Anisoscape is a map of isotope distributions. It is a spatially explicit prediction of elementalisotope ratios (δ) that is produced by executing process-levelmodels of elementalisotope fractionation or distribution in ageographic information system (GIS).
The word isoscape is derived fromisotope landscape and was first coined by Jason B. West.[1][2]
Isoscapes ofhydrogen,carbon,oxygen,nitrogen,strontium andsulfur[3] have been used to answer scientific or forensic questions regarding the sources, partitioning, or provenance of natural and synthetic materials or organisms via theirisotopic signatures. These include questions about Earth'selement cycles,human water use,climate,archaeological reconstructions,forensic science,pollution, organismalmigration patterns andfood web dynamics. Isoscapes of hydrogen and oxygen isotopes, modeling precipitation,[4][5] surface water,[6][7] groundwater,[8][9] and tap water[10] have been developed to better understand the water cycle at regional to global scales. Isoscapes of carbon and nitrogen isotopes have also been developed terrestrially and oceanographically[11][12] to help understand ecosystem dynamics.
Scientists are able to map carbon isotope ratios (δ13C) due to the predictable sorting of twostable isotopes ofcarbon:13C and12C. This sorting is known asisotope fractionation. In the ocean,δ13C changes due to many environmental factors including water temperature, upwelling of deep ocean water,diffusion ofCO₂ from the air into the ocean and the burning of fossil fuels. Carbon fixation byprimary producers also greatly influencesδ13C at the oceans surface. Different groups of primary producers such asphytoplankton andmacroalgae have different strategies for fixing carbon duringphotosynthesis and can further alterδ13C. As a result carbon isoscapes in the ocean largely reflect global patterns of temperature andprimary production.
Sinceδ13C is influenced by so many factors, isoscapes are powerful for visualizing spatial or temporal patterns and provide baseline context for applications ofstable isotope analysis in marine systems. Carbon isoscapes can be used in conjunction with stable isotope analysis of marineconsumers orapex predators to determine the relative contributions of different primary producers to afood web or infermigration patterns of a consumer between isotopically distinct locations.
Like carbon, scientists are able to map nitrogen isotope ratios (δ15N) due to thefractionation of two stable isotopes ofnitrogen:14N and15N. Marine nitrogen is sourced fromdiffusion ofN₂ from the air into the ocean, freshwater run-off from continents including fertilizers and other land-based nutrients, and nitrogen fixation by primary producers likecyanobacteria which can all influence the baselineδ15N of the ocean in a given area. From there, nitrogenfractionation is mainly controlled throughbiological processes that utilize nitrogen, further detailed in themarine nitrogen cycle. For example the process ofdenitrification and the use of NH4+ (ammonia), NO2-, and NO3- (nitrate) by marine organisms alters theδ15N in the water. As a result,δ15N patterns in the ocean reflect areas where nitrogen is being heavily altered throughdenitrification or by organismal use within afood web. It is important to note that seasonality influencingprimary productivity also plays a role inδ15N patterns at certain times of the year. For an example of marine nitrogen isoscape....[11]
Due to the large role of biological reactions on thefractionation of nitrogen,δ15N isoscapes provide valuable information forstable isotope analysis in marineecology. Nitrogen isoscapes provide spatial and temporalδ15N baselines that can be used to inform food web studies. Due to the alteration of nitrogen as it is passed up thefood chain,stable isotope analysis of marineconsumers can be paired withδ15N isoscapes to place a consumer at atrophic level within afood web.