SEASONAL VARIABILITY OF CENTRAL ARCTIC OCEAN SEA-ICE COVER: NEW BIOMARKER (IP25 AND PIP25) DATA FROM SEDIMENT TRAPS DEPLOYED ON SOUTHERN LOMONOSOV RIDGE

During the Polarstern 1995 Expedition, a long-term mooring system with two cone-shaped multi-sampling traps was deployed at the dominantly ice-covered western slope of the southern Lomonosov Ridge (81°04.5'N, 138°54.0'E, 1712 m water depth). One trap was installed at 150 m below the sea surface, the other at 150 m above the bottom at 1550 m depth; material was collected in 20 time intervals between September 1995 and August 1996. For background data see Fahl and Nöthig (2007). Here, we present new biomarker data recording the seasonal variability of sea-ice cover. This type of data representing modern seasonal variability of the sea-ice biomarker proxies, was not available so far but may help significantly the interpretation of these proxies to be used in sedimentary records for reconstruction of paleo-sea-ice distributions. In this study, we have focused on the novel sea ice proxy IP25, a direct proxy for sea ice coverage (Belt et al., 2007). Furthermore, we used the phytoplankton-IP25 index (PIP25 Index), a further development of the IP25 index, based on the coupling of the environmental information carried by IP25 (sea ice) and brassicasterol (open-water phytoplankton productivity) (Müller et al., 2011). The interval November 1995 to June 1996 is characterized by the absence of the sea-ice proxy IP25 (except very minor values for January and April), suggesting a predominantly permanent sea ice cover at the trap location. During July/August 1996, maximum fluxes of the diatom-specific fatty acids and brassicasterol as well as maximum contents of biogenic opal (Fahl and Nöthig, 2007) indicate increased primary productivity. The marine organic matter (here POC, brassicasterol, and fatty acids) and the IP25 values decrease systematically from 150 to 1550m depth, indicating the typical biogeochemical degradation with increasing water depth. Due to the coincidence of maximum abundances of sea-ice proxies and open-ocean primary productivity proxies during the July/August time interval we propose a ice-edge situation characterized by increased phytoplankton productivity and sea-ice algae input. This interpretation is also supported by the phytoplankton-IP25 index (PIP25 Index), reaching quite high values of 0.5-0.8. It seems to be that in general PIP25 values do not change significantly between the shallow and deep trap, i.e., with increasing water depth, an important observation when thinking about the interpretation of PIP25 sedimentary records. The distinctly reduced September/October values of brassicasterol and fatty acids suggest a decrease in primary productivity, probably related to the start of new-ice formation in late September. This situation is reflected in high IP25 values and high PIP25 ratios. Whereas for October no IP25 was determined in the shallow trap, medium-high IP25 values were determined in the deep trap with maximum PIP25 ratio of about 0.7. This may indicate lateral IP25 input, but also means that in this case the PIP25 ratios should be interpreted with caution

From Greenhouse to Icehouse: The late Mesozoic-Cenozoic Arctic Ocean Sea Ice and Climate History

Within this review paper, proxy records were used for reconstruc- tion of the late Mesozoic-Cenozoic long-term climate history of the Arctic Ocean with a focus on sea ice and sea-surface temperature. In this context, three examples representing different climatic stages of the Arctic Ocean on its way from Greenhouse to Icehouse conditions are presented and discussed: (1) the late Cretaceous, a time interval of pre-dominantly warm climate with strong seasonality and occasionally winter sea ice, some increased paleopro- ductivity, and probably oxygen-deficient conditions; (2) the mid-Eocene with continuing warm and euxinic conditions and partly increased paleoproduc- tivity, and the early onset of predominantly seasonal sea-ice conditions, and (3) the late Miocene characterized by relatively warm (SSTs of about 5 °C) and ice-free conditions during summer, as well as sea ice occurring during spring and autumn/winter

Modern spatial sea-ice variability in the central Arctic Ocean and adjacent marginal seas: Reconstruction from biomarker data

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