Cheshtaa Chitkara

• Vonnahme, Tobias Reiner; Chitkara, Cheshtaa; Krawczyk, Diana; Meire, Lorenz; Skogseth, Ragnheid & Vader, Anna [Show all 7 contributors for this article] (2025). Abrupt decline of microplankton species richness linked to coastal inflow in an Arctic fjord. Limnology and Oceanography. ISSN 0024-3590. 70(9), p. 2688–2702. doi: 10.1002/lno.70159. Full text in Research Archive Show summary

  Abstract Species richness can be important for the functioning and resilience of marine ecosystems, with planktonic protists forming the base of the marine food web. Climate change‐driven shifts in water mass distributions are projected to alter plankton diversity. This process is particularly relevant in Arctic fjords experiencing changes in coastal water inflow, affecting local hydrography, nutrients, and biodiversity. Yet, empirical data on the environmental effects on Arctic plankton diversity are scarce. In this study, we analyze a 15‐year time series from Nuup Kangerlua, a West Greenland fjord, and report an abrupt decline in microplankton (> 20  μ m) species richness following a high‐richness period from 2009 to 2013. The high‐richness period was also characterized by a period of substantial inflow of Atlantic type water (ATW). While ATW did not appear to directly introduce temperate species, it was associated with elevated surface temperatures and nitrate concentrations ‐ conditions that may have supported elevated microplankton richness. Nitrate is typically the key limiting nutrient in Arctic fjords and may support higher microplankton species richness consistent with the Species Energy theory.

• Chitkara, Cheshtaa; Juul-Pedersen, Thomas; Krawczyk, Diana; Søreide, Janne; Vader, Anna & Gradinger, Rolf Rudolf [Show all 8 contributors for this article] (2024). Seasonality in phytoplankton communities and production in three Arctic fjords across a climate gradient. Progress in Oceanography. ISSN 0079-6611. 227. doi: 10.1016/j.pocean.2024.103317. Full text in Research Archive Show summary

  Phytoplankton communities and production in Arctic fjords undergo strong seasonal variations. Phytoplankton blooms are periods with high primary production, leading to elevated algal biomass fueling higher trophic levels. Blooms are typically driven bottom-up by light and nutrient availability but may also be top-down controlled by grazing. While phytoplankton spring blooms are common across all Arctic systems, summer and autumn blooms and their drivers are less predictable. Here we compare the long-term (≥4 years) bloom phenology and protist community composition in three Arctic fjords: Nuup Kangerlua in western Greenland, Ramfjorden in northern Norway, and Adventfjorden in western Svalbard. While Nuup Kangerlua is impacted by tidewater glaciers, Ramfjorden and Adventfjorden are impacted by river-runoff. We discuss and contrast the presence and pre dictability of spring, summer, and autumn blooms in these fjords and the main physical, chemical, and biological drivers. Spring blooms occurred in all three fjords in April/May as soon as sufficient sunlight was available and typically terminated when nutrients were depleted. Chain-forming diatoms together with the haptophyte Phaeocystis pouchetii were key spring bloom taxa in all three fjords. Summer blooms were found in Nuup Kan gerlua and Ramfjorden but were not common in Adventfjorden. In Nuup Kangerlua nutrient supply via subglacial upwelling was the key driver of a diatom-dominated summer bloom. This summer bloom extended far into autumn with strong winds resupplying nutrients to the surface later in the season. In Ramfjorden runoff from a vegetated catchment provided organic nutrients for a flagellate-dominated summer bloom in 2019. A late autumn bloom dominated by Skeletonema spp. and other chain-forming diatoms was present after nutrients were resupplied by wind mixing. In Adventfjorden, we observed only minor summer blooms in 2 of the 8 years, while autumn blooms were never observed. With global warming, we suggest that summer blooms will be negatively impacted in fjords where tidewater glaciers retreat and become land terminating. In fjords with rich vegetated catchments, harmful algal blooms may occur more frequently as summers and autumns become warmer and wetter. However, for fjords in high-Arctic latitudes (>78 N), the day length will continue to restrict the potential for autumn blooms.

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• Marquardt, Miriam; Bodur, Yasemin V.; Chitkara, Cheshtaa; Vader, Anna & Reigstad, Marit (2022). Seasonality and vertical export of marine pelagic protists in the northern Barents Sea investigated by Illumina tag sequencing (2019 and 2021). Full text in Research Archive Show summary

