Enviromagnetic response of marine sediments off NE Brazil ... Enviromagnetic response of marine

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UNIVERSIDADE DE SO PAULO

INSTITUTO DE ASTRONOMIA, GEOFSICA E CINCIAS ATMOSFRICAS

DEPARTAMENTO DE GEOFSICA

GRASIANE LUZ MATHIAS

Enviromagnetic response of marine sediments off NE

Brazil to paleoclimatic and paleoceanographic changes in

the last 85 kyr BP

(Resposta magntica de sedimentos marinhos da margem adjacente ao NE

do Brasil s mudanas paleoclimticas e paleoceanogrficas nos ltimos

85.000 anos BP)

SO PAULO

2015

iii

GRASIANE LUZ MATHIAS

Enviromagnetic response of marine sediments off NE

Brazil to paleoclimatic and paleoceanographic changes in

the last 85 kyr BP

(Resposta magntica de sedimentos marinhos da margem adjacente ao NE

do Brasil s mudanas paleoclimticas e paleoceanogrficas nos ltimos

85.000 anos BP)

Tese apresentada ao Instituto de Astronomia, Geofsica e

Cincias Atmosfricas da Universidade de So Paulo para

obteno do grau de Doutora em Cincias Geofsicas.

rea de Concentrao: Geofsica

Orientador: Prof. Dr. Ricardo Ivan Ferreira da Trindade

SO PAULO

2015

iv

To Wilbor, my partner in crime.

v

AKNOWLEDGEMENTS

I would like to thank my advisor professor Dr. Ricardo Ivan Ferreira da Trindade for his

orientation, patience and friendship. Thanks also to my advisor in Germany, professor Dr.

Tilo von Dobeneck, for his guidance, serenity, friendship and long discussions.

During my PhD I had the support from Conselho Nacional de Desenvolvimento

Cientfico e Tecnolgico (CNPq) with scholarships in Brazil and Germany (SWE) and from

MARUM with additional support from a PhD guest student grant.

The Instituto de Astronomia, Geofsica e Cincias Atmosfricas (IAG-USP) provided

the necessary support for my PhD. I particularly thank Teca for making everything easier. The

work has benefited from the excellent infrastructure from Laboratrio de Paleomagnetismo

(USPmag) and the expertise of technicians Daniele Bradt, Plnio Jaqueto, Giovanni Moreira,

who are also friends.

The thesis has also befitted from the amazing infrastructure from the Research Group of

Marine Geophysics of University of Bremen and the IODP Bremen Core Repository. They

granted me with full access to equipments, helped me with measurements and sample

preparation and made available the cores used in my work. XRF analyses were performed in

the Center for Marine Environmental Science (MARUM) with the invaluable help of Vera

Lukies and Ursula Rhl. The members of the Laboratory for Paleo-, Rock and Environmental

Magnetics, received me so friendly and made my life abroad pleasant. Thanks particularly to:

Liane Brck, Heike Piero, Martina Braun, Christian Hilgenfeldt, Sebastian Razik, Benjamin

Baasch. I would like to thank Dr. Janna Just, Dr. Thomas Frederichs, MSc. Sophie Roud and

Dr. Andr Paul for the important and fruitful discussions that contributed immensely not only

for the thesis but for my general backround in paleoceanography.

I would like to thank the professor Dr. Cristiano Chiessi for making the contact with the

German workgroup possible, and also for his friendship and support during difficult moments

in my PhD.

Thanks to Prof. Dr. Igor Ivory Gil Pacca who followed my work from the beginning as

an internal reviewer for the important comments about my research.

Many thanks to my friends from the workgroup of Paleomagnetism: Elder Yokoyama,

Filipe Terra-Nova, Gelvam Hartmann, Jairo Savian, Janine Carmo, Mariana Rossafa, Karine

Carvas, Pedro Franco.

Thanks to my family, always present, always supporting me.

Finally, and most importantly, I would like to thank my husband Wilbor Poletti. His

patience, support, encouragement, discussions and mainly love were prime to make this thesis

possible. His forbearance to my recurrent bad mood in these final months was a solid prove of

his love and respect for me. Thanks also to our little star Alice that is so calm and sweet, and

put so many smiles on our face, even in the toughest days.

vi

Study the past if you would define the future.

