Sea surface temperatures reconstructed from alkenones of surface sediment samples of the Argentine Basin at stations GeoB1501-1 to GeoB2830-1

We analysed the alkenone unsaturation ratio (UK'37) in 87 surface sediment samples from the western South Atlantic (5°N-50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured UK'37 ratios were converted into temperature using the global core-top calibration of Müller et al. (1998, doi:10.1016/S0016-7037(98)00097-0) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by -2° to -6°C are found in the regions of the Brazil-Malvinas Confluence (35-39°S) and the Malvinas Current (41-48°S). From the oceanographic evidence these low UK'37 values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating UK'37 temperatures. In this way, particles and sediments carrying a cold water UK'37 signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.

U-Pb (zircon) geochronologic analyses for rocks of the Transantarctic Mountains (Table 4.3-1)

The Byrd Glacier discontinuity us a major boundary crossing the Ross Orogen, with crystalline rocks to the north and primarily sedimentary rocks to the south. Most models for the tectonic development of the Ross Orogen in the central Transantarctic Mountains consits of two-dimensional transects across the belt, but do not adress the major longitudinal contrast at Byrd Glacier. This paper presents a tectonic model centering on the Byrd Glacier discontinuity. Rifting in the Neoproterozoic producede a crustal promontory in the craton margin to the north of Byrd Glacier. Oblique convergence of the terrane (Beardmore microcontinent) during the latest Neroproterozoic and Early Cambrian was accompanied by subduction along the craton margin of East Antarctica. New data presented herein in the support of this hypothesis are U-Pb dates of 545.7 ± 6.8 Ma and 531.0 ± 7.5 Ma on plutonic rocks from the Britannia Range, subduction stepped out, and Byrd Glacier. After docking of the terrane, subduction stepped out, and Byrd Group was deposited during the Atdabanian-Botomian across the inner margin of the terrane. Beginning in the upper Botomian, reactivation of the sutured boundaries of the terrane resulted in an outpouring of clastic sediment and folding and faulting of the Byrd Group.

Lower Cretaceous nannofossils of the northwestern Australian margin

Moderately to sparsely nannofossiliferous Neocomian siliciclastics and rich Aptian-Albian nannofossil chalks were cored at two Leg 123 sites on the abyssal plains off northwestern Australia. At Site 765, the basal 70 m of cored section yields questionable Tithonian and Berriasian to early Hauterivian assemblages of moderate diversity containing Cruelellipsis cuvillieri, Tegumentum striatum, Speetonia colligata, and Crucibiscutum salebrosum. The overlying Hauterivianlower Aptian is represented by 140 m of sediments barren of nannofossils. Above this, the remaining 80 m of the Lower Cretaceous section has been assigned to the Rhagodiscus angustus Zone (late Aptian-early Albian in age) and the Prediscosphaera columnata Zone (middle-late Albian in age). Common species include Rhagodiscus angustus, Prediscosphaera columnata, Eprolithus floralis, Eprolithus sp., Chiastozygus litterarius, Rucinolithus irregularis, and Flabellites biforaminis. At Site 766, the Neocomian, represented by 200 m of sediment, yields C. cuvillieri, T. striatum, S. colligata, and C. salebrosum. Within the overlying Aptian-Albian sequence of 80 m, the Rhagodiscus angustus, and P. columnata zones were recognized. The paleobiogeographic patterns and implications are discussed, with special emphasis paid to the bipolar high-latitude distribution pattern of C. salebrosum in the Valanginian-Hauterivian. Biostratigraphically important species are discussed and their occurrence in the Indian Ocean is compared with one from the Tethys and Boreal realms. Two new species, Serbiscutum gaultensis and Eprolithus bettenstaedtii, are described.

(Table 1) Chemical composition of volcanic rocks from the Mariisky sequence and extrusive vent rocks of the Mary Cape, Schmidt Peninsula (North Sakhalin)

Early Cretaceous volcanic rocks of the Mariisky sequence and Early Cenozoic extrusive-vent rocks of the Mary Cape are exposed at the most northwest of the Schmidt Peninsula, North Sakhalin. In chemical composition, all the rocks are subdivided into four groups. Three groups include volcanic rocks of the Mariisky sequence, which consists, from bottom to top, of calc-alkaline rocks, transitional calc-alkaline-tholeiite rocks, and incompatible element-depleted tholeiites. These rocks show subduction geochemical signatures and are considered as a fragment of the Moneron-Samarga island arc system. Trace-element modeling indicates their derivation through successive melting of a garnet-bearing mantle and garnet-free shallower mantle sources containing amphibole; pyroxene; and, possibly, spinel. The mixed subduction and intra-plate characteristics of the extrusive vent rocks of the Mary Cape attest to their formation in a transform continental margin setting.

