Intraseasonal to interannual variability of the Brazil Current transport measured at 34.5°S M. P. Chidichimo* 1, A. R. Piola 1, C. S. Meinen 3, E. Campos 4, S. Garzoli 3,5, S. Speich 6, R. Perez 3,5, S. Dong 3,5, R. Matano 7, V. Combes 7 1 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Servicio de Hidrografía Naval, Universidad de Buenos Aires, Argentina 3 NOAA/AOML, Physical Oceanography Division, Miami, Florida, USA 4 Oceanographic Institute, University of Sao Paulo, Brazil 5 CIMAS, University of Miami, Miami, Florida, USA 6 ENS-Laboratoire de Météorologie Dynamique, Paris, France. 7 Oregon State University, Corvallis, Oregon, USA Nov. 2015, Aquarius Meeting, Buenos Aires, Argentina

●The Brazil Current is a key element of the South Atlantic circulation, as it advects warm water from subtropical to subpolar regions carrying components of Atlantic Meridional Overturning Circulation variability. ●In the South Atlantic, IES have been previously utilized to analize the variability of the Brazil Malvinas Confluence (Garzoli & Bianchi 1987; Garzoli & Garrafo 1989 ). Mean Brazil Current transport above 800 m of ~10 Sv at 37.5  S. ●Here: Continuous observations of the Brazil Current transport at 34.5°S since Introduction & Motivation

PIES/CPIES (NOAA, USP, UCP, UBR ) ADCP/BPR (USP) Short Moorings (UCP ) Tall Moorings (UBO) Bottom ADCP (UCP ) Thermistor mooring (UCP) Figure: Courtesy Chris Meinen SAMBA ARRAY Main Objective: Observe and understand the mechanisms that control the mean and time-varying MOC in the South Atlantic and the interocean exchanges.

SAM, Southwest Atlantic MOC project Study western boundary components of the MOC in the South Atlantic. Collaboration between US, Brazil and Argentina. 4 PIES (2009 – present) PIs: C. Meinen, S. Garzoli, R. Perez and S. Dong. Funded by NOAA, US. 3 CPIES (2012 – present) PI: E. Campos. Funded by FAPESP, Brazil. Depth [km]

CPIES: Current and Pressure Equipped Inverted Echo Sounder tau -- round trip travel times of acoustic pulses to sea surface and back. bottom pressure. bottom temperature. currents 50 m above the seafloor. tau combined with hydrography: estimates of full water column T, S, density and geopotential anomaly profiles using GEM look up tables (Meinen et al and 2013). Baroclinic component: geostrophic velocities rel. to the bottom. Barotropic component: Time varying geostrophic velocities from bottom pressure measurements. Add time-mean bottom velocity from model.

Time-mean absolute velocity section from PIES Adapted from Meinen et al  Southward flow of the Brazil Current at the western side of the array between sites A (51.5°W) and B (49.5°W).  Array misses a portion of the Brazil Current inshore of site A.  Strongest velocity variability in the upper m.  Time-mean bottom velocities from high-resolution model (Combes and Matano, 2014)

Salinity section at 34.5°S – SACW/AAIW interface? Water masses (Preu et al. 2012): SACW: S > 35 psu AAIW: S < psu UCDW: < γ n < O 2 < 4.5 mL L -1 NADW: < γ n < S > 34.8 psu. LCDW: < γ n < S < 34.8 psu AABW: θ < 0°C. Brazil Current: from the surface to SACW/AAIW interface at γ n = kg m -3 (same as Biló et al. 2014)

Brazil Current transport between 51.5°W (A) and 49.5°W (B)  Absolute transport is mostly southward; occasionally northward.  Large fluctuations of 30 Sv in short periods of 3 to 5 weeks. Absolute (including AA): -9.5 ± 7.5 Sv Baroclinic (including AA): -3.7 ± 5.8 Sv Barotropic (including AA): -5.6 ± 4.2 Sv AA

Transport inshore 51.5°W (A)? – CTD sections  Transport inshore A: -4.9 ± 2.4 Sv (baroclinic from 3 hydrographic sections).

