African Coast Research Articles

Late Pleistocene and Holocene fauna from Waterfall Bluff Rock Shelter, Mpondoland, South Africa

Archaeological deposits from Waterfall Bluff Rock Shelter (Eastern Cape) span from Marine Isotope Stage 3 (~39–29 ka) to the mid-Holocene (~8 ka), showing persistent human occupations. The site’s consistent proximity to the shoreline and stable coastline over millennia makes it key for exploring human settlement patterns. This study reports on preliminary results of identifiable fauna from Marine Isotope Stage 3 to the Early Holocene layers at Waterfall Bluff. The identified species may suggest a mosaic environment, although caution is warranted given the small sample size. Furthermore, leopard seal remains were recovered in layers dating to the Last Glacial Maximum. This is the first direct evidence of a leopard seal recovered from Pleistocene and Holocene archaeo-faunal assemblages along the South African coast.

Socio-ecological change in bait fisheries for the common sandprawn Kraussillichirus kraussi in Durban Harbour, South Africa

Bait fishing for the common sandprawn Kraussillichirus kraussi in Durban Harbour, on the east coast of South Africa, has a history going back to the early 20th century and has been influenced by port development and political changes over time. Recent controversy has centred on the fishers’ rights to port access and on the interactions between two sectors that harvest sandprawns for bait. The two sectors are a recreational bait fishery and an unlicensed subsistence (or small-scale) fishery that sells its catches to anglers for an income, in contravention of fisheries regulations. To determine the spatiotemporal extent of the fisheries and the impacts of bait fishing on the sandprawn resource, data on the fishing effort, catch and size composition were collected monthly at the sandbank sites Centre Bank and Wilson’s Wharf in Durban Harbour. A generalised linear modelling framework was used to analyse fishing effort and sandprawn size composition. Small-scale fishers dominated the bait fishery (83%), and fishing effort peaked at low tides and on public holidays and weekends, when the market demand for sandprawns as bait was higher. Fishing effort differed significantly between sandbanks and was dynamic, shifting to Centre Bank when sandprawn abundance at Wilson’s Wharf decreased. Small-scale fishers mainly retained large sandprawns, and did not adhere to daily catch limits, such as those regulating the recreational bait fishery. The results are interpreted from a socio-ecological systems perspective, and within the context of accommodating otherwise excluded small-scale fisheries within South African fisheries legislation.

Three new species of Pelargonium, section Hoarea (Geraniaceae) from the Western Cape Province, South Africa

Pelargonium auriculipetalum, P. leucopetalum, and P. tortandrum are described as new species. All three species are deciduous geophytes with turnip-shaped tubers belonging to section Hoarea. They differ with regard to flower colour, flower and leaf structure, and all of them occur in the winter rainfall area along the west coast of southern Africa. All three species are illustrated and distribution maps are provided for the species.

European anchovy's abundance, more affected by climatic conditions than fishing activities in the northwest African waters.

The marine waters off the coast of northwest Africa are known for being highly productive upwelling regions in the Eastern Atlantic Ocean. The present study evaluated the combined effects of climate change and sustainable fishing levels on the long-term sustainability of European anchovy (Engraulis encrasicolus), a target pelagic species found along the West African coastal waters. The present study used survey biomass time series from survey vessels and species catch time series from commercial fisheries operating in the region. Hence, we investigated the relationship between fishing dynamics and environmental factors. The status of anchovy stock was determined by analyzing changes in different initial depletion rates using a state-space Bayesian surplus production model. We used Principal component analysis to identify the essential environmental data set, while Generalized Additive Models (GAM) were employed to determine the influence of the environment on fisheries. The stock assessment model revealed that fishing intensity did not affect the abundance of anchovy in the region even when tested under different biomass depletion scenarios. However, by employing GAMs, the research assessed the impact of environmental variables on fish biomass, indicating that sea surface temperature (SST) significantly influences anchovy abundance in the region. The latitudinal gradient also had a significant influence on this species' abundance. These findings underscore the vulnerability of the small-scale fisheries sector in the tropical upwelling zone to climate change. The study concludes that even in the face of potential negative impacts from environmental factors, optimizing fishing methods can contribute to the preservation of pelagic resources in the region. It emphasizes the importance of managing fishery resources in a sustainable, economically viable, and socially acceptable way.

