Hydrography and currents on the Pernambuco Continental Shelf

Abstract

The present study presents the seasonal hydrography and currents of the Brazilian Northeast Continental Shelf. The study area is located on the Brazilian tropical coast of the Atlantic Ocean between 7.5 and 9 °S. This continental shelf is narrow (~35 km wide) and shallow, with shelf break lying at a depth of 60 m. Salinity and temperature data were collected monthly by means of hydrographic surveys, conducted across the shelf in a single transect in the central part of the study area, between March 2012 and May 2013. Two further campaigns were also conducted to characterize the winter (August 2013) and the summer (January 2014), covering the whole study area (4,600 km 2 ). Water level and currents were measured using an array of Acoustic Doppler Current Profilers (ADCP) moored at mid-shelf in the central area. Seasonal temperature ranged from 26 °C in September to 29.5 °C in April, with a 2-month lag between the minimum and maximum air temperatures. Salinity did not present a clear seasonal pattern, fluctuating between 36.5 and 37.0 psu throughout the year. The mean temperature and salinity values obtained in the winter and summer campaigns were 26.5 and 27.6 °C and 37.1 and 36.7 psu, respectively. Tropical Water (TW) was predominant, accounting for 95% to 97%, with presence of Coastal Water (CW) limited to the inner part of the shelf. The mean flow velocity values in the water column in winter and summer were 0.11 and 0.06 m/s, respectively, similarly to the seasonal wind regime. Northward currents were observed predominantly in winter, with a short period of inverted southward current. These episodes were related to periods of wind relaxation and presented periodicity of 6-13 days, observed through wavelet analysis. This periodicity may be associated with atmospheric instabilities at higher latitudes. Summer currents were sluggish, when the tides accounted for 75 and 43% of the variance in the cross-and along-shelf current components, respectively. TW is the main water mass in the Pernambuco Continental Shelf (PCS) in summer and winter. Current intensity is weak and without direction in summer and stronger towards the north in winter.Keywords: Water masses; Circulation; Brazilian Northeast Shelf. RESUMOEste trabalho apresenta a descrição sazonal da hidrografia e hidrodinâmica de uma plataforma continental localizada na borda oeste do Atlântico tropical, a área de estudo encontra-se entre as latitudes de 7,5 e 9 °S, possui apenas 35 km de largura e 187 km de extensão, com a quebra de plataforma em 60m de profundidade. A salinidade e temperatura foram coletadas em campanhas hidrográficas mensalmente entre março de 2012 e maio 2013 por meio de transectos na região central da área de estudo. Também, duas campanhas foram realizadas, uma para caracterizar o inverno (Agosto de 2013) e outra o verão (janeiro de 2014) cobrindo toda a área de estudo (4600 km 2 ). O nível da água e correntes também foram coletados com um Perfilado Acústico por efeito Doppler (ADCP) fundeado na região central da área de estudo. A ...

3D characterisation of the thermohaline structure in the southwestern tropical Atlantic derived from functional data analysis of in situ profiles

“…9 and 12) is the shoaling and the greater extension of the NBUC core (Dossa et al, under review;Schott et al, 1998;Silva et al, 2005;Stramma et al, 1995), increasing turbulence in surface layer and saline diffusion up to the ML. Our observations are coherent with Araujo et al (2011) and Domingues et al (2017) but the exact processes have yet to be elucidated.…”

Near-surface western boundary circulation off Northeast Brazil

“…Data were collected during two multidisciplinary 'Acoustic along the Brazilian Coast' (ABRAÇOS) surveys performed along the continental slope of the NEB (Figure 2) onboard the R/V Antea in austral spring 2015 (September 28 -October 21, 2015) and fall 2017 (April 9 -May 8, 2017) (Bertrand, 2015;2017). The survey pattern consisted of systematic cross-shore sections (Figure 2).…”

Aspectos Sedimentológicos E Batimétricos Da Plataforma Continental Norte De Pernambuco - Brasil

“…Isto fica evidenciado na figura 3 onde são observados 2 núcleos de acumulação de lama ao norte e ao sul adjacentes, respectivamente, ao sistema estuarino do Rio Goiana e ao complexo estuarino do Rio Capibaribe, associadas a paleovales que cortam estes alinhamentos de beachrocks. De fato, Pardal et al (2019 in press) observou a deposição sazonal de lamas ao largo da desembocadura do sistema Capibaribe, incluindo estações de coleta mais ao norte adjacentes à Olinda, sugere que estas lamas são exportadas para o norte a partir da desembocadura do sistema, conforme o sentido das correntes predominantes na costa (SW-NE) (Domingues et al, 2017), mas também para leste condicionada pelo Canal de Olinda (paleovale do Rio Capibaribe) (DHN, 2019).…”

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