Thaise Ricardo de Freitas

• 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.

• 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.

• Kohler, Stephen Gustav; Kull, Laura M.; Heimbürger-Boavida, Lars-Eric; Freitas, Thaise Ricardo de; Sanchez, Nicolas & Ndungu, Kuria [Show all 7 contributors for this article] (2022). Distribution pattern of mercury in northern Barents Sea and Eurasian Basin surface sediment. Marine Pollution Bulletin. ISSN 0025-326X. 185. doi: 10.1016/j.marpolbul.2022.114272. Full text in Research Archive Show summary

  Marine sediment is a significant sink for the global pollutant mercury. In a rapidly changing Arctic region, mercury (Hg) bioaccumulation in the marine ecosystem remains a prominent environmental issue. Here, we report surface sediment (0–2 cm) concentrations of Hg and other toxic elements of interest (Cr, Ni, Zn, Cu, As, Cd, Pb) in the northern Barents Sea and Eurasian Basin. We observed average Hg concentrations of 65 ± 23 ng/g with the highest concentration of 116 ng/g in the Eurasian Basin. Our calculated enrichment factors suggest low anthropogenic enrichment for mercury, chromium, nickel, and copper. Mercury and trace element geographic patterns are best explained by the origin and transportation of fine grain sediment towards the Eurasian Basin, with scavenging by both particulate organic carbon and metal oxides as significant delivery mechanisms.

• Freitas, Thaise Ricardo de; Bacalhau, Eduardo & Disaró, Sibelle (2021). Biovolume Method for Foraminiferal Biomass Assessment: Evaluation of Geometric Models and Incorporation of Species Mean Cell Occupancy. Journal of Foraminiferal Research. ISSN 0096-1191. 51(4), p. 249–266. doi: 10.2113/GSJFR.51.4.249. Full text in Research Archive
• Santana, Beatriz; Freitas, Thaise Ricardo de; Leonel, Juliana & Bonetti, Carla (2021). Biometric and biomass analysis of Quaternary Uvigerinidae (Foraminifera) from the Southern Brazilian continental slope. Marine Micropaleontology. ISSN 0377-8398. 169. doi: 10.1016/j.marmicro.2021.102041. Full text in Research Archive
• Cox, Kieran; Black, Morgan; Filip, Natalia; Miller, Matthew; Mohns, Kayla & Mortimor, James [Show all 11 contributors for this article] (2017). Community assessment techniques and the implications for rarefaction and extrapolation with Hill numbers. Ecology and Evolution. doi: 10.1002/ece3.3580. Full text in Research Archive

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• 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
• Ziegler, Amanda; Jørgensen, Lis Lindal; Bluhm, Bodil Annikki Ulla Barbro; Giebichenstein, Julia; Borgå, Katrine & Freitas, Thaise Ricardo de (2023). The effect of ice-free summer conditions on benthic food web structure in the Barents Sea. Full text in Research Archive Show summary

  Reduced Arctic sea-ice cover has been shown to alter phytoplankton community composition and reduce the magnitude of vertical flux, thereby reducing the strength of pelagic-benthic coupling. It is predicted that Arctic shelf ecosystems, like the Barents Sea, will transition into sub-polar-like ecosystems under future climatic conditions. However, few studies have provided a benthic perspective to the question of how ice-free conditions in the Arctic will affect food web structure. In this study, we aim to test whether ice-free summer conditions in the Barents Sea and adjacent Nansen Basin alter benthic food web structure and the strength of pelagic benthic coupling. To do so, we used bulk stable isotopes of carbon and nitrogen measured in food sources and benthic consumers, demersal fish, and zooplankton collected during summers with contrasting sea-ice conditions: August 2018 – low sea-ice extent and August 2019 – high sea-ice extent. We compared benthic food web structure across three oceanographically distinct regions from the sea-ice free central Barents Sea shelf and the seasonally ice-free northern Barents Sea shelf to the slope extending into the Nansen Basin. The results of this work will not only improve our understanding of the impact that Arctic sea-ice loss has on benthic communities but provide additional insight to the resiliency of Arctic benthic food webs.

• 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; Bluhm, Bodil; Jørgensen, Lis Lindal; Renaud, Paul Eric & Freitas, Thaise Ricardo de (2022). Pelagic-benthic coupling in the Northern Barents Sea: Insights from bulk stable isotope analysis of the benthic community. Full text in Research Archive
• Ziegler, Amanda; Freitas, Thaise Ricardo de; Bluhm, Bodil; Jørgensen, Lis Lindal & Renaud, Paul Eric (2022). Seasonal and spatial variability of pelagic-benthic coupling strength in the Northern Barents Sea: A benthic food web approach. 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
• Freitas, Thaise Ricardo de (2026). Benthic foraminifera in the warming Arctic: Seasonal dynamics, biodiversity, and response to phytodetrital pulses. Universitetet i Oslo. Full text in Research Archive Show summary

  Rising temperatures and melting sea ice are likely to affect the primary production and its fate in the Arctic Ocean seabed. Since seafloor communities rely on organic material that reaches the seafloor, these climate-driven changes will affect sedimentary organic carbon, food-web structure, and biodiversity in the area. Benthic foraminifera are valuable indicators of environmental change, playing a significant role in energy transfer and fast carbon consumption. In her doctoral research, Thaise Ricardo de Freitas integrated biogeochemical and ecological studies to quantify the contribution of benthic foraminifera to carbon processing and to examine how environmental factors and seasonal fluctuations in food supply influence their diversity and distribution in the northern Barents Sea. Arctic benthic foraminifera actively feed on phytodetritus, but differences between scavengers and suspension feeders are relevant. Warming alone didn’t impact overall feeding. Nevertheless, scavenger species adapted to high temperature variation and a steady food supply could be favoured under climate change. The study shows that along the northern Barents Sea margin, the diversity and composition of benthic foraminifera are primarily shaped by water depth, water masses properties, and food availability. Foraminiferal populations exhibit seasonal fluctuations that are not seen in macrofaunal organisms or the sedimentary record. The lack of seasonal or long-term variation in the latter indicates prolonged water residence time and rapid degradation of organic carbon. The complex productivity-diversity relationship observed in the study suggests a mismatch between the timing of resource production in the water column and its utilisation at the seabed. Future climate warming may modify the benthic carbon cycle through species-specific shifts that restructure biodiversity and trophic adaptations.

• Søreide, Janne; Gradinger, Rolf Rudolf; Amargant-Arumi, Marti; Amundsen, Rita; Blitz-Thorsen, Julie & Bodur, Yasemin V. [Show all 33 contributors for this article] (2022). Seasonal cruise Q4 2019 : Cruise Report. Septentrio Academic Publishing. 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.

• Gerland, Sebastian; Wold, Anette; Al-Habahbeh, Amalia Keck; Ortiz, Griselda Anglada; Amargant-Arumi, Marti & Bodur, Yasemin V. [Show all 35 contributors for this article] (2022). Seasonal Cruise Q1 2021: Cruise Report. Septentrio Academic Publishing. Full text in Research Archive

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