Mediterranean islands in Ptolemy's Geography: Mapping seas through geometrization

The Geography of Claudius Ptolemy is the sole work of ancient geography that presents an easily recognizable and rather realistic depiction of the Mediterranean Sea. The article ultimately aims to explain how Ptolemy achieved such results, given the available sources and methods of his time. It explores how Ptolemy structured the space of the Mediterranean Sea, examining how he positioned the major islands (Sicily, Sardinia, Corsica, Crete, Euboea, Rhodes) and two peninsulas (the Southern Balkans and the Crimea). It is argued that Ptolemy's outlines of the Mediterranean Sea can be accounted for as a result of using three theoretical tools available in his time for map construction: the so-called klimata or reference parallels, the wind rose for determining directions, and the so-called ‘opposite places’ or coastal points presumably situated on the same meridians. The overall outlines of Ptolemy's Mediterranean, and the position of Sicily in particular, are shaped by several latitudes established by earlier geographers. Two regions of Ptolemy's map, in the western and eastern parts of the Mediterranean Sea, are clearly structured based on the 12-point Timosthenes' wind rose, centered at Ostia and Rhodes, respectively. The position of Crete is found to be linked to the African coast by means of the ‘opposite places’ concept. In several cases, the outlines of Ptolemy's map distinctly correspond and can even serve as illustrations to the relevant descriptions found in Strabo's Geography.

A review of the genus Kalanchoe (Crassulaceae subfam. Cotyledonoideae) in the Euro-Mediterranean area, with an annotated catalogue and identification key

The genus Kalanchoe (with Bryophyllum included in its synonymy) (Crassulaceae subfam. Cotyledonoideae) has a wide natural geographical distribution range that stretches from Madagascar to some islands in the Indian Ocean off the east coast of Africa, to most of sub-Saharan and northern North Africa, and to the Near, Middle, and Far East. However, several representatives of the genus have been spread across mild-climate and even temperate parts of the world well beyond their natural distribution ranges because of their medicinal uses and because they are cultivated for ornamental (both indoor and outdoor) horticultural purposes. In addition, a number of taxa have become notorious in invasions biology as a result of casual introductions that probably resulted from surplus horticultural material being irresponsibly discarded. In the Euro-Mediterranean region 13 Kalanchoe taxa have spread widely into the natural and built environment. In the present paper the nomenclature of the 13 variously naturalised taxa is updated and corrected, and their country-level presence and spread in the Euro-Mediterranean are recorded. An analytical key is provided to facilitate the identification of the taxa that have escaped from cultivation in the Euro-Mediterranean region. A list of taxa that are cultivated but that have not become weedy, nor naturalised or invasive in the study area is provided. Most of the kalanchoes recorded here is illustrated.

Cola subgenus Distichae subg. nov. (Malvaceae-Sterculiaceae) of tropical Africa, a synoptic taxonomic revision with five new species

