The coast and shelf of east and northeast Brazil and material transport

Abstract

The east and northeast Brazil shelves of the Southwest Atlantic harbor some unique conditions for tropical passive margins with western boundary currents. The narrow and open shelf is almost entirely covered by carbonate sediments due to little freshwater input and the coast is impacted by the South Equatorial Current (SEC). The wide Abrolhos bank of the east Brazil shelf, presents more diverse conditions, as it forms a physical barrier to the Brazil Current, and upwelling and land input become more significant. The main characteristics of the coast and shelf and findings on biogeochemical, sedimentation, and paleoceanographical processes, addressed by the Joint Oceanographic Projects (JOPS) campaigns, are summarized.

Full text

B. Knoppers á W. Ekau á A. G. Figueiredo
The coast and shelf of east and northeast Brazil
and material transport
Abstract The east and northeast Brazil shelves of the
Southwest Atlantic harbor some unique conditions for
tropical passive margins with western boundary cur-
rents. The narrow and open shelf is almost entirely
covered by carbonate sediments due to little freshwater
input and the coast is impacted by the South Equatorial
Current (SEC). The wide Abrolhos bank of the east
Brazil shelf, presents more diverse conditions, as it forms
a physical barrier to the Brazil Current, and upwelling
and land input become more signi®cant. The main
characteristics of the coast and shelf and ®ndings on
biogeochemical, sedimentation, and paleoceanographi-
cal processes, addressed by the Joint Oceanographic
Projects (JOPS) campaigns, are summarized.
Introduction
Trailing edge (passive) continental shelves of the tropics
governed by western boundary currents are considered
to be among the least productive ocean margins of the
world, unless land run-o and eddy-induced shelf-edge
upwelling become signi®cant (Walsh 1988). The north-
east Brazil shelf sector (3°Sto13°S) of the tropical
southwest Atlantic is a good example of a tropical pas-
sive continental shelf. The shelf is narrow and open to
the sea, lies in the direct pathway of the oligotrophic
South Equatorial Current (SEC), receives relatively little
continental run-o, and is almost entirely covered by
biogenic carbonate sediments (Milliman 1975). The east
Brazil shelf, is more diverse and productive towards the
south due to a gradual increase in run-o and enlarge-
ment of the shelf at the Abrolhos bank, which forms a
topographic barrier to the southwest ¯owing Brazil
Current (BC). This special topographic feature induces
eddy spin-o and upwelling at the shelf edge and har-
bors the southernmost coral reef system of the southwest
Atlantic (Lea
Ä
o 1996; Castro and Miranda 1998) .
The northeast and east shelf regions of Brazil are the
least studied, but the geomorphology (Cruz et al. 1985;
Martins and Coutinho 1981), geology (Guerra 1962;
Mabesoone and Coutinho 1970; Emery and Uchupi
1984), evolution (Dominguez and Bittencourt 1996;
Martin et al. 1996), and sedimentology (Melo et al.
1975; Summerhayes et al. 1975, 1976) of the coast and
shelf are reasonably well known. The physical ocean-
ography has been discussed by Castro and Miranda
(1998), nutrients and plankton by Brandini et al. (1997),
and ®sheries resources by Paiva (1997). Coastal ocean-
ography, biogeochemistry, and material transport pro-
cesses have received relatively little attention before the
cruises of the Brazilian±German Joint Oceanographic
Projects (JOPS-I and -II) program, initiated in the 199 0s
(Ekau and Knoppers 1996, 1999). JOPS-I addressed the
origin and fate of clay minerals (Tintelnot 1995) and the
nature an d diagenesis of sedimentary organic matter
(Jennerjahn and Ittekkot 1997). JOPS-II focused on
sedimentation and biogeochemical processes in coastal
waters and at the inner shelf and upper shelf slope and
on paleoceanography of the Holocene/Late Pleistocene.
