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  • 1
    Electronic Resource
    Electronic Resource
    Lipid Content and fatty acid composition of algal communities in sea-ice and water from the Weddell Sea (Antarctica) (1993)
    Springer
    Polar biology 13 (1993), S. 405-409 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The lipid and fatty acid compositions of microalgae were investigated in sea-ice and water samples from six different habitats of the Weddell Sea (Antarctica). All sea-ice samples and ice-associated water contained high algal biomass dominated by centric and pennate diatoms. Cells partially filled with oil droplets and resting spores were found. In the cells from the ice platelet layer triacylglycerols formed the largest component of the lipids. The fatty acid composition of sea-ice microalgae was dominated by the 16:1(n-7), 16:0, 18:1(n-9) and 20:5 (n-3) fatty acids. Except 18:1, they are typical for diatom fatty acids. These fatty acids were most abundant in pieces of first year ice with a brown colouration (“brown-ice”) and in the water column directly below sea-ice (sub-ice water). The small amounts of non-diatom acids, as 22:6 (n-3) and 18:4 (n-3), clearly showed that the sea-ice communities were not purely composed of diatoms. The most striking difference, in comparison to the general fatty acid composition of diatoms, was the high proportion of the 18:1 fatty acid in all samples, which might be caused by detrital material or lipid accumulation within cells and resting spores. In general, no clear adaptation of the fatty acid composition to the Antarctic and sea-ice environment was found. The fatty acid composition of the particulate matter from the water column was totally different from all other samples dominated by the saturated fatty acids 16:0 and 18:0.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01681982
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    Paper (German National Licenses)
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  • 2
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    Natural variability or anthropogenically-induced variation? Insights from 15 years of multidisciplinary observations at the arctic marine LTER site HAUSGARTEN (2016)
    Elsevier
    In:  Ecological Indicators, 65 . pp. 89-102.
    Details
    Publication Date: 2019-02-01
    Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79° N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a Warm-Water-Anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.ecolind.2015.10.001
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Last interglacial surface water structure in the western Mediterranean (Balearic) Sea: Climatic variability and link between low and high latitudes (2014)
    Elsevier
    In:  Global and Planetary Change, 123 . pp. 67-76.
    Details
    Publication Date: 2019-09-23
    Description: Highlights • Climate progression in the Balearic basin is examined between 140 and 100 ka. • A number of MIS 5e intra-interglacial cooling events is recognized. • MIS 5e climate phasing in the Western Mediterranean resembles the one in the Nordic Seas. • Foraminiferal abundances are strongly tied to a water circulation regime. • The timing of ORL deposition during MIS 5e resembles that of during the Holocene. Abstract A multiproxy analysis based on planktic foraminiferal abundances, derived SSTs, and stable planktic isotopes measurements together with alkenone abundances and Uk′37 SSTs was performed on late MIS 6 to early MIS 5d sediment recovered from Site 975 (ODP Leg 161) in the South Balearic Islands Basin (Western Mediterranean) with emphasis on reconstructing the climate progression of the last interglacial period. A number of abrupt climate changes related to alternative influence of nutrient rich northern and oligotrophic southern water masses was revealed. Heinrich event 11 and cooling events C27, C26, C25, C24, and C23, which have been previously described in the North Atlantic, were recognized. However, in comparison to the eastern North Atlantic mid-latitude region, events C27 and C26 at Site 975 seem to be significantly more pronounced. Together with evidence of a two-phase climate optimum with maximum SSTs reached during its later phase, this implies a close similarity in climate dynamics between the Western Mediterranean and the Nordic seas. We propose that postglacial effects in the Nordic seas had an influence on the western Mediterranean climate via atmospheric circulation and that these effects competed with the insolation force.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.gloplacha.2014.10.004
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  • 4
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    Evidence for a steeper Eemian than Holocene sea surface temperature gradient between Arctic and sub-Arctic regions (1999)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 145 (1-3). pp. 95-117.
    Details
    Publication Date: 2019-09-23
    Description: Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/S0031-0182(98)00104-7
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  • 5
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    Biomarker distributions in surface sediments from the Kara and Laptev seas (Arctic Ocean): indicators for organic-carbon sources and sea-ice coverage (2013)
    Elsevier
    In:  Quaternary Science Reviews, 79 . pp. 40-52.