Age determination of sediment cores of the California Current System

Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136 ka. The temperature differences between these sites (Delta SST(NEP)=SST(ODP1014)-SST(ODP1016)) reflected the intensity of the California Current and varied between 0.4 and 6.1 °C. A high Delta SST(NEP) (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low Delta SST(NEP) (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the Delta SST(NEP) and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high Delta SST(NEP) (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Niño-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean-atmosphere interactions.

Organic carbon and nitrogen concentrations in surface waters of the North Atlantic along 20°E in July-August 1996

Redfield stoichiometry has proved a robust paradigm for the understanding of biological production and export in the ocean on a long-term and a large-scale basis. However, deviations of carbon and nitrogen uptake ratios from the Redfield ratio have been reported. A comprehensive data set including all carbon and nitrogen pools relevant to biological production in the surface ocean (DIC, DIN, DOC, DON, POC, PON) was used to calculate seasonal new production based on carbon and nitrogen uptake in summer along 20°W in the northeast Atlantic Ocean. The 20°W transect between 30 and 60°N covers different trophic states and seasonal stages of the productive surface layer, including early bloom, bloom, post-bloom and non-bloom situations. The spatial pattern has elements of a seasonal progression. We also calculated exported production, i.e., that part of seasonal new production not accumulated in particulate and dissolved pools, again separately for carbon and nitrogen. The pairs of estimates of 'seasonal new production' and 'exported production' allowed us to calculate the C : N ratios of these quantities. While suspended particulate matter in the mixed layer largely conforms to Redfield stoichiometry, marked deviations were observed in carbon and nitrogen uptake and export with progressing season or nutrient depletion. The spring system was characterized by nitrogen overconsumption and the oligotrophic summer system by a marked carbon overconsumption. The C : N ratios of seasonal new as well as exported production increase from early bloom values of 5-6 to values of 10-16 in the post-bloom/oligotrophic system. The summertime accumulation of nitrogen-poor dissolved organic matter can explain only part of this shift.

Impacts of ocean warming and acidification on the larval development of the barnacle Amphibalanus improvisus

The world's oceans are warming and becoming more acidic. Both stressors, singly or in combination, impact marine species, and ensuing effects might be particularly serious for early life stages. To date most studies have focused on ocean acidification (OA) effects in fully marine environments, while little attention has been devoted to more variable coastal ecosystems, such as the Western Baltic Sea. Since natural spatial and temporal variability of environmental conditions such as salinity, temperature or pCO2 impose more complex stresses upon organisms inhabiting these habitats, species can be expected to be more tolerant to OA (or warming) than fully marine taxa. We present data on the variability of salinity, temperature and pH within the Kiel Fjord and on the responses of the barnacle Amphibalanus improvisus from this habitat to simulated warming and OA during its early development. Nauplii and cyprids were exposed to different temperature (12, 20 and 27°C) and pCO2 (nominally 400, 1250 and 3250 µatm) treatments for 8 and 4 weeks, respectively. Survival, larval duration and settlement success were monitored. Warming affected larval responses more strongly than OA. Increased temperatures favored survival and development of nauplii but decreased survival of cyprids. OA had no effect upon survival of nauplii but enhanced their development at low (12°C) and high (27°C) temperatures. In contrast, at the intermediate temperature (20°C), nauplii were not affected even by 3250 µatm pCO2. None of the treatments significantly affected settlement success of cyprids. These experiments show a remarkable tolerance of A. improvisus larvae to 1250 µatm pCO2, the level of OA predicted for the end of the century.

Geochemistry of the Kimmeridge Clay Formation, Dorset Coast

The Kimmeridge Clay Formation (KCF) and its equivalents worldwide represent one of the most prolonged periods of organic carbon accumulation of the Mesozoic. In this study, we use the molybdenum (Mo) stable isotope system in conjunction with a range of trace metal paleoredox proxies to assess how seawater redox varied both locally and globally during the deposition of the KCF. Facies with lower organic carbon contents (TOC 1-7 wt %) were deposited under mildly reducing (suboxic) conditions, while organic-rich facies (TOC >7 wt %) accumulated under more strongly reducing (anoxic or euxinic) local conditions. Trace metal abundances are closely linked to TOC content, suggesting that the intensity of reducing conditions varied repeatedly during the deposition of the KCF and may have been related to orbitally controlled climate changes. Long-term variations in d98/95Mo are associated with the formation of organic-rich intervals and are related to third-order fluctuations in relative sea level. Differences in the mean d98/95Mo composition of the organic-rich intervals suggest that the global distribution of reducing conditions was more extensive during the deposition of the Pectinatites wheatleyensis and lower Pectinatites hudlestoni zones than during the deposition of the upper Pectinatites hudlestoni and Pectinatites pectinatus zones. The global extent of reducing conditions during the Kimmerigidan was greater than today but was less widespread than during the Toarcian (Early Jurassic) oceanic anoxic event. This study also demonstrates that the Mo isotope system in Jurassic seawater responded to changes in redox conditions in a manner consistent with its behavior in present-day sedimentary environments.

