Seafloor morphology in the Mozambique Channel: evidence for long-term persistent bottom-current flow and deep-reaching eddy activity

Breitzke, Monika; Wiles, Errol; Krocker, Ralf; Watkeys, M. K.; Jokat, Wilfried

doi:10.1007/s11001-017-9322-7

Cited by 46 publications

(47 citation statements)

References 86 publications

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“…1 and 7). The modelled current direction is once again in agreement with the inferred directions from morpho-sedimentary features and bottom photography described by Kolla et al (1980) and Breitzke et al (2017).…”

Section: Accepted Manuscriptsupporting

confidence: 85%

“…7). This bottom circulation pattern could be the cause of the arcuate and sub-circular bedforms observed by Breitzke et al (2017) in this area.…”

Section: Accepted Manuscriptmentioning

confidence: 81%

“…4). Kolla et al (1980), Breitzke et al (2017) and Wiles et al (2017b) showed that bedforms are more abundant on the basin floor west of the Zambezi Valley than east of the valley. This asymmetric distribution of the bedforms is in agreement with the modelling results, which show stronger bottom currents on the basin floor west of the Zambezi Valley (Figs.…”

Section: Modelled Observed and Inferred Circulation Near The Seafloomentioning

confidence: 98%

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The influence of bottom currents on the Zambezi Valley morphology (Mozambique Channel, SW Indian Ocean): In situ current observations and hydrodynamic modelling

et al. 2019

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Mixed turbidite-contourite systems can be found in oceans where bottom currents and turbidity currents interact. The Zambezi turbidite system, located in the Mozambique Channel (SW Indian Ocean), is one of the largest sedimentary systems in the world in length and area of the related catchments. The oceanic circulation in the Mozambique Channel is intense and complex, dominated by eddies flowing southwards and deep currents flowing northwards along the Mozambican margin. Current measurements obtained from moorings at 3400-4050 m water depth in the Zambezi and Tsiribihina valleys show periods of intense currents at the seafloor with peaks of 40-50 cm s−1 that last up to one month and are not related to turbidity currents. These strong bottom-current events are correlated with a change in current direction and an increase in temperature. The periods of current intensification may be related to eddies, since they present similar frequencies (around 7 per year). Moreover, modelling results show that during periods of intense deep circulation an anticyclonic eddy is present between the Mozambican slope and the centre of the Mozambique Channel, which may block the northward transport of the deep water mass and thus enhance the southward transport along the western slope of Madagascar. According to our hydrodynamic modelling of the circulation near the seafloor, intense currents are often present along the Zambezi Valley, especially along the valley flanks. Multi-channel seismic reflection data show that the Zambezi turbidite system does not show the typical characteristics of turbidite systems, being dominated by erosional processes, which mainly affect the valley flanks. Levees associated with the valley are absent in the main axis of the system. The effect of bottom currents on sedimentation in the basin is evidenced by the low sedimentation rates that witness winnowing in the basin, the presence of contouritic sand in the Zambezi Valley flanks and the abundance of current-related bedforms observed in multibeam bathymetry and seismic data. The intense oceanic processes observed in the Mozambique Channel may transport a large part of the fine sediment out of the basin and erode the seafloor even at great depths. Therefore, the Zambezi turbidite Highlights ► In situ measurements and modelling show strong currents along the Zambezi Valley. ► Measured bottom currents in the Zambezi and Tsiribihina Valleys reach 53 cm s −1. ► Eddies block the Mozambique Undercurrent, enhancing southward flow along the valley. ► Bottom currents erode the Zambezi Valley flanks and control its morphology.