SummaryA new subgenus, Cola subg. Distichae, is erected for 14 simple-leaved species sharing unique characters within the genus which are presumed synapomorphies: distichous phyllotaxy; petioles lacking pulvini; petioles of uniformly short length, <10 mm long; male flowers with short androphores <1 (– 2) mm long; stamens 4 – 5; stem indumentum, where present, dominated by short simple translucent hairs (except in C. philipi-jonesii where stellate); and, in many species, dark purple to black stems with contrasting bright white lenticels. All species have fruit with small, globose, unsculptured, orange mericarps c. 1 cm diam. (where fruits are known). The species of this subgenus range from SE Nigeria in the west to coastal Kenya and Tanzania in the east and Malawi in the south, but are absent from the Congo Basin. Species diversity is highest in the Cross-Sanaga and Eastern Arc-Coastal Forest biogeographic areas, consistent with these taxa being Pleistocene refuge species. The species are mainly monoecious, but dioecy cannot yet be ruled out in some. In two species, where sufficient material was available for investigation (C. chlorantha, C. roy sp. nov.), the simple cymes were found to be bisexual, the terminal flower female and the two lateral flowers often male: a pattern previously unreported in the genus. All species are understorey shrubs or small trees of evergreen lowland or submontane forest, except C. uloloma of coastal semi-deciduous forest in E Africa, which is unique in showing xerophilic characteristics. The species can be divided into two groups. A: five species mainly in E Africa, with rapidly glabrescent or glabrous stems, conspicuously asymmetric leaves, and, where known, few-flowered, pedunculate cymes (C. uloloma, C. chlorantha, C. roy sp. nov., C. ‘udzungwa’, C. asymmetrica sp. nov.); group B: nine species in Lower Guinea (Atlantic coast of Africa), with hairy stems, symmetric or inconspicuously asymmetric leaves and, where known, sessile, fasciculate inflorescences (C. mayimbensis, C. philipi-jonesii, C. metallica, C. moussavoui, C. stigmatosa, C. takamanda sp. nov., C. toyota sp. nov., C. ‘Campo-Ma’an’, C. zanaga sp. nov.). Of the seven new species to science described here, two are named informally, since the material is so incomplete (sterile) and five are formally named here. Species diversity is highest in Cameroon and Tanzania, each with four species, followed by Gabon with three species. It is expected that additional new species will be found in poorly-surveyed, surviving, evergreen forest habitat in each of these three countries. Conservation assessments are given for each species using the IUCN 2012 standard. All species but one are considered threatened, with ten Critically Endangered (the highest category of threat), each of which is known from a single location with their forest habitat threatened, mainly by clearance for agriculture.

Global extinction of Slender‐billed Curlew (Numenius tenuirostris)

In the current biodiversity crisis, conservation efforts are often focused on extinction prevention. However, it can be difficult to determine if a species is extinct, especially if the species has an extensive range, including being a transcontinental migrant, or is poorly known. The breeding range of the migratory Critically Endangered Slender‐billed Curlew Numenius tenuirostris is uncertain, and the species has an extensive non‐breeding range that spans central Asia, eastern Europe, the Middle East, the Mediterranean basin and the northwest African coast. There have been no incontrovertible sightings since 1995. In this time, extensive and intensive searches for the species have continued. Using an IUCN extinction probability framework, we incorporate potential threats to the species, search effort and past records (museum specimens and confirmed and unconfirmed sightings, all of which are primarily from its non‐breeding range) to assess the probability of extinction. The model indicates that there is a 96.0% probability that Slender‐billed Curlew is no longer extant, classing it as Extinct according to IUCN Red List guidelines. Posterior probability Bayesian extinction date estimation modelling suggests an extinction year around the time of the 1995 sighting. Although several threats to the species have been suggested, those that definitively drove the species to extinction will never be known. Other species of Numenius are under a range of pressures, and many are recognized as globally threatened. To ensure the continued survival of all shorebird species, we advocate flyway‐scale concerted, coordinated action, and caution against complacency even for widespread but threatened taxa in Europe.

Sedimentology of False Bay (Western Cape, South Africa): geological background information for the integrated environmental management of a physically confined coastal compartment

