Spectral Proximities

By analyzing a time-homogeneous Markov chain constructed using trajectories of undrogued drifting buoys from the NOAA Global Drifter Program, we find that probability density can distribute in a manner that resembles very closely the recently observed recurrent belt of high Sargassum concentration in the tropical Atlantic between 5 and 10°N, coined the Great Atlantic Sargassum Belt (GASB). A spectral analysis of the associated transition matrix further unveils a forward attracting almost-invariant set in the northwestern Gulf of Mexico with a corresponding basin of attraction weakly connected with the Sargasso Sea but including the nutrient-rich regions around the Amazon and Orinoco rivers mouths and also the upwelling system off the northern coast of West Africa. This represents a data-based inference of potential remote sources of Sargassum recurrently invading the Intra-Americas Seas (IAS). By further applying Transition Path Theory (TPT) to the data-derived Markov chain model, two potential pathways for Sargassum into the IAS from the upwelling system off the coast of Africa are revealed. One TPT-inferred pathway takes place along the GASB. The second pathway is more southern and slower, first going through the Gulf of Guinea, then across the tropical Atlantic toward the mouth of the Amazon River, and finally along the northeastern South American margin. The existence of such a southern TPT-inferred pathway may have consequences for bloom stimulation by nutrients from river runoff.

This paper demonstrates the importance of Levantine Intermediate Water (LIW) in the deep water formation process in the Mediterranean using the modular ocean general circulation model at 0.25° resolution, 19 vertical levels, over the entire Mediterranean with an open Gibraltar strait. LIW formation is strongly prescribed in the Rhodes Gyre region by Haney [1971] relaxation, while in other regions, surface salinity relaxation is much reduced by applying the ‘mixed’ thermohaline surface boundary conditions. Isopycnal diagnostics are used to trace water mass movements, and volume fluxes are monitored at straits. Low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal. The overall water budget is measured by an average flux at Gibraltar of 0.8 Sv, of which 0.7 Sv is exchanged with the eastern basin at Sicily. LIW (density around 28.95) spreads rapidly after formation throughout the entire Levantine due to baroclinic eddies. Toward the west, LIW accumulates in the northern and central Ionian, with some entering the Adriatic through Otranto and some mixing southward in eddies and exiting to the western Mediterranean through Sicily. LIW is converted to deep water in the south Adriatic at an average rate of 0.4 Sv. Water exchange through the Otranto strait appears to be buoyancy driven, with a strong bias to the end of winter (March–April), while at Sicily the exchange has a strong symmetric seasonal cycle, with maximum transport of 1.1 Sv in December indicating the effects of wind driving. LIW pathways in the west are complex and variable. In the Tyrrhenian, intermediate water becomes uniform on isopycnal surfaces due to eddy stirring. West of Sardinia, two LIW boundary currents are formed in the Balearic basin; one flows northward up the west coast of Sardinia and Corsica, and one westward along the northern African coast. The northward current is consistent with observations, while the westward current is intermittent for the first 10 years, often breaking up into eddies which enter the basin interior. Some observations of high‐salinity waters near the African coast may support this interpretation. LIW retains a subsurface salinity maximum of 38.4–38.5 practical salinity units (psu) when reaching the northwestern Mediterranean, contrasting with surface waters fresher than 38.0 psu. West Mediterranean deep water is formed below 1500 m depth with climatological characteristics, when it is mixed and cooled during winter convection in Lions Gyre.

This paper discusses Early Ironworking (EIW) pottery traditions of the southern coast of Tanzania. The beginning of the trend toward settled village communities in large parts of southeastern Africa was assumed to result from the southward movements of Bantu speakers who are presumed to have introduced the earliest evidence of domestication and sedentary behaviour, as well as iron- and pottery-making skills. The corollary of this was that the earliest settled villages of the coast were considered to have been of the Kwale tradition, which is a coastal variant of EIW ceramics that dates from the third and fourth centuries ad on the northern and central coasts of eastern Africa. Recent studies on the southern coast of Tanzania have revealed an EIW pottery tradition with a strong resemblance to the Nkope tradition of the southwestern interior, corresponding to the woodland belt on the southern edge of the equatorial forest zone. The temporal pattern of this tradition does not suggest any direction of movement but rather an axis of interactions between the coast and interior, at least since the last millennium bc.

Characterization of aerosol episodes in the greater Mediterranean Sea area from satellite observations (2000–2007)

Since the sensational discovery of a living coelacanth off the east coast of South Africa, the geographic distribution of viable coelacanth populations has been a subject of debate. In the past, the coelacanths off the African mainland were thought to be strays from the Comoros because most coelacanths captured were caught in the waters surrounding the Comoros archipelagos. However, in recent years, a large number of coelacanths were captured off the coast of Tanzania, including nine living specimens observed in a remotely operated vehicles survey. Thus, it is possible that there is a reproducing population inhabiting waters off the Tanzania coast. We have sequenced the complete mitochondrial genomes of 21 Tanzanian and 2 Comoran coelacanths and analyzed these sequences together with two additional full mitochondrial genomes and 47 d-loop sequences from the literature. We found that the coelacanth population off the northern Tanzanian coast is genetically differentiated from those of the southern Tanzania coast and the Comoros, whereas no significant genetic differentiation occurs between the latter two localities. The differentiation between the northern and southern Tanzanian coast populations is consistent with the hypothesis that the existence of northward-flowing ocean current along the Tanzanian coast may reduce or prevent gene flow from the northern to the southern population. Finally, we estimated that the population localized to the southern Tanzanian coast and the Comoros diverged from other coelacanths at least 200,000 y ago. These results indicate that the coelacanths off the northern Tanzania coast are not strays but a genetically distinct group. Our study provides important information for the conservation of this threatened "living fossil."