    Details
    Publication Date: 2014-08-29
    Description: Studies of spatial and temporal changes in modern and past sea-ice occurrence may help to understand the processes controlling the recent decrease in Arctic sea-ice cover. Here, we determined concentrations of IP25, a novel biomarker proxy for sea ice developed in recent years, phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and β-sitosterol) in the surface sediments from the Kara and Laptev seas to estimate modern spatial (seasonal) sea-ice variability and organic-matter sources. C25-HBI dienes and trienes were determined as additional palaeoenvironmental proxies in the study area. Furthermore, a combined phytoplankton-IP25 biomarker approach (PIP25 index) is used to reconstruct the modern sea-ice distribution more quantitatively. The terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries, reflecting the huge discharge by the major rivers Ob, Yenisei and Lena. Maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice-free central part of the Kara and Laptev seas. Neither IP25 nor PIP25, however, shows a clear and simple correlation with satellite sea-ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea-ice diatom in the water column. Differences in the diene/IP25 and triene/IP25 ratios point to different sources of these HBIs and different environmental conditions. The diene/IP25 ratio seems to correlate positively with sea-surface temperature, while negatively with salinity distributions.
    Type: Article , PeerReviewed
    DOI: 10.1016/j.quascirev.2012.11.028
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  • 6
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    The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system (2012)
    Elsevier
    In:  Palaeogeography, Palaeoclimatology, Palaeoecology, 333/334 . pp. 24-39.
    Details
    Publication Date: 2019-09-23
    Description: Temporal and spatial patterns in eastern North Atlantic sea-surface temperatures (SST) were reconstructed for marine isotope stage (MIS) 11c using a submeridional transect of five sediment cores. The SST reconstructions are based on planktic foraminiferal abundances and alkenone indices, and are supported by benthic and planktic stable isotope measurements, as well as by ice-rafted debris content in polar and middle latitudes. Additionally, the larger-scale dynamics of the precipitation regime over northern Africa and the western Mediterranean region was evaluated from iron concentrations in marine sediments off NW Africa and planktic δ13C in combination with analysis of planktic foraminiferal abundances down to the species level in the Mediterranean Sea. Compared to the modern situation, it is revealed that during entire MIS 11c sensu stricto (ss), i.e., between 420 and 398 ka according to our age models, a cold SST anomaly in the Nordic seas co-existed with a warm SST anomaly in the middle latitudes and the subtropics, resulting in steeper meridional SST gradients than during the Holocene. Such a SST pattern correlates well with a prevalence of a negative mode of the modern North Atlantic Oscillation. We suggest that our scenario might partly explain the longer duration of wet conditions in the northern Africa during MIS 11c compared to the Holocene.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.palaeo.2012.03.005
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  • 7
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    Holocene cooling culminates in sea ice oscillations in Fram Strait (2012)
    Elsevier
    In:  Quaternary Science Reviews, 47 . pp. 1-14.
    Details
    Publication Date: 2019-09-23
    Description: A reconstruction of Holocene sea ice conditions in the Fram Strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years BP. Organic geochemical analyses of sediment cores from eastern and western Fram Strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic (and atmospheric) circulation system. By means of the sea ice proxy IP25, phytoplankton-derived biomarkers and ice rafted detritus (IRD) increasing sea ice occurrences are traced along the western continental margin of Spitsbergen throughout the Holocene, which supports previous palaeoenvironmental reconstructions that document a general cooling. A further significant ice advance during the Neoglacial is accompanied by distinct sea ice fluctuations, which point to short-term perturbations in either the Atlantic Water advection or Arctic Water outflow at this site. At the continental shelf of East Greenland, the general Holocene cooling, however, seems to be less pronounced and sea ice conditions remained rather stable. Here, a major Neoglacial increase in sea ice coverage did not occur before 1000 years BP. Phytoplankton-IP25 indices (“PIP25-Index”) are used for more explicit sea ice estimates and display a Mid Holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern Fram Strait, while the inner East Greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire Holocene. Highlights ► Biomarker and IRD data give insight into Holocene sea ice conditions in Fram Strait. ► We find increasing sea ice coverage off West Spitsbergen throughout the Holocene. ► Oceanic/atmospheric variability caused Neoglacial sea ice fluctuations. ► Ice conditions along East Greenland shelf remain rather stable until 1000 years BP.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.quascirev.2012.04.024
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  • 8
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    High-resolution IP25-based reconstruction of sea-ice variability in the western North Pacific and Bering Sea during the past 18,000 years (2016)
    Springer
    In:  Geo-Marine Letters, 36 (2). pp. 101-111.
