Study of the equatorial Atlantic Ocean mixing layer using a one-dimensional turbulence model

The General Ocean Turbulence Model (GOTM) is applied to the diagnostic turbulence field of the mixing layer (ML) over the equatorial region of the Atlantic Ocean. Two situations were investigated: rainy and dry seasons, defined, respectively, by the presence of the intertropical convergence zone and by its northward displacement. Simulations were carried out using data from a PIRATA buoy located on the equator at 23º W to compute surface turbulent fluxes and from the NASA/GEWEX Surface Radiation Budget Project to close the surface radiation balance. A data assimilation scheme was used as a surrogate for the physical effects not present in the one-dimensional model. In the rainy season, results show that the ML is shallower due to the weaker surface stress and stronger stable stratification; the maximum ML depth reached during this season is around 15 m, with an averaged diurnal variation of 7 m depth. In the dry season, the stronger surface stress and the enhanced surface heat balance components enable higher mechanical production of turbulent kinetic energy and, at night, the buoyancy acts also enhancing turbulence in the first meters of depth, characterizing a deeper ML, reaching around 60 m and presenting an average diurnal variation of 30 m.

Ostracoda (Crustacea) from the Archipelago of São Pedro and São Paulo, Equatorial Atlantic, with emphasis on a new Hemicytheridae genus

The present study is a further contribution to the systematic knowledge of the shallow water marine ostracodes from the Brazilian oceanic islands. A total of 14 species belonging to 10 genera and eight families is herein identified. One new genus and species are described and illustrated: Berguecythere insularis gen. nov., sp. nov. In addition to this new taxon, the abundant species Loxocorniculum tricornatum Krutak, 1971, widely distributed in recent sediments in the Gulf of Mexico, Caribbean, north and northeast of Brazil and the Rocas Atoll, along with the cosmopolitan tropical ostracode Triebelina sertata Triebel, 1948, were also identified at specific level. The remaining 11 species were left at the genus level, and should provide new species. Ecological, zoo- and paleozoogeographical aspects were also briefly discussed.

New species of Xestoleberididae (Crustacea, Ostracoda) from Archipelago of São Pedro and São Paulo, Equatorial Atlantic

Two new species of Xestoleberididae: Xestoleberis brasilinsularis sp. nov. and Xestoleberis machadoae sp. nov., both endemic to Archipelago of São Pedro and São Paulo, are described. The record of these shallow marine waters species from Brazilian oceanic islands represents an important contribution to the knowledge of the evolutionary history the species inhabit areas.

STUDY OF THE EQUATORIAL ATLANTIC OCEAN MIXING LAYER USING A ONE-DIMENSIONAL TURBULENCE MODEL

The General Ocean Turbulence Model (GOTM) is applied to the diagnostic turbulence field of the mixing layer (ML) over the equatorial region of the Atlantic Ocean. Two situations were investigated: rainy and dry seasons, defined, respectively, by the presence of the intertropical convergence zone and by its northward displacement. Simulations were carried out using data from a PIRATA buoy located on the equator at 23 degrees W to compute surface turbulent fluxes and from the NASA/GEWEX Surface Radiation Budget Project to close the surface radiation balance. A data assimilation scheme was used as a surrogate for the physical effects not present in the one-dimensional model. In the rainy season, results show that the ML is shallower due to the weaker surface stress and stronger stable stratification; the maximum ML depth reached during this season is around 15 m, with an averaged diurnal variation of 7 m depth. In the dry season, the stronger surface stress and the enhanced surface heat balance components enable higher mechanical production of turbulent kinetic energy and, at night, the buoyancy acts also enhancing turbulence in the first meters of depth, characterizing a deeper ML, reaching around 60 m and presenting an average diurnal variation of 30 m.

Biology of Grapsus grapsus (LINNAEUS, 1758) (Brachyura, Grapsidae) in the Saint Peter and Saint Paul Archipelago, Equatorial Atlantic Ocean

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

DIET of THE BLUE MARLIN (MAKAIRA NIGRICANS, LACEPEDE 1802) (PERCIFORMES: ISTIOPHORIDAE) of THE SOUTHWESTERN EQUATORIAL ATLANTIC OCEAN.

Diet composition of the blue marlin, Makaira nigricans, from the southwestern equatorial Atlantic Ocean was analyzed between October 2004 and November 2005. In the 226 stomachs of fish ranging between 100 and 311 cm lower jaw -fork length (LJFL), 44 items were identified, including 31 fishes and 13 cephalopods. Seventy stomachs were empty (23.6 %). M. nigricans fed preferentially on heavy and muscular scombrid fishes especially upon the skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758), probably to sustain their high metabolism, and on a variety of other items composed mainly by epipelagic species of fish and cephalopods.

