Earthquake-triggered submarine canyon flushing transfers young terrestrial and marine organic carbon into the deep sea

Submarine canyons transfer substantial amounts of sediment and organic carbon (OC) into the deep ocean, nourishing deep-sea ecosystems and contributing to the global carbon cycle through OC burial and sequestration. Tracking lateral OC transport through submarine canyon systems is challenged by the deep-ocean setting, difficulties with constraining episodic depositional events, and the need to assess the composition and age of marine and terrestrial organic matter. We apply innovative parallel ramped pyrolysis oxidation-accelerator mass spectrometry and pyrolysis-gas chromatography-mass spectrometry with isotope analyses to track OC age and sources in the 2016 Kaikōura earthquake-triggered, canyon-flushing event that deposited along >1300 km of a submarine canyon-channel system, offshore Aotearoa New Zealand. Specifically, these techniques allow us to determine the ages, sources, and partitioning of OC within the Kaikōura turbidite deposit and test hypotheses of how submarine canyon systems contribute to lateral OC flux and burial. Our results show that, despite considerable canyon floor erosion, substantial amounts of young OC were flushed into the deep sea, with relatively little (∼2 %) pre-Holocene OC contributions. Even without a direct connection between rivers and submarine canyons, most (∼55 %) of the OC in the Kaikōura event bed is from terrestrial sources. However, the deposit also contains substantial amounts (∼22 %) of marine-derived OC and ∼23 % of the material is of unassignable origin. Particle sorting imparts variability on the age and composition of OC within turbidite deposits and along the turbidity current flow path. Terrestrial-derived OC is preferentially older than marine-derived OC and concentrated in coarser particle sizes found more commonly at the deposit base and in proximal settings. Young, marine-derived OC is concentrated at the surface of the deposits and tends to be enriched in finer particle sizes. Such OC partitioning in turbidites supports the relevance of depositional models for predicting and quantifying distribution of OC in deep-sea deposits. Earthquake-triggered, canyon flushing events and resulting turbidites enhance OC burial efficiency and can sequester OC effectively, contributing an important carbon sink to the sedimentary carbon cycle

Long-term patterns of hillslope erosion by earthquake-induced landslides shape mountain landscapes

Widespread triggering of landslides by large storms or earthquakes is a dominant mechanism of erosion in mountain landscapes. If landslides occur repeatedly in particular locations within a mountain range, then they will dominate the landscape evolution of that section and could leave a fingerprint in the topography. Here, we track erosion provenance using a novel combination of the isotopic and molecular composition of organic matter deposited in Lake Paringa, New Zealand. We find that the erosion provenance has shifted markedly after four large earthquakes over 1000 years. Postseismic periods eroded organic matter from a median elevation of 722 +329/−293 m and supplied 43% of the sediment in the core, while interseismic periods sourced from lower elevations (459 +256/−226 m). These results are the first demonstration that repeated large earthquakes can consistently focus erosion at high elevations, while interseismic periods appear less effective at modifying the highest parts of the topography

Insights into the ecological impact of trout introduction in an oligotrophic lake using sedimentary environmental DNA

Introduced trout can induce trophic cascades, however, a lack of pre-introduction data limits knowledge on their impact in many lakes. Traditional paleolimnological approaches have been used to study historic species changes, but until recently these have been restricted to taxa with preservable body-parts. To explore the ecosystem effects of Salmo trutta (brown trout) introduction on an oligotrophic lake in Aotearoa-New Zealand, we used a multi-marker sedimentary environmental DNA (sedDNA) approach coupled with pigments to detect changes across multiple trophic levels. DNA was extracted from core depths capturing approximately 100 years before and after the expected arrival of S. trutta, and metabarcoding was undertaken with four primer sets targeting the 12S rRNA (fish), 18S rRNA (eukaryotes) and cytochrome c oxidase (COI; eukaryotes) genes. The earliest detection of S. trutta eDNA was 1906 (1892–1919 CE with 95% high probability density function) suggesting their introduction was shortly before this. Native fish diversity (12S and 18S rRNA) decreased after the detection of S. trutta, albeit the data was patchy. A shift in overall eukaryotic and algal communities (18S rRNA and COI) was observed around 1856 (1841–1871 CE) to 1891 (1877–1904 CE), which aligns with the expected S. trutta introduction. However, taxonomy could not be assigned to many of the 18S rRNA and COI sequences. Pigment concentrations did not change markedly after S. trutta introduction. SedDNA provides a new tool for understanding the impact of disturbances such as the introduction of non-native species; however, there are still several methodological challenges to overcome

