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Y. Klanten, R.-M. Couture, K. S. Christoffersen, W. F. Vincent, D. Antoniades. (2023). Oxygen Depletion in Arctic Lakes: Circumpolar Trends, Biogeochemical Processes, and Implications of Climate Change (Vol. 37).
Abstract: Polar amplification of climate change has the potential to cause large-scale shifts in the dissolved oxygen (DO) dynamics of Arctic lakes, with implications for fish survival, greenhouse gas production, and drinking water quality. While DO is also a sentinel of environmental changes of physical, chemical, and biological nature (e.g., ice cover, temperature, dissolved organic carbon, photosynthesis, and respiration), no synthesis exists of current knowledge of DO dynamics across the diverse freshwater systems of the Arctic. We thus conducted a systematic review of the literature that yielded DO data from 167 sites north of the Subarctic limit (based on vegetation zones), spanning 76 years and including 40 sites with time series. The compilation revealed insufficient observations for adequate representativeness of oxygen dynamics over Arctic ecosystem gradients. We described the main processes controlling DO budgets of Arctic lakes and tested relationships of summer oxygen depletion with maximum depth and latitude. The meta-analysis showed that most sites with low O2 concentrations were shallow (<10 m) and situated toward the southern end of the latitudinal gradient. Permanently stratified lakes with deep, perennially anoxic basins were located toward the northern end of the gradient. By way of a conceptual model, we identified the direct and indirect drivers and mechanisms that lead to changes in oxygen budgets in the context of the warming Arctic. This comprehensive update on available data allowed us to suggest future research directions and recommend the use of moored instruments for continuous all-season observations, combined with modeling, remote sensing, and paleo-reconstructions.
Keywords: Arctic lakes biochemical processes climate change dissolved oxygen freshwater meta-analysis
Programme: 1042
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Yves Cherel, Colette Trouvé, Paco Bustamante. (2023). Cephalopod prey of light-mantled sooty albatross Phoebetria palpebrata, resource partitioning amongst Kerguelen albatrosses, and teuthofauna of the southern Indian Ocean (Vol. 198).
Abstract: The cephalopod diet of the light-mantled sooty albatross Phoebetria palpebrata was determined for the first time at the subantarctic Kerguelen Islands by sorting ∼7000 accumulated beaks from 66 regurgitated boluses. Twenty-two taxa were identified, including four dominant squid species that are all endemic to the Southern Ocean: Galiteuthis glacialis (49.8% of the lower beaks) Psychroteuthis glacialis (18.5%), Martialia hyadesi (16.2%) and Moroteuthopsis longimana (6.9%). Beak δ13C values indicated that all adult P. glacialis, almost all juvenile M. longimana, and most adult G. glacialis were caught in Antarctic waters, while albatrosses preyed upon juvenile M. hyadesi in subantarctic waters. Comparative analysis of lower beaks accumulated in food samples of Kerguelen albatrosses showed that the four main sympatric albatross species segregate primarily by species-specific foraging grounds. Light-mantled sooty albatross feed on the Antarctic P. glacialis, wandering albatross Diomedea exulans on subantarctic and subtropical histioteuthids (41.4%), and grey-headed albatross Thalassarche chrysostoma and black-browed albatross T. melanophris on subantarctic ommastrephids (69.3% and 65.7%, respectively), with black-browed albatross also preying upon neritic endemic octopuses (17.6%). Cephalopod prey of Kerguelen albatrosses highlight the abundance and importance of some squids in the functioning of the pelagic ecosystem of the southern Indian Ocean, such as ommastrephids, M. longimana, P. glacialis, Histioteuthis atlantica, H. eltaninae, and G. glacialis. Based on the diet of the light-mantled sooty albatross, P. glacialis appears common in high-Antarctic waters of the southern Indian Ocean, whereas the poorly known Psychroteuthis sp. B (Imber) is evidently present in Antarctic waters south of the Kerguelen Islands.
Keywords: Antarctica Bio-indication Procellariiformes Seabirds Southern Ocean Squids Stable isotopes
Programme: 109
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Zhendong Zhang, Jessica C. E. Irving, Frederik J. Simons, Tariq Alkhalifah. (2023). Seismic evidence for a 1000 km mantle discontinuity under the Pacific (Vol. 14).
Abstract: Seismic discontinuities in the mantle are indicators of its thermo-chemical state and offer clues to its dynamics. Ray-based seismic methods, though limited by the approximations made, have mapped mantle transition zone discontinuities in detail, but have yet to offer definitive conclusions on the presence and nature of mid-mantle discontinuities. Here, we show how to use a wave-equation-based imaging method, reverse-time migration of precursors to surface-reflected seismic body waves, to uncover both mantle transition zone and mid-mantle discontinuities, and interpret their physical nature. We observe a thinned mantle transition zone southeast of Hawaii, and a reduction in impedance contrast around 410 km depth in the same area, suggesting a hotter-than-average mantle in the region. Here, we furthermore reveal a 4000–5000 km-wide reflector in new images of the mid mantle below the central Pacific, at 950–1050 km depth. This deep discontinuity exhibits strong topography and generates reflections with polarity opposite to those originating at the 660 km discontinuity, implying an impedance reversal near 1000 km. We link this mid-mantle discontinuity to the upper reaches of deflected mantle plumes upwelling in the region. Reverse-time migration full-waveform imaging is a powerful approach to imaging Earth’s interior, capable of broadening our understanding of its structure and dynamics and shrinking modeling uncertainties.
Keywords: Geophysics Seismology
Programme: 133
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