(Table 1) Isotopes, calcite, aragonite and sample descriptions at DSDP Hole 55-433C

Calcite in the cavities and veins of igneous rocks has long been recognized as an alteration by-product (Dana, 1892). Elementary mineralogy textbooks report that the most common occurrence of aragonite is in the cavities of basalts and andesites (e.g., Kerr, 1977). Therefore, it is not surprising to find both carbonate minerals in association with the moderately to extensively altered basalt flows recovered during deep sea drilling on Suiko Seamount in the Emperor Seamount chain (DSDP Leg 55, Hole 433C). The thickness and vesicularity of the flows, along with the presence of oxidized flow tops, indicate that the basalt erupted subaerially (Site 433 Report, 1980). The stable isotopic contents of the carbonate phases filling and lining the veins and vesicles denote the environment of alteration. An isotopic study was undertaken to secure supportive evidence for a subaerial period in the development of the seamount. Also, the subsequent alteration history after submergence may be interpreted from this isotopic record.

(Table 1) Stabile isotopes at DSDP Leg 55 Holes

Deep sea drilling on four seamounts in the Emperor Seamount chain revealed that Paleogene shallow-water carbonate sediments of the "bryozoan-algal" facies crown the basalt edifices. According to the biofacies model of Schlanger and Konishi (1966, 1975), this bryozoan- algal assemblage suggests that the seamounts formed in cooler, more northerly waters than those presently occupied by the island of Hawaii; i.e., the paleolatitudes of formation were greater than 20 °N. Moving southward toward the youngest member of the seamount chain, a facies gradient indicative of warmer waters was observed. This gradient is interpreted as a reflection of a northward shift in isotherms during the time span in which the seamounts were progressively formed (Savin et al., 1975). On all seamounts, sedimentation at the drilling sites occurred in a high-energy environment with water depths of approximately 20 meters. Early-stage carbonate diagenesis began in the phreatic zone in the presence of meteoric water, but proceeded after subsidence of the seamounts into intermediate sea waters, where the bulk, stable isotopic composition was determined. The subsidence into intermediate waters was rapid, and permitted establishment of an isotopic equilibrium which, like the facies gradient, reflects the northward shift in isotherms during the Paleogene. Calcite and zeolite cements comprise the later-stage diagenesis, and originated from solutions arising from the hydrolysis of the underlying basalt. In conclusion, the results of this study of the shallow-water carbonate sediments are not inconsistent with a paleolatitude of formation for Suiko Seamount (Site 433) of 26.9 ±3.5 °N, as determined by paleomagnetic measurements (Kono, 1980).

Age determination of sediment cores from the western Svalbard margin

The deglaciation of the continental shelf to the west of Spitsbergen and the main fjord, Isfjorden, is discussed based on sub-bottom seismic records and sediment cores. The sea floor on the shelf to the west of Isfjorden is underlain by less than 2 m of glaciomarine sediments over a firm diamicton interpreted as till. In central Isfjorden up to 10 m of deglaciation sediments were recorded, whereas in cores from the innermost tributary, Billefjorden, less than a meter of ice proximal sediments was recognized between the till and the 'normal' Holocene marine sediments. We conclude that the Barents Sea Ice Sheet terminated along the shelf break during the Late Weichselian glacial maximum. Radiocarbon dates from the glaciomarine sediments above the till indicate a stepwise deglaciation. Apparently the ice front retreated from the outermost shelf around 14.8 ka. A dramatic increase in the flux of line-grained glaciomarine sediments around 13 ka is assumed to reflect increased melting and/or current activity due to a climatic warming. This second stage of deglaciation was interrupted by a glacial readvance culminating on the mid-shelf area shortly after 12.4 ka. The glacial readvance, which is correlated with a simultaneous readvance of the Fennoscandian ice sheet along the western coast of Norway, is attributed to the so-called 'Older Dryas' cooling event in the North Atlantic region. Following this glacial readvance the outer part of Isfjorden became rapidly deglaciated around 12.3 ka. During the Younger Dryas the inner fjord branches were occupied by large outlet glaciers and possibly the ice front terminated far out in the main fjord. The remnants of the Barents Sea Ice Sheet melted quickly away as a response to the Holocene warming around 10 ka.

Stable isotope ratios and abundances of selected foraminifera taxa from ODP Leg 172 sites

This data report describes the results of post-Leg 172 sampling of Sites 1054, 1055, and 1063 for two purposes: to investigate the climatic significance of red-colored intervals in the hemipelagic sediments cored during Leg 172 and to better understand the stratigraphy and chronology of Carolina Slope Sites 1054 and 1055. Gravity cores collected from the Carolina Slope on site survey cruise Knorr 140/2 show very high rates of sedimentation during the Holocene and lower rates during the last glacial maximum (LGM). Because of the high rates, many of the sediments in the recovered cores never reached the LGM. In other cores, it is possible that deglacial oscillations have been mistaken for the LGM. Although radiocarbon dating could solve that problem, some of the gravity cores are at or very close to the Ocean Drilling Program (ODP) sites, and it is useful to compare the isotope stratigraphies among them before proceeding with dating. Furthermore, some of the site survey cores have red-colored intervals and others do not, even though there is some indication they are time equivalent. Either the stratigraphy is wrong, diagenesis has affected the color of the sediment, or red sediment is carried to some sites but not to others that differ in depth by only a few hundred meters.

Discription of coastal shape at Bykovsky Peninsula

This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45210**6 t/a) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10210**6 t/a, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4210**6 t/a) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6210**6 t/a is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.