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dc.contributor.advisorReigstad, Marit
dc.contributor.authorKvernvik, Ane Cecilie
dc.date.accessioned2019-04-12T10:57:53Z
dc.date.available2019-04-12T10:57:53Z
dc.date.issued2019-03-29
dc.description.abstractThe ice-covered seas of the Arctic have two major types of primary producers; phytoplankton growing in open waters and sea ice algae growing within and on the underside of the sea ice. This thesis investigates the controlling role of light availability on Arctic pelagic and sympagic (i.e. ice-associated) algae, and how light-induced responses are modulated by NO3 and pCO2 levels. A combination of field sampling, in situ experimental studies, and laboratory experiments were performed in order to investigate photophysiological and biochemical characteristics of pelagic and sympagic algae and identify their respective responses to changes in their abiotic environment. The results revealed that in both pelagic and sympagic algae, a change in light availability exerted stronger control on photophysiological and biochemical characteristics than variations in NO3 and pCO2 levels. Pelagic algae have evolved pronounced mechanisms into being flexible with different irradiances they encounter in a wind-mixed pelagic environment. Even though the ambient light during the polar night was not enough to support any measurable net primary production, they maintained an active photosynthetic apparatus, which ensured a fast recovery and utilization of even very low constant irradiances upon re-illumination. Furthermore, they effectively exploited very low irradiances for carbon fixation, handled instantaneous light stress well, and exhibited high photoacclimative capacity towards increasing irradiances. In conclusion, these results imply a high capacity of pelagic algae to compensate for changes in the environment, which can be understood in light of environmental conditions they have adapted to. Sympagic algae also efficiently harvested low irradiances for light-dependent photosynthesis. However, they probably used more of the photosynthetic resources for tolerating extreme physico-chemical properties within sea ice, which resulted in lower rates of carbon assimilation compared to pelagic algae. Sympagic algae also showed higher sensitivity towards high light than pelagic algae, where the highest irradiances caused dysfunctional photophysiology and non-vital cells in the former. Moreover, they exhibited higher sensitivity towards a combination of multiple stressors. The Arctic ocean is changing fast in many respects, amongst which increased light regimes, stratification, and ocean pCO2 levels stand out as being most important for microalgal communities. The results of this study suggest that sea ice algae will struggle more with adapting to the expected environmental changes compared to phytoplankton. We therefore anticipate a change in sea ice-based vs. pelagic primary production with respect to timing and quantity in a future Arctic, with potentially cascading effects on downstream food webs. The clearly distinct responses of pelagic vs. sympagic algae to environmental differences also need to be incorporated into model-based scenarios of future Arctic algae blooms and considered when predicting implications for the entire ecosystem.en_US
dc.description.doctoraltypeph.d.en_US
dc.description.popularabstractSingle-celled algae are a main source of food for aquatic life and account for half of the photosynthetic activity on earth. The ice-covered seas of the Arctic have two major types of these primary producers: phytoplankton growing in open waters and sea ice algae growing within and on the underside of the sea ice. In the spring, algae populations grow exponentially – a spectacle known as an algal bloom. Sea ice algae production typically peaks in early spring when pelagic production is thought to be minimal, extending the period of primary production in spring. Sea ice algae and phytoplankton blooms do not only differ with respect to timing but are also utilized by different groups of grazers. Needless to say, it is important to understand how, and to what extent, sea ice-based vs. pelagic primary production will change with respect to timing and quantity in a future Arctic. This thesis investigates the controlling role of light availability on Arctic phytoplankton and sea ice algae. We assessed their photosynthetic performance (in terms of light-dependent photosynthesis, carbon fixation