Silvia Hess

• Freitas, Thaise Ricardo de; Nomaki, Hidetaka; Hess, Silvia; Renaud, Paul; Ogawa, Nanako O. & Ohkouchi, Naohiko [Show all 8 contributors for this article] (2026). Effects of temperature and food availability on Arctic benthic foraminifera: coupling field observations with feeding experiments. Marine Ecology Progress Series. ISSN 0171-8630. doi: 10.3354/meps15237. Full text in Research Archive Show summary

  Climate-driven increases in primary production are expected to alter the organic matter reaching the Arctic seafloor. While polar organisms can respond rapidly to changes in food pulses, there is limited information on how different benthic compartments exhibit distinct physiological and population-level responses. Here, we evaluated the responses of benthic foraminifera to the addition of 13C-labelled algae powder under ambient conditions and a warmer temperature setting. We quantified the species-specific ingestion rates of selected foraminifera taxa from shelf and slope regions characterised by distinct water depths and hydrographic conditions. Our results demonstrated that shelf foraminiferal assemblages had higher uptake than slope assemblages, despite the latter having generally higher abundance. Both suspension feeders and detritivores (e.g., Saccorhiza ramosa and Cribrostomoides subglobosus, respectively) had high feeding rates, indicating that species-specific uptake is related to feeding preferences and strategies. Most taxa did not exhibit increased feeding under warm conditions, except for C. subglobosus and certain calcareous taxa, suggesting that warming effects are secondary and species-specific. Background foraminiferal isotopic signatures (δ13C, δ15N) evidenced trophic plasticity in Arctic benthic foraminifera, as Lagenammina difflugiformis, Elphidium clavatum and Melonis affinis showed varying isotopic values across sites. Our findings indicate that future warming may alter benthic carbon cycling not through generalised metabolic acceleration due to higher water temperature, but through species-specific shifts that should restructure community biodiversity and trophic roles.

• Górska, Barbara; Grzelak, Katarzyna; Bluhm, Bodil; Hess, Silvia & Włodarska-Kowalczuk, Maria (2025). Does mesh size matter? Influence of mesh size on estimation of meiofauna abundance, biomass and on size spectra. Oceanologia. ISSN 0078-3234. 67(4). doi: 10.5697/rxwv1889. Full text in Research Archive Show summary

  For muddy-bottom meiofauna analyses, samples are typically sieved on 32 𝜇m sieves for animal extraction. However, some studies use a 63 𝜇m sieve to reduce fine sediment overload. Such variation in sieving protocols hampers comparisons across studies. We quantified and compared the effects of mesh size (63 versus 32 𝜇m) on meiofauna abundance, biomass, community composition, and size spectra in muddy sediments. Between 8 and 21% of individuals (mostly nematodes) were missed in the 63 𝜇m mesh-based analyses (compared to 32 𝜇m). However, the larger mesh size did not affect biomass estimations or the construction of size spectra. For muddy sediments, a 63 𝜇m sieve can be used interchangeably with a 32 𝜇m sieve for meiofauna biomass estimation.

• Kohlbach, Doreen; Fransson, Agneta; Arumí, Martí Amargant; Assmann, Karen; Assmy, Philipp Kurt Wolf & Bratbak, Gunnar [Show all 38 contributors for this article] (2025). Nansen and Amundsen basins: Gradients of physico-chemical properties and biota composition with implications for future resource management of the central Arctic Ocean. Elementa: Science of the Anthropocene. 13(1). doi: 10.1525/elementa.2024.00016. Full text in Research Archive Show summary

