Browsing by Author "Morris, Tamaryn"

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    Assessing techniques to successfully monitor the oceanography of the complex uThukela Marine Protected Area
    (2022) Ramsarup, Neha; Morris, Tamaryn; Hermes, Juliet
    Marine Protected Areas (MPAs) are increasingly being established to restore and protect coastal and marine environments. The newly established uThukela Marine Protected Area (MPA), located on the central KwaZulu-Natal Bight along the northeast coast of South Africa, has been identified as a key ecological region. The region provides recruitment and is a general nursery area for marine life on the Bight. Knowledge of the oceanographic dynamics in the region is essential for understanding the functioning of the ecosystem and the effectiveness of the MPA. This study analysed changes in ocean temperatures at 20 sites along the Bight over a 41-year period using in situ beach and UTR data, and satellite data. Significant warming of 0.03°C/year occurred at beach sites within and around the MPA. Beach temperatures increased at an average rate of 0.02°C/year across the Bight, during both summer and winter, whereas UTR temperatures warmed by 0.14°C/year during summer and 0.08°C/year during winter. At the event scale, a case study of a persistent decrease in in situ temperatures along the entire Bight during summer 2017/2018 was investigated. The decrease in temperatures was hypothesised to be as a result of the combined effects of a La Niña event and a Natal Pulse, which could have significant consequences for temperature-sensitive species. Temperature trends observed in beach temperatures over the 41 years were not reflected in beach temperatures over the past decade, highlighting the importance of large datasets when investigating climate change. Warm biases of up to 2°C observed in satellite-derived temperature measurements, and its failure to replicate trends seen in the beach data, suggests that in situ temperature measurements in MPAs are better suited for long-term monitoring efforts. These findings can help assess the success of MPAs and to guide monitoring and research activities within the region.
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    Building A Mean-state Of Oceanographic Properties (Temperature And Salinity) For The Kwazulu-natal Bight Using The Roms Model: A Contribution Towards Marine Protected Areas Analysis
    (2018) Malange, Mathabo Noxolo; Morris, Tamaryn; Collins, Charine; Lamont, Tarron; Ansorge, Isabel
    The KwaZulu-Natal Bight, located along the east coast of South Africa, is an important recruitment and nursery area for various marine species. In an effort to conserve a number of threatened species, two Marine Protected Areas (MPA) have been established in the Bight. The African Coelacanth Ecosystem Programme is conducting MPA analyses along the Bight through a series of biological and oceanographic studies and this study forms part of the oceanographic research component that will assist in the decision-making process of MPAs in the region. This study uses a 30-year, high-resolution, regional ROMS simulation to build a climatology representative of the mean-state of the Bight. The model is also used to investigate the seasonal and annual variability as well as the influence of the Agulhas Current on the shelf. The Bight was cooler and less saline than the surrounding waters and seasonal variation was limited to the upper 50 m of the water column. The depth of the Bight ranges from 50 m in the inner shelf to 100 m at the shelf edge in the central region of the Bight. In the northern and southern region of the Bight, the depth of the water column extends down to about 150 m at the shelf edge. In summer, surface temperatures were on average 4.8°C and 4.3°C warmer than in winter over the uThukela Banks and Aliwal Shoal respectively. Bottom temperatures at both MPAs had a mean seasonal variation of about 3°C. Salinity, a more conservative variable, showed little variability over the year throughout the water column except for at 50 m where lower salinities were observed in the winter months. Wavelet analysis showed that a strong annual (12 month) signal was dominant at the surface (10 m). Bottom temperatures displayed a weaker annual signal than the surface in addition to a slight semi-annual cycle. Further investigations indicated that the Agulhas Current influenced the Aliwal Shoal MPA more than the uThukela Banks MPA as they shared similar temperature values (at the surface and bottom) throughout the 30-year period. In contrast, the uThukela was cooler than the Agulhas Current by 0.5 to 1.5°C at the surface and 1 to 2.5°C at the bottom. These time series also enabled us to identify anomalous features such as the Natal Pulse that could have important implications for temperature-sensitive species in the area.
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    Downstream evolution of ocean properties and associated fluxes in the Greater Agulhas Current System: Ad hoc Argo experiments and modeling
    (2020) Morris, Tamaryn; Ansorge, Isabel; Hermes, Juliet; González, Borja Aguiar; Lamont, Tarron
    The evolution of cyclonic eddies across the Southern Mozambique Chanel and the downstream evolution of the Agulhas Current was investigated using Argo floats, in combination with output from ocean general circulation reanalysis models. Two dedicated experiments were undertaken in April and July 2013, whereby eight floats were deployed within two separate cyclonic eddies. Floats were set to either daily and five-daily profiling from 1000 db to the surface, with park depths ranging from 300 db to 1000 db. The two cyclonic eddies propagated southwestward across the Mozambique Channel from southwest Madagascar to the KwaZulu-Natal Bight, a distance of approximately 1300 km, in approximately 130 days at a mean speed of 0.13 m s−1 . Estimates indicate the April (July) eddy showed mean trapped depths of 595 ± 294 m (914 ± 107 m), volume transport of 13.4 ± 5.2 Sv (21.2 ± 9.1 Sv), heat flux of -0.07 ± 0.06 PW (-0.2 ± 0.09 PW) and freshwater flux of 0.04 ± 0.04 Sv (0.09 ± 0.05 Sv). These results highlight the role of Madagascar cyclonic eddies as transporters of cooled and freshened source waters into the Agulhas Current. During a third experiment, six floats were deployed in the Agulhas Current, and exited the current within 9 - 12 days at mean speeds of 0.51 – 0.76 m s−1 . An evolution of properties was shown from north to south for both Argo data and model output; for volume transport (16.76 – 38.18 Sv; 17.70 – 32.51 Sv), heat fluxes (0.85 – 1.79 PW; 0.99 – 1.91 PW) and salt fluxes (0.60 – 1.37 x 1012 kg s−1 ; 0.63 – 1.17 x 1012 kg s−1 ). This study illustrates the first near-real time survey of the Agulhas Current, and a potential method of quasi-synoptic surveys using Argo float technology. These experiments highlight alternative methods of studying regions of turbulence by altering the mission parameters of Argo floats. Increased observations of eddies and Western Boundary Currents are critical to our understanding of the global oceans and impacts on the earths climate. Even more so for the understudied Indian Ocean.