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oai:figshare.com:article/33979396 2026-09-24T04:31:39Z category_62 portal_316 item_type_3 month_year_09_2026

Table 1_Atmospheric and oceanic controls of coastal upwelling in the northern Gulf of Guinea: insights from Keta, Ghana.docx Emmanuel Gyimah Annor (25101844) Cyril Dziedzorm Boateng (25101847) Jeffrey Nii Armah Aryee (25101850) Leonard Kofitse Amekudzi (23391874) Marine Biology coastal upwelling Ekman transport geostrophic circulation GLORYS12V1 Gulf of Guinea interannual variability Keta sector multivariate EOF Introduction<p>Coastal upwelling along the northern Gulf of Guinea sustains fisheries and regulates tropical Atlantic sea-surface temperature, yet the combined roles of atmospheric and oceanic forcing remain incompletely characterized. This study quantifies the joint interaction between wind-driven Ekman transport and geostrophic circulation along the Ghana-Togo shelf, focusing on the Keta sector (0.5° E–1.5° E, 5.5° N–6.0° N) using deseasonalized monthly anomalies (2010–2022).</p>Methods<p>Two indices are derived: the Ekman Coastal Upwelling Index (ECUI), from wind stress rotated to a 20° coastline angle, and the Geostrophic Coastal Upwelling Index (GCUI), diagnosed directly from sea-surface height (SSH) gradients via geostrophic balance. These are integrated with GLORYS12V1 sea-surface temperature (SST) and SSH, utilizing Bretherton-corrected lagged correlations and multivariate empirical orthogonal function (mEOF) analysis.</p>Results<p>Lagged correlations, computed with variable-specific effective degrees of freedom, demonstrate that atmospheric forcing (ECUI) initiates immediate surface cooling (r = 0.47, lag 0, Neff = 126) and sustains a significant response through lags +1 and +2. GCUI shows no significant relationship with SST at lag 0 (r = -0.01), but exhibits a significant negative correlation at lags -5 and -6 (r = -0.23 and -0.20), indicating SST anomalies precede geostrophic anomalies by roughly half a year—distinct from the concurrent ECUI-SST response. The mEOF analysis identifies a dominant co-variability mode explaining 34.0% of shared interannual variance, well-separated by North's rule and stable under block-bootstrap resampling (congruence = 0.98). Temporal evolution indicates no discrete regime shift; instead, change-point analysis reveals a long-term trend (predominantly in SSH) superimposed on shorter-timescale interannual variability.</p>Discussion<p>The Keta sector combines the domain's strongest diagnosed atmospheric forcing with a spatially consistent geostrophic signal (absent in the western Gulf), identifying it as a particularly favorable dynamical sector for coastal upwelling. Sensitivity analyses confirm these findings are robust to coastline angle (10–30°), drag coefficient, and upwelling length scale variations. Ultimately, this study provides a transferable, robust diagnostic framework for examining joint atmospheric-oceanic upwelling dynamics in tropical coastal systems.</p> 2026-09-24T04:31:39Z Dataset Dataset 10.3389/fmars.2026.1953512.s001 https://figshare.com/articles/dataset/Table_1_Atmospheric_and_oceanic_controls_of_coastal_upwelling_in_the_northern_Gulf_of_Guinea_insights_from_Keta_Ghana_docx/33979396 CC BY 4.0