International Journal of Marine Science, 2024, Vol.14, No.3, 182-192 http://www.aquapublisher.com/index.php/ijms 183 2 Mechanisms of Coastal Circulation 2.1 Wind-driven circulation Wind-driven circulation is a critical component of coastal dynamics, particularly in upwelling systems. Climate change has intensified wind patterns in several major upwelling regions, such as the California, Humboldt, and Benguela systems, leading to increased upwelling of nutrient-rich waters. This intensification is attributed to the growing temperature and pressure differences between land and sea, which enhance alongshore winds (Sydeman et al., 2014; Arellano and Rivas, 2019). The Bakun hypothesis posits that increasing greenhouse gas concentrations will further intensify these winds, a trend supported by recent meta-analyses (Sydeman et al., 2014). This intensification can significantly impact marine productivity and biodiversity in these regions. 2.2 Tidal circulation Tidal forces play a significant role in coastal circulation by generating periodic currents that can influence sediment transport, nutrient mixing, and overall water movement. While the provided data does not directly address tidal circulation, it is important to note that tidal dynamics can interact with other mechanisms, such as wind-driven and thermohaline circulation, to shape coastal environments. 2.3 Thermohaline circulation Thermohaline circulation, driven by differences in water density due to temperature and salinity variations, is a major driver of global ocean circulation. Climate change can alter thermohaline circulation patterns, leading to significant impacts on coastal regions. For instance, the warming of the tropical Atlantic Ocean and the associated slowdown of thermohaline circulation during the last deglaciation highlight the sensitivity of this mechanism to climate shifts. Additionally, the potential for abrupt climate changes due to thermohaline circulation instability has been well-documented, with implications for both regional and global climate systems (Clark et al., 2002; Guemas and Salas-Mélia, 2008). Coastal topography can also dampen internal oscillations of thermohaline circulation, further influencing its behavior. 2.4 Influence of coastal topography Coastal topography significantly affects circulation patterns by modifying the flow of water and the distribution of currents. The damping effect of bottom topography on internal decadal-scale oscillations of thermohaline circulation is one example of how physical features can influence ocean dynamics. Coastal topography can also enhance or inhibit upwelling processes, depending on the interaction with wind and current patterns (Ou, 2017). For instance, the generation of barotropic flow in response to topographic features can aid in the adjustment of baroclinic currents, thereby influencing overall circulation. In summary, the mechanisms of coastal circulation are complex and interdependent, with each responding to climate change in unique ways. Understanding these interactions is crucial for predicting future changes in coastal environments and their broader ecological and climatic impacts. 3 Coastal Circulation Models 3.1 Overview of circulation models Coastal circulation models are essential tools for understanding the complex dynamics of coastal environments. These models simulate the movement of water and its interaction with various physical, chemical, and biological processes. They are crucial for predicting the impacts of climate change on coastal regions, including sea level rise, changes in wave patterns, and alterations in sediment transport. Coastal circulation models can be broadly categorized into three types: empirical models, analytical models, and numerical models. Each type has its strengths and limitations, and the choice of model depends on the specific research question and the available data (Marshall et al., 2015). 3.2 Numerical modeling techniques Numerical modeling techniques are crucial for the development and refinement of coastal circulation models. These techniques involve solving mathematical equations that describe fluid dynamics, heat transfer, and other relevant processes. Advanced methods, such as the Kalman filter and the adjoint method, are used to assimilate observational data into models, thereby improving their accuracy and predictive capabilities.
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