Ongoing glacial melt is rapidly altering Arctic and sub-Arctic fjord systems, with uncertain implications for their biogeochemical functioning. Yet, data on marine benthic nutrient recycling in such fjords remain sparse. This study investigates the sediment biogeochemistry of two neighboring sub-Arctic fjords in southwest Greenland characterized by different surface productivities related to their glacial regimes: high primary productivity in Nuup Kangerlua influenced by marine-terminating glaciers, and lower surface productivity in Ameralik impacted only by a land-terminating glacier. We assessed benthic mineralization rates by measuring total oxygen uptake and nutrient fluxes (NH4+, NO3-, PO43-), along with porewater profiles (including dissolved Fe and Mn), to evaluate whether fjord sediments act as sources or sinks of key dissolved nutrients. Total oxygen uptake varied markedly between fjords and seasons: in Ameralik the range was 3.55-9.69 mmol O2 m-2 d-1 in spring and 5.27-13.34 mmol O2 m-2 d-1 in late summer, whereas Nuup Kangerlua showed comparable spring and summer values, spanning 2.83-5.48 mmol O2 m-2 d-1 across both seasons. Despite the approximately 3-fold higher annual primary productivity in Nuup Kangerlua, sediment mineralization rates were highest in Ameralik, particularly in its outer basin. Sediments in both fjords acted as sinks for specific nutrients. In Nuup Kangerlua, sedimentary ammonium and phosphate retention dominated near glacial discharge zones, likely due to rapid burial and dilution of organic matter, and adsorption to metal oxides. Meanwhile, the entire Ameralik basin acted as a sink for both ammonium and nitrate as reflected in low effluxes and ratios of dissolved inorganic nitrogen to dissolved inorganic phosphorus well beneath Redfield. These findings underscore the need to consider organic matter preservation conditions, geomorphology, and particle reactivity in addition to glacial discharge regime when assessing the biogeochemical response of Arctic fjords to continued climate-driven glacier retreat.
Agroecology is both a practical agricultural science that mimics ecological functions to enhance and protect the integrity of agroecosystems and a political movement of grassroots actors, including women, rural peasants, and Indigenous farmers. Agroecological transitions aim to address localized issues of food insecurity, ecological and biodiversity crises, the legacies of slavery and colonialism, and the privatization and concentration of agricultural land. We are part of a research collaborative, Agroecología en Latinoamérica: Construyendo Caminos, working closely with the Ecuadorian Movement for Social and Solidarity Economy and the Andean agroecological collective, Ayllu Kurikancha, to explore how agroecological practices intersect with individual and collective well-being. This project involves storytelling and theorization from collaborator-participants through a feminist, decolonial, and relational research methodology. Project collaborators characterize agroecology as a way of life and set of conditions that facilitate well-being through “good relations,” putting into practice the prefigurative politics of Ayllu Kurikancha in shaping sustainable and equitable futures on the land for generations to come. This vision of relational well-being is tied to a narrative of autonomy and freedom which makes agroecology a desirable way of life. The lifeways shared here offer “possibility models” for transitioning toward a future of well-being for humans and nature through agroecological practices.
The Arctic region is experiencing rapid rates of warming due to anthropogenic climate change, leading to a dramatic decrease in sea-ice cover. Impacts of these changes on sea-ice biological communities, biogeochemical cycles, and Arctic food webs remain understudied, partially due to methodological challenges studying sea-ice biology. The main novelty of this study lies in the estimation of species-specific growth rates of sea-ice diatoms—the dominant primary producers in Arctic sea ice—from natural communities. Sea-ice algal communities from two Svalbard fjords, Tempelfjorden and Van Mijenfjorden, were incubated at different irradiance levels, including darkness, using PDMPO, a fluorescent probe that labels newly deposited biogenic silica, to track diatom cell division under near in situ conditions. Building on this approach, we were able to provide the first estimates of production for individual diatom species, based on species-specific growth rates and abundance data, and to link these production estimates to environmental conditions in the field. Our results demonstrate strong interspecific variability in light response and show that, in contrast to photosynthesis, growth can occur in darkness. No clear relationship between the species abundance and their growth rates was found, illustrating that the most abundant taxa are not necessarily the fastest growing and that growth history needs to be taken into account. Furthermore, our estimates of growth production based on the staining approach presented in this study differed substantially from carbon-based primary production estimates, highlighting the need to consider physiological processes beyond photosynthetic carbon fixation. Together, these findings highlight the need for a species approach in ecological models aiming to predict sea-ice ecosystem responses to ongoing Arctic change.
