Nannoliths and paleobiogeographic census from DSDP Site 56-435

Calcareous nannofossils were encountered at only one of the sites (435) drilled during DSDP Leg 56. Cores from Hole 435A yield fairly diverse early and late Pliocene assemblages. The section shows considerable reworking, however. Three to five biostratigraphic datum events provide a reasonable biochronology. The datums range from about 3.3 Ma in Core 11 to about 1.8 Ma in Core 3. Paleobiogeographic data indicate relatively stable and warm climatic conditions in this area in the early Pliocene, becoming more unstable in the late Pliocene when the cosmopolitan species become dominant.

Density and biomass of two copepod size fractions and various species obtained during Almirante Irizar cruises to the Drake Passage and Scotia Sea (2000-2003)

The relative importance of small forms of copepods has been historically underestimated by the traditional use of 200-300-µm mesh nets. This work quantified the distribution and abundance of copepods, considering two size fractions (<300 µm and >300 µm), in superficial waters (9 m deep) of the Drake Passage and contributed to the knowledge of their interannual fluctuations among three summers. Four types of nauplii and eleven species of copepods at copepodite and adult stages were identified, with abundance values of up to 13 ind/L and 28,300 µg C/m**3. The <300-µm fraction, composed of Oithona similis, small cyclopoids and nauplii, dominated the copepod communities in the 3 years; it accounted for more than 77% of the total number and for between 40 and 63% of the total biomass. Changes in density and biomass values among the three cruises differed according to copepod size fraction and water mass; the >300-µm fraction showed no changes among the 3 years, both in Antarctic (density and biomass) and in Subantarctic waters (density), whereas the <300-µm fraction showed higher (density and biomass) values in 2001 both in Subantarctic and in Antarctic waters. Sea surface temperature and its anomaly accounted for the largest proportion of variability in copepod density and biomass, particularly for the <300-µm fraction.

Concentrations of particulate phosphorus in different size fractions and dissolved organic and inorganic phosphorus in surface seawater of the Southeast Atlantic

Variations in concentration of total phosphorus in surface waters of dif¬ferent trophicity are discussed. Forms distinguished were: total particulate phosphorus in particles of size >150 ?m, and <20 ?m; dissolved organic phosphorus and dissolved phosphate. Even in hypertrophic waters, the dominant form is still dissolved phosphate (>65%). Concentrations of particulate phosphorus in different size fractions are additional indicators of the level of productivity of waters.