Description: Sediment fluxes were highest in the Norwegian Sea during late glacial/early deglacial periods, i.e., at oxygen isotope transition 43, below transition 65, at various levels within stage 6, and below stage 9. Dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine-based parts of the continental ice sheets in the southeastern sector of the Norwegian Sea. The high organic carbon content (0.5–1.3%) in these layers reflects input from erosion of terrigenious matter-rich sediments outcropping on the shelves. Partial oxidation of organic matter and decreased deep-water renewal may explain the strong carbonate dissolution observed during these periods. Interglacial environments were strongly variable throughout the last 350 ka. Circulation patterns of stage 5e best resemble modern conditions, while stage 7 and 9 sediments record a much weaker Norwegian Current.

Description: A 467-cm-long core from the inner shelf of the eastern Laptev Sea provides a depositional history since 9400 cal yr. B.P. The history involves temporal changes in the fluvial runoff as well as postglacial sea-level rise and southward retreat of the coastline. Although the core contains marine fossils back to 8900 cal yr B.P., abundant pf ant debris in a sandy facies low in the core shows that a river influenced the study site until similar to 8100 cal yr B.P. As sea level rose and the distance to the coast increased, this riverine influence diminished gradually and the sediment type changed, by 7400 cal yr B.P., from sandy silt to clayey silt, Although total sediment input decreased in a step-like fashion from 7600 to 4000 cal yr B.P., this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components, While this maximum probably resulted from middle Holocene climate warming, the low input of sand to the site after 7400 cal yr B.P. probably resulted from further southward retreat of the coastline and river mouth. Since about 4000 cat yr B.P., total sediment flux has remained rather constant in this part of the Laptev Sea shelf due to a gradual stabilization of the depositional regime after completion of the Holocene sea-level rise.

Description: To establish a chronology of the Holocene transgression in Arctic Siberia, a total of 14 sediment cores from the Laptev Sea continental slope and shelf were studied covering the water depth range between 983 and 21 m. The age models of the cores were derived from 119 radiocarbon datings, which were all analyzed on marine biogenic calcite (mainly bivalve shells). The oldest shell sample was found at the slope and dates back to about 15.3 cal. ka, indicating that the time interval investigated starts prior to the onset of the meltwater pulse 1A (similar to 14.2 cal. ka) when global sea-level rose dramatically. The inundation history was reconstructed mainly on the basis of major changes in average sedimentation rates (ASR), but also other sedimentological parameters were incorporated. A diachronous reduction in ASR from the outer to the inner shelf region is recognized, which was related to the southward migration of the coastline as the primary sediment source. We estimate that the flooding of the 50-, 43-, and 31-m isobaths was completed by approximately 11.1, 9.8, and 8.9 cal. ka, and that Holocene sea-level highstand was approached near 5 cal. ka. Between these time intervals, sea level in the Laptev Sea rose by 5.4, 13.3, and 7.9 mm/year, respectively.

Description: On the basis of various lithological, mircopaleontological and isotopic proxy records covering the last 30,000 calendar years (cal kyr) the paleoenvironmental evolution of the deep and surface water circulation in the subarctic Nordic seas was reconstructed for a climate interval characterized by intensive ice-sheet growth and subsequent decay on the surrounding land masses. The data reveal considerable temporal changes in the type of thermohaline circulation. Open-water convection prevailed in the early record, providing moisture for the Fennoscandian-Barents ice sheets to grow until they reached the shelf break at ∼26 cal. kyr and started to deliver high amounts of ice-rafted debris (IRD) into the ocean via melting icebergs. Low epibenthic δ18O values and small-sized subpolar foraminifera observed after 26 cal. kyr may implicate that advection of Atlantic water into the Nordic seas occurred at the subsurface until 15 cal. kyr. Although modern-like surface and deep-water conditions first developed at ∼13.5 cal. kyr, thermohaline circulation remained unstable, switching between a subsurface and surface advection of Atlantic water until 10 cal. kyr when IRD deposition and major input of meltwater ceased. During this time, two depletions in epibenthic δ13C are recognized just before and after the Younger Dryas indicating a notable reduction in convectional processes. Despite an intermittent cooling at ∼8 cal. kyr, warmest surface conditions existed in the central Nordic seas between 10 and 6 cal. kyr. However, already after 7 cal. kyr the present day situation gradually evolved, verified by a strong water mass exchange with the Arctic Ocean and an intensifying deep convection as well as surface temperature decrease in the central Nordic seas. This process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal. kyr and, eventually, to today's steep east–west surface temperature gradient. The time discrepancy between intensive vertical convection after 5 cal. kyr but warmest surface temperatures already between 10 and 6 cal. kyr strongly implicates that widespread postglacial surface warming in the Nordic seas was not directly linked to the rates in deep-water formation.

