WASCAL Scholar Collection:

Simulations and Projections of the South Atlantic Ocean Dipole Impacts on Regional Rainfall in CMIP6 Models

2023-01-01T00:00:00Z

Title: Simulations and Projections of the South Atlantic Ocean Dipole Impacts on Regional Rainfall in CMIP6 Models Authors: Nworgu, Uzoma Chukwuemeka Abstract: This study investigates the impacts of the South Atlantic Ocean Dipole (SAOD) on rainfall over land areas of the South Atlantic region during austral winter (June-July-August), using the latest Coupled Model Intercomparison Project phase 6 (CMIP6). We consider a historical reference period (1950-2014) and, future changes under the Shared Socioeconomic Pathway 5-8.5 (SSP585) from 2015 to 2079. Our historical analyses of observations revealed four regions with spatially-coherent correlations of grid-point rainfall with the SAOD namely; Northern Amazon, Guinea Coast, Central Africa and South East Brazil – a result generally consistent with similar analyses in earlier literature. The ensemble mean of 44 CMIP6 models’ historical simulations largely underestimated the SAOD-rainfall correlation in these regions, while individual model performance revealed a spread in model behavior in each region. Model performance was best in Central Africa with 52% of the models simulating statistically significant positive correlations, similar to observations. The worst performance was for South East Brazil with only 7% of the models performing well, while over the Guinea Coast and South East Brazil, more than 40% of the models simulated a negative sign correlation in opposition to observations. Observations showed that SAOD influence on rainfall varied between the regions, being strongest over the Guinea Coast and weakest over South East Brazil. Future simulations of an ensemble of the best-performing models in each region indicated a decrease in SAOD influence on rainfall variability, in all the respective regions, under the SSP585 scenario. Our results underscore the significant impacts of SAOD on regional rainfall variability and highlights the need to enhance CMIP6 models' ability to simulate the SAOD-rainfall relationship. Furthermore, a future with unabated greenhouse gas emissions could cause significant changes in rainfall patterns, leading to unpredictable impacts on the affected regions. Overall, these results could be a useful first step in improving the prediction of regional climate variability and planning adaptation of theregional ecosystems and human socio-economic activities to climate change. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Universidade Técnica do Atlântico, Cabo Verde in partial fulfillment of the requirements for the Master of Science Degree in Climate Change and Marine Science

Saharan Dust Transport towards the Tropical Atlantic Ocean and South America: A 3-Dimensional Analysis based on Livas Aerosol Climatology

2023-01-01T00:00:00Z

Title: Saharan Dust Transport towards the Tropical Atlantic Ocean and South America: A 3-Dimensional Analysis based on Livas Aerosol Climatology Authors: Dembele, Massitan Beny Abstract: Understanding the spatial distribution of aerosol particles is essential to evaluating their influence on the climate system. Saharan dust plume as a fundamental component of the global aerosol system requires a comprehensive analysis of its spatial structure. The main objective of this research was to study the Saharan dust plume structure over Mindelo City, in Cabo Verde, and during its transport towards remote areas of tropical Atlantic and Americas using the recently developed LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies (LIVAS), a 3-D multi-wavelength global aerosol optical database based on CALIPSO satellite products. LIVAS products' dependence on the radius used to aggregate CALIPSO profiles was also evaluated. A preliminary comparison of daily and monthly scales of the backscatter and extinction coefficient profiles between LIVAS and PollyXT, a ground-based lidar system operated at Mindelo City, indicated a good agreement. The application of LIVAS columnar and vertical optical properties products to characterize the seasonal variability of Saharan dust transport over Mindelo shows that most of the dust transported occurs from June to September and has a maximum of 2 to 5 km. During the winter season, from December to January, aerosol loading in the free troposphere is dramatically reduced, and most of the dust is transported within the (MBL,) in a layer up to ~2.5 km. Dust mean contribution to the backscatter profile during summer varied from ~90% in the free troposphere to less than 25% in the MBL. In the winter, the contribution in the free troposphere is reduced to less than 50%. Regarding the dependence on the aggregation radius, the main dependence found was for monthly (DOD), with smaller radii (<200 km) producing lower climatological values when compared with larger radii. The LIVAS application, which describes the seasonal transport of Saharan dust to remote western areas of the tropical Atlantic and Americas, also depicted patterns that are consistent with previous studies. The magnitudes of dust transport, as identified by the extinction coefficient profile are highest in boreal summer and spring and lowest in autumn. The northward shifts of the dust plume are further during the summer, reaching the latitude of 25oN. This displacement is mainly modulated by the seasonal migration of the (ITCZ), and it leads to the transport of dust toward Central America and the Caribbean. Winter is the season that the lowest amount of dust arrives in the remote western tropical Atlantic and South America, which can be explained by the low-level transport of dust and the efficient removal of dust along its way. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Universidade Técnica do Atlântico, Cabo Verde in partial fulfillment of the requirements for the Master of Science Degree in Climate Change and Marine Science

