Offshore oil and gas exploration and extraction have the potential to introduce harmful materials into marine food webs. These pollutants are typically associated with sediments; thus, benthic communities are most likely to be impacted. Trace element analysis is an effective tool for determining the presence of these materials in the marine environment. Pacific walruses (Odobenus rosmarus divergens) are benthic foragers, consuming a wide variety of prey items across broad areas of the seafloor. For this reason, walruses are considered a sentinel species for benthic communities. Walrus teeth grow continually and incorporate trace elements in concentrations proportional to those in the body of the walrus. These teeth can thus act as archives of element exposure, recording trace element concentrations experienced by walruses as they forage in benthic systems across the Alaskan Arctic. This study measured concentrations of 15 trace elements in the teeth of 99 female Pacific walruses collected between 1933 and 2016. Teeth were sectioned, and laser ablation inductively coupled plasma mass spectrometry (ICPMS) was used to measure element concentrations in a transect across the tooth cementum, thereby reconstructing a lifetime history of element concentrations experienced by each walrus. The objectives of this study were (1) to quantify the variability of 14 trace elements (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Mo, Ag, Cd, Ba, Pb) in teeth of female walruses, (2) to assess changes in 11 elements commonly associated with oil and gas activities (V, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Ba, Pb) during different phases of petroleum exploration and extraction in the Alaskan Arctic, and (3) to analyze longitudinal changes in trace element concentrations in the teeth of individual female walruses to identify lifetime trends in trace element exposure. Overall, most trace elements typically associated with oil and gas exploration and extraction did not change during the study period. In some cases, concentrations of these elements were lowest during the decades coinciding with the most intense petroleum-related activities (1970s–1980s, 1990s). The element concentrations presented here can, therefore, be treated as baseline values for future studies, with the exception of vanadium, arsenic, and iron, which changed substantially within the study period. Some elements showed consistent patterns within the teeth of individual walruses. Manganese, zinc, and lead tended to increase across a walrus’ life, whereas copper, strontium, and barium typically declined. Zinc and lead were strongly correlated with one another and with the microstructure of the tooth, exhibiting peak concentrations in the dark layers of the cementum and minima in the light layers. These elements also tended to reach an inflection midway through the life of the animal, after which their rates of accumulation increased substantially. Given the importance of zinc to reproduction and the timing of these inflection points (median = 5 years), we developed a working hypothesis that this change in uptake represents attainment of reproductive maturity. Examinations of changes in this parameter across the study period matched well with known fluctuations in the size of the walrus population, lending support to this hypothesis. This technique has the potential to become a valuable tool for managers to track the status of the Pacific walrus population.

USD: $25,000

2017-10-01 → 2018-09-30