False Bay is a large, physically confined embayment located along the southwest coast of South Africa. It is a classic example of a coastal compartment or littoral cell that acts as a receptor and sink of both terrestrial (siliciclastic) and marine (bioclastic) material. It is almost square in shape, measuring ∼35 km N-S and ∼39 km W-E and covering ∼1130 km2. Only a few small rivers discharge into the bay, as a consequence of which only small amounts of sediment are episodically supplied to the bay. The bathymetry reveals two well-defined terraces, one between 30 and 45 m, the other between 50 and 55 m water depth, which are indicative of extended Pleistocene sea-level stillstands. Sediment is dispersed by long-period ocean swells approaching from the southwestern quadrant, as well as nearshore swell- and wind-driven currents. The presence of a prominent rock pinnacle at the entrance to the bay (Rocky Bank) causes wave orthogonals to converge on its leeward side, and which results in substantial wave amplification along the eastern shore of the bay. Coarse-grained sediments (gravel, very coarse sand, coarse sand and medium sand) line the rocky shores in the west and east, and are dispersed around and away from submarine rock outcrops, whereas fine-grained sediments (fine sand, very fine sand and mud) are largely confined to an arcuate belt extending along the centre of the bay from shallow water in the northwest to the deepest parts in the south. This is documented by the distribution of individual size fractions and the mean grain size, and applies to both the siliciclastic and the bioclastic sediment components which appear to be in hydraulic equilibrium. There is a distinct N-S gradient from lower to higher bioclastic content with increasing water depth. The textural parameters (mean grain size, sorting and skewness) reveal the existence of two hydraulic populations that are mixed in various proportions in the course of their dispersal in the form of either bed load or suspended load transport. The mud fraction is closely linked to the dispersal pattern of the fine and very fine sand fractions, indicating that it is transported in the form of aggregates and/or faecal pellets, the bulk of which is evidently in hydraulic equilibrium with the finer-grained sands. It can be anticipated that, during lower Pleistocene sea levels, the palaeo-False Bay valley was occupied, or at least regularly visited, by large and small African mammals and early humans.

THE FUTURE WAR AND THE STRATEGIC ENVIRONMENT OF THE SOUTH ATLANTIC: AN ANALYSIS FOR THE DEVELOPMENT OF THE BRAZILIAN DEFENSE INDUSTRIAL BASE

This work aims to analyze the Future War, focusing on a scenario extending to 2039, and Brazil's interstate relations, with emphasis on the strategic environment of the South Atlantic, while observing classical geopolitical studies. Considering that the stability of the South Atlantic fundamentally depends on processes occurring on the western coast of Africa, this explains why Brazil's strategic environment extends to the other side of the Atlantic. This perspective also clarifies why Brazil contributes to the development of the African countries bordering the Atlantic Ocean. The study further extends its analysis to the Rio Grande Elevation Project. The entire context will serve as a foundation to examine the impacts on the development of the Brazilian Defense Industrial Base (BID). To carry out the research, the methodological approach is mixed: a qualitative perspective based on existing academic literature and field research, along with a quantitative structure, measuring data related to the BID and assessing the impacts of interstate relations on it. The direct result intended by this study is to produce new knowledge (scientific, doctrinal, and technological) in the field of defense through high-quality research, contributing to state policy. Indirectly, it aims to generate insights into Defense Studies and improve the decision-making process associated with the use of force, particularly as it relates to the BID.

Impact of biomass burning aerosols (BBA) on the tropical African climate in an ocean–atmosphere–aerosol coupled climate model