Paleoclimatic simulations are powerful tools to investigate past faunal biogeographical patterns, but they can fail to capture complex climatic conditions at specific regional or temporal scales. Here we show that species distribution models (SDMs) do not predict the expansion of suitable habitats for mammals that were present in the Sahara during the African Humid Period (AHP) according to radiocarbon-dated paleozoological records. We illustrate this issue by modeling the current and past distribution of the hartebeest (Alcelaphus buselaphus), a typical African savanna antelope with a wide Sub-Saharan distribution. Its Holocene paleozoological record shows that its distribution during the AHP included large areas of the Sahara and the northern African Mediterranean coast, from Morocco to Egypt and the Levant. We use Bayesian additive regression trees (BARTs) with an MCMC algorithm in combination with current climate and occurrence data to generate posterior distributions of habitat suitability, evaluate variable importance, and generate variable partial-dependence plots. From these, we learn that annual precipitation is the most important climatic variable determining the hartebeest’s current distribution. We then projected habitat suitability onto various paleoclimatic scenarios during the AHP and found that the estimated precipitation did not reach the minimum required for the viability of hartebeest populations. These results highlight the potential of the fossil record to test the regional precision of paleoclimatic simulations, ultimately helping to generate more realistic past environmental scenarios.

Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere.

Critical comments on the South Atlantic puzzle of reef fish biogeography [J.‐C. Joyeux, S.R. Floeter, C.E.L. Ferreira &amp; J.L. Gasparini (2001) Biogeography of tropical reef fishes: the South Atlantic puzzle. <i>Journal of Biogeography</i>, 28, 831–841

Regular remote sensing data from various sensors are used here for the study of the wind driven upwelling phenomenon along the African coast of the Strait of Gibraltar. It is shown for an extended summer period (May 15 till September 15, 2003) that sea surface temperature (SST) data in the strait are correlated with NCEP winds, each westward wind increase being followed by a clear surface temperature decrease. Local surface temperature of about 22°C at that time drops down to 15°C, value corresponding to the 80–120 m depth conditions. The analysis of subsequent images indicates that the cold upwelling plume typically moves first to the Atlantic during wind forcing, and then to the Mediterranean after the wind event. The presence of the northern coast of the strait is taken as responsible for a rise of a cross‐strait sea level gradient and the enhancement of the associated westward geostrophic current that explains the first stage of the plume deployment. Sea level difference measured between Tarifa (European coast) and Ceuta (African coast), well described by a linear equation in term of the westward wind component, supports this idea as well as the subsequent remotely sensed SST distributions.

Composition and origin of PM 10 in Cape Verde: Characterization of long-range transport episodes

The impact of climate change on the storm surges of the Mediterranean Sea: Coastal sea level responses to deep depression atmospheric systems

The western and central Sudan in the early period The Sudan (more precisely, bilād al-Sūdān, the land of the blacks) is the Arabic name for the trans-continental savannah belt, several hundred miles wide, lying between desert and forest. The Sudan has been the principal theatre for African Islamic history below the northern coast. Only rarely have Saharan movements exercised critical influence—e.g. the Almoravids (fifth/eleventh century) or the Sanūsiyya (nineteenth century). Only recently has Islam taken root in the forest: this is primarily a characteristic of the European colonial period, which checked local wars, opened roads, and encouraged trade and migrant labour—a situation equally true for Muslim penetration south from the savannah, or inland from the East African coast. The Sahara, with its Berber population, has, however, been of crucial importance as an avenue of approach. The northern Sudan cities, Timbuktu, Gao and others, were ports facing the desert just as the eastern coastal cities faced the Indian Ocean. Gold for export, salt for import, were staples of Saharan trade. Several major routes crossed the Sahara: from Morocco to the goldfields of the upper Senegal and Niger; from Tunisia to the area between the Niger and Lake Chad; from Tripoli to Lake Chad; from Libya to Waday. The eastern Sudan, though closest to the heartlands of Islam, was penetrated last, perhaps because of difficulties of communication along the Nile, and the persistence of Christian states astride the river. Below the northernmost Sudanic strip, called the Sāhil or Coast, another pattern of Muslim mobility developed, chiefly east-west.

Postmortem CT in the investigation of decomposed human remains: advantages and limitations

"Scorpion fish" is a nickname given by fishermen to members of the Trachinidae family as a result of their unusual stinging mechanism. These fish are found throughout the eastern Atlantic region from the North Sea through the Mediterranean and Black Seas and along the western coast of Northern and Central Africa. They are characterised by poisonous glands located at the base and sides of the spines of their anterior back fin and at the base of a spine located on the gill cover. Because of the unusual location of the glands, fishermen handling these fish frequently suffer local injuries. A case of necrosis of the tip of the middle finger after a "scorpion fish" sting is described.

This study proposes a two-channel satellite remote sensing algorithm for retrieving the aerosol optical thickness and the Angstrom exponent, which is an index for the aerosol size distribution. An efficient lookup table method is adopted in this algorithm to generate spectral radiances in channels 1 and 2 of National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) over ocean areas. Ten-day composite maps of the aerosol optical thickness and the Angstrom exponent have been obtained from AVHRR global area coverage data in January and July of 1988. Aerosol optical thickness maps show that the major aerosol sources are located off the west coast of northern and southern Africa, and the Arabian Peninsula. The most important contributor is soil-derived particles from the Sahara Desert that cross the Atlantic Ocean. The authors’ optical thickness values tend to be larger than values given by the NOAA operational algorithm. A 10-day composite map of Angstrom...