Sedimentology at the continental margin of the southern Weddell Sea

During four expeditions with RV "Polarstern" at the continental margin of the southern Weddell Sea, profiling and geological sampling were carried out. A detailed bathymetric map was constructed from echo-sounding data. Sub-bottom profiles, classified into nine echotypes, have been mapped and interpreted. Sedimentological analyses were carried out on 32 undisturbed box grab surface samples, as well as on sediment cores from 9 sites. Apart from the description of the sediments and the investigation of sedimentary structures on X-radiographs the following characteristics were determined: grain-size distributions; carbonate and Corg content; component distibutions in different grain-size fractions; stable oxygen and carbon isotopes in planktic and, partly, in benthic foraminifers; and physical properties. The stratigraphy is based On 14C-dating, oxygen isotope Stages and, at one site, On paleomagnetic measurements and 230Th-analyses The sediments represent the period of deposition from the last glacial maximum until recent time. They are composed predominantly of terrigenous components. The formation of the sediments was controlled by glaciological, hydrographical and gravitational processes. Variations in the sea-ice coverage influenced biogenic production. The ice sheet and icebergs were important media for sediment transport; their grounding caused compaction and erosion of glacial marine sediments on the outer continental shelf. The circulation and the physical and chemical properties of the water masses controlled the transport of fine-grained material, biogenic production and its preservation. Gravitational transport processes were the inain mode of sediment movements on the continental slope. The continental ice sheet advanced to the shelf edge and grounded On the sea-floor, presumably later than 31,000 y.B.P. This ice movement was linked with erosion of shelf sediments and a very high sediment supply to the upper continental slope from the adiacent southern shelf. The erosional surface On the shelf is documented in the sub-bottom profiles as a regular, acoustically hard reflector. Dense sea-ice coverage above the lower and middle continental slope resulted in the almost total breakdown of biogenic production. Immediately in front of the ice sheet, above the upper continental slope, a <50 km broad coastal polynya existed at least periodically. Biogenic production was much higher in this polynya than elsewhere. Intense sea-ice formation in the polynya probably led to the development of a high salinity and, consequently, dense water mass, which flowed as a stream near bottom across the continental slope into the deep sea, possibly contributing to bottom water formation. The current velocities of this water mass presumably had seasonal variations. The near-bottom flow of the dense water mass, in combination with the gravity transport processes that arose from the high rates of sediment accumulation, probably led to erosion that progressed laterally from east to West along a SW to NE-trending, 200 to 400 m high morphological step at the continental slope. During the period 14,000 to 13,000 y.B.P., during the postglacial temperature and sea-level rise, intense changes in the environmental conditions occured. Primarily, the ice masses on the outer continental shelf started to float. Intense calving processes resulted in a rapid retreat of the ice edge to the south. A consequence of this retreat was, that the source area of the ice-rafted debris changed from the adjacent southern shelf to the eastern Weddell Sea. As the ice retreated, the gravitational transport processes On the continental slope ceased. Soon after the beginning of the ice retreat, the sea-ice coverage in the whole research area decreased. Simultaneously, the formation of the high salinity dense bottom water ceased, and the sediment composition at the continental slope then became influenced by the water masses of the Weddell Gyre. The formation of very cold Ice Shelf Water (ISW) started beneath the southward retreating Filchner-Ronne Ice Shelf somewhat later than 12,000 y.B.P. The ISW streamed primarily with lower velocities than those of today across the continental slope, and was conducted along the erosional step on the slope into the deep sea. At 7,500 y.B.P., the grounding line of the ice masses had retreated > 400 km to the south. A progressive retreat by additional 200 to 300 km probably led to the development of an Open water column beneath the ice south of Berkner Island at about 4,000 y.B.P. This in turn may have led to an additional ISW, which had formed beneath the Ronne Ice Shelf, to flow towards the Filcher Ice Shelf. As a result, increased flow of ISW took place over the continental margin, possibly enabling the ISW to spill over the erosional step On the upper continental slope towards the West. Since that time, there is no longer any documentation of the ISW in the sedimentary Parameters on the lower continental slope. There, recent sediments reflect the lower water masses of the Weddell Gyre. The sea-ice coverage in early Holocene time was again so dense that biogenic production was significantly restricted.

