Sediment Budget Correlation with the Southern Oscilation Index of a

Journal of Coastal Research
371 - 374
SI 39
ICS 2004 (Proceedings)
Brazil
ISSN 0749-0208
Sediment Budget Correlation With the Southern Oscillation Index of a Foredune
Westward of Cabo Frio (Rio de Janeiro)
G.B. Fernandez † and D. Muehe‡
Laboratório de Geologia Marinha - Universidade
Federal Fluminense, Instituto de Geociências,
Av. Litorânea s/n, 4o andar, Gragoatá, Niterói, RJ.
Brasil. CEP 24210 340
[email protected]
‡ Laboratório de Geografia Marinha - Departamento
de Geografia, Universidade Federal do Rio de
Janeiro, Ilha do Fundão, Rio de Janeiro, Brazil.
Cep: 21949-900 Rio de Janeiro.
[email protected]
ABSTRACT
FERNANDEZ, G.B. and MUEHE, D., 2006. Sediment budget correlation with the Southern Oscillation index of a
foredune westward of cabo Frio (Rio de Janeiro). Journal of Coastal Research, SI 39 (Proceedings of the 8th
International Coastal Symposium), 371 - 374. Itajaí, SC, Brazil, ISSN 0749-0208.
Massambaba beach is located about 140 km eastward from Rio de Janeiro near cape Frio. The beach is exposed to a
high energy environment, with storm surges from the South mainly in the autumn and winter. Winds blowing during
all the year in the opposite direction (Northeast), remove sediments from the dunes to the beach and to the upper and
middle shoreface, while the input of sediments to the dune system occurs during cold-front penetrations from the
south trough wave overwash and aeolian transport. El Niño phenomenon lead to important changes in wind patterns
in SouthAmerica, due to the blocking of the polar frontal system in the western SouthAtlantic around the coast of the
state of Paraná, in Brazil. This causes a decrease in the number of storm events in the Rio de Janeiro coast. Between
April, 1996 and February, 2003 monthly topographic surveys were made in the area with the purpose to calculated
the volumetric changes of the foredune segment. The results showed an erosive trend increased during the El Niño
events with a volume reduction of 27% between the first and last survey. Besides this general trend of erosion,
monthly variation in sediment volume indicated a relation with the Southern Oscillation Index.
ADDITIONALINDEX WORDS: Overwash process, El Niño, sediment dynamics.
INTRODUCTION
The Rio de Janeiro coast can be divided into two distinct
alignments, with the cape Frio as a vertex of these segments
(MUEHE, 1998; MUEHE & VALENTINI, 1999; MUEHE et al.,
1999). Northward of cape Frio the general trend of the coast is in
the NNE-SSW direction, reflecting the dominant structural
alignments of Brazilian shield. Westward from cape Frio the
coastline changes abruptly assuming an east-west direction
paralleling the strike of oceanic fracture zone and intercepting
the direction of the general structural trend of the Brazilian
shield (Figure 1).
Successive beach arcs, oriented in the east-west direction
characterize this coastal segment. The beaches are separated by
rocky headlands resulting from the erosional retreat of the front
scour of the coastal range. The rectification of the coast was
obtained through of the building up of beach barriers, which
locked the river mouth, thus originating the succession of
lagoons, whose salinity increases in the direction of Cape Frio,
as result of decreased river input and increase of aridity. The
beach barrier most frequently occurs as double barriers, with the
internal and older ones located further inland with 3 to 4 meters
higher as the external and younger ones. The control for the
construction of the double system and the topographic
Figure 1. Coastline of Rio de Janeiro and the location of study
area.
difference in the barriers height are similar to the last two
positive oscillations along the Quaternary (TURC, et al., 1999).
Thus the internal barrier is probably of Pleistocene age, while
the external is associated with the Holocene sea level maximum
(IRLEAND, 1987; SUGUIO, et al., 1985).
The wave climate is characterized by two different patterns.