    Details
    Publication Date: 2019-09-23
    Description: Due to its strong influence on heat and moisture exchange between the ocean and the atmosphere, sea ice is an essential component of the global climate system. In the context of its alarming decrease in terms of concentration, thickness and duration, understanding the processes controlling sea-ice variability and reconstructing paleo-sea-ice extent in polar regions have become of great interest for the scientific community. In this study, for the first time, IP25, a recently developed biomarker sea-ice proxy, was used for a high-resolution reconstruction of the sea-ice extent and its variability in the western North Pacific and western Bering Sea during the past 18,000 years. To identify mechanisms controlling the sea-ice variability, IP25 data were associated with published sea-surface temperature as well as diatom and biogenic opal data. The results indicate that a seasonal sea-ice cover existed during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas during warmer intervals (Bolling-Allerod and Holocene) reduced sea ice or ice-free conditions prevailed in the study area. The variability in sea-ice extent seems to be linked to climate anomalies and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea, especially the Alaskan Stream injection though the Aleutian passes.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1007/s00367-015-0432-4
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  • 9
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    Paleo-sea ice distribution and polynya variability on the Kara Sea shelf during the last 12 ka (2018)
    Springer
    In:  arktos, 4 (1). pp. 1-16.
    Details
    Publication Date: 2021-02-08
    Description: The Kara Sea is an important area for paleo-climatic research since sea ice and brine formation take place on its shelf—two processes inducing supra-regional climatic implications and thereby connecting regional environmental variability with global climatic conditions. To gain information about past sea ice coverage and variations, three sediment cores distributed in the southern and central parts of the marginal Sea were investigated. By applying the sea ice biomarker IP25 and the PIP25 index [phytoplankton biomarker (dinosterol)-IP25 index] post-glacial sea ice variability could be detected in the central Kara Sea (Core BP00-36/4), with most intense sea ice cover between 12.4 and 11.8 ka coinciding with the Younger Dryas (12.9–11.6 ka), and reduced sea ice cover between 10 and 8 ka during the Holocene Thermal Maximum. During the last ~ 7 ka, increasing sea ice indicators might indicate a Holocene cooling trend, probably induced by declining summer insolation. Furthermore, temporal changes in the fast ice—polynya distribution in the southern Kara Sea were detected: expanding fast ice during the late Holocene and a cyclic short-term Holocene climate variability documented by abrupt changes in the sea ice coverage at the BP00-07/7 core site. Core BP99-04/7 from the Yenisei estuary recorded consistently seasonal sea ice cover since ~ 9.3 ka, apart from five short phases of fast ice expansion to the core site. The strong influence of river run-off as well as estuary processes might prevent the detection of (short-term) climatic signals at this study site.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s41063-018-0040-4
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  • 10
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    Holocene changes in sea-ice cover and polynya formation along the eastern North Greenland shelf: New insights from biomarker records (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • Highly variable sea-ice conditions off eastern North Greenland during the Holocene. • The mid to late Holocene is characterized by seasonal to marginal sea-ice conditions. • Seasonal formation of the Northeast-Water (NEW) Polynya during the last 1 ka. Understanding the processes controlling the natural variability of sea ice in the Arctic, one of the most dynamic components of the climate system, can help to constrain the effects of future climate change in this highly sensitive area. For the first time, a high-resolution biomarker study was carried out to reconstruct past sea-ice variability off eastern North Greenland. This area is strongly influenced by cold surface waters and drift ice transported via the East Greenland Current, meltwater pulses from the outlet glaciers of the Northeast Greenland Ice Stream and the build-up of landfast ice. The well-dated Holocene sedimentary section of Core PS93/025 provides insights into variations of the sea-ice conditions (regional and local sea-ice signal), oceanic and atmospheric circulation and the biotic response to these changes. These biomarker records show a reduced to variable sea-ice cover during the early Holocene between 10.2 and 9.3 ka, followed by a steady increase in sea-ice conditions during the mid Holocene. During the last 5–6 ka, sea-ice conditions remained more stable representing a seasonal to marginal sea-ice situation. Based on our biomarker records, stable sea-ice edge conditions, with a fully developed polynya situation occurred since the last 1 ka.
    Type: Article , PeerReviewed
    Format: text
    Format: archive
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