Local ice caps in Finderup Land,North Greenland,survived the Holocene Thermal Maximum     

Nicolaj K. Larsen  Laura B. Levy  Astrid Strunk  Anne Sofie Sndergaard  Jesper Olsen  Torben L. Lauridsen 《Boreas: An International Journal of Quaternary Research》2019,48(3):551-562

Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.  相似文献   

Isotopic composition of nitrate in five German rivers discharging into the North Sea   总被引：6，自引：0，他引：6  

Astrid Johannsen  Kirstin Dhnke  Kay Emeis 《Organic Geochemistry》2008,39(12):1678

We determined concentrations and isotopic composition of nitrate in five German rivers (Rhine, Elbe, Weser, Ems, and Eider) that discharge into the North Sea. Samples were obtained on a biweekly to monthly basis and chemical and isotopic analyses were conducted for the period January 2006 to March 2007 at sampling stations situated before estuarine mixing with North Sea water. We observed maximum nitrate loads in winter and fall, when both discharge and concentration of nitrate are highest. Mean annual isotope values in nitrate ranged from 8.2‰ to 11.3‰ for and 0.4‰ to 2.2‰ for . The ranges of isotope values suggest that nitrate in these rivers derives from soil nitrification, sewage, and/or manure. These and published data on other rivers in northern Europe and northern America reveal a correlation between agricultural land use (>60% in the catchment areas of rivers examined) and values. The rivers Rhine, Elbe, Weser and Ems show similar seasonal patterns of the isotopic fractionation of nitrate with increasing values and simultaneously decreasing concentrations during summer months, indicating that assimilation of nitrate is the main fractionation process of riverine nitrate. Isotopic signals in winter are more depleted than the mean summer isotope values, attributed to less microbial activity and assimilative processes. Load weighted nitrate δ¹⁵N of the riverine input to the German Bight Coastal Water mass before estuarine mixing and processing is between 8‰ and 12‰. The high δ¹⁵N value of river nitrate is matched by high δ¹⁵N of nitrate in surface sediments in the German Bight.  相似文献   

Spatial variation in abundance and catch composition of Cancer pagurus in Norwegian waters: biological reasoning and implications for assessment     

Woll  Astrid K.; van der Meeren  Gro I.; Fossen  Inge 《ICES Journal of Marine Science》2006,63(3):421-433

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Some Methods of Binding Prawn Diets and Their Effects on Growth and Assimilation     

Forster  J. R. M. 《ICES Journal of Marine Science》1972,34(2):200-216

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Comparing the Benguela and Humboldt marine upwelling ecosystems with indicators derived from inter-calibrated models   总被引：10，自引：0，他引：10  

Moloney  Coleen L.; Jarre  Astrid; Arancibia  Hugo; Bozec  Yves-Marie; Neira  Sergio; Roux  Jean-Paul; Shannon  Lynne J. 《ICES Journal of Marine Science》2005,62(3):493-502

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Modelling effects of fishing in the Southern Benguela ecosystem   总被引：2，自引：0，他引：2  

Shannon  Lynne J.; Cury  Philippe M.; Jarre  Astrid 《ICES Journal of Marine Science》2000,57(3):720-722

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Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence     

Jacco C. Kromkamp  Edward P. Morris  Rodney M. Forster  Claire Honeywill  Scott Hagerthey  David M. Paterson 《Estuaries and Coasts》2006,29(2):183-196

Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, F_o ¹⁵), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. F_o ¹⁵ was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for F_o ¹⁵. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.  相似文献   

Regional and temporal changes in epizoobiontic bryozoan-communities of Flustra foliacea (Linnaeus, 1758) and implications for North Sea ecology     

F. Bitschofsky  S. Forster  J. Scholz 《Estuarine, Coastal and Shelf Science》2011,91(3):423-433

Until recently, bryozoans have not been used as indicators for changes in bottom communities or climate control in the North Sea Basin, despite a 200-year history of bryozoan collecting. The epizoobiontic bryozoan fauna of Flustra foliacea (Linnaeus, 1758) was analysed on 51 sample stations kept in four German museums. The samples cover the entire North Sea and different time periods (1776–2008, mainly the period of 1904/1905 compared to 1980–87). Cluster analysis shows a differentiation into a northern and a southern North Sea assemblage. The northern assemblage is characterized by Amphiblestrum flemingii (Busk, 1854), Callopora dumerilii (Audouin, 1826) and Tricellaria ternata (Ellis & Solander, 1786), while the southern North Sea is characterized by Electra pilosa (Linnaeus, 1767), Crisia eburnea (Linnaeus, 1758) and Plagioecia patina (Lamarck, 1816). Spatial separation approximately follows the 50 m depth contour. The temporal distribution patterns of bryozoans are discussed in terms of NAO (North Atlantic Oscillation) and temperature variations.  相似文献   

An experimental investigation into ‘pledge and review’ in climate negotiations     

Scott Barrett  Astrid Dannenberg 《Climatic change》2016,138(1-2):339-351

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Atmospheric sensitivity to roughness length in a regional atmospheric model over the Ohio–Tennessee River Valley     

Arturo I. Quintanar  Rezaul Mahmood  Astrid Suarez  Ronnie Leeper 《Meteorology and Atmospheric Physics》2016,128(3):315-330

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