The buoyancy flux Bo at the air/sea interface is very useful to understand the variability of the stratification of the mixed layer, the oceanic mixing, the phytoplankton dynamics and then the coastal upwelling. The atmospheric reanalysis ERA5 and the oceanic reanalysis ORAP5 data have been used in this study to describe the sea surface Bo and, its influence on the variability of the mixing in the mixed layer and consequently on the coastal upwelling along the northern coast of the Gulf of Guinea. The Bo is negative along the coast and, is characterized by a seasonal variability dominated by the thermal buoyancy flux. This study has also shown that the mixing layer is very shallow along the coast and deeper offshore. The negative value of the Bo increases the stratification of the mixed layer and reduces the mixing. This could explain why the mixed layer is shallow in this region. This work suggests that an increasing trend of the global warming could have dramatic impact in this area by increasing the stratification in the mixed layer and would contribute to reducing the coastal upwelling intensity.
Toualy, E., Stanojevic, G., Kouadio, K.Y. and Aman, A. (2012) Multi-Decadal Variability of Sea Surface Temperature in the Northern Coast of Gulf of Guinea. Asian Journal of Applied Sciences, 5, 552-562. https://doi.org/10.3923/ajaps.2012.552.562
Caniaux, G., Giordani, H., Redelsperger, J-L., Guichard, F., Key, E. and Wade, M. (2011) Coupling between the Atlantic Cold Tongue and the West African Monsoon in Boreal Spring and Summer. Journal of Geophysical Research-Oceans, 116, Article ID: C040037. https://doi.org/10.1029/2010JC006570
Weingartner, T.J. and Weisberg, R.B. (1991) On the Annual Cycle of Equatorial Upwelling in the Central Atlantic Ocean. Journal of Physical Oceanography, 21, 68-82. https://doi.org/10.1175/1520-0485(1991)021 2.0.CO;2
Bakun, A. (1978) Guinea Current Upwelling. Nature, 271, 147-150. https://doi.org/10.1038/271147a0
Djakouré, S., Penven, P., Bourlès, B., Koné, V. and Veitch, J. (2017) Respective Role of the Guinea Current and Local Winds on the Coastal Upwelling in the Northern Gulf of Guinea. Journal of Physical Oceanography, 47, 1367-1387. https://doi.org/10.1175/JPO-D-16-0126.1.
Hardman-Mountford, N.J. and McGlade, J.M. (2003) Seasonal and Interannual Variability of Oceanographic Processes in the Gulf of Guinea: An Investigation Using AVHRR Sea Surface Temperature Data. International Journal of Remote Sensing, 24, 3247-3268. https://doi.org/10.1080/0143116021000021297
Pople, W. and Mensah, M. (1971) Evaporation as the Upwelling Mechanism in Ghanaian Coastal Waters. Nature Physical Science, 234, 18-20. https://doi.org/10.1038/physci234018a0
Scherena, P.A.G.M., Kroezeb, C., Janssena, F.J.J.G., Hordijkc, L. and Ptasinskia, K.J. (2004) Integrated Water Pollution Assessment of the Ebrié Lagoon, Ivory Coast, West Africa. Journal of Marine Systems, 44, 1-17. https://doi.org/10.1016/j.jmarsys.2003.08.002
Ali, K.E., Kouadio, K.E., Zahiri, E.P., Aman, A., Assamoi, A.P. and Bourlès, B. (2011) Influence of the Gulf of Guinea Coastal and Equatorial Upwellings on the Precipitation along Its Northern Coasts during the Boreal Summer Period. Asian Journal of Applied Sciences, 4, 271-285. https://doi.org/10.3923/ajaps.2011.271.285
Aman, A., Toualy, E. and Yoroba, F. (2018) On the Causes of the Minor Dry Season over the Coastal Region of the Northern Gulf of Guinea. Atmospheric and Climate Science, 8, 121-133. https://doi.org/10.4236/acs.2018.82009
