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Following the anomalous warming event occurring in the tropical North Atlantic in 2010, higher than usual surface fugacity of CO2 (fCO(2)) was observed. To evaluate the spatial extent of these anomalies and their drivers, and to quantify the sea-air CO2 flux at basin scale, the Mercator-Ocean model is used from 2006 to 2014 within the region 0-30 degrees N, 70-15 degrees W. Model outputs are generally in accordance with underway sea surface temperature, sea surface salinity, and surface fCO(2) recorded by two merchant ships. The anomalous warming of 2010 is well reproduced by the model and is the main driver of fCO(2) anomalies. The first coupled Empirical Orthogonal Function mode, between sea surface temperature and fCO(2), captures more than 70% of the total variance and is characterized by a basin-scale warming associated to positive fCO(2) anomalies. The corresponding principal components are correlated to the Tropical North Atlantic Index and identify 2010 as the year with the highest positive anomaly over 2006-2014. Exceptions to this general pattern are located near the African coast, where the weakening of the coastal upwelling causes negative inorganic carbon anomalies, and close to the Amazon River plume, where fCO(2) anomalies are primarily associated with sea surface salinity anomalies. Although the fCO(2) anomalies of 2010 appear mostly in spring, they affect the annual CO2 budget and lead to an increased CO2 outgassing twice as large (46.2 Tg C per year) as the mean annual flux over the 2006-2014 period (23.3 Tg C per year).

Hourly data of CO2 fugacity (fCO(2)) at 8 degrees N-38 degrees W were analyzed from 2008 to 2011. Analyses of wind, rainfall, temperature and salinity data from the buoy indicated two distinct seasonal periods. The first period (January to July) had a mean fCO(2) of 378.9 mu atm (n=7512). During this period, in which the study area was characterized by small salinity variations, the fCO(2) is mainly controlled by sea surface temperature (SST) variations (fCO(2) =24.4*SST-281.1, r(2)=0.8). During the second period (August December), the mean fCO(2) was 421.9 atm (n = 11571). During these months, the region is subjected to the simultaneous action of (a) rainfall induced by the presence of the Intertropical Convergence Zone (ITCZ); (b) arrival of fresh water from the Amazon River plume that is transported to the east by the North Equatorial Countercurrent (NECC) after the retroflection of the North Brazil Current (NBC); and (c) vertical input of CO2-rich water due to Ekman pumping. The data indicated the existence of high-frequency fCO(2) variability (periods less than 24 h). This high variability is related to two different mechanisms. In the first mechanism, fCO(2) increases are associated to rapid increases in SST and are attributed to the diurnal cycle of solar radiation. In addition, low wind speed contributes to SST rising by inhibiting vertical mixing. In the second mechanism, fCO(2) decreases are associated to SSS decreases caused by heavy rainfall.

Intraseasonal signals with periods of 2 to 3 weeks in near-surface alongshore current measurements are detected from four moorings (K1 - K4) deployed from 2000 to 2004 at the 11{degree sign}S section close to the Brazilian coast as part of the German CLIVAR Tropical Atlantic Variability Project. This section crosses the path of the North Brazil Undercurrent, the most powerful western boundary current in the South Atlantic Ocean. We investigate the origin of this intraseasonal variability of the North Brazil Undercurrentby relating the oceanic oscillation of the alongshore currents to its atmospheric counterpart, the meridional wind stress. On average, the results indicate a well-defined lagged (10 days) correlation (~0.6) structure between meridional wind stress and alongshore currents. The oceanic region with the highest cross-correlations is identified as a relatively narrow band along the Brazilian coast, from 22{degree sign}-36{degree sign}S and 40{degree sign}-50{degree sign}W, bounded in the north by an eastward change in coastline orientation. The cross-wavelet transform establishes the common power between the time series of meridional wind stress and alongshore currents, predominantly during austral winter and spring. These signals propagate equatorward with an alongshore speed of 285{plus minus}63 km day-1, consistent with Coastal Trapped Wave theory.

p. 63-73. Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-03-29T13:56:50Z No. of bitstreams: 1 __www.ocean-sci.net_7_63_2011_os-7-63-2011.pdf: 5061005 bytes, checksum: 3caf166cbeded252eaac0e891541bfa4 (MD5) Made available in DSpace on 2012-03-29T13:56:50Z (GMT). No. of bitstreams: 1 __www.ocean-sci.net_7_63_2011_os-7-63-2011.pdf: 5061005 bytes, checksum: 3caf166cbeded252eaac0e891541bfa4 (MD5) Previous issue date: 2011 High-resolution hydrographic observations of temperature and salinity are used to analyze the formation and distribution of isothermal depth (ZT), mixed depth (ZM) and barrier layer thickness (BLT) in a section of the southwestern Atlantic (0º30´N–14°OO`S; 31 240–41 480 W), adjacent to the northeastern Brazilian coast. Analyzed data consists of 279 CTD casts acquired during two cruises under the Brazilian REVIZEE Program. One occurred in late austral winter (August–October 1995) and another in austral summer (January–April 1997). Oceanic observations are compared to numerical modeling results obtained from the French Mercator-Coriolis Program. Results indicate that the intrusion of subtropical Salinity MaximumWaters (SMW) is the major process contributing to the seasonal barrier layer formation. These waters are brought by the South Equatorial Current (SEC), from the subtropical region, into the western tropical Atlantic boundary. During late austral winter southeastern trade winds are more intense and ITCZ precipitations induce lower surface salinity values near the equator. During this period a 5–90m thick BLT (median=15 m) is observed and BLT>30m is restricted to latitudes higher than 8 S, where the intrusion of salty waters between 8 –12.3 Screates shallow mixed layers over deep (ZT 90 m) isothermal layers. During austral summer, shallow isothermal and mixed layers prevail, when northeasterly winds are predominant and evaporation overcomes precipitation, causing saltier waters at the surface/subsurface layers. During that period observed BLT varies from 5 to 70m and presents thicker median value of 35 m, when comparing to the winter. Furthermore, BLT 30m is observed not only in the southernmost part of the study area, as verified during late winter, but in the latitude range 2 –14 S, where near-surface salty waters are transported westward by the SEC flow. These results indicate that the inclusion of salinity dynamics and its variability are necessary for studying mixed and barrier layer behaviors in the tropical Atlantic, where ocean-atmosphere coupling is known to be stronger.