First dedicated hydrographic survey of the Comoros Basin

Abstract

The Comoros Basin, a region of eddies that propagate into the Mozambique Channel and subsequently the Agulhas Current, has not been well studied. This paper presents the findings from the first dedicated research cruise in the basin. ADCP data collected during the cruise show that the circulation in the Comoros Basin is dominated by the strong westward flowing North East Madagascar Current, which bifurcates twice: once upon encountering the Davie Ridge and again upon reaching the East African coast. One of the branches flows southward along the African coastline and appears to continue into the Mozambique Channel while the other branch turns northward to become the East African Coastal Current. The ADCP data also show evidence of a cyclonic eddy along the northwest coast of Madagascar. Water mass analysis indicates that all the major Indian Ocean water masses are present in the Comoros Basin. Surprisingly, North Atlantic Deep Water, a water mass previously assumed to only occur south of ∼16°S in the Mozambique Channel, was found to be present in the basin at depths below 2000 m. Antarctic Intermediate Water is found to enter the basin via two routes; from the west within the North East Madagascar Current and from the south within the northward flowing Mozambique Undercurrent.

Modern sedimentation and geochemical imprints in sediments from the NW Madagascar margin

“…The circulation in the Comoros Basin and the NW margin of Madagascar is characterized by intense mesoscale eddies that result in a high variability in the direction and intensity of oceanic currents (Collins et al, 2014;2016;Pripp et al, 2014). Anticyclonic eddies are mainly generated west of Cape Amber (northernmost tip of Madagascar) and are associated with the North East Madagascar Current (NEMC), while cyclonic eddies are mainly formed along the northwestern margin of Madagascar due to strong baroclinic instability (Collins et al, 2014).…”

“…Anticyclonic eddies are mainly generated west of Cape Amber (northernmost tip of Madagascar) and are associated with the North East Madagascar Current (NEMC), while cyclonic eddies are mainly formed along the northwestern margin of Madagascar due to strong baroclinic instability (Collins et al, 2014). The NW Madagascar margin is very often affected by cyclonic eddies that generate currents flowing SW along the slope that can Journal Pre-proof J o u r n a l P r e -p r o o f 5 deflect the river plumes and affect sediment transfer from the continent to the deep sea (Figure 1C; Collins et al, 2016;Pripp et al, 2014).…”

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.…”

Exceptional Tropical Cyclone Kenneth in the Far Northern Mozambique Channel and Ocean Eddy Influences

“…It is possible that this strengthening effect of the A2-C2 eddy pair may have played a role in the wind underestimation. The location of C2 near the Mozambican coast may have also posed challenges to forecasters since most eddies in the northern Channel occur in the open Channel or near the Madagascan coast (Collins et al, 2014(Collins et al, , 2016.…”

“…To identify eddies, SLA data were extracted from HYCOM + NCODA and from observed AVISO via Copernicus Marine Environment Monitoring Service (https://resources.marine.copernicus.eu/?option=com_csw%26view=order%26record_id=bd5a176b-350e-4d5f-8683-da457637bdcb). Eddies are common in the Channel south of the Comoros but not near the northern Mozambican coast (Backeberg & Reason, 2010; Collins et al, 2014, 2016). To quantify their contribution, we use the eddy feedback factor defined by Wu et al (2007) as follows: where Δ p in (Δ p out ) is the change in sea level central pressure when the storm encounters (leaves) the ocean eddy.…”