  The projected transition of the central Arctic Ocean (CAO) into a warmer, seasonally ice-free ocean requires more knowledge of this environment to predict changes in the structure and dynamics of its ecosystems. We aimed to compare the state and underlying processes of Nansen Basin and Amundsen Basin ecosystems observed in August–September 2021 and assess impacts of Atlantic Water inflow and fresher Transpolar Drift waters, respectively, on these ecosystems. The basins differed in features of sea ice, hydrography, and chemical and biological compositions. The near-slope open water in western Nansen Basin showed a clear fingerprint of warm, saline Atlantic Water, with larger vertical turbulent fluxes facilitating nutrient transport across the pycnocline and supporting larger standing stocks of bacteria, protists, and zooplankton. Pelagic primary production and microbial and faunal stocks decreased northward and into Amundsen Basin, likely due to lower nutrient concentrations, stronger stratification, and reduced light through the more continuous and thicker ice and snow cover in Amundsen Basin, possibly also impacted by seasonally declining light levels. Transpolar Drift signals included lower salinity, stronger stratification, and higher silicate concentrations in Amundsen Basin surface waters. Similarities to earlier observations included the increase in small-sized algae from Nansen Basin into Amundsen Basin and overall low faunal abundances in the CAO, suggesting that overarching patterns remained unchanged over past decades. Examples of species range extensions and notable taxon absences relative to earlier studies, however, could be due to borealization and changes in sea-ice conditions, respectively. Higher density ecosystem sampling and consistent time series are recommended to confirm such conclusions. The distinct basin differences call for a regional approach to future management of the CAO. We especially caution against using the area of strong Atlantic Water inflow in southern Nansen Basin as representative of the entire basin, let alone Amundsen Basin or the CAO.

• Freitas, Thaise Ricardo de; Hess, Silvia; Renaud, Paul Eric; Appleby, Peter & Alve, Elisabeth (2024). Drivers of organic carbon distribution and accumulation in the northern Barents Sea. Progress in Oceanography. ISSN 0079-6611. 225. doi: 10.1016/j.pocean.2024.103286. Full text in Research Archive Show summary

  Sedimentary properties and accumulation rates on the continental shelf and in the deep sea reflect temporal oceanographic, biological and chemical processes occurring in the water column and the sediment surface. We used the radionuclides 210Pb, 226Ra, and 137Cs activities to estimate sedimentation rates during the last century at nine stations in the northern Barents Sea region. Elemental (C, N) and stable isotopic composition (δ13C, δ15N) were also analysed from the nine stations sampled in August 2018, and, for five other stations sampled in August and December 2019, and in March and May 2021. Sediment accumulation rates varied between 130 and 1 410 g m−2 y−1. The < 63 μm normalized total organic carbon (TOC63) and the total nitrogen from the sediment surface varied between 0.90–2.56 % and 0.13–0.33 %, respectively. Ice-free shelf stations had higher TOC63 and possibly fresher organic matter (high δ13C, low δ15N) than ice-covered more northern stations. The opposite trend was observed for total inorganic carbon. We found that these trends in biogeochemical parameters were spatially structured by the winter sea ice concentration and biological production differences, and exhibited a south-north separation of the Polar Front region. The low and stable organic carbon accumulation rate (1.7–13.4 g Corg m-2 y−1; ARtoc) is a function of slow sedimentation rates, and high degradation and residence time in the water column and at the sediment–water interface. Overall, the ARtoc has been stable for the past 100 years, with a slight increase from the early 1970s to the present at the shelf and slope stations. Our results highlight that spatial scales of variability of the studied sedimentary parameters are linked to spatial patterns of important environmental variables (e.g., chlorophyll-a, sea ice concentration) in the region. In contrast, no seasonal differences were observed in the sediment parameters of revisited stations, and the dated sediment geochemical profiles did not exhibit substantial longer-term variation. This means that climate-induced changes in variables that modify the sedimentary geochemistry of the environment may affect benthic community activity and structure before leaving a record in ARtoc.

• Sen, Arunima; Molina, Èric Jordà; Freitas, Thaise Ricardo de; Hess, Silvia; Reiss, Henning & Bluhm, Bodil Annikki Ulla Barbro [Show all 7 contributors for this article] (2024). Benthic remineralization under future Arctic conditions and evaluating the potential for changes in carbon sequestration in warming sediments. Scientific Reports. 14(1). doi: 10.1038/s41598-024-73633-z. Full text in Research Archive Show summary

  Benthic (seafloor) remineralization of organic material determines the fate of carbon in the ocean and its sequestration. Bottom water temperature and labile carbon supply to the seafloor are expected to increase in a warming Arctic and correspondingly, benthic remineralization rates. We provide some of the first experimental data on the response of sediment oxygen demand (SOD), an established proxy for benthic remineralization, to increased temperature and/or food supply across a range of Arctic conditions and regimes. Each factor significantly increased SOD rates (with different degrees of variability); however the largest increases were seen with both factors combined (50% to ten-fold increases), consistently across the four seasons and the spatial gradient covering shelf to deep basin included in our study. This ability of the Arctic benthos to process increased pulses of carbon suggests that increased sedimented carbon under warming conditions is likely to be utilized and processed, not accumulated, impacting carbon storage and decreasing the Arctic’s role as a global carbon sink.