Oceanography during TYDEMAN cruise DCM (DeepChlorMax) to the Equatorial Atlantic

The cruise with RV Tydeman was devoted to study permanently stratified plankton systems in the (sub)tropical ocean, which are characterised by a deep chlorophyll peak between 80 and 150 m. To minimise lateral effects by horizontal transport of nutrients and organic matter from river outflow and upwelling regions, stations were selected in the middle of the North Atlantic Ocean between the continents of America and Africa. (5 - 35° N and 50 - 15° W). Here the vertical distributions of light and nutrients control the abundance and growth of autotrophic algae in the thermically stratified water column. This phytoplankton is numerically dominated by the prokaryotic picoplankters Synechococcus spp. and Prochlorococcus spp., which are smaller than 2 ?m. The productivity of the 100 to 150 m deep euphotic zone can be high, because a high heterotrophic/autotrophic biomass ratio induces a rapid regeneration of nutrients and inorganic carbon. Primary grazers are mainly micro-organisms such as heterotrophic nannoflagellates and ciliates, which feed on the small algae and on bacteria. Heterotrophic bacteria can outnumber the autotrophic algae, because their number is related to the substrate pools of dissolved and particulate dead organic matter. These DOC and detritus pools reach equilibrium at a concentration, where the rate of their production (proportional to algal biomass) equals their mineralisation and sinking rate (proportional to the concentration and weight of POC and detritus). At a relatively low value of the weight-specific loss rates, the equilibrium concentration of these carbon pools and their load of bacteria can be high. The bacterial productivity is proportional to the mineralisation rate, which in a steady state can never be higher than the rate of primary production. Hence the ratio in turnover rate of bacteria and autotrophs tends to be reciprocally proportional to their biomass ratio.

Cenomanian/Turonian sea surface temperatures of the equatorial Atlantic reconstructed from geochemical data

Oceanic anoxic event 2 (OAE-2) occurring during the Cenomanian/Turonian (C/T) transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 Myr. However, the impact of this major perturbation on and interaction with global climate remains unclear. Here we report new high-resolution records of sea surface temperature (SST) based on TEX86 and d 18O of excellently preserved planktic foraminifera and stable organic carbon isotopes across the C/T transition from black shales located offshore Suriname/French Guiana (Demerara Rise, Ocean Drilling Program Leg 207 Site 1260) and offshore Senegal (Cape Verde Basin, Deep Sea Drilling Project Leg 41 Site 367). At Site 1260, where both SST proxy records can be determined, a good match between conservative SST estimates from TEX86 and d 18O is observed. We find that late Cenomanian SSTs in the equatorial Atlantic Ocean (33°C) were substantially warmer than today (27°-29°C) and that the onset of OAE-2 coincided with a rapid shift to an even warmer (35°-36°C) regime. Within the early stages of the OAE a marked (4°C) cooling to temperatures lower than pre-OAE conditions is observed. However, well before the termination of OAE-2 the warm regime was reestablished and persisted into the Turonian. Our findings corroborate the view that the C/T transition represents the onset of the interval of peak Cretaceous warmth. More importantly, they are consistent with the hypotheses that mid-Cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide (CO2) and that major OAEs were capable of triggering global cooling through the negative feedback effect of organic carbon-burial-led CO2 sequestration. Evidently, however, the factors that gave rise to the observed shift to a warmer climate regime at the onset of OAE-2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 Myr.

Organic carbon accumulation in the equatorial Atlantic

Organic geochemical records of the last 940 kyr are presented for equatorial Atlantic Ocean Drilling Program (ODP) sites 663 and 664 and discussed with regard to the development of ocean productivity and African paleoclimate. Proportions of marine and terrigenous organic matter (OM) are estimated from elemental, pyrolytic, isotopic, and petrologic data. Spectral analyses reveal a strong power at the eccentricity and obliquity band, indicating a close response of tropical organic sedimentation to the climatic evolution at high latitudes. The orbital covariance of organic carbon with biogenous opal and terrigenous records favor that glacially enhanced dust supply and surface water mixing were primary controls for deposition of organic carbon. Wind-borne supply of terrigenous OM contributes 26 to 55% and 0 to 39% to the bulk OM based on microscopic and isotopic records, respectively. Admixture of C4 plant matter was approximated to contribute up to 16% to the bulk organic fraction during peak glacial conditions.