Some of these results are presented in this volume,
whereas studies on the productivity of coastal shelf
waters during JOPS-II are published in Archive of
Fishery and Marine Research (1999 Volume 47, 2/3).
Geography, geology and hydrology
of the coast and shelf
The Brazilian coastline from Cape Orange (lat. 4°N) to
Chui (lat. 34°S) measur es 7400 km, excluding contours
of bays and islands (Muehe and Neves 1996) (Fig. 1).
Geo-Marine Letters (1999) 19: 171±178
Ó
Springer-Verlag 1999
B. Knoppers
Departamento de Geoquõ
Â
mica, Universidade Federal Fluminense,
Outeiro de Sa
Ä
o Joa
Ä
o Batista s/n, 24020-007 Nitero
Â
i, RJ, Brazil
W. Ekau
Zentrum fu
È
r Marine Tropeno
È
kologie, Universita
È
t Bremen,
Fahrenheitstrasse 1, 28359 Bremen, Germany
A. G. Figueiredo
Laborato
Â
rio de Geologia Marinha, Universidade Federal
Fluminense, Av. Litoraà nea s/n 24210-340 Nitero
Â
i, RJ, Brazil

Geographical and hydrological criteria distinguish the
coastal zone into ®ve main regions, the North, North-
east, East, Southeast and South (Silveira 1964; Cruz
et al. 1985), (Table 1). The east (13°S, 39°W to 22°S,
42°W) and northeast (3°S, 42°W to 13°S, 38°W) coasts
account for about 18 and 24% of Brazil's shoreline,
respectively. The y have been divided into subsections
(Table 1), according to the degree of freshwater runo
and the nature of coastal habitats, shelf geomorphology,
sedimentology, and also biological criteria adopted from
JOPS-II (Ekau and Knoppers 1999). Geological criteria
distinguish four sections, the northern Quaternary (4°N
to 3°S), eastern Tertiary (3 to 20°S), southeastern
granitic (20 to 29°S), and the southern Quaternary (29 to
34°S) coasts (Guerra 1962) (Fig. 1). The Tertiary coast
corresponds to regions Northeast and East, is generally
narrow up to a few kilometers wide (Lacerda et al.
1993), and is characterized by the Tertiary Barreiras
Formation, which may outcrop as fossil blus along the
shoreline. Characteristic formations of the coastal zone
are dunes, typical ria type estuaries with man groves
(Herz 1991) and fringing and bank reefs, including those
of Abrolhos (Lea
Ä
o 1996; Wells 1988). Some of the bio-
geochemical features of east coast rias were ®rst ad-
dressed by Ovalle et al. (this issue). The ultimate
extension of the Barreiras Formation and the Paraõ
Â
ba do
Sul coas tal plain form the transition between the Ter-
tiary and granitic coast (Southeast region), where the
Atlantic Serra do Mar mountain range of pre-Cambrian
metamorphic and igneous rocks lie parallel near the
coast.
The climate of the Northeast varies from tropical dry/
semi arid of Ko
È
ppen type Bs in the north to tropical
humid of Ko
È
ppen type Af from the East to the South
(Nimer 1972) (Fig. 1). The total drainage basin area (A
B
)
of the Northeast, including the Sa
Ä
o Francisco river, is
1.33 ´ 10
6
km
2
and the cumulative annual freshwater
discharge (Q
r
) is about 4400 m
3
s
)1
(Table 1). The Par-
naõ
Â
ba (A
B
= 0.33 ´ 10
6
km
2
, Q
r
= 640 m
3
s
)1
) and Sa
Ä
o
Francisco (A
B
= 0.63 ´ 10
6
km
2
, Q
r
= 2850 m
3
s
)1
)
are medium-sized rivers, the remaining are insigni®cant
and of the torrential type. The Sa
Ä
o Francisco basin is
considered as a seperate unit, as it is located inland be-
hind the Northeast and East basins (Milliman 1975;
ANEEL 1998).
The climate of the East is largely tropical humid of
Ko
È
ppen type Af, with Aw to the south (Nimer 1972).
