(Supplement T1) Clay mineral compositions at the Aleutian Basin of the Bering Sea from IODP sites 323-U1343

The clay mineral composition at IODP Exp. 323 Site U1343 in the Bering Sea was analyzed so as to unravel their provenance over glacial-interglacial cycles for the last 2.4 Ma. Smectite was negatively correlated with the sum of illite and chlorite; therefore, their ratio [S/(I + C)] was used as an indicator of clay mineral composition changes. In general, the S/(I + C) ratio was rather similar for glacial and interglacial periods during most of the last 2.4 Ma. In addition, these results overlap with those of surface sediments in the modern East Aleutian Basin, which suggests that smectite-rich clay particles are delivered from the Aleutians by the northward Bering Slope Current (BSC) rather than from rivers in western Alaska. However, some clay mineral compositions of the glacial periods after the Mid-Pleistocene Transition (MPT: 1.25-0.7 Ma) were characterized by low illite and relatively high smectite. During this period, extensive ice-rafting might have transported the smectite-rich clay particles to Site U1343 from the glacial shelf off Alaska and/or from glacial rivers from that area.

Mesozooplankton investigations in Bornholm Basin, Baltic Sea

Mesozooplankton production was estimated by using a new sampling technique and two alternative calculation methods. In essence, production estimates are based on significantly higher abundances. The contribution of juvenile stages to copepod and fish dynamics was generally low, so that the omission of juvenile stages in budgets will result in a small error. The situations reported in this study present a unique food web szenario, which in detail, however, was strongly dependent on methodology. Furthermore relations between trophic levels were considered with respect to vertical distribution.

Pb-, Sr-, and Nd-isotopic composition of basaltic rocks from the Lau Basin

New Pb, Sr, and Nd isotope data are presented for 64 samples from the six backarc sites drilled during Leg 135. Systematic changes in Pb and Sr compositions illustrate significant isotopic variations between and within sites as well as provide two key pieces of information. First, a recent influx of asthenosphere with Indian Ocean mantle affinities has occurred and has successfully displaced older "Pacific" asthenosphere from the mantle underlying the backarc region. Second, clear evidence exists for mixing between these two asthenospheric end-members and at least one "arc-like" component. The latter was not the same as most material currently erupting in the Tofua Arc, but it must have had a more radiogenic Pb-isotope signature, perhaps similar to rocks analyzed from the islands of Tafahi, and Niuatoputapu. A comparison between the isotopic variations and the tectonic setting of the drill sites reveals consistent and important information regarding the mantle dynamics beneath the evolving backarc basin. We propose a model in which the source of upwelling magmas changes from Pacific to Indian Ocean asthenosphere with the propagation of seafloor spreading, a model with important implications for the rate of mantle influx into this region. Although the chemistries of backarc magmas have been profoundly influenced by this process, an additional consequence is the advection of Indian Ocean asthenosphere into the sub-arc mantle source. The isotopic compositions of arc rocks from the vicinity have been reevaluated on the basis of the proposed mantle advection model. We suggest that the slab-derived flux of trace elements into the arc wedge has remained relatively uniform with time (i.e., ~40 Ma), so that the change in arc chemistry results from mantle source substitution, rather than from differences in the composition of the downgoing plate.

High-resolution paleomagnetic investigation in the Iceland Basin

Based on discrete samples, we report new high-resolution records of the ~185 kyr Iceland Basin (IB) geomagnetic excursion from Ocean Drilling Project (ODP) Site 1063 on the Bermuda Rise (sedimentation rate 32 cm/kyr) and from ODP Site 983 in the far North Atlantic (sedimentation rate 18 cm/kyr). Two records from Holes 1063A and 1063B are very consistent, and provide the highest resolution of the detailed field behaviour during the IB excursion obtained so far. Inclination records from Holes 983B and 983C in the far North Atlantic are also very consistent, whereas declination anomalies deviate more notably. The pseudo-Thellier (PT) technique was applied along with more conventional palaeointensity proxies (NRM/ARM and NRM/kappa) to recover relative palaeointensity (RPI) estimates from Hole 1063A and Hole 983B. As expected, these proxies indicate that the field intensity generally dropped at both sites during the IB excursion, but also that the history of RPI from the two sites is different. VGPs from Site 1063 indicate that the field at this location experienced some stop-and-go behaviour between patches of intense vertical flux over North America and the tip of South America, areas which coincide fairly well with patches of preferred transitional VGP clustering from reversals and zones of high seismic velocity in the lower mantle. Changes in RPI at this location were generally gradual, possibly due to the proximity of these flux patches, and the first period of VGP-clustering over North America was accompanied by a conspicuous increase in RPI. VGPs from Site 983 track along a different path, and the associated RPI changes are very abrupt and completely synchronous with the onset and termination of the excursion. The differing VGP paths from Sites 1063 and 983 indicate that the global field structure during the IB excursion was not dominated by a single dipole.

