Browsing by Author "Smit, Albertus"

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    Coastal marine heatwaves: Understanding extreme forces
    (University of the Western Cape, 2017) Schlegel, Robert William; Smit, Albertus
    Seawater temperature from regional to global scale is central to many measures of biodi- versity and continues to aid our understanding of the evolution and ecology of biolog- ical assemblages. Therefore, a clear understanding of the relationship between marine biodiversity and thermal structures is critical for effective conservation planning. In the an- thropocene, an epoch characterised by anthropogenic forcing on the climate system, future patterns in biodiversity and ecological functioning may be estimated from projected climate scenarios however; absent from many of these scenarios is the inclusion of extreme thermal events, known as marine heatwaves (MHWs). There is also a conspicuous absence in knowl- edge of the drivers for all but the most notorious of these events. Before the drivers of MHWs along the coast of South Africa could be determined, it was first necessary to validate the 129 in situ coastal seawater temperature time series that could be used to this end. In doing so it was found that time series created with older (longer), lower precision (0.5 Degrees Celsius) instruments were more useful than newer (shorter) time series produced with high precision (0.001 Degrees Celsius) instruments. With the in situ data validated, a history of the occurrence of MHWs along the coastline (nearshore) was created and compared against MHWs detected by remotely sensed data (offshore). This comparison showed that the forcing of offshore temperatures onto the nearshore was much lower than anticipated, with the rates of co-occurrence for events between the datasets along the coast ranging from 0.2 to 0.5. To accommodate this lack of consistency between datasets, a much larger mesoscale area was then taken around southern Africa when attempting to determine potential mesoscale drivers of MHWs along the coast. Using a self organising-map (SOM), it was possible to organise the synoptic scale oceanographic and atmospheric states during coastal MHWs into discernible groupings. It was found that the most common synoptic oceanographic pattern during coastal MHWs was Agulhas Leakage, and the most common atmospheric pattern was anomalously warmoverland air temperatures.With these patterns known it is now necessary to calculate how often they occur when no MHW has been detected. This work may then allow for the development of predictive capabilities that could help mitigate the damage caused by MHWs.
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    Detecting marine heatwaves with sub-optimal data
    (Frontiers, 2019) Smit, Albertus
    Marine heatwaves (MHWs), or prolonged periods of anomalously warm sea water temperature, have been increasing in duration and intensity globally for decades. However, there are many coastal, oceanic, polar, and sub-surface regions where our ability to detect MHWs is uncertain due to limited high quality data. Here, we investigate the effect that short time series length, missing data, or linear long-term temperature trends may have on the detection of MHWs. We show that MHWs detected in time series as short as 10 years did not have durations or intensities appreciably different from events detected in a standard 30 year long time series.
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    Introducing the seaweed specialist group of the IUCN species survival commission
    (Cambridge University Press, 2024) Arafeh-Dalmau, Nur; Smit, Albertus; Erlania
    In June 2023, the IUCN Species Survival Commission created the Seaweed Specialist Group. This international group of scientists and practitioners will work to assess and improve the conservation status of seaweeds, build networks and partnerships to prioritize conservation actions and communicate the importance of seaweed species. Seaweeds (macroalgae) are found in all oceans and seas, with > 10,000 known marine species that include the red (Rhodophyta, c. 6,200 species), brown (Ochrophyta, c. 1,800) and green (Chlorophyta, c. 1,800) taxa. However, climate change and other anthropogenic stressors threaten many seaweeds globally, including iconic habitat-forming species such as kelps, fucoids and rhodoliths.