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Ocean Biological Deserts
Published in Ajai, Rimjhim Bhatnagar, Desertification and Land Degradation, 2022
With the increase in industrialization, urbanization and burning of fossil fuels, the amount of GHG emissions have increased significantly over the years. Between 1900 and 2014, carbon dioxide emission has increased by almost ten times (www.epa.gov). The most prominent increase is after the 1970s. Simulations by General Circulation Model predict that increase in atmospheric carbon dioxide will result in an average global temperature increase by 1.8 to 4.0°C by the end of the 21st century (IPCC 2007). The substantial increase in GHG emissions has resulted in the trapping of more amount of sunlight, the oceans are absorbing more heat, resulting in increased sea surface temperature. A boundary called pycnocline forms between the cooler, saltier water and the warmer, fresher water. Warmer temperatures reduce the rate at which oxygen is exchanged with the top layers of oceanic waters (Meler et al. 2011). Biogeochemistry embedded ocean circulation models predict that oxygen concentration in the oceans will decrease in the coming times as a consequence of global warming. Researchers are reporting that the Ocean deserts are growing, especially as the shallow waters of the gyres are warming and at a pace much faster than global warming models predict. The climate models predict that this trend will continue, potentially threatening marine ecosystems. In fact, global warming exacerbates the occurrence of algal blooms and also favours toxic algal species (Chu et al. 2007).
Chapter 4: Air-Sea Exchange of Pollutants
Published in Gunnar Kullenberg, Pollutant Transfer and Transport in the Sea, 1982
There is a variety of physical processes involved in transferring substances from the atmosphere to the sea and vice versa. Some of these are illustrated in Figure 1. The sea-surface microlayer is essentially the boundary between the atmosphere and the sea water, and plays a vital role in the transfer of substances across the air-sea interface. The processes that occur there are especially important to the upward flux of materials, and were described by Garrett and Smagin33 for air-sea exchange of petroleum hydrocarbons. Some of the processes that convey substances from bulk sea water to the sea surface are examined and reviewed here.
Modelling Procedures
Published in Vanesa Magar, Sediment Transport and Morphodynamics Modelling for Coasts and Shallow Environments, 2020
In some cases, regional coastal models require wind data (specifically, wind shear stresses, either an input or computed within the model from wind speed data) and sea-surface pressure. For models with large domains, the density gradients need to be considered as well, as the main driving forces of ocean currents. The sea-surface temperature is also of relevance, as the air–sea temperature difference will drive the heat fluxes between the ocean and the atmosphere. Finally, precipitation and evaporation are also part of the atmospheric forcing on the surface of the ocean. Generally, the wind stress is proportional to the square of the wind speed, with a drag coefficient being the constant of proportionality. As part of the meteorological forcings, one may consider heat fluxes between the ocean and the atmosphere. Although heat fluxes may also be caused by underwater volcanoes or other geothermal activity at the seafloor, once the basics of ocean–atmosphere heat fluxes are understood, it is relatively easy to define heat fluxes between the Earth’s crust and the ocean. Heat may be considered as a passive tracer being transported by currents and stirred by waves and by turbulence. Usually only the advective heat flux, QADV, is considered. Heat loss or gain takes place at the domain boundaries: at the ocean surface, at the seafloor, at estuaries or rivers, and at the boundaries that are connected with the open ocean. The surface heat flux, QSUR, has four components as follows: sensible heat flux, QSH—heat transport by conductionlatent heat flux QLH—heat transport by evaporation or condensationlong-wave radiation QLW—heat transport by back radiationshort-wave radiation QSW—heat inflow by solar radiation at the sea surface
Variational data assimilation of sea surface height into a regional storm surge model: Benefits and limitations
Published in Journal of Operational Oceanography, 2023
David Byrne, Kevin Horsburgh, Jane Williams
A storm surge is the regional increase in sea level due to passage of a storm and can last from hours to days and span hundreds of square kilometres. In European shelf seas, they can produce sea levels several metres higher than tides alone (Wadey et al. 2015). The primary mechanisms that contribute to the generation of a storm surge (Pugh and Woodworth, 2014) are: The inverse barometer effect increases sea level due to local areas of low air pressure generating converging currents. This is the larger contribution away from the coast.Momentum transfer from strong winds to the sea surface by wind setup drives water against coastal boundaries. This is the dominant mechanism in shallower coastal areas.
Assessment to 2100 of the effects of reef formation on increased wave heights due to intensified tropical cyclones and sea level rise at Ishigaki Island, Okinawa, Japan
Published in Coastal Engineering Journal, 2021
However, the world’s coral reefs are now degraded by global climate change, including elevated sea-surface temperature (SST) and ocean acidification, and by local impacts, including sedimentation, coastal development, and watershed pollution (Burke et al. 2011; Gattuso, Hoegh-Guldberg, and Pörtner 2014). In particular, losses of coral cover cause a decrease in reef bottom roughness and wave dissipation (Sheppard et al. 2005). This indicates that losses of coral cover will increase the risks of coastal damage by intensified TCs by 2100. However, sedimentological and biological studies have shown that corals have kept pace with sea level rise (SLR) at a rate of <10 m/kyr (1 kyr = 1000 years) and reef formation has occurred during the last postglacial period (Montaggioni and Brainthwaite 2009; Woodroffe and Webster 2014). This implies that reef formation may be able to respond to future global SLR by 2100. Therefore, a quantitative study evaluating the effectiveness of coral reefs in the context of intensified TCs, decline of corals, and SLR by 2100 is needed. If future coral reefs are degraded due to various stresses, reef restoration and conservation strategies (e.g. direct coral transplantation) will be considered. For the effective strategies, the target coral species will be also identified.
An assessment of the impact of oceanic initial conditions on the interaction of upper ocean with the tropical cyclones in the Arabian Sea
Published in Journal of Operational Oceanography, 2020
Tanuja Nigam, Kumar Ravi Prakash, Vimlesh Pant
TC intensity found to be governed by the Sea Surface Temperature (SST), atmospheric vertical velocity shear and relative humidity (Gray 1968; DeMaria et al. 2001). The translational speed of TC is another important parameter that decides the duration of thermodynamic interaction between atmosphere and ocean (Jacob et al. 1999). The slow moving storms can cause more sea surface cooling comparative to the fast moving storms (Price 1981; Mei et al. 2012). As compared to the fast moving cyclones, the TCs with lower translational speed found to have stronger baroclinic shear (Price 1981; Sanford et al. 1987; Shay et al. 1992, 1998). TCs with slower translational speed have more time to generate inertial oscillations that can stir the upper-ocean water column. The sea surface cooling caused by the cyclone weakens the Tropical Cyclone Heat Potential (TCHP), a measure of the upper-ocean heat content to sustain the TC. The lowering of TCHP eventually leads to a decrease in the intensity of cyclone (Price 1981; Mei et al. 2012).