Abstract:

Abstract. Column ozone variability has important implications for surface photochemistry and the climate. Ice-core nitrate isotopes are suspected to be influenced by column ozone variability and δ¹⁵N(NO) has been sought to serve as a proxy of column ozone variability. In this study, we examined the ability of ice-core nitrate isotopes to reflect column ozone variability by measuring δ¹⁵N(NO) and Δ¹⁷O(NO) in a shallow ice core drilled at the South Pole. The ice core covers the period 1944–2005, and during this period δ¹⁵N(NO) showed large annual variability ((59.2 ± 29.3) ‰ ), but with no apparent response to the Antarctic ozone hole. Utilizing a snow photochemical model, we estimated 6.9 ‰ additional enrichments in δ¹⁵N(NO) could be caused by the development of the ozone hole. Nevertheless, this enrichment is small and masked by the effects of the snow accumulation rate at the South Pole over the same period of the ozone hole. The Δ¹⁷O(NO) record has displayed a decreasing trend by ∼ 3.4 ‰ since 1976. This magnitude of change cannot be caused by enhanced post-depositional processing related to the ozone hole. Instead, the Δ¹⁷O(NO) decrease was more likely due to the proposed decreases in the O₃ HO_x ratio in the extratropical Southern Hemisphere. Our results suggest ice-core δ¹⁵N(NO) is more sensitive to snow accumulation rate than to column ozone, but at sites with a relatively constant snow accumulation rate, information of column ozone variability embedded in δ¹⁵N(NO) should be retrievable.

Abstract: Although mitochondrial DNA has been widely used in phylogeography, evidence has emerged that factors such as climate, food availability, and environmental pressures that produce high levels of stress can exert a strong influence on mitochondrial genomes, to the point of promoting the persistence of certain genotypes in order to compensate for the metabolic requirements of the local environment. As recently discovered, the gentoo penguins (Pygoscelis papua) comprise four highly divergent lineages across their distribution spanning the Antarctic and sub-Antarctic regions. Gentoo penguins therefore represent a suitable animal model to study adaptive processes across divergent environments. Based on 62 mitogenomes that we obtained from nine locations spanning all four gentoo penguin lineages, we demonstrated lineage-specific nucleotide substitutions for various genes, but only lineage-specific amino acid replacements for the ND1 and ND5 protein-coding genes. Purifying selection (dN/dS < 1) is the main driving force in the protein-coding genes that shape the diversity of mitogenomes in gentoo penguins. Positive selection (dN/dS > 1) was mostly present in codons of the Complex I (NADH genes), supported by two different codon-based methods at the ND1 and ND4 in the most divergent lineages, the eastern gentoo penguin from Crozet and Marion Islands and the southern gentoo penguin from Antarctica respectively. Additionally, ND5 and ATP6 were under selection in the branches of the phylogeny involving all gentoo penguins except the eastern lineage. Our study suggests that local adaptation of gentoo penguins has emerged as a response to environmental variability promoting the fixation of mitochondrial haplotypes in a non-random manner. Mitogenome adaptation is thus likely to have been associated with gentoo penguin diversification across the Southern Ocean and to have promoted their survival in extreme environments such as Antarctica. Such selective processes on the mitochondrial genome may also be responsible for the discordance detected between nuclear- and mitochondrial-based phylogenies of gentoo penguin lineages.

Abstract: The Flores Thrust is a southward-dipping, low-to-moderate angle submarine active fault in the eastern Sunda-Banda back-arc (Indonesia). Significant shallow-depth destructive earthquakes have been reported along this fault zone. From 2002 to 2009, one of its fault segments, called the Sumbawa segment, experienced five earthquakes with moment magnitude (MW) values of 6.2–6.6. In this study, we performed finite-fault rupture inversions for these earthquakes, constrained with teleseismic body and surface waveforms, to investigate the characteristics of earthquake ruptures along this fault zone. We obtained the source-time-functions and finite-fault rupture models for these five earthquakes. Results indicated that ruptures often propagated along-strike or down-dip. The ruptures were initiated from the middle crust (depth of approximately 12–17 km) and exhibited a comparable initiation behavior to their entire rupture. The rupture speeds and stress drops were approximately 2.0–2.5 km/s and 1.0–2.0 MPa, respectively. Five cascading asperities ruptured neighboring fault patches and did not overlap each other. The characteristics of earthquake source parameters and rupture processes obtained in this study are robust and helpful for future regional seismic hazard assessment and earthquake early warning studies. These cascading asperities might be related to the fault immaturity of the western Flores Thrust. Alternatively, these earthquakes may act as asperities located at the down-dip patches of the Sumbawa segment, and its shallower section still has a potential of ruptures with MW > 7.0.

Abstract: The Green Edge project was designed to investigate the onset, life and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in arctic ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the arctic environment will affect it. Green Edge was a large multidisciplinary collaborative project bringing researchers and technicians from 28 different institutions in seven countries, together aiming at understanding these changes and their impacts into the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice-camp and a research vessel in the Baffin Bay, canadian arctic. This paper describes the sampling strategy and the data set obtained from the research cruise, which took place aboard the Canadian Coast Guard Ship (CCGS) Amundsen in spring 2016. The dataset is available at https://doi.org/10.17882/59892 (Massicotte et al., 2019a).