1,721,031 research outputs found
Potential drivers of the downward carbon and particle flux in Arctic marine ecosystems under contrasting hydrographical and ecological situations
Full text linkDetailed predictions of the downward particulate organic carbon (POC) flux in a future Arctic are challenging due to the poor understanding of potential drivers. Short-term sediment traps, partly modified with gel-containing jars, were deployed in the Barents Sea (BS) and in Adventfjorden, Svalbard, to determine the downward POC flux and the particle flux (≥ 0.05 mm equivalent spherical diameter ESDimage) in a parallel manner. In this way, the quality of the sinking material could be linked to the downward POC flux and this link gave new insights into potential drivers of the carbon flux. In the Barents Sea, the highest downward POC flux (260-670 mg POC m^-2 d^-1) occurred in ice-free, deeply mixed waters. Sinking particles were < 1.00 mm ESDimage and had a high POC: volume ratio. Pulsed nitrate injections from deeper layers most likely stimulated new production, and the downward flux was enhanced by vertical mixing and “biomass repackaging” into fast-sinking pellets by zooplankton. In Adventfjorden, the highest POC flux (770-1530 mg POC m^-2 d^-1) occurred during autumn, coinciding with glacial run-off. Large, fast-sinking particles (0.05-3.62 mm ESDimage) apparently enhanced the downward POC, despite their low POC: volume ratio. In addition, entrained terrestrial POC enhanced the downward POC flux. Ballasting effects by entrained lithogenic material, flocculation and aggregate formation by pteropods are likely, but need further investigation. The present study illustrates that a high downward POC flux in Arctic marine ecosystems may occur during the phytoplankton bloom, but the highest POC downward fluxes found in the BS and Adventfjorden were found in deep-mixed waters during a post bloom situation or during an autumn situation influenced by glacial run-off, respectively. It is also shown, that a high POC downward flux may not only be caused by large particles, but also by small particles with a high POC: volume ratio
Ecophysiological Responses of Sea Ice Algae and Phytoplankton to a Changing Arctic
Full text linkThe 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
Vertical nitrate fluxes in the Arctic Ocean
Full text linkUpward mixing of remineralized nutrients is essential for photosynthesis in the upper ocean. Weak vertical mixing, which restricts nutrient supply, and sea ice, which leads to low light levels, conspire to severely inhibit marine primary productivity in the Arctic Ocean. However, little has been known about their relative contributions. No large-scale quantitative estimates of the vertical nutrient supply had previously been presented, which has impeded an understanding of its role in shaping the ecology and carbon cycle of the Arctic Ocean.
In order to estimate the vertical flux of nitrate into the surface layer in contrasting hydrographic and dynamic regimes, profiles of turbulent microstructure and nitrate concentrations were measured as part of a number of cruises and ice camps in the area extending from eastern Fram Strait into the Nansen Basin. These have been supplemented with obervations of the seasonal nutrient cycle at a mooring in the same area, and a reanalysis of available data on nitrate concentrations and turbulent mixing in other parts of the central Arctic Ocean.