The total drainage basin area of the East is
0.55 ´ 10
6
km
2
and the cumulative annual freshwater
discharge is 3600 m
3
s
)1
(Table 1). Discharge increa ses
gradually from north to south, the main rivers being Das
Contas, Pardo, Jequetinhonha, Mucuri, Doce, Itapemi-
rim and Paraõ
Â
ba do Sul, which account for about 85% of
the total discharge [National Agency of Electric Energy
(ANEEL) personal communication]. All rivers exhibit a
unimodal seasonal pattern of discharge, with maxima
during the austral summer and minima during the aus-
tral winter.
Knowledge of suspended sediment concentrations of
the rivers remains as rudimentary and con¯icting as a few
decades ago (Milliman 1975), but some information is
now found in technical reports (Eletrobra
Â
s 1992, 1998).
The small rivers of the Northeast (A
B
= 10
3
±10
4
km
2
),
have a median suspended matter (SPM) concentration
of 110 mg l
)1
(n = 7) and yield of 17 t km
)2
yr
)1
(n = 7). The SPM concentration of the Sa
Ä
o Francisco
has been estimated at 144 mg l
)1
and the yield at
23 t km
)2
yr
)1
(Bessa and Paredes 1990). Slightly higher
median SPM concentrations (159 mg l
)1
, n = 5) and
yields (36 t km
)2
yr
)1
, n = 5) are encountered for the
larger rivers (A
B
= 10
4
±10
5
km
2
) along the East section.
The low SPM contents and yields have previously been
attributed (Milliman 1975) as due to the lack of youthful
topography of the drainage basins, enhanced in the
Northeast by the semiarid climate. Milliman (1975)
stated that river SPM concentrations were <100 mg l
)1
,
but many basins have recen tly been subject to enhanced
erosion due to deforestation and monoculture (euca-
lyptus and sugar cane) practices. Only 6% of the original
forest coverage remains in the East (Leipe et al. this
Table 1 Physiographic features and main oceanic currents aecting the east-northeast coastal-shelf regions of Brazil
Location NORTHEAST EAST
Parnaõ
Â
ba
Cape S. Roque
41.5°±36.5°W
Cape S. Roque
Salvador
5°±13 °S
Salvador
Belmonte
13°±16 °S
Belmonte
Regeà ncia
16°±19.5 °S
Regeà ncia
Cape S. Tome
Â
19.5°±22 °S
Climate (ko
È
ppen)
2
Bs As Af Af Aw
Drainage Basin (km
2
)
3
526000 800000* 170000 154000 141000
River descharge (m
3
s
)
1)
3
1000 3400 880 940 2000
Coastline (km)
4
1038 737 473 514 337
Mangrove area (km
2
)
5
343 476 877 239 179
Shelf width (km) 35 to 90 20 to 50 10 to 45 75 to 245 45 to 90
Shelf area (km
2
)
1
48350 28500 12340 59620 20880
Water regime
6
NBC NBC, SEC, BC BC BC BC, SACW
a
Sources:
1
Ekau and Knoppers (1999),
2
Nimer (1972),
3
ANEEL (1998)
4
GERCO-PNMA (1996)
5
Herz 1991,
6
Castro and Miranda (1998). SEC = South Equatorial Current,
NBC = North Brazil Current, BC = Brazil Current, SACW =
South Atlantic Central Waters.
172

issue), but no link has as yet been established between
higher river loads and sedimentation rates along the
coast due to human impact in the basins. Many dams are
found along the river courses (Eletrobra
Â
s 1998).
