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Submarine canyons enhance shelf–slope sediment exchange and influence hydrodynamic processes, with consequences for biogeochemical cycles. This work documents variations in the vertical export of biogenic matter on the northern shore of the lower St. Lawrence Estuary (LSLE, Quebec, eastern Canada), which is characterized by the presence of an active submarine canyon system. A total of three moorings were deployed from November 2020 to September 2021. One nearshore mooring (PDMc) was deployed in the main axis of the Pointe-des-Monts (PDM) canyon system and was equipped with an acoustic Doppler current profiler (ADCP), and two moorings equipped with sediment traps were deployed in the distal PDM canyon system (PDM-154, PDM-224) and offshore Baie-Comeau (BC-133). The ADCP data revealed the occurrence of a minor sediment remobilization event (December 2020) and a small turbidity current (February 2021) in the canyon. Concurrent elevated fluxes of total particulate matter, particulate organic carbon, particulate nitrogen, and chloropigments showed that these events left a signature in sediment traps PDM-154 and PDM-224 located > 2.6 km further offshore by enhancing lateral dispersion of resuspended sediments. The composition of diatom and dinoflagellate assemblages was similar in the canyon system and offshore BC, but the diatom bloom occurred 2 weeks earlier (in mid-April) at the PDM site. A bloom of the potentially toxic diatom Pseudo-nitzschia seriata was also observed during the second half of September 2021 at the BC site. Annual diatom and dinoflagellate fluxes were almost 2 times lower at the PDM site than at the BC site, possibly due to differences in riverine input and the structure of the water column, as well as increased sediment input and resuspension at the PDM site, leading to limited light availability. This study notably helps identify the relationship between near-bed canyon processes and biogenic matter export in the water column, thereby directly influencing the ecosystem offshore PDM. The study period further covered an anomalously nearly ice-free winter, and thus, in the context of climate change, it provides valuable insight into future trends of biogenic matter export in the LSLE. [ABSTRACT FROM AUTHOR]

The complex topography surrounding submarine canyons influences local hydrodynamics. For example, canyon-induced upwelling can supply nutrients to the surface waters and stimulate biological productivity. Canyons may also represent hazard hotspots [...]

Vast amounts of methane (CH 4) stored in submarine sediments are susceptible to release in a warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH 4 over pan-regional scales to detect early signs of CH 4 release. However, our ability to monitor CH 4 is hampered in remote northern regions by sampling and logistical constraints, and few good baseline data exist in many areas. From high-resolution atmospheric CH 4 measurements and discrete surface water samples, we estimated instantaneous sea–air CH 4 fluxes at various locations. We also created a baseline study of current background levels of CH 4 in North Atlantic waters based on the atmospheric CH 4 data over 22 d in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay between 55 and 72 ∘ N. In addition, we measured CH 4 concentrations across the water column at various stations. Measured atmospheric mixing ratios of CH 4 ranged from 1944 to 2012 ppbv, with a mean of 1966 ± 8 ppbv and a baseline of 1954–1981 ppbv. Dissolved CH 4 concentrations in the near-surface water peaked at 5.3 nmol L -1 within 1 km down-current of a known cold seep at Scott Inlet and were consistently oversaturated throughout the water column in Southwind Fjord, which is an area that has been recently affected by submarine landslides. Local sea–air CH 4 fluxes ranged from 0.003–0.119 µ mol m -2 d -1 , indicating that the ocean released only small amounts of CH 4 to the atmosphere at all stations. Atmospheric CH 4 levels were also driven by meteorological, spatial, and temporal variations, and both onshore and ocean-based contributions to atmospheric CH 4 mixing ratios are likely. Coupled high-resolution measurements of marine and atmospheric CH 4 data have the potential to provide ongoing monitoring in a region susceptible to CH 4 releases, as well as critical validation data for global-scale measurements and modelling. [ABSTRACT FROM AUTHOR]

Author(s): Stefan Schwietzke (corresponding author) [1, 2]; Owen A. Sherwood [3]; Lori M. P. Bruhwiler [2]; John B. Miller [1, 2]; Giuseppe Etiope [4, 5]; Edward J. Dlugokencky [2]; Sylvia [...]

The coastal shelf of Pointe-des-Monts (PDM), located on the northern shore of the Lower St. Lawrence Estuary (LSLE), is characterized by active submarine canyons. Despite the presence of regional biological [...]

The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean (1). Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters (2, 3). It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes (2-4). It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend (5). Here we analyse records of bulk and amino-acid-specific [sup.15]N/[sup.14]N isotopic ratios ([δ.sup.15]N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, [δ.sup.15]N decreases between 1850 and the present. The total shift in [δ.sup.15]N of -2 per mil over this period is comparable to the total change in global mean sedimentary [δ.sup.15]N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster (6). We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records (7, 8) suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age. Gly 0.99 0.31 1.00 0.13 Glx 0.92 0.43 0.88 0.23 -0.01 0.03 Gly 0.36 0.005# 0.78 Glx 0.20 0.049# 0.46 0.001# 0.00 0.880, Recent satellite observations have shown that globally, the permanently oligotrophic subtropical gyres are expanding at a rate of 1% to 4% per year, generally commensurate with global decreases in net [...]