Hydrography was found to be the biggest driver of variability in nitrate fluxes. Strong stratification, wherever encountered, restricted nitrate supply, often in concert with concurrently weak turbulent mixing, both in the seasonal nitracline (0.3–0.7 mmol N m-2 d-1) and the deep basin (0.01–0.2 mmol N m-2 d-1). Thus deep winter mixing supplies the bulk of the nitrate pool on the relatively productive shelves (e.g. 2.5 mmol N m-2 d-1 in the inflow of Atlantic Water during winter), but in the strongly stratified Canadian Basin, fluxes are low year-round (on the order of 0.01 mmol N m-2 d-1) and place a tight limit on new production. Only the weakly stratified Atlantic derived water in the Nansen Basin close to Fram Strait seems to have a certain potential to support future increases in new production under a seasonal ice cover
Trophic relationships and the role of Calanus in the oceanic ecosystems south and north of Iceland
Full text linkThe waters south and north of Iceland vary greatly both oceanographically and biologically with the rather stable and warm Atlantic waters south and west of Iceland and the more variable and cold Arctic and sub-Arctic waters, north and east of Iceland. The aim of this study was to increase the knowledge on the role of Calanus copepods and trophic relations of the key components of the oceanic ecosystems south-west (over the Reykjanes Ridge) and north (in the Iceland Sea) of Iceland. The trophic relationships and energy transfer to higher trophic levels were estimated by using fatty acid trophic markers, by comparing fatty acid profiles among species and by applying stable isotopes of carbon and nitrogen. The inter-annual variability in abundance and community composition of zooplankton on the shelves south and north of Iceland in relation to environmental condition in spring were also observed. The energy rich Calanus species are key links between primary producers and higher trophic levels in the Icelandic waters. The Calanus species dominate the zooplankton biomass around Iceland and their markers (20:1n9 and 22:1n11) are found in high amount in animals at higher trophic levels. Calanus finmarchicus plays important role as a forage species in the Atlantic water south-west of Iceland while its high importance is replaced by the larger lipid rich C. hyperboreus in the Arctic and sub-Arctic waters north of Iceland. Even though Calanus based food-web is the main driver in both areas, there exist a pathway where Calanus species are of less importance and the energy is channeled via euphausiids to higher trophic levels. Around four trophic levels were observed in the two oceanic ecosystems where adult fish occupied the highest trophic levels. Over the Reykjanes Ridge vertically migrating mesopelagic fish, in pronounced deep-scattering layers, are actively bringing energy to deeper layers by feeding on C. finmarchicus in the upper layers. In the Iceland Sea comparable deep-scattering layers were not observed. Epipelagic schools of capelin (Mallotus villosus) are important component of the pelagic ecosystem in the Iceland Sea. After feeding intensively in the Iceland Sea, they migrate and thus transfer the energy to adjacent ecosystems. The ecosystem around Iceland is extremely sensitive to climate variations. Increase in sea temperature has been related to shift in distribution and feeding migrations of capelin in the Iceland Sea with the result of diet switch of older capelin. The importance of the Arctic amphipod Themisto libellula in the diet of adult capelin increased in their new distribution area in the colder western part of the Iceland Sea. A shift in distribution of species may thus influence the whole ecosystem structure and food web interactions in larger area. This study presents novel important knowledge on the food web structures and carbon flow in Icelandic waters
Fate of production in the Arctic seasonal ice zone. An investigation of suspended biomass, vertical export and the impact of grazers during the onset of the spring bloom north of Svalbard
Full text linkIn the Arctic Ocean, biological productivity is largely determined by sea ice, making the seasonal sea ice zone (SSIZ) its most productive region. The current study is a combined investigation of the suspended biomass, vertical export of organic material, and potential retention processes by zooplankton, during a crucial period of bloom development in the Eurasian SSIZ north of Svalbard, where few studies have previously been done. To evaluate the magnitude and composition of the bloom and subsequent vertical export, short-term sediment traps, at five depths between 30 and 200m, were deployed at eight sea ice stations. Daily patterns of chlorophyll a, particulate organic carbon (POC) and contribution of zooplankton fecal pellets (FP) were discovered in distinct assemblages – conditions ranging from pre- to mid-bloom development. Daily loss rates of POC increased from 0.6 to 2.7% as the bloom progressed from a pre- to mid-bloom phase, but the vertical carbon export rates in the shallower depths exceeded those in the deeper layers as the bloom developed accordingly. Phytoplankton carbon (PPC) was found to be a more important component to the vertical POC flux than FP carbon (FPC), especially as the bloom progressed. PPC and FPC contributed 5-75% and 0.5-24% to POC export respectively. The contribution of FPC flux to total POC flux was found to be in line with previous studies, revealing that the relative contribution FPC flux to vertical carbon export is variable but may diminish northward with the SSIZ. The impact of grazers was further investigated through FP production experiments of key Calanus species. The proportion of Calanus finmarchicus community-produced FPC exported to 40m decreased from 36% to 4% from early- to mid-bloom conditions, suggesting stronger zooplankton-mediated retention as the bloom intensifies. Additionally, under slower bloom development, grazers appeared to be effectively controlling and inhibiting the accumulation of biogenic biomass and subsequent vertical flux. The current study reveals that the northern ice-covered Barents Sea shelf break can provide comparable vertical export rates of organic material during the spring bloom to the productive and shallower central Barents Sea
