Nd, Sr and Pb isotopes and clay minerals in sediment cores from the Gulf of Cadiz and the Portuguese margin

The assemblages of marine sediments on the SW Iberian shelf have been controlled by contributions from distinct sources, which have varied in response to environmental changes since the Last Glacial Maximum (LGM). The rapid, decadal scale Mediterranean overturning circulation permits mixing of suspended particles from the entire Mediterranean Sea. They are entrained into the suspended particulate matter (SPM) carried by Mediterranean Outflow Water (MOW), which enters the eastern North Atlantic through the Strait of Gibraltar and spreads at intermediate depths in the Gulf of Cadiz and along the Portuguese continental margin. Other major sediment sources that have contributed to the characteristics and budget of SPM along the flow path of MOW on the SW Iberian shelf are North African dust and river-transported particles from the Iberian Peninsula. To reconstruct climate- and circulation-driven changes in the supply of sediments over the past ~23000 cal yr B.P., radiogenic Nd, Sr and Pb isotope records of the clay-size sediment fraction were obtained from one gravity core in the Gulf of Cadiz (577 m water depth) and from two gravity cores on the Portuguese shelf (1745 m, 1974 m water depth). These records are supplemented by time series analyses of clay mineral abundances from the same set of samples. Contrary to expectations, the transition from the LGM to the Holocene was not accompanied by strong changes in sediment provenance or transport, whereas Heinrich Event 1 (H1) and the African Humid Period (AHP) were marked by significantly different isotopic signatures reflecting changes in source contributions caused by supply of ice rafted material originating from the North American craton during H1 and diminished supply of Saharan dust during the AHP. The data also reveal that the timing of variations in the clay mineral abundances was decoupled from that of the radiogenic isotope signatures.

(Table 6) Number of specimens of Polymastiidae and Suberitidae spp. found in ANDEEP I and II stations, POLARSTERN cruises ANT-XIX/4 and ANT-XXII/3

The Antarctic deep-water fauna of Polymastiidae and Suberitidae is revised using recently collected material from the Weddell Sea. The former family appeared to be more abundant and diverse than the latter family in the studied area. Seven species within five polymastiid genera and three species within three suberitid genera are described. Relatively high sponge abundance at two stations deeper than 4700 m was mainly constituted by a polymastiid species Radiella ant- arctica sp. nov. Previously, representatives of Radiella have never been found in the Antarctic. An eurybathic species, Polymastia invaginata , well known from the Antarctic and subantarctic, appeared to be especially abundant at less than 1000 m depth. Another eurybathic polymastiid species, Tentorium cf. semisuberites , known for its bipolar distribution, was the third abundant species at the depths between 1000-2600 m, with the highest density found at the deeper stations. Tentorium papillatum , endemic of the Southern Hemisphere, was registered only at a depth of about 1000 m. Other spe- cies studied were less abundant. Astrotylus astrotylus , the representative of the endemic Antarctic genus, was found exclusively deeper than 4500 m, often together with R. antarctica . Acanthopolymastia acanthoxa , the endemic deep- water Antarctic species, was registered at 3000 m. The discovery of suberitid Aaptos robustus sp. nov. at about 2300 m is the first signalization of Aaptos in the Antarctic and at such a considerable depth. The finding of Suberites topsenti deeper than 4700 m is also remarkable. In general the results achieved confirm the high degree of geographical ende- mism of the Antarctic deep-water sponge fauna and the eurybathic distribution of many Antarctic sponge species.

Long-term biogenic particle fluxes in the Bering Sea and the central subarctic Pacific Ocean

Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally located subarctic pelagic Station SA (49°N, 174°W; water depth 5406 m) was simultaneously studied along with the marginal sea Station AB (53.5°N, 177°W; water depth 3788 m) in the Aleutian Basin of the Bering Sea. A mooring system was tethered to the sea-floor with a PARFLUX type trap with 13 sample bottles, which was placed at 600 m above the sea-floor at each of the two stations. Sampling intervals were synchronized at the stations, and they were generally set for 20 days during highly productive seasons, spring through fall, and 56 days during winter months of low productivity. Total mass fluxes, which consisted of mainly biogenic phases, were significantly greater at the marginal sea Station AB than at the pelagic Station SA for the first four years and moderately greater for the last year of the observations. This reflects the generally recognized higher productivity in the Bering Sea. Temporal excursion patterns of the mass fluxes at the two stations generally were in parallel, implying that temporal changes in their biological productivity are strongly governed by a large-scale seasonal climatic variability over the region rather than local phenomena. The primary reason for the difference in total mass flux at the two stations stems mainly from varying contributions of siliceous and calcareous planktonic assemblages. A significantly higher opal contribution at Station AB than at Station SA was mainly due to diatoms. Diatom fluxes at the marginal sea station were about twice those observed at the pelagic station, resulting in a very high opal contribution at Station AB. In contrast to the opal fluxes, CaCO3 fluxes at Station AB were slightly lower than at Station SA. The ratios of Corg/Cinorg were usually significantly greater than one in both regions, suggesting that preferentially greater organic carbon from cytoplasm than skeletal inorganic carbon was exported from the surface layers. Such a process, known as the biological pump, leads to a carbon sink which effectively lowers p CO2 in the surface layers and then allows a net flux of atmospheric CO2 into the surface layer. The efficiency of the biological pump is greater in the Bering Sea than at the open-ocean station.

Calcite saturation and dissolution index of core-top sediment samples from the Ontong Java Plateau, Mid-Atlantic Ridge, the Caribbean and the Ceara Rise, the Indian Ocean, the Ninety-East Ridge and from the east of Madagascar

X-ray computed tomography (CT) provides an insight into the progression of dissolution in the tests of planktonic foraminifera. Four species of foraminifera (G. ruber [white], G. sacculifer, N. dutertrei and P. obliquiloculata) from Pacific, Atlantic and Indian Ocean core-top samples were examined by CT and SEM. Inner chamber walls began to dissolve at Delta[CO3**2-] values of 12-14 µmol/kg. Close to the calcite saturation horizon, dissolution and precipitation of calcite may occur simultaneously. Inner calcite of G. sacculifer, N. dutertrei and P. obliquiloculata from such sites appeared altered or replaced, whereas outer crust calcite was dense with no pores. Unlike the other species, there was no distinction between inner and outer calcite in CT scans of G. ruber. Empty calcite crusts of N. dutertrei and P. obliquiloculata were most resistant to dissolution and were present in samples where Delta[CO3**2-] ~ -20 µmol/kg. Five stages of preservation were identified in CT scans, and an empirical dissolution index, XDX, was established. XDX appears to be insensitive to initial test mass. Mass loss in response to dissolution was similar between species and sites at ~ 0.4 µg/µmol/kg. We provide calibrations to estimate Delta[CO3**2-] and initial test mass from XDX.