(Table 1) Geochemistry of Nauru Basin basalts from the lower portion of DSDP Hole 61-462A

Atomic-absorption spectrophotometry and instrumental neutron activation analysis were used to determine concentrations of SiO2, Al2O3, FeOt, MgO, CaO, Na2O, K2O, MnO, La, Ce, Sm, Eu, Tb, Yb, Lu, Sc, Co, Cr, Th, Hf, and Ta for 14 basalt samples from the lower portion of Hole 462A in the Nauru Basin. The basalts are similar to normal midocean ridge basalt (MORB) for the elements analyzed, and light rare-earth elements (LREE) are depleted relative to heavy rare-earth elements (HREE). Two samples are extensively altered to smectites and show significant reductions in Al2O3, CaO, MnO, Na2O, REE, Sc, Co, and Hf and gains in MgO and FeOt relative to unaltered samples. The increase in MgO and decrease in CaO indicate that alteration was caused by hydrothermal solutions.

Transverse drainages of the Susquehanna River basin, Pennsylvania, USA

While large-scale transverse drainages (TDs) such as those of the Susquehanna River above Harrisburg, PA, have been recognized since the 19th century, there have been no systematic surveys done of TDs since that of Ver Steeg's in 1930. Here, the results are presented of a topographic and statistical analysis of TDs in the Susquehanna River basin using Google Earth and associated overlays. 653 TDs were identified in the study area, 95% of which contain streams with discharges of less than 10 m3/s. TD depths ranged from a 23 m deep water gap near Blain, PA, to the 539 m deep gorge of the Juniata River through Jacks Mountain. Although TD depth tended to increase with stream size, many small streams were located in deep gaps, and eight streams with discharges of 10 m3/s or less were found in gorges whose depths matched or exceeded the deepest TD of the Susquehanna, the largest stream in the basin. Streams of less than 10 m3/s made up the majority of TDs regardless of the rock type capping the breached structure. Overall, TDs through sandstone-capped ridges were deeper than those topped by shales, and TDs in both sandstones and shales displayed a lognormal distribution of depths, which may be indicative of a preferred value. Stream flow direction was primarily perpendicular to local structural strike, with 47% of streams flowing NW and 53% flowing SE. 19% of the TDs were found to be in alignment with at least one other TD, with aligned segment lengths ranging from .5 to 14.8 km. The majority of TDs were in rocks of Paleozoic age. The techniques described here allow the frequency and distribution of TDs to be quantified so that they can be integrated into models of basin evolution.

Pollen and macrofossils profiles and age determination from the Pittsburg Basin in the lowlands of south-central Illinois