Fair weather conditions generated waves in the east and
northeast direction, and swell waves come from the south,
southeast and southwest related to migratory cold fronts.
During extreme conditions, the waves may reach periods more
than 14 seconds, and heights with up to 3 to 4 meters in the
breaker zone are not rare.
This area presents a local microclimate characterized by
semi-arid conditions (BARBIERI, 1999) due to the increased
distance to the coastal range, upwelling and strong Northeast
winds.
Although the massive occupation of the coastal zone, some
parts of the Rio the Janeiro coast still maintain the natural
structure of beach-foredune relatively preserved. One example
occurs along the extreme east sector of Massambaba beach
(Figure 2).
The dominant wind regime blows during spring and summer
from east and northeast direction, which affects the foredunes
Figure 2. General view of de foredune system in the
Massambaba beach.
Journal of Coastal Research, Special Issue 39, 2006
372
Fernandez and Muehe
documented as only a few works describe the effect of this event
over coastal process. SOUZA and ANGULO (1999) found that
beach profiles measured in Santa Catarina coast, between June
1997 and March 1998, present an erosional trend. This trend
was related to the El Niño event, because of anomalous rainfall
and storm surges that affected the area during the monitoring
period. In Salvador, Bahia, BITTENCOURT et al.(1987)
identified, during a 19th months survey of beach profiles,
different sequences of erosion and accretion in the extremities
of the Armação beach arc. The identified differences were
associated to the influence of El Niño occurred in 1982 and
1983 that changes the wind and wave regime and created a new
pattern in sediment transport along the beach arc. Dune fields,
controlled by trade winds in the east and southeast directions,
characterize the Northeast. The cyclical changes in sediment
transport direction from the beach to the dune field are
controlled by climate (B ITTENCOURT et al . , 1990).
RODRIGUES (1999) identified an increase in the aeolian
sediment supply to the dunes in Cauípe, Ceará, in 1997, due to a
decrease in rainfall during this strong El Niño year. CASTRO
(2001), studying the dune field of Paracuru, also in Ceará, found
evidences of an increase of barchan dunes during the dry season
and parabolic dunes during the rainy season, related
respectively to the El Niño and La Niña events.
The major difficulty for the interpretation of the El Niño
Southern Oscillations influence over the geomorphic processes
lays in the lack of long period observations which generally do
not exceeded more than 2 years leading easily to
misinterpretations.
Figure 3. Atmospheric circulation during normal (a) and El
Niño (b) conditions. (modified from KOUSKY et al., 1984).
by removing sediments in the offshore direction. In autumn and
winter successive cold fronts penetrations with strong winds
and high waves from the South forces the transport of sediments
in direction to the beach and foredunes trough wave overwash
and wind transport. The volumetric changes of a segment of the
foredune field, associated to the pattern of seasonal fair weather
and storm conditions partially driven by the El Niño - La Niña
Southern Oscillation, based on eight years of monthly
topographic surveys, is the objective of this work.
The term El Niño and La Niña was primary used in South
America Pacific coast by fishermen that observed the sharp
decrease of fishery yield associated to a sporadic event of warm
ocean current at the end of year (December) and lasting for
several mouths. Actually the El Niño describes the warm phase
of cyclical changes in the sea surface temperature that occur in
the tropical Pacific Ocean.
Actually the El Niño oscillation of the Pacific Ocean is
correlated with the Southern Oscillation Index (SOI) based on
the measure of the monthly differences in atmospheric pressure
between the isle of Tahiti and Darwin in north Australia. The
determination is done by taking the difference between each of
the monthly mean sea level pressure (mslp) anomalies at both
locations and normalizing each of the differences by dividing
them by the standard deviation of the monthly differences in
mslp anomalies at both locations. The value is then multiplied
by 10 to create monthly SOI values. Periods of strong,
protracted negative values relate to El Niño episodes, while
periods of strong, protracted positive values relate to La Niña
episodes.
