Diagnostic ratios and compound-specific isotopic analysis (CSIA) are two tools that can help identify and differentiate the petrogenic and biogenic sources of hydrocarbons found in environmental samples. The present study aims to evaluate the concentration and type of n-alkanes and isoprenoids found in the oligotrophic waters of the Gulf of Mexico (n = 14), and through the typical diagnostic ratios reported for n-alkanes and its carbon isotopic composition (δ¹³C) to establish and differentiate the possible source of the hydrocarbons. Additionally, crude oil samples (n = 10) extracted in the Gulf of Mexico were evaluated by CSIA as a possible source of hydrocarbons to the study area. We found that the CSIA of δ¹³C for n-alkanes (n-C₁₁ to n-C₃₀) and isoprenoids (pristane and phytane) found in the surface water samples varied from − 25.55 to − 37.59‰ and from − 23.78 to − 33.97‰ in the crude oil samples, values which are more related to petrogenic sources. An analysis of the δ¹³C for pristane vs. phytane suggests that only three surface water samples show an origin in common that those observed in crude oils of the Gulf of Mexico. A low incidence of odd- and even-numbered n-alkanes higher than n-C₂₅ in the water samples indicate low to negligible presence of terrigenous sources into the area, which was supported by the carbon isotopic composition of the individual n-alkanes.

诊断比率和特定化合物同位素分析 (CSIA) 是两种工具，可以帮助识别和区分环境样品中发现的碳氢化合物的岩石和生物来源。本研究旨在评估在墨西哥湾贫营养水域 ( n  = 14) 中发现的正构烷烃和类异戊二烯的浓度和类型，并通过报告的正构烷烃及其碳同位素组成 (δ ¹³ C) 建立和区分碳氢化合物的可能来源。此外，原油样品 ( n = 10) CSIA 评估了在墨西哥湾提取的碳氢化合物可能是研究区域的碳氢化合物来源。我们发现地表水样品中发现的正构烷烃（n -C ₁₁至n -C ₃₀）和类异戊二烯（原始烷烃和植烷）的 δ ¹³ C的 CSIA变化范围为 - 25.55 至 - 37.59‰和 - 23.78 至-C ₃₀ − 原油样品中的 33.97‰，与岩源相关的数值。对原始烷烃与植烷烃的 δ ¹³ C分析表明，只有三个地表水样品显示出与在墨西哥湾原油中观察到的样品相同的来源。奇数和偶数正构烷烃的发生率低于水样中的n -C ₂₅表明进入该地区的陆源来源很少甚至可以忽略，这得到了单个正烷烃的碳同位素组成的支持。