Alkenones as a temperature proxy in fin whale (Balaenoptera physalus) tissues

Abstract

Alkenones are a group of extremely resilient molecules produced by cosmopolitan haptophyte organisms. The unsaturation index (U k 0 37) of di-vs. tri-unsaturated C 37 alkenones (C 37:2 Á(C 37:2 + C 37:3) −1) can be used to estimate the temperature of the water in which the alkenone-producing organisms grew. Alkenones have been widely used in paleoceanography, but they have received little attention in other fields. In this study, a method to detect alkenones in fin whale (Balaenoptera physalus) tissues is developed to adapt this technique to the marine ecology field. Five replicas of five tissues (stomach content, external blubber, internal blubber, muscle, and liver) were analyzed using gas chromatography coupled to mass spectrometry. Alkenones were present in both blubber tissues (66 ± 57 ng g −1 in external blubber and 145 ± 89 ng g −1 in internal blubber), and in the stomach content (3126 ± 2643 ng g −1). The calculated U k 0 37 index was very similar in the three tissues: 0.54 ± 0.03 in the external blubber, 0.55 ± 0.08 in the internal blubber, and 0.71 ± 0.06 in the stomach content. These indexes are equivalent to a sea surface temperature estimates of 17.79 ± 0.68 C in the external blubber, 17.84 ± 1.84 C in the internal blubber, and 21.07 ± 1.23 C in the stomach content, which are very similar to the expected temperature for the region. The results of the current study indicate that alkenones biodilute in the trophic web, which could hinder the analyses of alkenones in species with a high trophic level. However, it is shown that alkenones can be detected in fin whale tissues and can be used to approximate the environmental water temperature where these animals feed.