Description: Sediment patterns derived from sediment sampling and acoustic subbottom profiling were mapped on the Reykjanes Ridge (North Atlantic) between 59°N and 60°N. Five discrete sediment echo patterns were distinguished and mapped on a regional scale. The prolonged and layered echo facies, which mainly reflect sediment filled basins on the ridge flanks, indicate deposition of predominantly fine-grained sediments deposited by the Iceland-Scotland Overflow Water. A combination of westward flowing currents spilling over the ridge crest due to the Coriolis force together with the existing morphology probably caused the N-S trending facies distribution pattern on the northwest flank. Furthermore, the modern surface sediment distribution is controlled by biological productivity, which is closely related to the mixing zone of cold subpolar surface water masses and the warm North Atlantic Current, and bottom water transport processes. The effect of bottom current transport is reflected in the pattern of settling velocity and sediment grain size. The clay mineral composition indicates that most of the fine-grained material is supplied predominantly from the Icelandic province by the Iceland-Scotland Overflow Water. Erosional processes are concentrated on narrow zones on top of the axial ridges and on the steep flanks of the Catalonia Seamount. Well-sorted foraminiferal sands on these exposed regions are assumed to represent residual sediments.

Description: A closely spaced grid of seismic reflection profiles has permitted a description of the structure of the Vesterisbanken Seamount (Greenland Sea) and the distribution of the surrounding sediments. This isolated seamount is situated at 73°30′N, 9°10′W in the Greenland Basin and rises from the basin floor at a water depth of about 3100 m to ∼ 130 m below sea level; the maximum inclination of its slope is 26°. It is of basaltic origin, and reveals chaotic reflectors on the seismic profiles. No inhomogeneities are visible within the volcanic rocks of Vesterisbanken and the basement complex surrounding it. Dredge samples from the summit of Vesterisbanken reveal an age of ∼ 100,000 years. In the seismic records, there was no sediment cover discernable on top of or on the flanks of the seamount. At the base of Vesterisbanken, the seismic reflection characteristics suggest an alternation of sediments and basaltic rocks, the latter probably being the result of young lava flows. In some places the volcanic rocks disturb the sedimentary sequence to such a high degree, that the stratification is virtually eliminated. Volcanic activity also occurs in the vicinity of the seamount: for example, about 20 km northwest of Vesterisbanken an intrusion has pierced through 1000 m of sediment, almost reaching the seafloor. The sediment thickness is variable and it smooths the irregular basement topography. In addition, the sediment is characterized by local unconformities associated with onlap structures.

Description: During cruise ARK IV/3 with RV Polarstern (1987) volcanic rocks were recovered from the Nansen-Gakkel Ridge (NGR), a slow spreading (half rate approximately 0.5 cm) ridge with an axial depth of more than 5000 m. The NGR is one of the slowest and deepest mid-ocean ridges so far known and calculations based on the distance of sampling location from the axial valley yielded ages of approximately 600 ka for the rocks investigated here. According to petrographic and geochemical results i.e. spinifex textures, mg 〉 70 and MgO 〉 9 wt.%, the volcanics are termed komatiitic basalts. Dark spherical droplets of basanitic composition within the komatiitic basalts are believed to be relicts of an incomplete magma-mixing whose basanitic end-member could well account for the enriched character of the NGR basalts in terms of rare earth elements, Ti and incompatible trace elements. Based on Nd-isotope as well as high Sm/Nd ratios, mantle metasomatism (i.e. veined-mantle model) could be responsible for the enrichment of incompatible trace elements in the source region of komatiitic basalts of the NGR.