KOUSKY et al.(1984) observed that during an El Niño event
the blockage of the migration of cold front systems along the
South Brazilian coast by a subtropical jet stream (Figure 3).
This situation induces modifications in the wind patterns, and
consequently in the wind regime and wave surges along the
coast.
The influence of El Niño along the Brazilian coast is poorly
METHODS
Monthly topographic surveys were carried out along a grid of
110 m length to 60 m wide with the long axis parallel to the
shoreline and a grid interval of 10 m fixed by small plastic rods.
The change of volume between successive surveys where
calculated in relation to the first survey. The software used for
the volume calculation was the Surfer 7 from Golden Software
Inc.
Eighty-three field surveys were made, beginning in April
1996 to February 2003 and are still maintained.
The Southern Oscillation Index was obtained in the
COMMONWEALTH BUREAU OF METEOROLOGY
(www. bom.gov.au) that presents these results. The climate
bulletin of the Brazil is monthly available in the CPTEC
(www.cpte.inpe.br), where presented data from origin and
evolution of cold fronts along Brazilian coastline and different
maps and graphics of the weather conditions in Brazil.
RESULTS AND CONCLUSIONS
The first volume measurement of 9,959 m3 in April 1996,
reduced to 7,237 m3 in 2003, which shows a decrease of about
30% in 7 years. This decrease in sediment volume and
associated topographic height, although a general trend, are
marked by continuous oscillation as a response to sediment loss
in direction to the sea and partial gain in the opposite direction,
due to the prevailing Northeast trade winds mainly in summer
Table 1. Results of volumetric budget between El Niño and La Niña events during the period of observation.
Year
Event
1996
La Niña/ Normal
3
Volumetric budget: El Niño ( m )
3
Volumetric budget: La Niña ( m )
273,8
1997
El Niño
1998
La Niña
1999
La Niña
- 329, 4
2000
La Niña
175, 85
2001
El Niño
- 1190,5
2002
El Niño/Normal
364,2
Results
- 913,7
- 544,11
- 1726, 3
Journal of Coastal Research, Special Issue 39, 2006
-985, 3
373
Southern Oscillation Index and Foredune System
Figure 4. Correlation between foredune volume and Southern Oscillation Index (SOI).
SOI and foredune volume, with sediment loss associated to
episodes of SOI increase.
and spring. Short recoveries trough aeolian sand transport and
wave overwash during the cold front penetrations from the
South, occurs in autumn and winter. This episodic sediment
transport reversal has not been able to compensate the sediment
loss of the foredune field that shows a remarkable change in
topography with reduction of dune height, enlargement of the
overwash depressions and an erosive retreat of about 10 m of the
foredune scarp.
Besides this general trend minor oscillations in the sediment
volume seems to correlate to seasonal climate changes as also
with the Southern Oscillation Index (Fig. 4) as pointed out by
MUEHE and FERNANDEZ (1999), RIBEIRO (2000) and
FERNANDEZ (2003). For instance during the period 1996-2003,
sediment loss was almost twice as large during the El Niño as
under La Niña year (Table 1). In this sense cold front
penetrations seems to act more as a sediment budget recover as
pointed out by MUEHE et al. (2001) independent of the
associated beach erosion. Table 2 seems to support this
hypothesis as the number of cold front penetration who reaches
Cabo Frio is twice as numerous during the spring and autumn of
the La Niña event as during the El Niño. Nevertheless the
relation between loss and gain in sediments with the Southern
Oscillation Index (Figure 4) seems to indicate an opposite
conclusion the relation depicted in the graph reflects basically a
graphical correlation of sediment volume with the SOI
associated to La Niña and normal conditions, while a strong El
Niño effect occurred only during 1997 and the beginning of
1998. Therefore the relation is not conclusive and will need a
longer period of observation.Sediment volume changes of a
segment of foredunes eastward of cabo Frio are submitted to
two opposite mechanisms of sediment transport direction both
closely related to the relation between Northeast trade winds
removing sediments in direction to the ocean and wind and
wave action driving sediments from the beach to the foredunes
during the passage of cold fronts. Both mechanisms are
connected to the normal seasonal climate variation but also to
interruption of the most common climate pattern due to El Niño
- La Niña Southern Oscillation. These influences are expressed
in the increase of wind intensity with increased removal of
sediments during the El Niño episode as occurred during 1997
and the beginning of 1998. Afterward sediment transport was
commanded by oscillations between the La Niña and normal
climate conditions, expressed by a reverse relation between the
ACKNOWLEDGEMENTS
The authors would like to thanks all the graduated and post
graduated students that participated in the field experiments
during eight years. The work has been supported by Conselho
Nacional de Desenvolvimento Científico e Tecnológico,
Coordenação de Aperfeiçoamento de Pessoal de Ensino
Superior (CAPES), and Fundação de Amparo à Pesquisa do
Estado do Rio de Janeiro (FAPERJ).
