Representation of the Weddell Sea deep water masses in the ocean component of the NCAR-CCSM model

We examine Weddell Sea deep water mass distributions with respect to the results from three different model runs using the oceanic component of the National Center for Atmospheric Research Community Climate System Model (NCAR-CCSM). One run is inter-annually forced by corrected NCAR/NCEP fluxes, while the other two are forced with the annual cycle obtained from the same climatology. One of the latter runs includes an interactive sea-ice model. Optimum Multiparameter analysis is applied to separate the deep water masses in the Greenwich Meridian section (into the Weddell Sea only) to measure the degree of realism obtained in the simulations. First, we describe the distribution of the simulated deep water masses using observed water type indices. Since the observed indices do not provide an acceptable representation of the Weddell Sea deep water masses as expected, they are specifically adjusted for each simulation. Differences among the water masses` representations in the three simulations are quantified through their root-mean-square differences. Results point out the need for better representation (and inclusion) of ice-related processes in order to improve the oceanic characteristics and variability of dense Southern Ocean water masses in the outputs of the NCAR-CCSM model, and probably in other ocean and climate models.

Benthic foraminiferal assemblages of the South Brazil: Relationship to water masses and nutrient distributions

Using distributions of benthic Foraminifera and bottom-water variables (depth, salinity, temperature, oxygen, suspended matter, organic matter, phosphate, silicate, nitrite, and nitrate), we investigated movements of water masses on the South Brazilian Shelf (27-30 degrees S) and assessed the seasonality of continental runoff on the distribution of shelf water masses. The data were obtained from water and sediment samples collected in the austral winter of 2003 and austral summer of 2004 in three transects. The terrestrial nutrient input was significantly reduced at stations away from the coast, but high values of nutrients were maintained in subsurface waters due the presence of South Atlantic Central Water (SACW) at greater depths. At shallow sampling stations the influence of freshwater runoff was related to (1) the dominance of calcareous benthic Foraminifera, such as lagoon-related Pseudononion atlanticum, Hanzawaia boueana, Bulimina marginata, Bolivina striatula, Elphidium poeyanum, together with several agglutinated species, including Arenoparrella mexicana, Gaudryina exilis, and Trochammina spp., common in coastal environments subject to wide salinity fluctuations. In contrast, smaller forms and higher species diversity characterized the assemblage at offshore stations. In winter, the presence of Buccella peruviana and Uvigerina peregrina at Santa Marta Cape suggest the possible transport of those species of Subantarctic Shelf Waters (SASW) origin. Foraminifera associated to Subtropical Shelf Water (STSW) were dominated by Globocassidulina subglobosa in both seasons. In summer, the occurrence of U. peregrina in the shallower stations suggested the influence of SACW nutrients brought up by upwelling of deeper waters. (C) 2008 Elsevier Ltd. All rights reserved.

Changes in the intermediate water mass formation rates in the global ocean for the Last Glacial Maximum, mid-Holocene and pre-industrial climates

The paleoclimate version of the National Center for Atmospheric Research Community Climate System Model version 3 (NCAR-CCSM3) is used to analyze changes in the water formation rates in the Atlantic, Pacific, and Indian Oceans for the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) control climate. During the MH, CCSM3 exhibits a north-south asymmetric response of intermediate water subduction changes in the Atlantic Ocean, with a reduction of 2 Sv in the North Atlantic and an increase of 2 Sv in the South Atlantic relative to PI. During the LGM, there is increased formation of intermediate water and a more stagnant deep ocean in the North Pacific. The production of North Atlantic Deep Water (NADW) is significantly weakened. The NADW is replaced in large extent by enhanced Antarctic Intermediate Water (AAIW), Glacial North Atlantic Intermediate Water (GNAIW), and also by an intensified of Antarctic Bottom Water (AABW), with the latter being a response to the enhanced salinity and ice formation around Antarctica. Most of the LGM intermediate/mode water is formed at 27.4 < sigma(theta) < 29.0 kg/m(3), while for the MH and PI most of the subduction transport occurs at 26.5 < sigma(theta) < 27.4 kg/m(3). The simulated LGM Southern Hemisphere winds are more intense by 0.2-0.4 dyne/cm(2). Consequently, increased Ekman transport drives the production of intermediate water (low salinity) at a larger rate and at higher densities when compared to the other climatic periods.