Abstract. The impact of biomass burning aerosols (BBA) emitted in central Africa on the tropical African climate is studied using the ocean–atmosphere global climate model CNRM-CM, including prognostic aerosols. The direct BBA forcing, cloud feedbacks (semi-direct effects), effects on surface solar radiation, atmospheric dynamics and precipitation are analysed for the 1990–2014 period. During the June–July–August (JJA) season, the CNRM-CM simulations reveal a BBA semi-direct effect exerted on low-level clouds with an increase in the cloud fraction of ∼5 %–10 % over a large part of the tropical ocean. The positive effect of BBA radiative effects on low-level clouds is found to be mainly due to the sea surface temperature response (decrease of ∼0.5 K) associated with solar heating at 700 hPa, which increases the lower-tropospheric stability. Over land, results also indicate a positive effect of BBA on the low-cloud fraction, especially for the coastal regions of Gabon and Angola, with a potentially enhanced impact in these coupled simulations that integrates the response (cooling) of the sea surface temperature (SST). In addition to the BBA radiative effect on SST, the ocean–atmosphere coupled simulations highlight that the oceanic temperature response is noticeable (about −0.2 to −0.4 K) down to ∼80 m depth in JJA between the African coast and 10° W. In parallel to low-level clouds, reductions of ∼5 %–10 % are obtained for mid-level clouds over central Africa, mainly due to BBA-induced surface cooling and lower-tropospheric heating inhibiting convection. In terms of cloud optical properties, the BBA radiative effects induced an increase in the optical depth of about ∼2–3 over the ocean south of the Equator. The result of the BBA direct effect and feedback on tropical clouds modulates the surface solar radiation over the whole of tropical Africa. The strongest surface dimming is over central Africa (∼-30 W m−2), leading to a large reduction in the continental surface temperature (by ∼1 to 2 K), but the solar radiation at the oceanic surface is also affected up to the Brazilian coast. With respect to the hydrological cycle, the CNRM-CM simulations show a negative effect on precipitation over the western African coast, with a decrease of ∼1 to 2 mm d−1. This study also highlights a persistent impact of BBA radiative effects on low-level clouds (increase in cloud fraction, liquid water content and optical depth) during the September–October–November (SON) period, mainly explained by a residual cooling of sea surface temperature over most of the tropical ocean. In SON, the effect on precipitation is mainly simulated over the Gulf of Guinea, with a reduction of ∼1 mm d−1. As for JJA, the analysis clearly highlights the important role of the slow response of the ocean in SON and confirms the need to use coupled modelling platforms to study the impact of BBA on the tropical African climate.

Strength and timing of austral winter Angolan coastal upwelling

The tropical Angolan upwelling system (tAUS) is a highly productive ecosystem of great socio-economic importance. Productivity peaks in austral winter and is linked to the passage of remotely forced upwelling coastal trapped waves (CTWs), where the strength of the productivity peak is associated with the amplitude of the upwelling CTW. Here, we analyze the year-to-year variability in the timing and amplitude of the austral winter upwelling CTW by examining sea surface temperature, sea level anomaly, and wind fields. Our results show that the timing of the CTW is influenced by variability in the equatorial region and along the southern African coast. Weaker equatorial easterlies from April to July delay the generation of the upwelling Kelvin wave, leading to a later arrival of the upwelling CTW. In contrast, the amplitude of the CTW is primarily influenced by variability in the eastern equatorial Atlantic and the central South Atlantic, where the South Atlantic Anticyclone is located. A cooling in the eastern equatorial Atlantic three to four months before the arrival of the CTW causes stronger zonal winds, ultimately leading to a stronger austral winter upwelling CTW. Our results suggest that the timing and amplitude of the upwelling CTW in the tAUS during austral winter are predictable on seasonal time scales.

Dakar Niño under global warming investigated by a high-resolution regionally coupled model

Abstract. In this study, we investigated interannual variability in sea surface temperature (SST) along the northwestern African coast, focusing on strong Dakar Niño and Niña events and their potential alterations under the RCP8.5 emission scenario for global warming, using a high-resolution regional coupled model. Our model accurately reproduces the SST seasonal cycle along the northwestern African coast, including its interannual variability in terms of amplitude, timing, and the position of maximum variability. Comparing Dakar Niño variability between the 1980–2010 and 2069–2099 periods, we found that it intensifies under a warmer climate without changing its location and timing. The intensification is more pronounced during Dakar Niñas (cold SST events) than during Dakar Niños (warm SST events). In the future, SST variability will be correlated with ocean temperature and vertical motion at deeper layers. The increase in Dakar Niño variability can be explained by the larger variability in meridional wind stresses, which is likely to be amplified in the future by enhanced land–sea thermal contrast and associated sea-level-pressure anomalies extending from the Iberian Mediterranean area. A heat budget analysis of the mixed layer suggests that surface heat flux and horizontal-advection anomalies are comparably important for Dakar Niño and Niña events in the present climate. However, the future intensification of Dakar Niños and Niñas is likely to be driven by surface heat flux (latent heat flux and shortwave radiation). While horizontal- and vertical-advection anomalies also contribute to the intensification, their roles are secondary.