Annual population dynamics of the small harpacticoid copepod Microsetella norvegica in a high latitude fjord (Balsfjord, Northern Norway)
Full text linkAnnual population dynamics and vertical distribution of the small (< 0.6 mm) hapacticoid copepod, Microsetella norvegica, was investigated through monthly sampling at station Svartnes in Balsfjord, Northern Norway from May 2013 to June 2014. M. norvegica is a pelagic particle feeder, and distributed from temperate waters to sub-arctic fjords, but frequently underestimated because of its small size. The species is therefore often overlooked and its biology poorly understood. In order to sample all stages of M. norvegica, from nauplii to adult appropriately, we used both a WP-2 net with 90 µm mesh size (175-50 and 50-0 m), and a 20 L Go-Flo water bottle (5, 20, and 50 m depth). Nauplii and copepodite stages from CI to adult were identified to determine total abundance, population structure, vertical and seasonal distribution. There were great differences in abundances and stage distribution dependent on sampling method. The Go-Flo bottle sampled all stages, from nauplii to adult stages, while the WP-2 net collected mostly adult stages. The discrepancy in sampling efficiency between the two gears is also clearly reflected when comparing the abundances. In June 2014 the total maximum abundance of M. norvegica, when integrating Go-Flo from 50-0 m, was 7.8 x 106 ind. m-2. When sampling with WP-2 we found a total maximum abundance of 1.2 x 106 ind. m-2. Minimum abundances of M. norvegica were found in January 2014. Females carrying egg-sac were observed in April to June and in August. Females carrying egg-sac peaked in June, with a total abundance of 754 270 ind. m-2, when integrating Go-Flo from 0 to 50 m. Also, total abundance of females and egg-sacs in the upper 50 m was used to calculate the egg-sac:female ratio, where we found the highest ratio at 1.6 in May. Nauplii and small copepodite stages peaked in the upper 50 m in spring and summer, suggesting that their main reproductive period takes place in May and June. The older copepodite stages from CIV to adults dominated in winter from October to March. To investigate the body condition of females during winter, carbon content of M. norvegica was measured, and was found to have a strong seasonality. The lowest carbon content, when normalized to length, was found in January, and was highest in May. M. norvegica was highly abundant year-round in Balsfjord, but the sampling design is crucial for more reliable determination of their true abundance and population dynamics. Improved quality of abundance estimates may be a first step towards improving our knowledge about the biology and ecological role of this tiny but potentially important copepod
Sampling strategies, distribution and concentration of planktonic salmon lice copepods in the Outer Hardangerfjord and the Altafjord
Full text linkSalmon lice are parasitic copepods with three planktonic larvae stages, consisting of two nauplii stages and a copepodite stage. The parasite spread during these stages as plankton, and with the increased number of host represented by salmonid fish in aquaculture it is important to know the concentrations and ecology of the fee-living stages. Both Lepeophtheirus salmonis and Caligus elongatus are parasitic lice on salmon and trout, and will be referred to as salmon lice through this thesis.
Finding suitable sampling strategies to collect salmon lice copepods makes it possible to obtain field observed concentrations of salmon lice in their infective stage and in open water. Through this thesis, three different kinds of gear (Go-Flo water sampler, net hauls and a provisional bilge pump) and in total seven different strategies (different depths and volumes sampled) have been tested. In total 117 samples were collected and analysed. The vertical net haul proved to be best suited for the task of collecting salmon lice copepods under sub-optimal weather conditions, as often is the case in Norwegian fjords. In the two fjords investigated, the outer Hardangerfjord and the Altafjord concentrations ranged between 0-30 ind. m-3 and between 0-13 ind. m-3, respectively. These field data were compared with results from a hydrodynamic salmon lice model, and concluded that the range of concentrations found in the field was within the same range of concentrations simulated by the model. The concentrations obtained were also similar to concentrations found during previous studies in aquaculture impacted regions around Scotland and the Faroe Islands. This study found that areas less influenced by aquaculture had lower concentrations of salmon lice copepods (10 km from the nearest salmonid farm. Due to rough weather during the October cruise and only sampling through the autumn in Altafjord, this thesis had insufficient data to determine any seasonal distribution of salmon lice.
Knowledge on field concentrations and the spatial distribution of salmon lice is important to ensure a sustainable growth and management of the salmon farm industry in Norway
Carbon Bridge to the Arctic
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Carbon Bridge to the Arctic
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
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