Description: DSDP/ODP drilling in the northern North Atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice-rafted debris (IRD) in deep-sea sediments can be traced back to the middle Miocene. The Greenland ice sheet has probably the longest history on the northern hemisphere. Leg 151 site 909 (Fram Strait) recovered a unique continuous sediment record dating from early/middle Miocene. The composition of the coarse fraction indicates that the oldest IRD pulses are documented around 14 Ma in the Fram Strait (site 909) and around 12.6 Ma on the Vöring Plateau (leg 104, site 642) in the Norwegian–Greenland Sea. Fram Strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral IRD pulses during late Miocene (between 10.8 and 8.6 Ma, around 7.2, 6.8 and 6.3 Ma), which ultimately led to a drastic intensification of northern hemisphere glaciation during Plio–Pleistocene. The deep-sea sediment records show that Plio–Pleistocene strengthening of IRD pulses have been observed since approximately 4.0 Ma in the westernmost Norwegian–Greenland Sea and Labrador Sea; by contrast, strengthening of IRD pulses are observed at approximately 3.2–2.7 Ma on the eastern side of the Norwegian–Greenland Sea, including the Barents Sea margin. Sediment composition and physical properties of the drilled, mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep-water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre-glacial Miocene, Pliocene and early Quaternary and to 100 ka periods of eccentricity dominant during the past 600,000–700,000 years. The stratigraphy of ice-rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the Norwegian–Greenland Sea. It is particularly evident from the composition of the ice-rafted material that the Eurasian ice sheets delivered IRD to the eastern part of the Norwegian–Greenland Sea, whereas Greenland source areas are represented in the drill sites of the east Greenland continental margin and in the Labrador Sea. The stratigraphic sequences on the Yermak Plateau suggest that the Svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then. Invasions of temperate Atlantic waters during interglacials can be observed as short-lived and rather irregular events. It never reached the area off eastern Greenland except during the Pliocene interval, when tundra floras were able to develop on north-eastern Greenland and planktonic foraminifers suggesting the presence of temperate water masses in the Fram Strait as been documented in the drill sites from the Yermak Plateau.

Description: The upper 500 or 1000 m of the water column in the Okhotsk Sea was sampled for living planktic foraminifera. The polar species Neogloboquadrina pachyderma (sinistral) strongly dominates the foraminiferal assemblage; the subpolar to temperate species Globigerina bulloides accounts for 10–25%. Other species account for up to 3% only. The shell δ18O and δ13C values of the species N. pachyderma (sin.) are compared to water δ18O values and δ13C values of dissolved inorganic carbon (DIC). The strong gradient in δ18O composition and temperature in the upper water column is reflected in the δ18O of N. pachyderma (sin.). Relative to the values expected for inorganic calcite precipitated under equilibrium conditions N. pachyderma (sin.) displays a vital effect of about 1‰ in δ18O. The δ13C composition of N. pachyderma (sin.) is about constant with water depth and the reflection of δ13CDIC in the foraminiferal shell seems to be masked by other effects. Most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column. The gradient of δ13CDIC extends well below this depth, therefore the lack of correlation can partly be attributed to this fact. The remaining discrepancy between δ13C of N. pachyderma (sin.) and δ13CDIC correlates with the carbonate ion concentration in the water column. This leads to the conclusion that the ‘carbonate ion effect’ (CIE), which has been derived from culturing experiments for other species [Spero et al. (1997) Nature 390, 497–500], is found here under natural conditions. When the magnitude of the CIE derived for G. bulloides is applied to N. pachyderma (sin.), CIE-corrected δ13C of N. pachyderma (sin.) is a direct reflection of δ13CDIC in the water column with a constant offset of 1.2‰.