Geomorphology and oceanography of the shelf
Maximum shelf widths are attained o the Amazon in
the north (350 km), at the Abrolhos bank in the east
(245 km), and o Santos in the southeast (200 km). In
contrast, the northeastern and the eastern shelf sectors
up to the Royal Charlotte Banks are only 20±50 km
wide. The narrowest shelf of 8 km is found o Salvador
(Fig. 1). The shelf break varies in depth from 75 to 80 m
in the north, from 40 to 80 m in the northeast and east,
and from 100 to 160 m in the southeast and south. The
depth of the base of the slope is 2000±3300 m in the
north, 1600±3600 m in the northeast and east and 2,000±
3,600 in the south. The slope gradient in the northeast
and east is high (1:5, 11°) and reaches a maximum of 28°
at the Abrolhos bank. The oceanic basins of the north-
east and east are characterized by a chain of seamounts,
of which several pierce the surface, including the Fer-
nando de Noronha and the Saint Peter and Saint Paul
islands (Fig. 1).
Three branches of the South Equatorial Current
(SEC) impinge the coast between 7° and 17°S (Stra mma
et al. 1990). At about 10°S, the northwestward ¯owing
North Brazil Current (NBC) is formed (Silveira et al.
1994) and slightly to the south, the weak southeastward
¯owing Brazil Current (BC) (Evans and Signorini 1985,
Peterson and Stramma 1991). The sector including the
Royal Charlotte and Abrolhos banks to Cape Sa
Ä
o
Tome
Â
, is denominated by Castro and Miranda (1998) as
the Abrolhos±Campos Region (ACR, 15°±23°S). The
Abrolhos bank and the Vito
Â
ria±Trindade ridge form a
topographical barrier to BC, inducing fundamental
changes and spatial variability in physical, chemical, and
biological features over the shelf and along the shelf edge
(Castro and Miranda 1998; Ekau and Knoppers 1999;
Gaeta et al. 1999). Eddies are generated along the east-
ern shelf edge, forming cyclonic vortices (i.e., Vito
Â
ria
Fig. 1 The coast and shelf of Brazil: climate (Nimer 1972), geological
regions (Guerra 1962), geographical regions (Cruz et al. 1975), tidal
regimes (tide tables, Brazil Navy), and western boundary currents
(Peterson and Stramma 1991). Bars delimit the East±Northeast Brazil
shelf sector
173

Eddy) (Schmid et al. 1995) at the southern edge of the
Abrolhos bank.
Coastal upwelling of nutrient-rich South Atlantic
central waters (SACW) characterizes the area south of
Abrolhos in spring and summer (Summerhayes et al.
1976), resulting in higher primary production. Results of
JOPS-II revealed (Gaeta et al. 1999) that the lower sector
of the East or ACR is a distinct functional region, where
primary production may temporarily be sustained by
three dierent material sources: the rivers, coastal and
shelf edge upwelling, and the Vito
Â
ria Eddy impinging on
the shelf (Ekau and Knoppers 1999). In spite of the
extremely low concentrations of SPM (>0.25 to <1.0
mg l
)1
) along the inner shelf, most is of organic nature
derived from biological production (Summerhayes et al.
1976; Balzer and Knoppers 1996; Gaeta et al. 1999).
Evolution
During the Late Jurassic (150 my BP), Gondwana land
was still a continent an d sedimentary basins in Brazil
and Africa, where the South Atlantic is located today,
shared the same lithologic, paleonthologic, and geologic
features (Maxwe ll and Von Herzen 1970). However,
prior to this, during the Early Jurassic (205 my) in the
North Atlantic, a proto-ocean seperated Laurasia
(North America and Europe) from occidental Gond-
wana (South America and Africa) (Dietz 1961; Dietz
and Holden 1970). An early rift of this time characterizes
the north Brazilian margin. The opening of the South
Atlantic started in the Early Cret aceous (120 Myr BP)
from the south towards the north, with South America
rotating clockwise and Africa anticlockwise . The ®rst
deposits in the basin were nonmarine and ch anged from
lacustrine to salt and marine (Van Andel et al. 1977;
Asmus 1984). Until the Late Cretaceous, the South and
North Atlantic were isolated from each other due to a
connection between the continents, located in the region
of States of Pernambuco and Paraõ
Â
ba, Brazil, and
Cameroon and Nigeria, Africa, based on fossil ®ndings
(Beurlen 1961, 1962).