Transport inshore 51.5°W (A)? – Models  Absolute transport inshore A represents ~30% of the mean transport.  Transport A to B overestimates variability by ~ 15-20% (compared with transport from the coast to B) Model time-mean absolute meridional velocity along 34.5°S between the coast and site B. BB ROMS_AGRIF (Combes and Matano, 2014) OFES Inshore A -3.8 ± 4.6 Sv Inshore A -3.0 ± 1.6 Sv

Spectral analysis – Brazil Current transport Absolute transport: 60% of the variance associated with periods shorter than 80 days. Peaks at 40, 20, and 10 days. Baroclinic transport: 75% of the variance associated with periods less than 120 days. Barotropic transport: 65% of the variance associated with periods shorter than 50 days. 40 d 20 d 10 d 20,10 d

Spectral analysis – geopotential anomaly Φ and bottom pressure at 51.5°W (A) and 49.5°W (B) (endpoints)  Φ at B: more variability at longer periods (50 to 80 days) compared to Φ at A.  Bottom pressure at A and B: peaks at 30, 20, 10 days.

Seasonal and interannual variability - Brazil Current transport Brazil Current: strengthens on May and Dec; weakens on Feb and July No significant seasonal cycle is found during

Seasonal and interannual variability - Brazil Current transport Mean annual absolute transport is remarkably steady. Brazil Current: strengthens on May and Dec; weakens on Feb and July No significant seasonal cycle is found during

Observed basin-wide MOC and Brazil Current transport at 34.5°S

Strength of basin-wide MOC and Brazil Current not significantly correlated during first year of continuous measurements. r = 0.22

Conclusions ●Absolute Brazil Current transport at 34.5°S is  0.8 Sv with a temporal standard deviation of 6.3 Sv. ●Fluctuations with periods shorter than 80 days account for 60% of the absolute transport variance. ●Baroclinic transport mostly contributes variability at periods less than 100 days; barotropic transport contributes shorter-term fluctuations with periods less than 30 days. ●Baroclinic transport variability accounts for the largest fraction of the absolute transport variability (80%). ●No significant seasonal cycle is found during ●Mean annual absolute transport is remarkably steady.

Conclusions ●Absolute Brazil Current transport at 34.5°S is  0.8 Sv with a temporal standard deviation of 6.3 Sv. ●Fluctuations with periods shorter than 80 days account for 60% of the absolute transport variance. ●Baroclinic transport mostly contributes variability at periods less than 100 days; barotropic transport contributes shorter-term fluctuations with periods less than 30 days. ●Baroclinic transport variability accounts for the largest fraction of the absolute transport variability (80%). ●No significant seasonal cycle is found during ●Mean annual absolute transport is remarkably steady. THANK YOU!

ROMS AGRIF

ROMS_AGRIF (Combes and Matano, 2014) Parent grid: Spatial resolution 1/4˚ (~23 km near 34˚S). Child grid: 82˚W a 41˚W; 64˚S- 20˚S, spatial resolution 1/12˚. 40 sigma levels in the vertical; increased resolution near the surface. Transport inshore 51.5°W? – high-res. model

AuthorSourceMean/st d dev (Sv) Average Mean/std dev (Sv) Notes Meinen et al. (2013)18 XBT sections-2.1/2.5Baroclinic OFES-3.0/1.6Absolute NEMO-4.6/3.3Absolute This studyCTD SAMOC07 (Jul/12) -3.4Baroclinic CTD SAMOC08 (Nov-Dec/12) /2.4Baroclinic CTD STSF2013 (Oct/13) -7.6Baroclinic ROMS_AGRIF (Combes and Matano, 2014) -3.8/4.6Absolute Transport inshore 51.5°W ? - Summary

A095

Gridded SHH Product Low orrelations ( ) with PIES at A SSH from PIES and SSH from altimetry –Site A

Transport inshore A? - SSH from PIES and SSH from altimetry

Water masses - neutral density layers (γ n, kg m -3 ) from PIES

Transport calculation f: Coriolis parameter L: distance between sites Baroclinic component (relative geostrophic velocities) Φ: geopotential anomaly Barotropic component: -Time varying absolute geostrophic velocities from bottom pressure gauges. -Add time-mean bottom velocity from model.

Mean absolute meridional velocity ROMS_AGRIF

ROMS AGRIF