Fog in western coastal ecosystems: inter-disciplinary challenges and opportunities with example concepts from the Pacific Northwest, USA

Coastal fog occurs along many of the world’s west coast continental environments. It is particularly consequential during summer when an increased frequency of fog co-occurs with the seasonal dryness characteristic of most west coast climate systems, for example, in the Pacific coast of North and South America, the southwestern African coast, and southern coastal Europe. Understanding coastal fog formation and effects has consequences for many disciplines, including the physical (e.g., atmospheric science, oceanography), biological (e.g., biogeography, ecophysiology), and socio-ecological realms (e.g., Indigenous cultural knowledge, public safety, economics). Although research practices differ across disciplines, they share many of the challenges needed to advance fog science. For example, coastal fog remains difficult to reliably monitor when, where, and why it occurs, which adds difficulty to understanding fog’s effects on all facets of the integrated coastal system. These shared challenges provide ripe opportunities for interdisciplinary collaboration, a template with past success in advancing fog-related science that can continue to have success in the future. In this perspectives review, we summarize the current status and frontiers of fog-related science from multiple disciplines, leveraging examples primarily drawn from the Pacific Northwest coastal region of the United States to show how interdisciplinary collaboration is needed to continue to advance our collective understanding of coastal fog formation and effects on west coast environments.

“I Authored This Book in the Absence of My Slave”: Enslaved East Africans and the Production of Occult Knowledge across the Omani Empire

What role did enslaved East Africans play in producing and transmitting the occult sciences between East Africa and Oman? This article explores the relationship between enslaved East Africans and the occult sciences in the works of Nāṣir bin Abī Nabhān (1778–1846), a jurist and practitioner of the occult sciences who lived between Oman and East Africa. It argues that enslaved East Africans were instrumental in producing and disseminating valuable occult knowledge. The analysis informs how occult knowledge operated and circulated between the Arabian and African coasts, animated in occultist idioms, and was written in Arabic and Swahili. Moreover, it explores how East African and Omani actors articulated occultist knowledge by paying attention to the interlinkages between power dynamics and knowledge hierarchies during the expansion of the Bu Saidi Empire in the nineteenth century. This study explores uncharted waters in a transoceanic sphere by tracing translation processes and non-European imperial knowledge production in the Indian Ocean world.

Distinct management units for the Critically Endangered angelshark (Squatina squatina) revealed in the Canary Islands

AbstractThe angelshark, Squatina squatina, is listed as Critically Endangered on the IUCN Red List of Threatened Species, and remaining populations are highly fragmented throughout its historical distribution. The Canary Islands archipelago in the North East Atlantic has been identified as a uniquely large stronghold for the species. In the present study, we compared the population genetic structure of S. squatina across different islands of the Canary Island archipelago using both microsatellite and single nucleotide polymorphism (SNP) markers. Both markers revealed significant differentiation of angelsharks between islands in the archipelago, with three main genetic units at: (1) Tenerife, (2) Gran Canaria and (3) the island group consisting of La Graciosa, Lanzarote and Fuerteventura. Our results imply a connectivity barrier between some adjacent islands, most likely driven by abyssal depths, and varying geological history and formation of each island and oceanographic patterns (i.e. seasonal coastal upwellings off the African coast). Therefore, we suggest that in the Canary Islands, S. squatina populations should be managed locally, with conservation and research priorities designed and implemented specifically for each of the three genetic units.

