Isotope cross-plots organized by site years (color scale) since the DWH oil spill. Panel a presents the data from the Reference site (AT-357). The isotope space occupied by the data is fit with a grey polygon which is carried into panels b and c. Panel b presents the data from the Seep site (GC-600). Note the displacement to the lower left field in the graph which occurred in late 2012 (2–3 years after the spill). Panel c presents the data from the DWH site (OC-26). Following the oil spill, values were displaced to the lower left field but had returned to background values by July 2013 (3 years after the spill). DOI: https://doi.org/10.1525/elementa.298.f4