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Section: Accepted Manuscriptsupporting

confidence: 85%

“…7). This bottom circulation pattern could be the cause of the arcuate and sub-circular bedforms observed by Breitzke et al (2017) in this area.…”

Section: Accepted Manuscriptmentioning

confidence: 81%

Section: Modelled Observed and Inferred Circulation Near The Seafloomentioning

confidence: 98%

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The influence of bottom currents on the Zambezi Valley morphology (Mozambique Channel, SW Indian Ocean): In situ current observations and hydrodynamic modelling

et al. 2019

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“…Sediment waves, scours, sediment ridges, and drifts occur (Figures 1 and 3a-3c) providing information on the interactions of bottom currents on the seafloor over prolonged periods of time indicating areas of erosion, lateral sediment-transport, and deposition (Stow et al, 2002;Uenzelmann-Neben, 2001;Uenzelmann-Neben & Huhn, 2009;Uenzelmann-Neben et al, 2007;Wiles et al, 2014aWiles et al, , 2014b. These landforms have already been described and interpreted by Breitzke et al (2017) for Mozambique Channel linking them to the flow paths of Antarctic Bottom Water and North Atlantic Deep Water as part of the meridional overturning circulation (Breitzke et al, 2017;Sultan et al, 2007). For the Mozambique, Transkei, and Agulhas Basin, similar analyses are still missing.…”

Section: Resultsmentioning

confidence: 78%

The Southwest Indian Ocean Bathymetric Compilation (swIOBC)

Dorschel

Jensen

Arndt

et al. 2018

Geochem Geophys Geosyst

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We present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data‐constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N‐S trending Zambezi Channel could be imaged in the central Mozambique Basin.

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“…6B) are generally low and contourite drift occurrence is almost exclusively confined to southern Africa, where the Agulhas Current and its associated rings are simulated. Flow is slightly constricted through the Mozambique Channel and leads to relatively high speeds, where various sediment wave fields and erosional bedforms have been mapped in this area (Breitzke et al, 2017).…”

Section: Regions Of Interestmentioning

confidence: 99%

Controls on the global distribution of contourite drifts: Insights from an eddy-resolving ocean model

Thran

Dutkiewicz

Spence

et al. 2018

Earth and Planetary Science Letters

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Contourite drifts are anomalously high sediment accumulations that form due to reworking by bottom currents. Due to the lack of a comprehensive contourite database, the link between vigorous bottom water activity and drift occurrence has yet to be demonstrated on a global scale. Using an eddyresolving ocean model and a new georeferenced database of 267 contourites, we show that the global distribution of modern contourite drifts strongly depends on the configuration of the world's most powerful bottom currents. Bathymetric obstacles frequently modify flow direction and intensity, imposing additional finer-scale control on drift occurrence. Mean bottom current speed over contourite-covered areas is only slightly higher (2.2 cm/s) than the rest of the global ocean (1.1 cm/s), falling below proposed thresholds deemed necessary to re-suspend and redistribute sediments (10-15 cm/s). However, currents fluctuate more frequently and intensely over areas with drifts, highlighting the role of intermittent, high-energy bottom current events in sediment erosion, transport, and subsequent drift accumulation. We identify eddies as a major driver of these bottom current fluctuations, and we find that simulated bottom eddy kinetic energy is over three times higher in contourite-covered areas in comparison to the rest of the ocean. Our work supports previous hypotheses which suggest that contourite deposition predominantly occurs due to repeated acute events as opposed to continuous reworking under averageintensity background flow conditions. This suggests that the contourite record should be interpreted in terms of a bottom current's susceptibility to experiencing periodic, high-speed current events. Our results also highlight the potential role of upper ocean dynamics in contourite sedimentation through its direct influence on deep eddy circulation.

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Seafloor morphology in the Mozambique Channel: evidence for long-term persistent bottom-current flow and deep-reaching eddy activity

Cited by 46 publications

References 86 publications

The influence of bottom currents on the Zambezi Valley morphology (Mozambique Channel, SW Indian Ocean): In situ current observations and hydrodynamic modelling

The influence of bottom currents on the Zambezi Valley morphology (Mozambique Channel, SW Indian Ocean): In situ current observations and hydrodynamic modelling

The Southwest Indian Ocean Bathymetric Compilation (swIOBC)

Controls on the global distribution of contourite drifts: Insights from an eddy-resolving ocean model

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