Isoscape

An isoscape is a map of isotope distributions. It is a spatially explicit prediction of elemental isotope ratios (δ) that is produced by executing process-level models of elemental isotope fractionation or distribution in a geographic information system (GIS).

The word isoscape is derived from isotope landscape and was first coined by Jason B. West.^[1][2]

Isoscapes of hydrogen, carbon, oxygen, nitrogen, strontium and sulfur^[3] have been used to answer scientific or forensic questions regarding the sources, partitioning, or provenance of natural and synthetic materials or organisms via their isotopic signatures. These include questions about Earth's element cycles, human water use, climate, archaeological reconstructions, forensic science, pollution, organismal migration patterns and food 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.

Marine Isoscapes

Carbon Isoscapes^[12][7]

Marine carbon isoscape based on carbon isotope ratios in phytoplankton^[13]

Scientists are able to map carbon isotope ratios (δ¹³C) due to the predictable sorting of two stable isotopes of carbon: ¹³C and ¹²C. This sorting is known as isotope fractionation. In the ocean, δ¹³C changes due to many environmental factors including water temperature, upwelling of deep ocean water, diffusion of CO₂ from the air into the ocean and the burning of fossil fuels. Carbon fixation by primary producers also greatly influences δ¹³C at the oceans surface. Different groups of primary producers such as phytoplankton and macroalgae have different strategies for fixing carbon during photosynthesis and can further alter δ¹³C. As a result carbon isoscapes in the ocean largely reflect global patterns of temperature and primary production.

Since δ¹³C is influenced by so many factors, isoscapes are powerful for visualizing spatial or temporal patterns and provide baseline context for applications of stable isotope analysis in marine systems. Carbon isoscapes can be used in conjunction with stable isotope analysis of marine consumers or apex predators to determine the relative contributions of different primary producers to a food web or infer migration patterns of a consumer between isotopically distinct locations.

Nitrogen Isoscapes ^[11][7]

Marine nitrogen cycle

Like carbon, scientists are able to map nitrogen isotope ratios (δ¹⁵N) due to the fractionation of two stable isotopes of nitrogen: ¹⁴N and ¹⁵N. Marine nitrogen is sourced from diffusion of N₂ from the air into the ocean, freshwater run-off from continents including fertilizers and other land-based nutrients, and nitrogen fixation by primary producers like cyanobacteria which can all influence the baseline δ¹⁵N of the ocean in a given area. From there, nitrogen fractionation is mainly controlled through biological processes that utilize nitrogen, further detailed in the marine nitrogen cycle. For example the process of denitrification and the use of NH4+ (ammonia), NO2-, and NO3- (nitrate) by marine organisms alters the δ¹⁵N in the water. As a result, δ¹⁵N patterns in the ocean reflect areas where nitrogen is being heavily altered through denitrification or by organismal use within a food web. It is important to note that seasonality influencing primary productivity also plays a role in δ¹⁵N patterns at certain times of the year. For an example of marine nitrogen isoscape... ^[11].

Due to the large role of biological reactions on the fractionation of nitrogen, δ¹⁵N isoscapes provide valuable information for stable isotope analysis in marine ecology. Nitrogen isoscapes provide spatial and temporal δ¹⁵N baselines that can be used to inform food web studies. Due to the alteration of nitrogen as it is passed up the food chain, stable isotope analysis of marine consumers can be paired with δ¹⁵N isoscapes to place a consumer at a trophic level within a food web.

See also

• Isotopic signature
• Isotope analysis
• Isotope geochemistry
• Stable isotope composition of amino acids