic instabilities. Anticyclonic eddies, with a mean lifespan of about 3 months, reside in the basin for half their lifespan before propagating into the Mozambique Channel. On the other hand, the majority of cyclonic eddies, with a similar mean lifespan, dissipate within the basin. Initially, the anticyclones, with translation speeds of 6-8 km d21 and mean radii of 80-100 km, follow the trajectory of the North East Madagascar Current and turn south upon reaching the African coast. The cyclonic eddies tend to be smaller (60 km) and have slower translation speeds (2.5-3.5 km d 21 ) than their anticyclonic counterparts.

Aligning marine spatial conservation priorities with functional connectivity across maritime jurisdictions

“…Similar findings were reported by Schott et al (2009). Instabilities in the current results in formation of Comoros eddies (Collins, Hermes, & Reason, 2014), which have important implications for connectivity as they entrap larvae released within the Comoros Basin. Instabilities in the current results in formation of Comoros eddies (Collins, Hermes, & Reason, 2014), which have important implications for connectivity as they entrap larvae released within the Comoros Basin.…”

“…On the east coast of Madagascar, the SEC accelerates past the tip of Madagascar as Northeast Madagascar Current (NEMC), in effect facilitating the observed larval dispersal from northeast tip of Madagascar into Comoros and further along the East African coast (Figures 1, 3, and 4). Instabilities in the current results in formation of Comoros eddies (Collins, Hermes, & Reason, 2014), which have important implications for connectivity as they entrap larvae released within the Comoros Basin. On reaching the East Africa mainland coast, the NEMC splits into the northward flowing East African Coastal Current (EACC) and southwards as eddies in the Mozambique Channel.…”

Estimating Connectivity Through Larval Dispersal in the Western Indian Ocean

“…The other noticeable drift patterns are the anticyclonic pathways in the Comoros Basin all year round, as a result of the mesoscale eddies occurring there (Collins et al, ), and cyclonic movement south of 15°S in the Mozambique Channel during January and February.…”

“…The North‐East Madagascar Current (NEMC) flows past the tip of Madagascar, and on reaching the mainland part of the current flows northward as the East African Coastal Current (EACC) along the Tanzania and Kenya coasts (Manyilizu et al, , ). Part of the flow past the northern tip of Madagascar results in the formation of the Comoros eddies due to barotropic and baroclinic instabilities (Collins et al, ) and the propagation of mesoscale eddies south through the Mozambique Channel (Backeberg & Reason, ; Ridderinkhof & De Ruijter, ; Schouten et al, ). These southward propagating eddies then merge with westward propagating eddies generated south of Madagascar into the Agulhas Current (Halo et al, ).…”

Seascape genetics of the spiny lobster Panulirus homarus in the Western Indian Ocean: Understanding how oceanographic features shape the genetic structure of species with high larval dispersal potential

“…A large, seasonal anticyclonic cell prevails at the northern entrance to the Mozambique Channel (Donguy & Piton, 1991), followed by a succession of mesoscale cyclonic and anticyclonic eddies propagating southwards through the channel (Collins, Hermes, & Reason, 2014;Collins, Hermes, Roman, & Reason, 2016;Halo et al, 2017). These eddies create strong dynamic gradients which act on larval dispersal.…”