LITERATURE CITED
BARBIERI, E.B. 1999. Origin and evolution of Quaternary
coastal plain between Guaratiba and cape Frio, State of Rio
de Janeiro, Brazil. In Knoppers, B.A., Bidone, E.D. & Abrão,
.J.J. (Eds.). Environmental Geochemistry of Coastal Lagoon
System of Rio de Janeiro Brazil. Série Geoquímica
Ambiental, 6: 47-56 pp.
BITTENCOURT, A.C.S.P.; DOMINGUEZ, J.M. & MOITA FILHO,
O. 1990. Variações texturais induzidas pelo vento nos
sedimentos da face de praia (praia da Atalaia-Piauí). Revista
Brasileira de Geociências, 20:201-207.
BITTENCOURT, A.C.S.P.; FARIAAS, F.F. & ZANINI, A. 1987.
Reflexos das variações morfodinâmicas praiais nas
características texturais dos sedimentos da praia daArmação,
Salvador Bahia. Revista Brasileira de Geociências, 17:276282.
CASTRO, J.W.A. 2001. Geomorfologia do sistema sedimentar
eólico de Paracuru - Ceará. Federal Universidade Federal do
Rio de Janeiro. Departamento de Geografia. Doctor thesis.
201 pp.
CASTRO, J.W.A. & CALHEIROS, A.L.S. 2003. Geoindicadores
resultantes dos episódios El Niño/La Niña em dunas
costeiras do litoral setentrional do Nordeste brasileiro. IX
Congresso da Associação de Estudos do Quaternário
(ABEQUA).Anais. CD-Rom. Recife, Pernambuco. Brasil.
COMMONWEATH BUREAU OF METEROLOGY.
www.bom.gov.au.
CENTRO DE PREVISÃ O DE TEMPO E ESTUDOS CLIMÁ TICO CPTEC. www.cptec.inpe.br.
Table 2. Influence of El Niño and La Niña events in migration of cold fronts along Cabo Frio coast. Note the significant decrease of the
number of cold fronts that reached Cabo Frio during El Niño event. (Data from CLIMANALISE bulletin, CPTEC).
1996
Generated cold fronts
along the year
76
Cold fronts that
reach Cabo Frio
40
Generated cold fronts
between march and august
35
Cold fronts that reach Cabo Frio
between march and august
20
La Niæa
1997
78
29
34
10
El Niæo
1998
78
46
38
24
La Niæa
1999
81
46
39
21
La Niæa
2000
77
42
38
22
La Niæa
2001
73
25
37
12
El Niæo
2002
71
22
37
12
El Niæo
Year
Journal of Coastal Research, Special Issue 39, 2006
Event
374
Fernandez and Muehe
FERNANDEZ, G.B. 2003. Morfologia e dinâmica do sistema
praia-duna frontal e antepraia em ambiente de alta energia.
Praia da Massambaba Leste, litoral do estado do Rio de
Janeiro.
UNIVERSIDADE FEDERAL DO RIO DE JANEIRO. Departamento de
Geografia. 140 pp.