Late Neogene benthic foraminifera and stable carbon isotope record of the blake Outer Ridge

Carbon isotope and benthic foraminiferal data from Blake Outer Ridge, a sediment drift in the western North Atlantic (Ocean Drilling Program Sites 994 and 997, water depth ~ 2800 m), document variability in the relative volume of Southern Component (SCW) and Northern Component Waters (NCW) over the last 7 Ma. SCW was dominant before ~5.0 Ma, at ~3.6-2.4 Ma, and 1.2-0.8 Ma, whereas NCW dominated in the warm early Pliocene (5.0-3.6 Ma), and at 2.4-1.2 Ma. The relative volume of NCW and SCW fluctuated strongly over the last 0.8 Ma, with strong glacial-interglacial variability. The intensity of the Western Boundary Undercurrent was positively correlated to the relative volume of NCW. Values of Total Organic Carbon (TOC) were > 1.5% in sediments older than ~ 3.8 Ma, and not correlated to high primary productivity indicators, thus may reflect lateral transport of organic matter. TOC values decreased during the intensification of the Northern Hemisphere Glaciation (NHG, 3.8-1.8 Ma). Benthic foraminiferal assemblages underwent major changes when the sites were dominantly under SCW (3.6-2.4 and 1.2-0.8 Ma), coeval with the 'Last Global Extinction' of elongate, cylindrical deep-sea benthic foraminifera, which has been linked to cooling, increased ventilation and changes in the efficiency of the biological pump. These benthic foraminiferal turnovers were neither directly associated with changes in dominant bottom water mass nor with changes in productivity, but occurred during global cooling and increased ventilation of deep waters associated with the intensification of the NHG.

Annotated record of the detailed examination of Mn deposits in the submarine canyons off George Bank taken by the R/V ATlantis in 1939

New surveys were completed and data from the field sheets were kindly furnished by the U. S. Coast and Geodetic Survey to the Woods Hole Oceanographic Institution for use in dredging and coring operations. This field work, first reported in 1936, was continued from time to time until 1941 as new soundings became available. Rock dredging and coring has been carried out in every major canyon on the slope from Corsair Canyon at the tip of Georges Bank to Norfolk Canyon off the entrance to the Chesapeake. Numerous cores have also been taken from the areas in between; and while the whole slope from Georges to the Chesapeake has not been covered, it is believed that no significant areas have been missed. In the following report the tows and cores will be described by areas from Georges Bank southwards, as the same region was revisited in successive years. The various samples, however, will be referred to by number followed by the year in which they were taken. The material is in storage in the Woods Hole Oceanographic Institution and in the Museum of Comparative Zoology at Harvard University.

Clay-mineral composition and biogenic opal content of Late Neogene to Quaternary sediments of the Antarctic Peninsula region

Clay-mineral composition and biogenic opal content in upper Miocene to Quaternary drift sediments recovered at two Ocean Drilling Program (ODP) sites from the continental rise in the Bellingshausen Sea had been analyzed in order to reconstruct the climatic and glacial history of the Antarctic Peninsula. The clay mineral composition at both sites is dominated by smectite, illite, and chlorite, and alternates between a smectite-enriched and a chlorite-enriched assemblage throughout the last 9.3 my. The spatial distribution of clay minerals in Holocene sediments west of the Antarctic Peninsula facilitates the identification of particular source areas, and thus the reconstruction of transport pathways. The similarity to clay mineral variations reported from upper Quaternary sequences suggests that the short-term clay-mineralogical fluctuations in the ODP cores reflect glacial-interglacial cyclicity. Thus, repeated ice advances and retreats in response to a varying size of the Antarctic Peninsula ice cap are likely to have occurred throughout the late Neogene and Quaternary. The clay minerals in the drift sediments exhibit only slight long-term variations, which are caused by local changes in glacial erosion and in supply of source rocks, rather than by major climatic changes. The opal records at the ODP sites are dominated by long-term variations since the late Miocene. We infer that the opal content in the drift sediments, although it is influenced by dissolution in the water column and the sediment column and by the burial with lithogenic detritus, provides a signal of paleoproductivity. Because the annual sea-ice coverage is regarded as the main factor controlling biological productivity, the opal signal helps to reconstruct paleoceanographic changes in the Bellingshausen Sea. Slightly enhanced opal deposition during the late Miocene indicates slightly warmer climatic conditions in the Antarctic Peninsula area than at present. During the early Pliocene, enhanced opal deposition in the Pacific sector of the Southern Ocean and coinciding high opal concentrations in sedimentary sequences from the Atlantic and Indian sectors document a strong reduction of sea-ice cover and relatively warm climatic conditions. Thereby, the early onset of the Pliocene warmth in the Bellingshausen Sea points to a positive feedback of regional Antarctic climate on the global thermohaline circulation. A decrease of opal deposition between 3.1 and 2.6 Ma likely reflects sea-ice expansion in response to reduced supply of northern-sourced deep-waters to the Southern Ocean, caused by the onset of Northern Hemisphere glaciation. Throughout the Quaternary, a relatively constant level of opal deposition on the Antarctic continental margin indicates relatively stable climatic conditions.