Geng, B., Xiu, P., Shu, C., Zhang, W.-Z., Chai, F., Li, S. and Wang, D. (2019) Evaluating the Roles of Wind- and Buoyancy Flux-Induced Mixing on Phytoplankton Dynamics in the Northern and Central South China Sea. Journal of Geophysical Research: Oceans, 124, 680-702. https://doi.org/10.1029/2018JC014170
Picaut, J. (1983) Propagation of the Seasonal Upwelling in the Eastern Equatorial Atlantic. Journal of Physical Oceanography, 13, 18-37. https://doi.org/10.1175/1520-0485(1983)013 2.0.CO;2
Jouanno, J., Marin, F., du Penhoat, Y., Molines, J.M. and Sheinbaum, J. (2011) The Seasonal Modes of Surface Cooling in the Gulf of Guinea. Journal of Physical Oceanography, 41, 1408-1416. https://doi.org/10.1175/JPO-D-11-031.1
N’Guessan, B.K., Kouassi, A.M., Trokourey, A., Toualy, E., Kanga, D.K. and Brehmer, P. (2020) Eastern Tropical Atlantic Mixed Layer Depth: Assessment of Methods from in Situ Profiles in the Gulf of Guinea from Coastal to High Sea. Thalassas: An International Journal of Marine Sciences, 36, 201-212. https://doi.org/10.1007/s41208-019-00179-7
Karstensen, J. and Lorbacher, K. (2011) A Practical Indicator for Surface Ocean Heat and Freshwater Buoyancy Fluxes and Its Application to the NCEP Reanalysis Data. Tellus A, 63, 338-347. https://doi.org/10.1111/j.1600-0870.2011.00510.x
Zhang, H.M. and Talley, L.D. (1998) Heat and Buoyancy Budgets and Mixing Rates in the Upper Thermocline of the Indian and Global Oceans. Journal of Physical Oceanography, 28, 1961-1978. https://doi.org/10.1175/1520-0485(1998)028 2.0.CO;2
MacIntyre, S., Jonsson, A., Jansson, M., Aberg, J., Turney, D.E. and Miller, S.D. (2010) Buoyancy Flux, Turbulence, and the Gas Transfer Coefficient in a Stratified Lake. Geophysical Research Letters, 37, L24604. https://doi.org/10.1029/2010GL044164
Cronin, M.F. and Sprintall, J. (2001) Wind and Buoyancy-Forced Upper Ocean. In: Steele, J.H., Ed., Elements of Physical Oceanography, Academic Press, Cambridge, 3217-3224. https://doi.org/10.1006/rwos.2001.0157
Gill, A.E. (1982) Atmosphere-Ocean Dynamics. International Geophysics Series, Academic Press, New York.
Anitha, G., Ravichandran, M. and Sayanna, R. (2008) Surface Buoyancy Flux in Bay of Bengal and Arabian Sea. Annales Geophysicae, 26, 395-400. https://doi.org/10.5194/angeo-26-395-2008
Large, W.G. and George Nurser, A.J. (2001) Chapter Ocean Surface Water Mass Transformation. International Geophysics Series, 77, 317-336. https://doi.org/10.1016/S0074-6142(01)80126-1
Fairbanks, R. (1989) A 17,000-Year Glacio-Eustatic Sea Level Record: Influence of Glacial Melting Rates on the Younger Dryas Event and Deep Ocean Circulation. Nature, 342, 637-642. https://doi.org/10.1038/342637a0
Vellinga, M. and Wood, R.A. (2002) Global Climatic Impacts of a Collapse of the Atlantic Thermohaline Circulation. Climate Change, 54, 251-267. https://doi.org/10.1023/A:1016168827653
Zuo, H., Balmaseda, M.A. and Mogensen, K. (2017) The New Eddy-Permitting ORAP5 Ocean Reanalysis: Description, Evaluation and Uncertainties in Climate Signals. Climate Dynamics, 49, 791-811. https://doi.org/10.1007/s00382-015-2675-1
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz-Sabater, J., et al. (2020) The ERA5 Global Reanalysis. Quarterly Journal of the Royal Meteorological Society, 146, 1999-2049. https://doi.org/10.1002/qj.3803
Madec, G. (2008) NEMO Ocean Engine. Note du Pôle de modélisation, No 27, Institut Pierre-Simon Laplace (IPSL), France.
Large, W.G. and Pond, S. (1981) Open Ocean Momentum Flux Measurements in Moderate to Strong Winds. Journal of Physical Oceanography, 11, 324-336. https://doi.org/10.1175/1520-0485(1981)011 2.0.CO;2
Obukhov, A.M. (1946) Turbulence in an Atmosphere with a Non-Uniform Temperature. Boundary-Layer Meteorology, 2, 7-29. https://doi.org/10.1007/BF00718085