Niels Nørgaard-Pedersen

Late glacial and Holocene marine records from the Independence Fjord and Wandel Sea regions, North Greenland

The first marine sediment cores from the unexplored Independence Fjord system and theWandel Sea, North Greenland, have been investigated to reveal the glacial marine history of the region. Two key sites in the Independence Fjord system, and an earlier analysed site from the Wandel Sea continental slope, off the mouth of Independence Fjord, are presented. The Independence Fjord sites reveal an early Holocene record (10.0–8.9 Kya) of fine-grained reddish muds with calcareous microfossils, dominated by the benthic foraminifera Cassidulina neoteretis. We suggest that a semi-permanent fast ice cover characterized the region in the early Holocene, and that the deeper troughs in the mouth region of the Independence Fjord system were intruded by subsurface Atlantic water. A stiff diamicton, at least 1.3 m thick, with coal and sandstone clasts of mainly local origin, and a 0.5-m-thick Holocene cover, are found in one of the sites. The diamicton is assumed to represent a subglacial till predating the early Holocene sediments (> 10 Kya). Shallow seismic records off the mouth of Independence Fjord reveal kilometre-sized troughs with signs of glacial erosion, till deposition and a Holocene glaciomarine deposition. These features could indicate that glacial ice debouching from the Independence Fjord system at some time during the last glacial period extended to the mid-outer Wandel Sea shelf. Data from a high-resolution sediment core previously retrieved from the adjacent Wandel Sea slope indicate that the maximum ice sheet advance in this area culminated about 25–20 Kya.

The depositional environment of the Laptev Sea continental margin: Preliminary results from the R/v polarstern ARK IX-4 cruise

Marine geological investigations were performed across the Laptev Sea continental shelf and slope, Thirty sampling sites were selected covering a depth range of ca 3500 m. Maximum core recovery was 9 m. PARASOUND sub-bottom profiling was used for site surveying and provided important information on the depositional environment of the continental margin together with sedimentological and stratigraphical investigations. Undisturbed horizontal layering of the sea-floor sediments is a common feature for the Laptev Sea shelf. There is no indication for glaciation of the broad shelf region during the Last Glacial, since moraine deposits are missing. However. a high number of plough marks in places points to recent to sub-recent ice-erosion which has led to an intensive sediment reworking on the shelf. Several broadly incised river channels recorded near the shelf edge are related to Pleistocene drainage systems of large Siberian rivers which cut into the dry shelves during the Last Glacial Maximum and were subsequently filled during the Holocene. During the Last Glacial we therefore suspect a significant freshwater contribution from the Eurasian continent to the Arctic Ocean. The composition of the normally consolidated core sediments indicates a strong flux of terrigenous material, which is mainly provided by the Siberian rivers. Currents distributing the suspension load and sea ice are supposedly major agents transporting sediments aaoss the shelf to the central arctic deep sea basin. Sediment cores from the upper and middle continental slope exhibit only minor lithological changes. Bioturbated, fine-grained sediments with high organic carbon contents dominate. The presence of free hydrogen sulphide gas within the sediment column indicates that an intense decay of organic matter under reducing conditions is taking place. Sedimentation rates are estimated to be ca. 50 cm/1000 years at the upper slope of the western Laptev Sea, being approximately 10 times higher than at the continental rise. The suboxic to anoxic environment diminishes at deep sea sites of the western Laptev Sea. where sedimentation rates and influx of organic matter are reduced.

Linking the Modern Distribution of Biogenic Proxies in High Arctic Greenland Shelf Sediments to Sea Ice, Primary Production, and Arctic‐Atlantic Inflow

The eastern North coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here, we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea shelf, the entrance to the Independence, Hagen and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic-walled dinoflagellate cysts is controlled by the local bathymetry and sea-ice conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea-ice and the specific biomarker IP25, highlighting the potential of this species for paleo sea-ice studies. The information inferred from our multi-proxy study has important implications for the interpretation of the biogenic-proxy signal preserved in sediments from circum-Arctic fjords and shelf regions and can serve as a baseline for future studies. This is the first study of its kind in this area.