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The study describes the annual cycle of southern elephant seals for the increasing colony of Peninsula Valdés, and compares it to the haul-out pattern reported for stable or decreasing sub-Antarctic colonies of the species. Data were collected during censuses of the entire colony (nine breeding seasons, two moulting seasons and one autumn--winter haul-out), monthly surveys of coastline and mark-recapture of pups. Pup production during the study period grew from 12 113 to 14 621 animals (1995-2003). Most relevant events of the cycle were similar for all colonies studied, independent of the geographical location, size or population trend. Compared with other locations where southern elephant seals breed and moult, distinct features for Peninsula Valdés were: i) breeding occurs earlier in the spring, and ii) most adult females reproduce and moult in the same colony. The increasing number of animals ashore was correlated with the expansion in pup production. Population trends and stability of demographic events could be related to a consistent physical environment (ocean fronts) during foraging phases of the annual cycle. [ABSTRACT FROM AUTHOR]

Varied approaches (palaeobiodiversity, palaeobiogeography, bioerosion, geochemistry) to unique Patagonian late Quaternary molluscan assemblages in the southwestern Atlantic, with ages especially from interglacial Marine Isotope Stage (MIS) 5e and MIS 1, provide large-scale and long-temporal palaeoenvironmental data for the southern SWA. Together with new patterns of δ18O and δ13C variations in modern, mid-Holocene, and Late to Middle Pleistocene shells of Protothaca antiqua (Bivalvia) and the coeval Pleistocene Tegula atra (Gastropoda), the overall sources of evidence illustrate possible responses to recent palaeoclimate and sea-ice changes around the southernmost SWA-western Antarctica, leading to modern conditions. For the mid-Holocene, the influence of the Hypsithermal is confirmed. In the northern Golfo San Matías, the highest δ18O and δ13C values support higher salinity and sea surface temperatures (SST), and a Golfo San Matías Front stronger than today. Lower δ18O values in the northern Golfo San Jorge (GSJ) compared to the Late to Middle Pleistocene suggest warmer mid-Holocene waters, independently supported by thermally anomalous molluscan taxa, geographical shifts of areas of endemism and absence of T. atra (cold water proxy); overall higher δ13C values compared to present suggest higher productivity. For the Late to Middle Pleistocene (particularly MIS 5e), highest δ13C values (relative to modern and mid-Holocene trends) match with the location of tidal fronts and areas of maximum chlorophyll-a concentrations today. Accordingly, these fronts may have been already active and significantly intensified due to the prevailing climate conditions that included colder waters and stronger upwelling from the southern GSJ southwards. This is independently supported by palaeobiogeographical and bioerosion trends and the dominance of the cold water species T. atra during the Pleistocene, which is dispersed from the SE Pacific into the SWA by rafting on kelps and whose occurrence is controlled by SST, light, winds, and nutrient concentration/productivity. Repeated, abrupt climate oscillations during the last glacial cycle with significant impact on SST, ice melting and surface-ocean stratification in the western Antarctica-Weddell Sea-Antarctic Circumpolar Current realm are so far the only available plausible explanations to account for the different mid-Holocene and modern patterns, and for the regional disappearance of T. atra after MIS 5e. Further palaeoceanographic research in this key area is needed to understand how all these mechanisms operated in the past, potentially influencing the Patagonian shelf waters and coastal fronts. • Biotic responses to SST, salinity, palaeoceanographical changes along Patagonia • Late to Middle Pleistocene carbon and oxygen patterns different from Holocene and present • Together with palaeobiogeography-bioerosion trends confirm different circulation. • Colder, higher productivity/upwelling setting in SWA during MIS 5e favoured T. atra. • Stronger SWW, enhanced SASW and ocean fronts explain its dispersal from the SEP. [ABSTRACT FROM AUTHOR]