Using bomb[sup.14]C dating and growth ring counting methods, we Calculate life spans and growth rates of six species of deep-sea corals collected at depths of between 400 and 900 m from the continental slope of Newfoundland and Labrador. Bamboo corals (Acanella arbuscula, Keratoisis ornata) and antipatharians (Stauropathes arctica) secrete concentric growth rings in their axial skeletons, which were proven to form annually for K. ornata and S. arctica. These species had the lowest radial growth rates of 33 [+ or -] 11 to 75 [+ or -] 11[micro]m x [year.sup-1]. Primnoa resedaeformis and Paramuricea spp. had higher radial growth rates of 83 [+ or -] 6 to 215 [+ or -] 37 [micro]m x [year.sup.-1]. Paragorgia arborea had the highest radial growth rate of 830 [+ or -] 120 [micro]m x [year.sup.-1]. Axial growth rates ranged from 0.56 [+ or -] 0.05 cm x [year.sup.-1] for a specimen of Paramuricea spp. to 2.61 [+ or -] 0.45 cm x [year.sup.-1] for a specimen of Primnoa resedaeformis. Life spans ranged from 18 [+ or -] 4 years for a live-collected P. resedaeformis to 200 [+ or -] 30 years for a subfossil specimen of K. ornata. Because all of the corals were from heavily fished areas, it is likely that age distributions are biased towards smaller and younger colonies. Recovery of deep-sea corals from fishing-induced damage will take decades to centuries. L'utilisation de methodes de datation basees sur le [14.sup]C des essais nucleaires et le denombrement des anneaux de croissance nous a permis de determiner la duree de vie et les taux de croissance de six especes de coraux marins d'eau profonde recoltees sur la pente continentale de Terre-Neuve et du Labrador, a des profondeurs de 400 m a 900 m. Les Coraux bambous (Acanella arbuscula, Keratoisis ornata) et antipathariens (Stauropathes arctica) secretent des anneaux de croissance concentriques sur leur squelette axial et il est demontre que chez K. ornata et S. arctica ces anneaux se forment annuellement. Ces especes possedent les taux de croissance radiale les plus bas, de 33 [+ or -] 11 [micro]m x [an.sup.-1] a 75 [+ or -] 11 [micro]m x [an.sup.1]. Primnoa resedaeformis et Paramuricea spp. ont des taux de croissance radiale plus eleves, 83 [+ or -] 6 [micro]m x [an.sup.-1] a 215 [+ or -] 37 [micro]m x [an.sup.-1]. Paragorgia arborea presente le taux de croissance radiale le plus eleve, 830 [+ or -] 120 [micro]m x [an.sup.-1]. Les taux de croissance axiale varient de 0,56 [+ or -] 0,05 cm x [an.sup.-1] chez un specimen de Paramuricea spp. a 2,61 [+ or -] 0,45 cm x [an.sup.-1] chez un specimen de P. resedaeformis. Les durees de vie vont de 18 [+ or -] 4 annees chez un P. resedaeformis recolte vivant a 200 [+ or -] 30 ans pour un specimen subfossile de K. ornata. Puisque tous les coraux proviennent de regions soumises a une peche intensive, il est vraisemblable que les distributions d'age favorisent les colonies plus petites et plus jeunes. La recuperation des coraux marins d'eau profonde des dommages infliges par la peche prendra des decennies et meme des siecles. [Traduit par la Redaction], Introduction In recent years there has been increasing interest in the ecology and biology of deep-sea or cold-water coral ecosystems (Freiwald and Roberts 2005; Roberts et al. 2006). Off eastern [...]

Vast amounts of methane (CH4) stored in permafrost and submarine sediments are susceptible to release in warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH4 over panregional scales to detect early signs of CH4 release. However, our ability to monitor CH4 is hampered in remote northern regions by sampling and logistical constraints and few good baseline data exist in many areas. To create a baseline study of current background levels of CH4 in North Atlantic waters, we collected continuous real-time atmospheric CH4 data, along with ambient air temperature and wind parameters over 22 days in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay up to 71°N. In addition, we measured CH4 concentrations in the water column using discrete water samples at selected stations. Measured atmospheric mixing ratios of CH4 ranged from 1944.7 ppb to 2012.0 ppb, with mean of 1966.0±7.4 ppb and a baseline of 1954.2-1980.6 ppb. Dissolved CH4 concentrations in the near-surface water peaked at 56.58±0.05 nM within 1 km down-current of a known cold seep at Scott Inlet but were consistently super-saturated throughout the water column in Southwind Fjord, which is an area recently affected by submarine landslides. Local sea-air CH4 fluxes ranged from 0.1-14.1 µmol m-2 d-1 indicating that the ocean acted as a CH4 source to the atmosphere. Atmospheric CH4 levels were also driven by meteorological, spatial, and temporal variations. Highest atmospheric CH4 mixing ratios were detected in the Cumberland Sound in Nunavut, suggesting onshore sources from nearby waterbodies and wetlands, whereas ocean-based contributions at this location could not be ruled out. Coupled real-time measurements of marine and atmospheric CH4 data have the potential to provide ongoing monitoring in a region susceptible to CH4 releases, as well as critical validation data for global-scale measurements and modelling. [ABSTRACT FROM AUTHOR]