Particulate organic matter provides energy for life in the ocean and plays a critical role in the global carbon cycle. It is the primary food source for benthic fauna inhabiting abyssal plains (3,000–6,000 m water depth) and is a key determinant of deep-sea biodiversity and community structure. The Clarion-Clipperton Zone of the eastern equatorial Pacific abyssal plain has high densities of polymetallic nodules, and there is increased interest in deep-sea mining for nodule exploitation. The effects of deep-sea mining on sediment particulate organic matter are largely unknown. In this research, we determined the quantity, quality and distribution of particulate organic matter in sediments at the Ocean Minerals Company test mine site (known as the OMCO site, central Clarion-Clipperton Zone) within the collector tracks and adjacent plume area compared to a control site 44 years after the mining test. We determined organic matter quantity and quality using total organic carbon and nitrogen, stable carbon and nitrogen isotopes and lipid biomarkers. Forty-four years later, we found differences in the particle size distributions between the Ocean Minerals Company test tracks and surrounding area. We also found that the quantity and quality of organic matter in the mining track sediments were depressed and more heterogeneous compared to the surrounding area and that these patterns were linked to particle size distributions, demonstrating the long-term impact of the Ocean Minerals Company mining test. Faunal densities (foraminifera, xenophyophores and megafauna) were also linked to organic matter quality, being higher at the control and plume area where organic matter quality was highest, suggesting that organic matter quality plays a key role in community composition. These results suggest that the long-term impacts of mining on organic matter availability in sediments will influence the recovery and resilience of benthic biological communities.
Despite the ubiquitous distribution of the sub-ice diatom Melosira arctica across the Arctic Ocean, its biochemical composition and role as a food source for Arctic grazers remain poorly understood. We analyzed lipid-based trophic markers in Melosira assemblages from three research expeditions and contrasted them with unialgal M. arctica cultures. We also conducted a feeding experiment with two ice-associated (sympagic) amphipod species. To identify potential distinct biochemical traits, we compared trophic marker contents of Melosira samples with pelagic and ice-associated particulate organic matter, as well as with pelagic and sympagic diatom-dominated bloom communities. Despite pronounced variability among Melosira field assemblages, including fatty acid (FA) and stable isotope compositions, some consistent patterns emerged, such as overall high contributions of typical diatom-associated FAs. Polyunsaturated FAs, indicating nutritional quality, contributed up to 30% of total FAs in samples from Fram Strait and the Yermak Plateau/Nansen Basin, as well as in the cultures. Lower levels of polyunsaturated FAs (17%) in central Arctic Ocean samples likely reflected differences in cell developmental stages, nutrient supply, and ice properties. These Melosira assemblages had developed over a longer time than those collected from the other locations and, as expected, exhibited early indications of senescence. Across all samples, diatom-produced highly branched isoprenoids were absent, suggesting that Melosira does not produce these compounds. Overall, the chemical composition of Melosira was found to be typical of a centric diatom; only the sterol composition with a dominance of campesterol differed from that of pelagic (brassicasterol-dominated) and ice-associated (β-sitosterol-dominated) particulate organic matter. The experimental work indicated that amphipods interacted with Melosira, exhibiting varying degrees of algal consumption. Melosira can thus serve as both an under-ice habitat and a food source for Arctic grazers, but tracking its trophic interactions may be challenging given an absence of specific biochemical markers.
