ALBERT

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 ß-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 paleoenvironmental 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, show 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.

Description: Arctic sea-ice extent has been declining rapidly throughout the past decades. To understand the past temporal and spatial sea-ice variability is of significant importance for predicting the future development. Within this thesis, the recently developed sea-ice proxy IP25, exclusively produced by diatoms in sea ice, has given a new insight into the reconstruction of sea ice across major parts of the Arctic Ocean during modern time and the Last Glacial Maximum (LGM). In the first study, determination of IP25, phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and ß-sitosterol) in surface sediments from the Kara and Laptev seas is used to estimate modern spatial (seasonal) sea-ice variability and organic-matter sources. C25-HBI diene and triene were determined as additional paleoenvironmental proxies in the study area. Furthermore, a combined phytoplankton-IP25 biomarker approach (PIP25 index) is used to reconstruct the modern seaice distribution more quantitatively. Neither IP25 nor PIP25, however, show a clear and good correlation with satellite sea-ice distribution due to the complex environmental conditions in our study area. Differences in the diene/IP25 and triene/IP25 ratios point to different sources of these HBIs and different environmental conditions. The diene/IP25 ratio correlates positively with sea-surface temperature, and thus might be used as a potential SST index. Further studies are, however, needed to validate this index. Furthermore, in the second study, a comprehensive data set of these biomarkers was produced using surface sediment samples from the Central Arctic Ocean proper (〉80°N latitude) and the Chukchi Plateau/Basin. In addition, published data from other Arctic and sub-Arctic regions were added to the new data to generate an overview distribution map of IP25 across major parts of the Arctic Ocean. The phytoplankton biomarkers brassicasterol and dinosterol were also determined alongside IP25 to distinguish between two extreme scenarios, either ice-free or permanent ice conditions. PIP25 index values show a positive correlation with satellite-derived spring/summer sea-ice concentration. When calculating and interpreting the PIP25 proxy for reconstructions of Arctic sea-ice conditions, the uncertainties of the origin of the sterols need to be considered and thus more than one phytoplankton biomarker should be involved and the resulting PIP25 values should be compared. In the third study, Arctic Ocean sea-ice conditions during the Marine Isotope Stage (MIS) 3–1 were reconstructed by means of IP25 and phytoplankton-derived biomarkers data obtained from 7 sediment cores. The summer ice edge remained north of the Barents Sea even during extremely cold (i.e., Last Glacial Maximum (LGM)) as well as during warm periods (i.e., Bølling-Allerød). Spatial sea-ice conditions were reconstructed for the Central Arctic Ocean and adjacent areas by means of biomarker data from 16 sediment samples covering the LGM time-slice. The western Spitsbergen margin and northern Barents Sea margin were found to be productive regions. In contrast, the LGM high Arctic (〉84°N) was covered by thick permanent sea ice throughout the year with rare break up. The spring/summer sea-ice margin significantly extended southwards during LGM in the marginal seas.

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.

Description: Sea ice is a fundamental component of Earth's climate system, contributing to heat reduction (albedo) and deep-water formation. In order to understand processes controlling the recent dramatic reduction in Arctic sea ice cover, it is essential to determine spatial and temporal changes in sea ice occurrence and its natural variability in the present and past. Here, we present new biomarker data from surface sediments and related to the modern spatial (seasonal) sea ice variability in the Kara and Laptev seas. That means, we determined concentrations of the sea ice diatom-derived biomarker "IP25" (isoprenoid with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and ß-sitosterol) to estimate recent sea ice conditions in the study area. Assessment of sea ice conditions based on these biomarkers shows that a marginal ice zone exists along the continental shelf/slope of Kara and Laptev seas during summer/early fall. Elevated IP25 as well as brassicasterol and dinosterol values occurring in the central Kara and Laptev seas are related to extended sea-ice-cover and higher primary production (close to ice edge situation). Further to the north, lower IP25 and phytoplankton biomarker concentrations point to a more close sea ice cover situation. There are no IP25 and very low brassicasterol and dinosterol concentrations in the river mouths but high terrigenous biomarker (campesterol and ß-sitosterol) concentrations due to the fresh water inflow transporting terrigenous matter to estuaries. A combined phytoplankton-IP25 biomarker approach ("PIP25 index"; Müller et al., 2009, 2011) is used to reconstruct the modern sea ice distribution more quantitatively.

Description: Sea ice is a fundamental component of Earth’s climate system, contributing to heat reduction (albedo) and deepwater formation. In order to understand processes controlling the recent dramatic reduction in Arctic sea ice cover, it is essential to determine spatial and temporal changes in sea ice occurrence and its natural variability in the present and past. Here, we present new biomarker data from surface sediments and related to the modern spatial sea ice variability in the Kara and Laptev seas. That means, we determined concentrations of the sea ice diatom-derived biomarker „IP25“ (isoprenoid with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and ß-sitosterol) to estimate recent sea ice conditions as well as terrigenous input in the study area. Assessment of sea ice conditions based on these biomarkers shows that a marginal ice zone exists along the continental shelf/slope of Kara and Laptev seas during summer/early fall. Elevated IP25 as well as brassicasterol and dinosterol values occurring in the central Kara and Laptev seas are related to extended sea-ice-cover and higher primary production (close to ice edge situation). Further to the north, lower IP25 and phytoplankton biomarker concentrations point to a more close sea ice cover situation. There are no IP25 and very low brassicasterol and dinosterol concentrations in the river mouths but high terrigenous biomarker (campesterol and ß-sitosterol) concentrations due to the fresh water inflow transporting terrigenous matter to estuaries. A combined phytoplankton-IP25 biomarker approach („PIP25 index“; Müller et al., 2009, 2011) is used to reconstruct the modern sea ice distribution more quantitatively.

Description: Sea ice is a fundamental component of Earth’s climate system, contributing to heat reduction (albedo) and deep-water formation. In order to understand processes controlling the recent dramatic reduction in Arctic sea-ice cover, it is essential to determine spatial and temporal changes in sea-ice occurrence and its natural variability in the present and past. Here, we present biomarker data from surface sediments and related to the modern spatial (seasonal) sea-ice variability in the central Arctic Ocean and adjacent marginal seas (i.e., Bering, Chukchi, Laptev and Kara seas) as well as the Fram Strait/Yermak Plateau area. We determined concentrations of the sea-ice diatom-derived biomarker “IP25″ (highly-branched isoprenoid – HBI – with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and Î_-sitosterol) to estimate recent sea-ice conditions in the study area. A combined phytoplankton-IP25 biomarker approach (“PIP25 index”; Müller et al., 2009, 2011) is used to reconstruct the modern sea-ice distribution more quantitatively. In addition, the distribution pattern of HBI-diene/IP25 ratios has been determined to test a proposed relationship between the diene/IP25 ratio and sea-surface temperatures in Arctic marginal ice-zone environments (Fahl and Stein, 2012; Stein et al., 2012). Assessment of sea-ice conditions based on these biomarker data display that a quite stable marginal ice zone exists along the continental shelf/slope of Kara and Laptev seas during summer/early fall. Elevated IP25 as well as brassicasterol and dinosterol values occurring in the central Kara and Laptev seas are related to extended sea-ice-cover and higher primary production (close to ice-edge situation). Further to the north and the central Arctic Ocean, lower IP25 and phytoplankton biomarker concentrations point to a more close sea-ice cover situation.

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.