Vertical Migration and Distribution of Zooplankton along a Latitudinal Transect in the Eastern North Atlantic

2023-01-01T00:00:00Z

Title: Vertical Migration and Distribution of Zooplankton along a Latitudinal Transect in the Eastern North Atlantic Authors: Traore, Sienfoungo Abstract: Zooplankton are diverse animals found in the ocean, ranging from microscopic to larger invertebrates, and they are crucial to marine ecosystems. Some zooplankton species migrate vertically towards the oxygen-poor waters during the day, which could affect oxygen consumption and release of dissolved compounds, such as ammonium, into deep water. This study provides an overview of zooplankton distribution in the eastern North Atlantic Ocean. Zooplankton was sampled depth stratified along a transect from Cabo Verde to the English Channel using a 150 μm multinet. An analysis of taxon composition identified 11 taxa. Copepoda and Sagittoidea were the most abundant organisms. Stations located in upwelling areas had high biomasses. Stations sampled at night had higher abundances than those sampled during the day. Hydroacoustic data from the EK80 indicated that organisms migrated vertically between day and night. Biomass in the oxygen minimum zone (OMZ) was high. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Universidade Técnica do Atlântico, Cabo Verde in partial fulfillment of the requirements for the Master of Science Degree in Climate Change and Marine Science

A regional Taxonomic Analysis of Commercial Fishes in Cabo Verde based on Genetic Data: A Case Study on the Haemulidae Family

2023-01-01T00:00:00Z

Title: A regional Taxonomic Analysis of Commercial Fishes in Cabo Verde based on Genetic Data: A Case Study on the Haemulidae Family Authors: Dias Dos Santos, Sarah Sofia Abstract: Haemulidae is one of the fish families that has given confusion regarding to its taxonomy and geographical distribution. In Cabo Verde, the species are widely caught for consumption, and it is therefore imperative to clarify the species that have a distribution in the archipelago, as well as to make the phylogenetic relationship between the species that are part of the same family. So, the main objective of this study was to evaluate the relationship between species of Haemulidae based on morphological data and genetic diversity, using a standard mtDNA genetic marker. To do this, specimens were collected for morphological analysis, and 35 tissue samples from Cabo Verde were sequenced. In total, 75 DNA sequences come from both published and unpublished sources. The morphological data and the tissues collected showed the existence of four (4) species in Cape Verde: Pomadasys incisus, Parapristipoma humile, Pomadasys jubelini, and Parapristipoma macrops, which were confirmed by DNA barcoding. The maximum likelihood value among Haemulidae species was moderate, and intraspecific distances ranged from 0.005 to 0.301, helping to confirm the 4 species. The species P. incisus demonstrated absolute monophyly, confirming its distinct status. While P. jubelini was monophyletic, it was grouped with Pomadasys perotaei and Pomadasys rogerii. On the other hand, Brachydeuterus auritus proved to be a monophyletic species. There was a complete separation of P. humile, but in this same clade, a species of P. rogerii appeared, indicating a potential taxonomic error. The P. macrops specimens display a separation within the P. humile branch, revealing close genetic proximity. In P. rogerii population structure, minimal genetic variation was noted and P. macrops and P. humile displayed low genetic distance, evident in a sparse mutational-step haplotype network. Conversely, P. incisus samples exhibited notable Cabo Verde genetic variance compared to Mediterranean and South Atlantic counterparts. This revealed two distinct groups: an exclusive Cabo Verde group and another including haplotypes from different regions. This study highlights the fusion of morphology and genetics to better identify the species of the Haemulidae family. Genetic validation of Cape Verdean species helps resource management. The research contributes new knowledge, forming a basis for future molecular and taxonomic studies, and serving as reference data for DNA barcodes. Description: A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Universidade Técnica do Atlântico, Cabo Verde in partial fulfillment of the requirements for the Master of Science Degree in Climate Change and Marine Science