• Appleby, Peter G.; Piliposyan, Gor & Hess, Silvia (2021). Detection of a hot 137Cs particle in marine sediments from Norway: potential implication for 137Cs dating. Geo-Marine Letters. ISSN 0276-0460. 42. doi: 10.1007/s00367-021-00727-2. Full text in Research Archive
• Klootwijk, Anouk Tosca; Sweetman, Andrew K.; Hess, Silvia; Alve, Elisabeth; Dunlop, Kathrine M. & Renaud, Paul Eric (2021). Benthic foraminiferal carbon cycling in coastal zone sediments: The influence of the assemblage structure and jellyfish detritus. Estuarine, Coastal and Shelf Science. ISSN 0272-7714. 261. doi: 10.1016/j.ecss.2021.107535. Full text in Research Archive
• Klootwijk, Anouk Tosca; Alve, Elisabeth; Hess, Silvia; Renaud, Paul Eric; Sørlie, Carsten & Dolven, Jane Karine Lønne (2020). Monitoring environmental impacts of fish farms: Comparing reference conditions of sediment geochemistry and benthic foraminifera with the present. Ecological Indicators. ISSN 1470-160X. 120. doi: 10.1016/j.ecolind.2020.106818. Full text in Research Archive Show summary

  Intensive fish farming is a major industry, but the extent of organic matter (OM) and heavy metal pollution by fish farms is debated. This study established in situ reference conditions using geochemical parameters and fossil benthic foraminiferal assemblages in dated sediment cores to identify potential impacts of fish farming in two basins of the inner Øksfjord, Northern Norway. Living (rose Bengal stained) benthic foraminifera were used to assess the present day environmental conditions. The fossil foraminiferal records were compared with the living foraminifera, which in turn were compared with macrofaunal data. Long-term (> 100 yrs) sediment core records of the geochemical parameters (TOC63, C/N, δ13CVPDB TOC and heavy metals) and foraminiferal indices (Norwegian Quality Index (fNQI), AZTI’s Marine Biotic Index (fAMBI), fHlog2, ES100) did not indicate an impact from fish farming through time. Long-term changes in foraminiferal absolute abundances and relative abun- dances of ecological groups (EGs) reflecting organic matter (OM) tolerance suggest that the OM supply slightly increased compared to reference conditions. Relative abundances of Brizalina skagerrakensis and Epistominella vitrea, previously associated with phytodetrital input, suggest a minor increase in primary productivity com- pared to reference conditions. The Stainforthia group (S. fusiformis and S. feylingi), indicative of OM enrichment, in the living foraminiferal assemblages may indicate a response to fish farming activities, but foraminiferal seasonality could not be excluded as a potential cause. The indices of both fossil and living foraminifera, in addition to the macrofauna showed a good to high Ecological Quality Status (EcoQS) through time and at present. This indicates that environmental conditions have been and still are acceptable.

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• Barras, Christine; Bouchet, Vincent; Hess, Silvia; Hyams-Kaphzan, Orit; Martinez-Colon, Michael & Polovodova-Asteman, Irina (2024). FOBIMO Workshop - The reboot. Full text in Research Archive
• Fransson, Agneta; Bluhm, Bodil Annikki Ulla Barbro; Kohlbach, Doreen; Assmy, Philipp Kurt Wolf; Bratbak, Gunnar & Amargant, Marti [Show all 37 contributors for this article] (2024). Nansen vs. Amundsen Basin: Constrasting physico-chemical properties and biota composition to inform management. Full text in Research Archive
• Hess, Silvia & Dauvi, Adriana Amundsen (2023). Mikrofossiler avslører Oslofjordens miljøtilstand. Full text in Research Archive
• Asteman, Irina Polovodova; Alve, Elisabeth; Dolven, Jane; Eliassen, Nicole; Ferraro, Mattia & Hess, Silvia [Show all 18 contributors for this article] (2023). Spreading of an alien benthic foraminifer in the North Sea: a reason to be worried? Full text in Research Archive Show summary

