Banca de DEFESA: ÚRSULA MARTIN DAMASCENO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ÚRSULA MARTIN DAMASCENO
DATE: 20/11/2024
TIME: 10:00
LOCAL: Videoconferência / Canal Youtube PPGG - Youtube.com/@ppggufrn
TITLE:

Hydrodynamics in Submarine Canyons of the Rio Grande do Norte Continental Margin

KEY WORDS:

submarine canyons; western boundary current; continental slope; equatorial margin

PAGES: 105
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geofísica
SPECIALTY: Sensoriamento Remoto
SUMMARY:

Physical processes at continental margins control the transport of heat, sediments, chemical compounds, and nutrients between the ocean basin and the continental shelf, which affects the ecosystems nearby. The shelf-edge submarine canyons interact with the currents and are potential flow channelers between the coastal zones and the oceanic basin. Despite the importance of these phenomena, canyon-flow interactions in low latitudes of the Atlantic Ocean are poorly understood. This study aims to characterize the hydrodynamic phenomena of the Brazilian tropical margin, specifically the submarine canyons in areas of shelf break zones on the eastern and northern shores of Rio Grande do Norte (RN). Physical processes were investigated using the Coastal Regional Oceanic Community Model (CROCO). The first analysis presented here pertains to the Natal Canyon and was developed in CROCO using regional bathymetry interpolated from nautical charts and global databases, validated with in situ data. This study aims to analyze the hydrodynamics of the Natal Canyon and its effects on the exchange between the shelf and the ocean, and suspended particles. The correlation analysis includes the components of canyon flow, the North Brazil Current, the transport of the outer-middle shelf, and wind stress. Additionally, a drifter model was built using the velocity field of the oceanic model with the Ichthyop model for three different positions: on the southern edge of the canyon, at the head of the canyon, and along the current path on the slope. The results show two main forces

driving the canyon dynamics: i) the meridional wind, which has the highest correlation coefficient with canyon transport (-0.75), and ii) the North Brazil Undercurrent with the second highest correlation coefficient (-0.64). In all three simulated scenarios, the current is strong enough to transport most of the suspended particles (~95%) northward. Despite the general westward transport of the canyon, the current is not strong enough to prevent the capture of particles (~2%) within the canyon. A small portion of particles (<2%) reaches the inner shelf through the canyon head and the coastal current. The results indicate that the dynamics of the Natal Canyon are wind-driven and favor downward flow. This context impacts suspended particles and may explain the starved condition in low-latitude shelves, such as the eastern margin of Rio Grande do Norte, Brazil.

The second part of the study involves a similar simulation developed for the northern margin of RN, in the region of the Acu canyons, validated with in situ data. The main objective is to analyze the physical processes and investigate the occurrence of upwelling or uplift in this region. The analysis was conducted using annual time series from six vertical sections of transport, velocities, and temperature, as well as 16 temperature profiles, with 8 at isobaths of 35 m and 8 at 70 m (corresponding to the outer shelf and the shelf break, respectively). The Barrier Layer Thickness (BLT) was calculated for the shelf break area to examine its influence on physical processes. Maximum transports of the North Brazil Undercurrent(NBUC) were observed in March, late July, and mid-September. Although no upwelling events were recorded, the results indicate the occurrence of uplifts at the shelf break, both in the canyons and in adjacent areas, between January and June. The period of highest frequency of uplifts occurred in March, coinciding with maximums NBUC transport and weaker trade winds. Conversely, the absence of uplifts from July to September, despite strong ocean currents, was associated with intense trade winds and a thicker barrier layer, which acted as an obstacles. Thus, the interactions between the NBUC and the bathymetry influence the current-induced processes on the outer shelf and the northern slope of RN, highlighting the influence of westward boundary currents (WBCs) on the maintenance of the ecosystems in the Brazilian equatorial margin. Therefore, the results of this study demonstrate that the interactions between WBCs, the physiography of the margin, and submarine canyons occur in distinct ways between the eastern and northern sectors of Rio Grande do Norte, contributing to the understanding of the sedimentary and ecological differences between the eastern and northern shelves of the Brazilian Continental Margin.

COMMITTEE MEMBERS:
Externa à Instituição - MIRELLA BORBA SANTOS FERREIRA COSTA - UFPE
Externo à Instituição - GBEKPO AUBAINS HOUNSOU GBO - UFC
Externo ao Programa - 3342435 - ANTONIO RODRIGUES XIMENES NETO - nullExterno à Instituição - FELIPE MENDONCA PIMENTA - UFSC
Externo ao Programa - 2276514 - MARCIO MACHADO CINTRA - nullPresidente - 2042405 - MOAB PRAXEDES GOMES