Recent benthic foraminiferal distribution and related environmental factors in Ezcurra Inlet, King George Island, Antarctica

This investigation attempts to determine which environmental parameters of the bottom water and sediment control recent foraminifera fauna at Ezcurra Inlet (King George Island, Antarctica), using data collected during four summers (2002/03, 2003/04, 2004/05 and 2006/07). The study revealed that Ezcurra Inlet contain typical Antarctic foraminifera fauna with three distinct assemblages and few differences in environmental parameters. The species Bolivina pseudopunctata, Fursenkoina fusiformis, Portatrochammina antarctica, and Adercotryma glomerata were abundant in the samples. An elevated abundance, richness and diversity were common at the entrance of the inlet at depths greater than 55 m, where the inlet was characterized by low temperatures and muddy sand. In the inner part of the inlet (depth 30-55 m), richness and diversity were low and the most significant species were Cassidulinoides parkerianus, C. porrectus, and Psammosphaera fusca. Shallow waters showed low values of richness and abundance and high temperatures coupled with coarser sediment. In areas with high suspended matter concentrations and pH values associated with low salinity the most representative species were Hippocrepinella hirudinea and Hemisphaerammina bradyi.

Benthic foraminiferal distribution on the southeastern Brazilian shelf and upper slope

Foraminiferal data were obtained from 66 samples of box cores on the southeastern Brazilian upper margin (between 23.8A degrees-25.9A degrees S and 42.8A degrees-46.13A degrees W) to evaluate the benthic foraminiferal fauna distribution and its relation to some selected abiotic parameters. We focused on areas with different primary production regimes on the southern Brazilian margin, which is generally considered as an oligotrophic region. The total density (D), richness (R), mean diversity (H) over bar`, average living depth (ALD(X) ) and percentages of specimens of different microhabitats (epifauna, shallow infauna, intermediate infauna and deep infauna) were analyzed. The dominant species identified were Uvigerina spp., Globocassidulina subglobosa, Bulimina marginata, Adercotryma wrighti, Islandiella norcrossi, Rhizammina spp. and Brizalina sp.. We also established a set of mathematical functions for analyzing the vertical foraminiferal distribution patterns, providing a quantitative tool that allows correlating the microfaunal density distributions with abiotic factors. In general, the cores that fit with pure exponential decaying functions were related to the oligotrophic conditions prevalent on the Brazilian margin and to the flow of the Brazilian Current (BC). Different foraminiferal responses were identified in cores located in higher productivity zones, such as the northern and the southern region of the study area, where high percentages of infauna were encountered in these cores, and the functions used to fit these profiles differ appreciably from a pure exponential function, as a response of the significant living fauna in deeper layers of the sediment. One of the main factors supporting the different foraminiferal assemblage responses may be related to the differences in primary productivity of the water column and, consequently, in the estimated carbon flux to the sea floor. Nevertheless, also bottom water velocities, substrate type and water depth need to be considered.

The Southern Ocean and Its Climate in CCSM4

The new Community Climate System Model, version 4 (CCSM4), provides a powerful tool to understand and predict the earth's climate system. Several aspects of the Southern Ocean in the CCSM4 are explored, including the surface climatology and interannual variability, simulation of key climate water masses (Antarctic Bottom Water, Subantarctic Mode Water, and Antarctic Intermediate Water), the transport and structure of the Antarctic Circumpolar Current, and interbasin exchange via the Agulhas and Tasman leakages and at the Brazil-Malvinas Confluence. It is found that the CCSM4 has varying degrees of accuracy in the simulation of the climate of the Southern Ocean when compared with observations. This study has identified aspects of the model that warrant further analysis that will result in a more comprehensive understanding of ocean-atmosphere-ice dynamics and interactions that control the earth's climate and its variability.