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  • 1
    Digitale Medien
    Digitale Medien
    Photosynthetic responses of Arctic sea-ice microalgae to short-term temperature acclimation (1989)
    Springer
    Polar biology 9 (1989), S. 437-442 
    Details
    ISSN: 1432-2056
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In April-May 1986, sea-ice microalgae (southcastern Hudson Bay, Canadian Arctic) were acclimated to temperatures ranging from-1.5° to 10°C for short periods (3 h), after which photosynthesis and carboxylating enzyme activities were measured. P max b increased after acclimation to 10°C while photosynthetic parameters α, β and Ik as well as activities of PePC and PePCk did not show any significant change after temperature acclimation. Contrary to P max b , the activity of RuBPC was lower for algae acclimated to 3°-10°C, the observed response increasing with temperature. There was also a seasonal trend in the response of RuBPC, the ability to compensate for rapid temperature changes being higher in May. These results show that ice algae were photosynthetically adaptable in the range of temperatures tested. For RuBPC, adaptability developed seasonally when the environmental temperature started to fluctuate in May. Photosynthetic acclimatization to temperature may be of high ecological significance in extending the growth season of ice-algae.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00443230
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  • 2
    Digitale Medien
    Digitale Medien
    Springtime coupling between ice algal and phytoplankton assemblages in southeastern Hudson Bay, Canadian Arctic (1993)
    Springer
    Polar biology 13 (1993), S. 441-449 
    Details
    ISSN: 1432-2056
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Microalgal assemblages from the bottom ice, the ice-water interface and the water column were systematically sampled from April to June 1986, in southeastern Hudson Bay (Canadian Arctic). The taxonomic similarity between samples from the three environments was assessed using a clustering procedure. There were two groups that comprised samples from both the ice-water interface and the water column, while five other groups were made of samples originating from a single environment. Taxonomic compositions of the two mixed groups suggest two types of connexion between the ice-water interface and the water column, i.e. before the phytoplankton bloom, there was seeding of the water column by ice algae and, during ice melt, interfacial algae contributed to the water column communities that were otherwise typically phytoplankton. Overall, the phytoplankton community underwent a succession from pennate to centric diatoms. Sinking rates of algae from the ice-water interface were estimated using settling columns (SETCOL). The sinking rates increased seasonally (0.4–2.7 m d−1), which enhanced accessibility of ice-algal cells to the pelagic grazers. Ice algae contributed to water column production as they became accessible to the pelagic grazers, and also by seeding the water column before the phytoplankton bloom.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00233135
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  • 3
    Digitale Medien
    Digitale Medien
    Effects of clonidine, dihydralazine and splanchnic nerve stimulation on the release of neuropeptide Y, MET-enkephalin and catecholamines from dog adrenal medulla (1993)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 348 (1993), S. 379-384 
    Details
    ISSN: 1432-1912
    Schlagwort(e): Catecholamines ; Neuropeptides ; Adrenal medulla ; Clonidine ; Dihydralazine ; Splanchnic nerve stimulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Various neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release (evaluated by adrenal vein plasma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkephaline (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)] from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of clonidine (10 μg/kg) and dihydralazine (1 mg/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. The increment in the release of catecholamines and neuropeptides was evaluated for dihydralazine and splanchnic nerve stimulation. Dihydralazine (at its maximal effect) induced a significant preferential increase in catecholamines (expressed as mean (SEM): NA: 17.3 (5.4) fold, A: 13.1 (2.6) fold) and ME (16.0 (7.1) fold) versus basal values. However, the significant increase in NPY-LI was only 2.0 (0.4) times the baseline. Splanchnic nerve stimulation induced a frequency-dependent increase in catecholamines and neuropeptides. When the stimulation frequency was increased from 1 Hz to 5 Hz, NA and A levels increased 17.9 (4.3) and 14.0 (2.2) fold, respectively and ME levels 14.1 (3.0) fold. By contrast, NPY-LI was increased only 2.3 (0.3) fold under the same conditions. Increasing the stimulation frequency from 5 Hz to 10 Hz resulted in similar elevations of NA, ME, and NPY-LI adrenal plasma levels (about 4 times) whereas A only increased twice. Clonidine decreased catecholamine and ME adrenal plasma levels (the maximal percent decrease when compared with control values was about 75%) whereas NPY adrenal plasma levels remained unchanged. In conclusion, the present data indicate that (i) both adrenal ME and NA always exhibit corelease in a parallel fashion which is not the case for NPY art; (ii) different populations of chromaffin vesicles could be preferentially mobilized according to different physiological and pharmacological patterns.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00171337
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  • 4
    Digitale Medien
    Digitale Medien
    Is neuropeptide Y co-released with catecholamines in experimental arterial hypertension following sinoaortic denervation? (1992)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 345 (1992), S. 431-436 
    Details
    ISSN: 1432-1912
