loading page

Numerical modelling of the upwelling and associated hydrodynamics at various scales along the coral reefs at Sodwana Bay, South Africa
  • Calvin Wells,
  • Justin Pringle,
  • Derek Stretch
Calvin Wells
University of KwaZulu Natal
Author Profile
Justin Pringle
University of KwaZulu-Natal

Corresponding Author:[email protected]

Author Profile
Derek Stretch
University of KwaZulu-Natal
Author Profile

Abstract

This study investigates hydrodynamics and short-term temperature fluctuations at high-latitude coral reefs, focusing on Sodwana Bay in South Africa. A refined hydrodynamic model nested within a global ocean model was developed to investigate s temperature anomalies. On-reef hydrodynamics were also measured using Tilt Current Meters over eight months between 25/08/2021 and 16/05/2022 to describe the on-reef hydrodynamics at Sodwana during temperature anomaly events. During temperature anomaly events, the predominant current direction is south-southwestward, occasionally reversing to the north with cold water temperature anomalies. Current speeds range from 0.1 to 0.2m/s, peaking at 0.35m/s at the shallow low rugosity site. The nested model, developed using the Delft 3D Flexible Mesh hydrodynamic modelling suite, successfully replicates the observed temperature anomalies in 2004. The nested modelled better replicates the temperature anomaly amplitudes compared to the reanalysed NEMO global ocean model due to the high model resolution around Sodwana. A nested hydrodynamic model is necessary for accurate analysis of short-term temperature fluctuations. A representative anomaly in February 2004 was investigated using the nested model. The anomaly was associated with remote upwelling of cold water near the Delagoa Peninsula, followed by advection towards Sodwana. As it reaches the region, the entire Sodwana region is engulfed by the cold upwelled water. The model revealed that local upwelling occurs within the Sodwana canyons during this event, making the water in the canyons 1 °C colder than the surrounding water. When the locally upwelled water spreads over the reef system, the anomaly amplitude is enhanced by approximately 20%.
29 Jun 2023Submitted to ESS Open Archive
08 Jul 2023Published in ESS Open Archive