  The Barents Sea is experiencing rapid changes and is therefore regarded as a key area to study the influence of sea ice loss and increased inflow of Atlantic Water on arctic marine ecosystems. Implications for pelagic-benthic coupling are unknown, however, these physical changes will affect the pelagic communities and thereby the vertical transport of organic matter to the seafloor. The seasonality and contribution of marine pelagic protists to the vertical export was investigated by deploying short-term sediment traps along the same latitudinal transect in the Northern Barents Sea during four contrasting seasons (August and December 2019, March and May 2021). Protists (> 0.22 μm) sampled at 3-4 depths from short-term sediment traps were investigated by Illumina tag sequencing of the 18S rRNA gene. Samples for particulate organic carbon (POC), chlorophyll a and microscopic analyses of protist communities were also taken and are presented in Bodur et al. (PB - poster presentation at AeN annual meeting 2022). The high vertical export measured in August and May and low vertical export in winter (PB) agreed with DNA yield measurements in this study. In August Alveolata, especially Ciliophora, Syndiniales and Gymnodinium sp., dominated the vertical export, as well as different Chlorophyta with a predominance of the small arctic species Micromonas polaris. In the dark winter the community was characterized by small-sized heterotrophic taxa such as choanoflagellates (Ophistokonta) and OTUs belonging to Alveolata and Hacrobia. When the light started to come back in March but sea ice extent was at its largest, the vertical export was negligible and only a few protist OTUs were recorded in the sediment traps. The May samples represented a more typical spring bloom community with more phototrophic groups contributing to the vertical export including the ice alga Entomoneis sp. (Bacillariophyceae) at some of the stations. Rhizaria was detected mainly at ice-covered stations in May and August. In contrast to the microscopy results (PB), the molecular tools did not detect a dominance of Phaeocystis pouchetii in August. Seasonality and sea ice cover seem to be major drivers influencing the export of pelagic protists in this study. Our preliminary results demonstrate that vertical export of marine pelagic protists is not limited to the productive period. Small taxa such as Micromonas polaris which was even found at 200 m depth, are important contributors to the vertical export.

• Chitkara, Cheshtaa (2021). Eukaryotes from the (not so) frozen Arctic! - Polar Pint of Science. Full text in Research Archive
• Chitkara, Cheshtaa (2021). Tiny Arctic wildlife matters (sciencenorway.no). doi: https:/sciencenorway.no/blog-nansen-legacy-project-blog-researchers-zone/tiny-arctic-wildlife-matters/1834170. Full text in Research Archive
• Chitkara, Cheshtaa (2021). Mikroliv i Arktis er òg viktig (forskning.no). doi: https:/blogg.forskning.no/arven-etter-nansen/mikroliv-i-arktis-er-g-viktig/1835831. Full text in Research Archive
• Chitkara, Cheshtaa (2025). Arctic marine microbial eukaryotes–Spatiotemporal drivers of community structure and ecological impacts of Atlantification. Universitetet i Agder. ISSN 9788284272610. Full text in Research Archive Show summary

  Microbial eukaryotes serve not only as primary producers but also occupy other trophic modes in the marine food web. In the European Arctic, microbial eukaryotic community dynamics are threatened by the increasing inflow of warm Atlantic water (Atlantification). This process has accelerated the warming of the Arctic, which now experiences temperature increases four times greater than the global average. While previous studies have identified potential shifts in microbial eukaryotic communities, most have not examined these changes over large spatial and temporal scales or considered variations among different fjord types based on geomorphology. To address these gaps, my thesis investigates the community structure and resilience of microbial eukaryotes in the Isfjorden-Adventfjorden (IsA) system from 2011 to 2021, using long-term seasonal observations from continuous sampling. It also compares IsA with other time series across a latitudinal gradient. Water and net samples were collected from four sites—Ramfjorden (RAM), Nuup Kangerlua (NK), Isfjorden-Adventfjorden (IsA), and Billefjorden-Adolfbukta (BAB)—and analysed for DNA (metabarcoding), microscopy, chlorophyll-a biomass, primary production, and grazer abundances. Additionally, nutrients and other environmental drivers were estimated through water column measurements, including temperature, salinity, water mass type, mixed-layer depth, and stratification index. Results indicate that seasonal changes in light availability is the primary driver of community composition across latitudinal gradients, with the influence of varying water masses (temperature and salinity) acting as a significant secondary factor, especially during periods of continuous daylight and prolonged darkness. All fjords exhibited similar spring bloom species; however, the timing varied independently of latitudinal differences. While no clear trend of Atlantification was evident at IsA in the studied timeframe, warming pulses correlated with alterations in microbial eukaryotic abundances. This was particularly notable in the appearance of certain indicator species during the warm 2014 and 2019 years. Furthermore, summer phytoplankton blooms that are not so common at this station were observed during the high Arctic summers of 2017, 2019, and 2021. Changes in community structure at IsA, particularly during the light-rich spring and summer seasons, highlight the ecosystem's vulnerability during these periods. In conclusion this thesis highlights microbial responses to environmental change in the Arctic and the necessity for continued long-term monitoring to decipher ongoing shifts. While the overall eukaryotic microbial community demonstrates resilience, the potential for critical shifts in species richness, diversity and composition could be a concern for ecosystem stability in the future due to prolonged Atlantification.

• Vader, Anna; Marquardt, Miriam; Chitkara, Cheshtaa & Bodur, Yasemin V. (2022). Chlorophyll A and phaeopigments Nansen Legacy cruise 2021703. Norwegian Marine Data Centre. Full text in Research Archive
• 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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