Material taxonomies and beads on the East African coast, seventh-fifteenth centuries AD

ABSTRACT Beads found in assemblages from the coast of East Africa have received significant archaeological attention. Glass beads were imported in large numbers to coastal sites from Indian Ocean trade networks from at least the seventh century AD; they give an important indication of the volume and direction of trade. Beads produced locally from materials such as shell have normally been understood in the same ways, seen as objects of trade for partners within and beyond Africa. In this paper, bead evidence is instead considered as an index of local values and uses. Beads of different materials are reviewed and a more flexible approach to taxonomy is suggested, highlighting local categories of object that do not entirely align with archaeological taxonomies based on raw materials and technology. A set of skeuomorphic beads from the Tanzanian sites of Kilwa Kisiwani and Songo Mnara is considered as an example of how local categories might transcend materials-based taxonomic systems.

SNPs Analysis Indicates Non-Uniform Origins of Invasive Mussels (Mytilus galloprovincialis Lamarck, 1819) on the Southern African Coast.

Understanding the origins of invasive species is necessary to manage them and predict their potential for spreading. The mussel genus Mytilus forms an important component of coastal ecosystems in the northern and southern hemispheres. M. galloprovincialis is an important invasive species globally, first appearing on the South African coast in the 1970s. Studies using nuclear and mitochondrial DNA indicated that the invasion probably originated from the north-east Atlantic. We used fifty-five polymorphic SNPs to genotype mussels from sites across the coast of South Africa with reference samples from the Mediterranean, the Atlantic, and New Zealand to test for possible introgression of the northern and southern taxa. Low levels of genetic differentiation were confirmed, and all samples grouped with reference samples of the Atlantic form of M. galloprovincialis, supporting previous studies. The SNP genotyping, however, allowed the detection of some individuals with genotypes typical of the Mediterranean, indicating that introduced populations in South Africa do not have a uniform origin. The initial population introduced to South Africa may have been genetically heterogenous from the start, coming from a region influenced by both the Atlantic and Mediterranean. Alternatively, multiple introductions may have taken place, originating from different regions, specifically North Africa, southern Europe, and the Mediterranean, building up the final heterogeneity.

Shifts in Maritime Trade Routes as a Result of Red Sea Shipping Crisis Detected in TROPOMI NO2 Data

AbstractObservations from space‐borne spectrometers have been lately used to quantify shipping emissions of nitrogen oxides (ΝΟΧ). Here we present a method that enhances the shipping signal of NO2 TROPOspheric MOnitoring Instrument (TROPOMI) satellite sensor observations in order to assess the impact of the Red Sea ship attacks on NO2 levels in three important shipping routes along the Red Sea, the Cape of Good Hope, and the Gibraltar Strait. Major shipping carriers, sailing usually via the Red Sea, have responded to the attacks by transiting their fleet around the African continent. The shipping signal from TROPOMI declines by ∼55% in the Red Sea and ∼15% in the Gibraltar Strait while an increase of ∼40% is found off the South African coast between January–June 2024 and the same period in 2023. These changes correlate well with vessel statistics, demonstrating the ability to track abrupt changes in NO2 shipping levels with satellite measurements.

Dynamic Coastal Mapping Using Sentinel-1 and Sentinel-2 Data Through Digital Earth Africa

Abstract. Coastal erosion poses a continuous threat to ecosystems, infrastructure, and property. To address these challenges and mitigate the effects of coastal changes, effective and current monitoring is essential. It is particularly important to monitor coastlines and coastal changes in Africa, where a significant portion of the population resides in coastal regions. While optical satellite imagery has been used for large-scale annual coastlines and change monitoring for Africa, its availability and quality are largely limited by the presence of cloud and cloud shadow. In comparison, using radar satellite observations such as Sentinel-1 data can provide consistent coastal mapping and change detection regardless of cloud presence. This paper outlines a fully automated supervised machine learning workflow using Sentinel-1 data and training samples extracted from Sentinel-2 data. It also explores the performance of the workflow for different coastal morphology types across the African coast. The workflow has proved to perform better and produced results that were visually more consistent with Sentinel-2 data compared to thresholding methods. While challenges exist to distinguish between land and water over smooth sandy beaches and rough near-shore water surfaces, our workflow provides an alternative method for coastal change mapping where optical satellites provide insufficient observations free from clouds. Python code of the proposed methodology has been made publicly available.