Populism, inequality and representation: Negotiating ‘the 99%’ with Occupy London

When Occupy London emerged with a global wave of protest movements in October 2011, it embodied and advanced discursive forms that have characterised the unsettling of political consensus following the financial crisis. The central claim that ‘We are the 99%’ staged a fundamental tension, between a populist appeal to the figure of ‘the people’, and a contrary orientation seeking to critique inequality while rejecting forms of representation and identity. This article – which draws on three years of ethnographic fieldwork with Occupy London (October 2011–October 2014) and a critical theorisation of the figure of ‘the people’ in radical movements – follows movement participants’ negotiation of the tension at the heart of the discourse of ‘the 99%’. It offers an account of the conflicting meanings and practices that emerged, arguing that the result was a creative contradiction that sustained the movement for a time, while setting the terms of its ultimate breakdown. Identifying the concept of ‘representation’ as the site of particular controversy, this is unpicked through a number of key figures (Pitkin, Marx, Spivak, Puchner, Deleuze and Guattari) as the basis for an empirical account of Occupy’s practice of assembly, which offered partial, imperfect ‘solutions’ to these tensions. The article concludes with some implications for the limits and possibilities of both a grassroots populism and a politics against representation, in the context of political developments since

Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

International audienceFault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation

Pretreatment of Terrestrial Macrofossils

ABSTRACTAcid-alkali-acid (AAA) pretreatment is widely used to clean terrestrial plant macrofossil samples for radiocarbon (14C) dating. There is wide variation amongst laboratories in the AAA method details and less rigorous AAA pretreatment is often used on fragile or small samples. Yet there is little evidence as to the efficacy of the different methods and whether the use of less rigorous methods is justified. We investigated four variations of AAA pretreatment: acid only (no alkali wash); room temperature AAA; “standard” AAA at 85°C; and “aggressive” AAA at 85°C with alkali washes repeated until no discoloration was detected. We tested six different terrestrial macrofossils from four different locations and ranging in age from mid-Holocene to the Last Glacial Maximum. Our results demonstrate that while acid only is not always sufficient to remove young material, there is no difference in 14C age of samples pretreated by any of the AAA variants. We also observed mass loss of 85–90% in the standard and aggressive AAA pretreatments, and much more modest mass loss in the room temperature AAA pretreatment. Therefore, we conclude that room temperature AAA pretreatment is optimal to remove contaminating material from fragile terrestrial macrofossils while retaining the majority of the authentic sample material.</jats:p

An integrative approach to assess the impact of disturbance on native fish in lakes

Freshwater fish are in a perilous state with more than 30% of species considered critically endangered. Yet significant ecological and methodological complexities constrain our ability to determine how disturbances are impacting native fish communities. We review current methods used to assess the responses of fish communities, especially native fish, to disturbances, with a focus on lakes. These methods include contemporary population surveys, manipulative experimental approaches, paleolimnological approaches and Indigenous Knowledge and social histories. We identify knowledge gaps, such as a lack of baseline data for native fish, an inability to assess the impact of historical disturbances, stressor response dynamics in contemporary multi‐stressor environments, and natural disturbance regimes. Our assessment of the current methods highlights challenges to filling these knowledge gaps using the reviewed methods. We advocate strongly for the implementation of an integrative approach that combines emerging technologies (i.e. molecular‐based techniques in contemporary surveys and paleolimnology) and underutilised knowledge streams (i.e. Indigenous Knowledge and social histories) which should be used in concert with conventional methods. This integrative approach will allow researchers to determine the key drivers of decline and the degree of change, which will enable more informed and successful management actions