IRELAND, S. 1987. The Holocene sedimentary history of the
coastal lagoons of Rio de Janeiro State, Brazil. In: M. J.
Tooley & I. Shennan (ed.). Sea level changes. Basil
Blackwell. The Institute of British Geographers Special
Publications Series. p. 26-66.
KOURKY, V.E.; KAGANO, M.T. & CAVALCANTI, I.F.A. 1984. A
review of Soutern Oscilation: oceanic-atmosfericcirculation changes and related rainfall anomalies. Tellus,
36A: 490-504. In Turc et.al. (1999) Environmental
Geochemistry of Coastal Lagoon System. Knoppers, B.;
Bidone, E.D. & Abraão, J.J. (eds.). Serie Geoquímica
Ambiental, 6: 25-46.
MUEHE, D. 1998. O litoral brasileiro e sua compartimentação.
In CUNHA, S.B. & GUERRA, A.J.T. (ed.) Geomorfologia do
Brasil. Capítulo 7. Ed. Bertand Brasil.
MUEHE, D. & FERNANDEZ, G.B. 1999. O efeito de tempestades
como realimentador do estoque de sedimentos de dunas
frontais submetidas a vento predominante da terra para o
mar. VII Congresso da ABEQUA. 3 - 9 de outubro.
Associação Brasileira de Estudos do Quaternário. Porto
Seguro, Ba.
MUEHE, D. & VALENTINI, E. 1998. O litoral do estado do Rio de
Janeiro - uma caracterização físico-ambiental. Fundação de
Estudos do Mar - FEMAR. 99p.
MUEHE, D.; SILVA, C.G. & FERNANDEZ, G.B. 1999. The
coastline between Rio de Janeiro and Cabo Frio. Excursion
Guide. Regional Conference on Geomorphology. The
International Associacion of Geomorphologists and The
Brazilian Geomorphological Union. Rio de Janeiro, Brazil.
12 p.
MUEHE, D.; FERNANDEZ, G.F. & SAVI, D.C. 2001. Resposta
morfodinâmica de um sistema praia-antepraia a oeste do
cabo frio exposto às tempestades de maio de 2001. VIII
Congresso daABEQUA. Mariluz, Imbé, RS. 63-64.
RODRIGUES, A.C.B. 1999. Taxa de migração e transporte eólico
nas dunas do Ceará da Região do Cauípe costa oeste do
Estado do Ceará. VIII Congresso da Assossiação Brasileira
de Estudos do Quaternário. Porto Seguro, Bahia. Anais em
CD ROM.
RIBEIRO, A.Y. 2000. Balanço sedimentar num sistema de dunas
frontais sob o regime de ventos dominantes da terra para o
mar. Praia de Massambaba, Arraial do Cabo - RJ. M.Sc.
Thesis. Programa de Pós-Graduação em Geografia.
Universidade Federal do Rio de Janeiro. 258pp.
S UGUIO , K.; M ARTIN , L.; B ITTENCOURT , A.C.S.P.;
DOMINGUEZ, J.M.L. FLEXOR, J.M. & AZEVEDO, A.E.G.
1985. Flutuações do nível do mar durante o Quaternário
Superior ao longo do litoral brasileiro e suas implicações na
sedimentação costeira. Revista Brasileira de geociências.
15(4): 273-286.
TURC, B.; MARTIN, L.; FLEXOR, J.M.; SUGUIO, K. &
TASAYACO-ORTEGA, L. 1999. Origin and evolution of
Quaternary coastal plain between Guaratiba and cape Frio,
State of Rio de Janeiro, Brazil. In Knoppers, B.A., Bidione,
E.D. & Abrão, .J.J. (Eds.). Environmental Geochemistry of
Coastal Lagoon System of Rio de Janeiro Brazil. Série
GeoquímicaAmbiental, 6: 25-46 pp.
Journal of Coastal Research, Special Issue 39, 2006