    Schlagwort(e): Catecholamines ; NPY ; Conscious dogs ; Sinoaortic denervation ; Yohimbine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The release of catecholamines and their co-neurotransmitter neuropeptide Y (NPY) was investigated in conscious dogs with neurogenic arterial hypertension elicited by sinoaortic denervation. One month after denervation, an elevation of catecholamine levels (measured by HPLC) without elevation of NPY-like immunoreactivity (NPY-LI) levels in plasma (evaluated by RIA) has been found. This dissociation could be explained by 1) a transient release of NPY during the first weeks after surgery, 2) a depletion of neuronal NPY due to the permanent sympathetic stimulation, or 3) an insufficient increase in sympathetic tone. To test these hypotheses, we investigated the time courses of catecholamine and NPY-LI levels in arterial plasma during the first five weeks after sinoaortic denervation and responses to yohimbine (an alpha2 antagonist which enhances transmitter release). Resting NPY-LI levels in plasma remained normal during the first five weeks after sinoaortic denervation. In normal dogs, a high dose of yohimbine (0.5 mg/kg i. v.) elevated both catecholamine (6-fold) and NPY-LI levels (1.5-fold), whereas a lower dose (0.05 mg/kg i. v.) induced a two fold elevation of catecholamine levels without changing NPY-LI concentrations. In sinoaortically denervated dogs, yohimbine elicited elevation of both catecholamines and NPY-LI whatever the dose used. Thus, neurogenic arterial hypertension in dogs seems to involve catecholamines but not NPY. Moreover, the present work suggests that a high level of sympathetic stimulation is required for a co-release of catecholamines and NPY.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00176621
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  • 5
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    Phaeocystis versus diatoms blooms in the ice covered European Arctic (2018)
    In:  EPIC3SCAR/IASC Open Science Conference & Open COMNAP Session, Davos, 2018-06-19-2018-06-23
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    Publikationsdatum: 2019-04-23
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
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  • 6
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    Contrasting Ice Algae and Snow‐Dependent Irradiance Relationships Between First‐Year and Multiyear Sea Ice (2019)
    In:  EPIC3Geophysical Research Letters, 46(19), pp. 10834-10843, ISSN: 0094-8276
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    Publikationsdatum: 2020-05-12
    Beschreibung: During the 2018 Multidisciplinary Arctic Program‐Last Ice in the Lincoln Sea, we sampled 45 multiyear ice (MYI) and 34 first‐year ice (FYI) cores, combined with snow depth, ice thickness, and transmittance surveys from adjacent level FYI and undeformed MYI. FYI sites show a decoupling between bottom‐ice chlorophyll a (chl a) and snow depth; however, MYI showed a significant correlation between ice‐algal chl a biomass and snow depth. Topographic control of the snow cover resulted in greater spatiotemporal variability of the snow over the level FYI, and consequently transmittance, compared to MYI with an undulating surface. The coupled patterns of snow depth, transmittance, and chl a indicate that MYI provides an environment with more stable light conditions for ice algal growth. The importance of sea ice surface topography for ice algal habitat underpins the potential ecological changes associated with projected increased ice dynamics and deformation.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 7
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    The importance of the Atlantic inflow for shaping productivity and biodiversity of microbial communities along the ice covered European Arctic margin in spring (2017)
    In:  EPIC3Arctic Frontier 2017, 2017-01-23-2017-01-27
    Details
    Publikationsdatum: 2017-02-01
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
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  • 8
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    Pan-Arctic sea ice-algal chl a biomass and suitable habitat are largely underestimated for multiyear ice (2017)
    In:  EPIC3Global Change Biology, 23(11), pp. 4581-4597, ISSN: 13541013
    Details
    Publikationsdatum: 2018-01-15
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
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  • 9
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    Comparing springtime ice-algal chlorophyll a and physical properties of multi-year and first-year sea ice from the Lincoln Sea (2015)
    PUBLIC LIBRARY SCIENCE
    In:  EPIC3PLoS ONE, PUBLIC LIBRARY SCIENCE, 10(4), pp. 1-26, ISSN: 1932-6203
    Details
    Publikationsdatum: 2015-11-20
    Beschreibung: With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , peerRev
    Format: application/pdf
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  • 10
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    Snow depth on Arctic sea ice derived from airborne radar measurements (2019)
    In:  EPIC3IGS Sea Ice Symposium: Sea Ice at the Interface, Winnpeg, Manitoba, Canada, 2019-08-19-2019-08-23
    Details
    Publikationsdatum: 2019-09-13
    Beschreibung: The snow layer on sea ice has high importance for polar climate as it affects heat, radiation, and fresh-water budgets. Additionally, snow loading is a critical parameter for the sea-ice freeboard-to-thickness conversion for satellite radar and laser altimeters. Despite its importance, there is a lack of snow observations spanning different spatial and temporal scales, thus introducing a significant source of uncertainty to altimetric sea-ice thickness retrievals. The ultra-wideband microwave radar (UWBM) Snow Radar, a 2–18 GHz airborne frequency-modulated continuous-wave (FMCW) radar developed by the Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas, can accurately detect the air/snow and snow/ice interfaces to measure snow thickness. Since 2009, an airborne Snow Radar has been operated onboard NASA’s Operation IceBridge (OIB) campaigns. In 2017, the UWBM Snow Radar was operated for the first time on an Alfred Wegener Institute (AWI) research aircraft, together with an airborne laser scanner for surface topography and freeboard measurements and an electromagnetic induction sounding instrument (EM Bird) to measure total ice thickness. The AWI airborne surveys operate at a low survey altitude (60 m a.g.l.) and slow aircraft speed, enabling fine-resolution mapping of the snow layer. Furthermore, the unique instrument setup on board the AWI research aircraft and the concurrent measurements of snow freeboard, total sea-ice thickness and snow depth allow us to directly investigate the freeboard-to-thickness conversion on regional scales for the first time. Here, we evaluate the performance of the radar installation and present radar-derived snow depth retrieved with a wavelet technique from recent airborne campaigns, PAMARCMiP2017 and IceBird winter 2019, over Arctic sea ice in the Greenland, Lincoln, Beaufort and Chukchi Seas and the central Arctic Ocean in March–April of the respective years.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
    Format: application/pdf
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