Impacts of climate change in the South Atlantic on the physics, biology and biogeochemistry off the South and Southeastern Brazilian coastal zone
The coastal region off Brazil, from the Abrolhos Bank to the Uruguayan border, is part of the western limits of the South Atlantic Subtropical Gyre and, consequently, impacted by the global ocean circulation. Changes in the large scale ocean circulation resulting from changes in Earth’s climate will certainly have significant impacts on the oceanic region adjacent to the Brazilian shores, affecting the temperature, salinity and heat content in the upper-layer of the ocean. Changes in these physical properties will result in alterations of the local climate, with impacts on the hydrological cycle and on the fluvial discharge regimes along the coastal regions. These regional climate alterations, associated with changes in the Brazil Current dynamics and in the wave and wind regimes, will alter the coastal hydrodynamics and the upwelling systems, with profound impacts on the biological pump and the biogeochemical cycles on the continental shelf.
Studies related to global warming and the consequent retreat of the sea-ice cover (e.g.: Knorr and Lohmann, 2003) suggest that a gradual warming of the Austral Ocean could induce an abrupt intensification of the thermohaline circulation in the Atlantic. This intensification would be triggered by the increase of mass transport into the Atlantic by the “warm rout” (waters from the Indian Ocean) and the “cold route” (waters from the Pacific). More recently, Steigl et al. (2009) confirmed a significant increase in the temperature over the Antarctic continent. It is very likely that this warming would be followed by sea-ice melting and, consequently, by changes in the “cold route” contribution to the Atlantic Meridional Overturning Cell (MOC). In the “warm route”, studies published by Biastoch et al. (2008a,b and 2009) show that the import of waters from the Indian Ocean by means of rings and filaments in the region of retroflection of the Agulhas Current (the “Agulhas Leakage”) has been increasing in the past decades.
These studies show that the additional waters from ice melting and from the Indian Ocean are contributing to the strengthening of the subtropical gyre in the South Atlantic. Alterations in the subtropical gyre have been confirmed by other studies, such as Lumpkin and Garzoli (2011); Curry and Mauritzen (2005); Sato and Polito (2008); Campos (2010).
Considering the strong connection between the environmental conditions in coastal zones and the oceanic and atmospheric large-scale circulations, it is to be expected that an altered South Atlantic will imply in serious impacts on the physics, on the biology and on biogeochemical processes in a great extent of the Brazilian coastal zone, both over the ocean and the continent.
This projects main goal is to identify, understand and monitor changes in the western region of the South Atlantic, resulting from changes in the large-scale ocean and atmospheric circulations, and the consequent impacts on coastal processes and on the regional climate
This investigation will be conducted by means of analysis of available data, including satellite data, the in situ observation of oceanic and atmospheric variables in fixed observational platforms and in regular oceanographic cruises, and by numerical experiments with ocean general circulation models.
The in situ observational part of this project will be conducted primarily in the Santos Bight, in cooperation with the activities being developed in the context of the Ocean sub-project of the National Institute of Science and Technology for Climate Change (INCT-MC). The INCT-MCT-Ocean has as central objective the development of a meteorological-oceanographic buoy to be deployed off Santa Catarina State, near 28°S, 42°W. Taking advantage of the maintenance program of this buoy, which will require one cruise per year, in the present project it is proposed another annual cruise, along a transect between Santos and the location of the buoy. The conduction of a second cruise, in an opposite season, will allow the assessment of seasonal variability, thus contributing to the understanding of how possible climate change are affecting physical, chemical and biological processes in the region.
Parallel to the in situ observational program, data being collected by underway national and international remote sensing programs will be obtained, treated and stored for the development of studies related to possible impacts of climate change on the physics, biology and chemistry of the western South Atlantic.
For the study of possible impacts of changes in climate on physical, chemical and biological processes in the oceanic region adjacent to the Brazilian territory, a hierarchy of models will be adopted, covering scales from global to coastal and estuarine. This work will be performed using the High Performance Computing (HPC) system of the IOUSP’s Ocean Modeling Laboratory (LABMON), as well as the Rede-Clima Super Computer system at INPE. This approach will be divided in three parts: large scale modeling; mesoscale modeling; and coastal and estuarine modeling.
To answer questions on the impacts of climate change on precipitation over the region it is necessary to understand the evolution of the dominant modes of variability of sea surface temperature (SST) over the Pacific and Atlantic Oceans and the coupled interactions with the atmospheric circulation. In the context of numerical modeling, this requires a coupled ocean-atmosphere model able to simulate well enough the modes of variability of SST in both oceanic regions. The MICOM speedy model, successfully used at LABMON with these purpose will be used in the investigation of ocean-atmosphere interaction processes and possible changes of the Brazilian continental climate.
The ocean modeling in large scale will be done with an implementation of the Hybrid Coordinate Ocean Model (HYCOM, Halliwell et al., 1998; Bleck, 2020) for the entire Atlantic and Indian Ocean basins. This model, already in use at LABMON, will be run in dated mode. That is, using as forcing products of the NCEP/Reanalysis since 1948. The main focus of this numerical investigation is to try to identify tendencies in the circulation and other physical properties in the upper layers of the South Atlantic, and look for correlations with already detected changes in the atmosphere.
Two numerical models will be used in the regional studies: HYCOm and ROMS (Regional Ocean Modeling System). The strategy to be followed will be based on experiences already in course at LABMON, in which regional high-resolution implementations are nested into the larger scale model. This is done in such a way that the physics of the larger domain is transferred to the smaller, with a higher spatial resolution.
On the coastal the shelf, coastal and estuarine zones, it will be used implementations of different numerical modeling platforms, which include the ROMS and COHERENS (Luyten et al., 1999). This last one is also already being used at LABMON, in cooperation with its developer, P. Luyten, of the Management Unit of North Sea Mathematical Models (MUMM), in Belgium. In addition to ROMS and COHERENS, it will also be used physical-biological Individual Based Models (IBMs), wave models and biogeochemical models.
Besides the strengthening of the cooperation and synergism amongst several participants, the activities of this sub-project will yield four important products: (i) original time series of the meteo-oceanographic variables in a region highly susceptible to the effects of global warming; (ii) the systematization of a hierarchy of numerical models specific for the study of the regional climate; (iii) the establishment of a system to support the prediction of extreme events in the Southwest Atlantic; and (iv) the formation and training of human capacity in very relevant areas of climate science.