Pollen and macrofossil evidence for the nature of the vegetation during glacial and interglacial periods in the regions south of the Wisconsinan ice margin is still very scarce. Modern opinions concerning these problems are therefore predominantly derived from geological evidence only or are extrapolated from pollen studies of late Wisconsinan deposits. Now for the first time pollen and macrofossil analyses are available from south-central Illinois covering the Holocene, the entire Wisconsinan, and most probably also Sangamonian and late Illinoian time. The cores studied came from three lakes, which originated as kettle holes in glacial drift of Illinoian age near Vandalia, Fayette County. The Wisconsinan ice sheet approached the sites from the the north to within about 60 km distance only. One of the profiles (Pittsburg Basin) probably reaches back to the late Illinoian (zone 1), which was characterized by forests with much Picea. Zone 2, most likely of Sangamonian age, represents a period of species-rich deciduous forests, which must have been similar to the ones that thrive today south and southeast of the prairie peninsula. During the entire Wisconsinan (14C dates ranging from 38,000 to 21,000 BP) thermophilous deciduous trees like Quercus, Carya, and Ulmus occurred in the region, although temporarily accompanied by tree genera with a more northerly modern distribution, such as Picea, which entered and then left south-central Illinois during the Woodfordian. Thus it is evident that arctic climatic conditions did not prevail in the lowlands of south-central Illinois (about 38°30' lat) during the Wisconsinan, even at the time of the maximum glaciation, the Woodfordian. The Wisconsinan was, however, not a period of continuous forest. The pollen assemblages of zone 3 (Altonian) indicate prairie with stands of trees, and in zone 4 the relatively abundant Artemisia pollen indicates the existence of open vegetation and stands of deciduous trees, Picea, and Pinus. True tundra may have existed north of the sites, but if so its pollen rain apparently is marked by pollen from nearby stands of trees. After the disappearance of Pinus and Picea at about 14,000 BP (estimated!), there developed a mosaic of prairies and stands of Quercus, Carya, and other deciduous tree genera (zone 5). This type of vegetation persisted until it was destroyed by cultivation during the 19th and 20th century. Major vegetational changes are not indicated in the pollen diagram for the late Wisconsinan and the Holocene. The dating of zones 1 and 2 is problematical because the sediments are beyond the14C range and because of the lack of stratigraphic evidence. The zones dated as Illinoian and Sangamonian could also represent just a Wisconsinan stadial and interstadial. This possibility, however, seems to be contradicted by the late glacial and interglacial character of the forest vegetation of that time.

Annotated record of the detailed examination of Mn deposits from the SO 79 (SEDIPERU - TUSCH) expedition from R/V Sonne

The research cruise SO79 with RV SONNE (April 18 to June 09 1992) aimed to assess the impact of a potential mining activity on the sensitive deep-sea ecosystem of the Peru Basin. Up to now only results of reconnaissance surveys of the extended manganese nodule field discovered in 1978 in the Peru Basin are available. The hydroacoustic, sedimentological, and geochemical studies on data and sample material of SO79 came to the following results: a small-scaled variation in thickness respectively type of surface sediments shown by the sediment echosounder respectively the side-scan-sonar is assumably due to variations in deposition or erosion. The composition of sediments is controlled by climatic cycles of different length which were caused by the variable influence of glaciation of the northern hemisphere. We think that during the quaternary a deep-water circulation reduced in intensity and O2-content may have produced a suboxic diagenetic environment which led to a remobilization and redeposition of Mn forming manganese nodules in the oxic surface sediments. Near the distinct redox boundary at about 10 cm depth the growth conditions for nodules are extremely favourable. Due to the great variability of sediments the impact of deep-sea mining will be highly variable and the disturbance of the seafloor will change the ecosystem considerably.

Benthic foraminiferal record from Santa Barbara basin

The oxygen minimum zone (OMZ) of the late Quaternary California margin experienced abrupt and dramatic changes in strength and depth in response to changes in intermediate water ventilation, ocean productivity, and climate at orbital through millennial time scales. Expansion and contraction of the OMZ is exhibited at high temporal resolution (107-126 year) by quantitative benthic foraminiferal assemblage changes in two piston cores forming a vertical profile in Santa Barbara Basin (569 m, basin floor; 481 m, near sill depth) to 34 and 24 ka, respectively. Variation in the OMZ is quantified by new benthic foraminiferal groupings and new dissolved oxygen index based on documented relations between species and water-mass oxygen concentrations. Foraminiferal-based paleoenvironmental assessments are integrated with principal component analysis, bioturbation, grain size, CaCO3, total organic carbon, and d13C to reconstruct basin oxygenation history. Fauna responded similarly between the two sites, although with somewhat different magnitude and taxonomic expression. During cool episodes (Younger Dryas and stadials), the water column was well oxygenated, most strongly near the end of the glacial episode (17-16 ka; Heinrich 1). In contrast, the OMZ was strong during warm episodes (Bølling/Allerød, interstadials, and Pre-Boreal). During the Bølling/Allerød, the OMZ shoaled to <360 m of contemporaneous sea level, its greatest vertical expansion of the last glacial cycle. Assemblages were then dominated by Bolivina tumida, reflecting high concentrations of dissolved methane in bottom waters. Short decadal intervals were so severely oxygen-depleted that no benthic foraminifera were present. The middle to late Holocene (6-0 ka) was less dysoxic than the early Holocene.