as well as pigment composition) towards changes in their abiotic environment; In particular, variations in light and nutrient levels as well as their response towards ocean acidification (i.e. increased CO2 levels and lowered ocean pH). The high Arctic is characterized by an extreme seasonal change in light availability, and at the study sites used in this thesis (~78°N) the sun stays above the horizon for approximately four months (polar day), and below the horizon for another four months (polar night). This particularly challenging for photosynthetic organisms, which captures the energy from sunlight and uses it to produce organic compounds. The results from this thesis, show that Arctic phytoplankton has evolved pronounced mechanisms into being flexible with different light levels they encounter; They maintained the photosynthetic machinery during the polar night, effectively exploited very low light for carbon fixation, handled light stress well, and successfully acclimated and took advantage of high light. Arctic pelagic phytoplankton also showed a high resilience towards variations in nutrient and CO2 levels. In contrast, the ability of sea ice algae to take advantage of increases in light was restricted to rather low ranges, and they exhibited much higher sensitivity towards high light stress compared to phytoplankton. Furthermore, they showed an increased sensitivity towards high light stress when they were exposed to multiple stressors (i.e. nutrient depletion and ocean acidification). The Arctic is warming more rapidly than any other oceanic region on the planet (commonly termed Arctic amplification), leading to reduced sea ice extent and thickness, earlier melt onset and declining snow cover. As a result light levels are expected to increase in a future Arctic and nutrient regimes are expected to change due to increased stratification of the water layers. Furthermore, atmospheric pCO2 is rising, leading to elevated concentrations of CO2 and lowered pH in seawater. Due to all the ongoing and predicted changes it is obvious that productivity in the Arctic is going to change – but still, there is very little reliable information available on that, and modeling attempts are limited. Based on the results from this study, it is reasonable to assume that the balance between sea ice-based and oceanic production will change with respect to timing and quantity in a future Arctic, with potentially cascading effects on higher trophic levels.en_US
dc.description.sponsorshipSvalbard Science Forum Arctic field granten_US
dc.identifier.isbn978-82-8266-167-6
dc.identifier.urihttps://hdl.handle.net/10037/15199
dc.language.isoengen_US
dc.publisherUiT The Arctic University of Norwayen_US
dc.publisherUiT Norges arktiske universiteten_US
dc.relation.haspart<p>Paper I: Kvernvik, A.C., Hoppe, C.J.M., Lawrenz, E., Prášil, O., Greenacre, M., Wiktor, J.M. & Leu, E. (2018). Fast reactivation of photosynthesis in arctic phytoplankton during the polar night. <i>Journal of Phycology, 54</i>, 461-470. The article is available in the file “thesis_entire.pdf”. Also available at <a href=https://doi.org/10.1111/jpy.12750>https://doi.org/10.1111/jpy.12750</a>. <p>Paper II: Kvernvik, A.C., Hoppe, C.J.M., Greenacre, M., Verbiest, S., Wiktor, J.M., Gabrielsen, T.M., Reigstad, M. & Leu, E. Arctic sea ice algae differ markedly from phytoplankton in their ecophysiological characteristics. (Manuscript). <p>Paper III: Kvernvik, A.C., Rokitta, S.D., Leu, E., Harms, L., Gabrielsen, T.M., Rost, B. & Hoppe, C.J.M. Higher sensitivity towards light stress and ocean acidification in an Arctic sympagic compared to a pelagic diatom. (Submitted manuscript).en_US
dc.relation.projectIDinfo:eu-repo/grantAgreement/RCN/KLIMAFORSK/243702/Norway/Future Arctic Algae Blooms - and their role in the context of climate change/FAABulous/en_US
dc.rights.accessRightsopenAccessen_US
dc.subject.courseIDDOKTOR-002
dc.subjectVDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Plantefysiologi: 492en_US
dc.subjectVDP::Mathematics and natural science: 400::Zoology and botany: 480::Plant physiology: 492en_US
dc.subjectVDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Økologi: 488en_US
dc.subjectVDP::Mathematics and natural science: 400::Zoology and botany: 480::Ecology: 488en_US
dc.titleEcophysiological Responses of Sea Ice Algae and Phytoplankton to a Changing Arcticen_US
dc.typeDoctoral thesisen_US
dc.typeDoktorgradsavhandlingen_US


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