  In the Skagerrak-Kattegat (eastern North Sea), the alien benthic foraminifer Nonionella sp. T1 (previously referred to as “Nonionella stella”) was reported for the first time in 2011 and 2012 in the Swedish and southern Norwegian fjords, respectively. Based on dated sediment cores its first occurrence can be traced back to the 1980s in the Gullmar Fjord, to the 2000s in the Öresund and to 2010 in the Oslofjord. Since then, Nonionella sp T1 has spread all over the Kattegat and coastal Skagerrak, according to sampling campaigns performed between 2016 and 2022. The species is now highly abundant in the entire Kattegat, including the Öresund, as well as in fjord mouths of the seasonally hypoxic Gullmar Fjord, the oxic Hakefjord and the long-term polluted Idefjord as demonstrated by molecular and morphospecies data. At the same time, Nonionella sp T1 is rare to absent in the Baltic Sea, Skagerrak deep basin and in deep fjords of western and northern Norway. This study shows some preliminary results on the species’ present distribution in the study area and raises questions about the driving factors and potential effects on the local biodiversity.

• Hess, Silvia; Alve, Elisabeth & Helland, Aud (2023). Retrospective benthic foraminiferal community studies: a sensitive method to determine early environmental changes. Full text in Research Archive
• Freitas, Thaise Ricardo de; Hess, Silvia; Renaud, Paul Eric & Alve, Elisabeth (2023). Spatio-temporal distribution patterns of benthic foraminifera in the northern Barents Sea. Full text in Research Archive
• Ziegler, Amanda; Freitas, Thaise Ricardo de; Altenburger, Andreas; Alve, Elisabeth; Bluhm, Bodil & Bodur, Yasemin V. [Show all 17 contributors for this article] (2022). Lack of (or weak) seasonality in Barents sea and Nansen Basin sediments and biota? A preliminary assessment. Full text in Research Archive
• Freitas, Thaise Ricardo de; Hess, Silvia; Renaud, Paul Eric & Alve, Elisabeth (2022). Seasonal variability on living benthic foraminiferal biodiversity in the northern Barents Sea: preliminary results. Full text in Research Archive
• Freitas, Thaise Ricardo de; Hess, Silvia; Renaud, Paul Eric & Alve, Elisabeth (2022). Benthic foraminiferal biodiversity in the northern Barents Sea: preliminary results. Full text in Research Archive
• Freitas, Thaise Ricardo de; Alve, Elisabeth; Hess, Silvia & Renaud, Paul Eric (2021). Drivers of organic carbon distribution and accumulation in the Northern Barents Sea. Full text in Research Archive
• Ludvigsen, Martin; Assmy, Philipp; Adams, Matthew James Samuel; Arumi, Marti A.; Mo-Bjørkelund, Tore & Bodur, Yasemin V. [Show all 36 contributors for this article] (2022). Seasonal cruise Q2 2021: Cruise Report. Septentrio Academic Publishing. Full text in Research Archive Show summary

  The spring season was the target for the Nansen Legacy cruise organized in late April and first half of May 2021 following the transect defined for this series of cruises to capture the variations of the year sampling physical, biological and chemical conditions in the ice and the sea. The transect went through both open water and ice. Seven process stations were visited (P1 through P7) together with smaller NLEG stations according to the program for the seasonal investigations. The first station (P1) was in open waters, while the remaining six main station had ice coverage of varying degree. Each of the process stations lasted 24 hours or more to allow a full diurnal cycle. Sampling included ice physics, ice samples, phytoplankton, zooplankton, marine chemistry and eco toxicology using acoustic, optical and robotics methods together with lab analyses of physical samples. Remote sensing data were also matched with in situ observations of both sea and ice conditions.

• Hess, Silvia; Alve, Elisabeth & Helland, Aud (2021). E 16 og Vossebanen, Arna-Stanghelle. Miljøforholdene i Sørfjorden og Veafjorden, Vestland, dagens og tidligere tiders tilstand. Statens vegvesen, rapport UAS-01-Q-00029. Full text in Research Archive

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