Whale teeth as witnesses: assessing anthropogenic impact on whale ecology through a multi-proxy analysis

Whales are critical organisms in the ocean ecosystems, but direct and indirect human impact has decimated their populations. Because whales have long lifespans and migrate over large areas, there is no ecological baseline to evaluate their population dynamics. However, such information is available in fossil whale remains. Geoscientific expertise can aid conservation by interpreting proxy values from the most chemically stable tissue: their teeth. In this project we focus on North Atlantic toothed whales from the late Pleistocene on, with the aim to reconstruct their migrations and ecologies.

Whale teeth contain information about both the individual and its environmental conditions, depending on the proxy that is evaluated. An integrative methodology was developed to be applied on modern and fossil specimens. This includes oxygen isotope analysis to reconstruct migration and bathymetric niches, Sr/Ca and Ba/Ca ratios to assess trophic position and dietary patterns, and Raman spectroscopy for elemental composition and crystallography. Additionally, Scanning Electron Microscopy (SEM) enables growth analysis and measurements of chemical composition through EDX. However, fossil teeth in a marine environment might be altered by diagenesis, making their proxy values unrealistic and not comparable with modern values. By quantifying these changes we can identify and correct for altered proxy values: thus allowing reconstruction of ecologies.

In this initial phase of the project the modern teeth have been analysed using Raman spectroscopy and SEM. Notably, Raman has shown that both the enamel and cementum can be used to produce reliable spectra, while the dentine does not allow this. Chemical composition from the EDX can be assessed over growth layers and correlated with the Raman results. We provide an interdisciplinary framework to assess multiple proxies found in fossil and modern teeth, using geochemical methods to answer biological questions. In addition, we utilize physiological data obtained from stranded individuals whose teeth were sampled, along with historical records of whale populations. There is a large emphasis on anthropogenic impact, by evaluating specimens along a timeline for impact of fishing, whaling, climate change and pollution.