Confucius

vii

RESUMO

O NE do Brasil uma regio semi-rida influenciada pela migrao para sul da Zona de

Convergncia Intertropical (ITCZ), que a principal sistema atmosfrico que controla o aumento

sazonal da precipitao nessa regio. bem estabelecido que esses perodos midos se

correlacionam temporalmente com os Eventos Heinrich (EH) perodos em que ocorre um

aumento da deposio de ice-rafted debris no Atlntico Norte. Entretanto, a resposta

oceanogrfica local a essa descarga de gua doce no Atlntico Norte e como isso influencia o

transporte de sedimentos ao longo da margem adjacente ao NE do Brasil sao ainda motivo de

debate na literatura. Este trabalho apresenta dados magnticos e geoqumicos para quatro

testemunhos coletados na parte sul do Oceano Atlntico equatorial, para os ltimos 85 ka BP.

Os testemunhos esto distribudos entre as longitudes 38W and 36W. Alm disso, ns fizemos

um estudo de end-members baseado nas curvas de aquisio de IRM, a partir do qual

elucidamos as possveis fontes dos sedimentos. Os parmetros magnticos revelam um aumento

significativo na concentrao de minerais magnticos durante os stadials, que acompanhado

por uma mudana na proporo relativadas fases magnticas. Os picos de concentrao de

minerais magnticos coincidem com picos nos indicadores geoqumicos utilizados para traar

a intendidade de intemperismo no continente. Portanto, os aumentos no aporte de material

magntico para a plataforma coincidem com um aumento na precipitao no continente no NE

do Brasil durante os EH. Alm da variao da quantidade de material magntico observada, a

contribuio relativa de cada fase magntica muda de oeste para leste. Durante os stadials, fases

de alta coercividade (como hematita e goetita) so dominantes na poro oeste da regio

estudada e as fases de baixa coercividade so dominantes a leste. Essa diferena devida,

principalmente, oxidao diferencial no continente, mas secundariamente ns sugerimos um

transporte W-E de material coercivo, causado pelo enfraquecimento da Corrente Norte do

Brasil (NBC) durante os stadials logo a leste da desembocadura do Rio Parnaba, como previsto

em alguns modelos paleoclimticos.

Palavras-chave: NE Brasil, Heinrich Events, magnetismo ambiental

viii

ABSTRACT

NE Brazil is a semi-arid region influenced by the southward displacement of the Intertropical

Convergence Zone (ITCZ), which is the main atmospheric system that modulates the seasonal

increasing in precipitation over this region. It is well established that these wet periods correlate

temporally with Heinrich Events (HE) periods of higher input of ice-rafted debris in the North

Atlantic. However, the local oceanographic response to fresh water pulses in the North Atlantic

and how this process influences sediment transport along the margin off NE Brazil are still a

matter of discussion. We present here rock magnetic and geochemical element data for four

marine cores collected in the south equatorial Atlantic Ocean, covering the last 85 ka. The cores

are distributed between longitude 38W and 36W. We also performed end-member analysis

based on the IRM acquisition curves bringing a better understanding about sediment sources.

Magnetic proxies show a marked increase in concentration of magnetic minerals during

stadials, with a concomitant change in the proportion of magnetic mineral types. Peaks in

magnetic concentration parameters coincide with peaks in geochemical proxies for weathering

intensity on land, being thus compatible with an increase in precipitation in NE Brazil during

HE. Yet, the relative contribution of magnetic phases across the NE Brazil margin changes from

west to east. During stadials the high-coercive phases (like hematite and goethite) are dominant

for cores located in the western part of the study area and low-coercive phases are dominant for

the core located further east. This difference is due mainly to differential oxidation over land,

but secondarily we suggest a transport from W-E of high coercive material, possibly caused by

the weakness of NBC during stadials just to the east of the mouth of the Parnaiba River as

predicted in some paleoclimate models.

Keywords: NE Brazil, Heinrich Events, environmental magnetism

ix

SUMMARY

1 INTRODUCTION ......................................................................................................... 1

2 CLIMATE ................................................................................................................... 5

2.1. Present day in South America ............................................................................. 5

2.2. Holocene in South America ................................................................................ 7

2.3. Last Glacial Period .............................................................................................. 8

2.3.1. Heinrich Events ......................................................................................... 9

2.3.2.