Antarctic marine ecosystems are spatially and temporally dynamic. Regional climate change is significantly altering the patterns and magnitudes of this dynamism with cascading impacts on biogeochemistry, productivity, and food web architecture. Isoscapes (or isotopic maps) provide a valuable analytical framework to characterize ecosystem processes and address questions about trophic dynamics, animal movement, and elemental cycling. Applications of stable isotope methods to Antarctic ecosystems are currently limited by a paucity of information on geospatial isotope characteristics within the Southern Ocean. In response, we have created the first empirically derived zooplankton isoscapes for West Antarctica based on analysis of bulk nitrogen (N) and carbon (C) isotope values (δ 15 N and δ 13 C, respectively) in 94 zooplankton specimens from the Drake Passage, West Antarctic Peninsula (WAP), and Amundsen and Ross Seas. The zooplankton δ 15 N values increased by 3 ‰ from north of the Polar Front (3.3 ± 0.6 ‰) to the Ross Sea (6.2 ± 0.8 ‰), reflecting a productivity gradient across this region. Abundant open water polynyas in the Amundsen and Ross Seas exhibit strong nitrate drawdown, resulting in more 15 N-enriched phytoplankton and zooplankton relative to those from the generally less productive WAP and Drake Passage. Zooplankton δ 13 C values decreased by 3 ‰ from north of the Polar Front (-24.2 ± 0.9 ‰) to the Ross Sea (-27.5 ± 1.6 ‰), likely driven by decreasing sea surface temperatures with increasing latitude. Our isoscapes are a valuable first step in establishing isotopic spatial patterns in West Antarctica and are critical for addressing numerous ecosystem questions.

Persistent organic pollutants (POPs), contaminants that may bioaccumulate in upper trophic level organisms, were detected in the milk of a top predator, the Antarctic fur seal (Arctocephalus gazella). Multiparous females had significantly lower concentrations of certain POPs (trans-nonachlor, p,p'-DDE, and several PCBs) in their milk than primiparous females, likely due to the annual lactational transfer of the POP burden from mother to pup. Furthermore, there were significant interannual differences in POP concentrations in multiparous females' milk from five breeding seasons between 2000 and 2011. Decreasing trends in concentrations of certain POPs over the recent decade coincide with declining global emissions, yet atmospheric concentrations in the Antarctic are not always consistent with global trends, suggesting that additional factors may contribute to temporal trends of POPs in fur seals. Climate shifts and corresponding availability of krill over the past decade were not consistent with trends observed in POP concentrations in fur seal milk, suggesting that climate may not be a key factor. Additional mechanisms, such as variability in the geographic ranges of individual seals during overwintering migrations are discussed and should be explored further.

Decalcification is not needed to measure bulk isotope values in dentin from this modern odontocete, probably because the lipid and carbonate concentrations are low and the carbon isotope values of dentin protein and carbonate are similar. This method should not be applied in some cases (e.g., with fossil dentin and modern bone). Decalcification should still be used prior to CSIA since significant matrix issues occur with raw dentin processing and decalcification does not alter the amino acid molar composition or isotopic values of dentin.

Ross seals Ommatophoca rossii are one of the least studied marine mammals, with little known about their foraging ecology. Research to date using bulk stable isotope analysis suggests that Ross seals have a trophic position intermediate between that of Weddell Leptonychotes weddellii and crabeater Lobodon carcinophaga seals. However, consumer bulk stable isotope values not only reflect trophic dynamics, but also variations in baseline isotope values, which can be substantial. We used compound-specific isotope analysis of amino acids (CSI-AA) to separate isotopic effects of a shifting base line versus trophic structure on the foraging ecology of these ecologically important Antarctic pinnipeds. We found that Ross seals forage in an open ocean food web, while crabeater and Weddell seals forage within similar food webs closer to shore. However, isotopic evidence suggests that crab eater seals are likely following sea ice, while Weddell seals target productive areas of the continental shelf of West Antarctica. Our CSI-AA data indicate that Ross seals have a high trophic position equivalent to that of Weddell seals, contrary to prior conclusions from nitrogen isotope results on bulk tissues. CSI-AA indicates that crabeater seals are at a trophic position lower than that of Ross and Weddell seals, consistent Weddell seal female and her pup in McMurdo Sound, Antarctica. Photo: Daniel P. Costa with a krill-dominated diet. Our results redefine the view of the trophic dynamics and foraging ecology of the Ross seal, and also highlight the importance of quantifying base line isotope variations in foraging studies.

Polybrominated diphenyl ethers (PBDEs) are “emerged” contaminants that were produced and used as flame retardants in numerous consumer and industrial applications for decades until banned. They remain ubiquitously present in the environment today. Here, a unique set of >200 biotic samples from the Antarctic was analyzed for PBDEs, including phytoplankton, krill, fish, and fur seal milk, spanning several sampling seasons over 14 years. PBDE-47 and -99 were the dominant congeners determined in all samples, constituting >60% of total PBDEs. A temporal trend was observed for ∑7PBDE concentrations in fur seal milk, where concentrations significantly increased (R2 = 0.57, p < 0.05) over time (2000–2014). Results for krill and phytoplankton also suggested increasing PBDE concentrations over time. Trends of PBDEs in fur seal milk of individual seals sampled 1 or more years apart showed no clear temporal trends. Overall, there was no indication of PBDEs decreasing in Antarctic biota yet, whereas numerous studies have reported decreasing trends in the northern hemisphere. Similar PBDE concentrations in perinatal versus nonperinatal milk implied the importance of local PBDE sources for bioaccumulation. These results indicate the need for continued assessment of contaminant trends, such as PBDEs, and their replacements, in Antarctica.