Despite the long time since the opening of the At-
lantic, most of the features of the continental margin are
still preserved today. Only minor changes have been
induced by erosion, volcanism, or sediment burial. The
shelf width and shelf break depth re¯ect the tectonic
behaviour and the depositional conditions of the Bra-
zilian margin (Fig. 1). Because of the sediment load
from land and continuous subsidence of the margin, the
south and southeast shelf has a thic k prograding sedi-
ment sequence at the shelf break and slope and has a
deeper shelf break with a more gentle transition to the
slope. In contrast, the narrow shelf and shallow shelf
break of the northeast and east up to the Abrolhos bank
indicate, that terrigenous sediments had only minor and
local in¯uence due to the lack of river run-o and a
more stable margin with little erosion. As a conse-
quence, the shelf-slope transition is abrupt, the slope is
very steep, and oceanic circulation reaches the coast
(Martins and Coutinho 1981). The shelf edge and slope
are cut through by canyon s and channels, remainders of
the drainage during periods of regression. The lack of
clear connection between canyons and the present
drainage basins suggests that erosional features have
been buried under a sediment cover.
The evolution of the coast during the Late Pleistocene
until today has been well documented from geomor-
phological and sea-level change studies (Suguio et al.
1985; Dominguez and Bittencourt 1996; Martin et al.
1996; Tomazelli and Villwock 1996). Sand barriers and
coastal lagoons, frequent in the East, Northeast, and
South, attained peak expansion during two major sea-
level high stands. The ®rst, occurring approximately
123,000 yr BP, corresponded to the last Pleistocene in-
terglacial stage with a relative sea level at 8  2 m
above the present level. The second, occurring at 5100 yr
BP, corresponded to the Holocene sea-level high stand,
with sea level 4.8  0.5 m above the present. In contrast
to rising sealevel in North America in the last 7000 yr,
the sea level of Brazil has undergone a drop. Other
secondary oscillations could have occurred 4100±
3800 yr BP and 3000±2700 yr BP (Suguio et al. 1985),
but are contested by Angulo and Lessa (1997). At
present, there is a slight trend in relative sea-level rise
from Rio Grande in the south to Recife in the Northeast
(Pirazolli 1986; Aubrey et al. 1998). At about 12,000 yr
BP, most of the northeast and east shoreline was set
between the 50- and 70-m isobaths of the presentday
shelf edge (Arz et al. this issue), enhancing material
transport from land directly to the upper shelf slope
(Tintelnot 1995; Jennerjahn and Ittekkot 1997).
Sediment distribution on the shelf
The Northeast, in particular, represents one of the few
areas in the world where an open, passive margin is
almost completely covered by biogenic carbonate sedi-
ments (Summerhayes et al. 1975). The interplay between
terrigenous and carbonate sedimentation is clearly
re¯ected by the sediment distribution. The higher the
freshwater input, the lower the content of carbonate
sediment. The sediment in the northeast and east up to
the Abrolhos bank are largely composed of carbonates
(>75%). To the south of the Abrolhos bank up to Cape
Sa
Ä
o Tome
Â
, the sediment is terrigen ous, in part relict
(Fig. 2), (Melo et al. 1975; Summerhayes et al. 1975).
The carbonate sediments vary from coarse sand to
gravel, with the latter predominating at the outer shelf.
The carbonate is derived from branching algae and
Halimeda. Corals, bryozoans, and incrusting algae form
the reefs of the Abrolhos region (Lea
Ä
o 1996). Relict
terrigenous sediments cover some isolated sections of the
inner and mid shelf o Ceara
Â
in the northeast. The Sa
Ä
o
Francisco, Jequitinhonha, Doce, Mucuri and Paraõ
Â
ba do
Sul rivers in the east have modern terrigenous sediment
o their mouths (Summerhayes et al. 1975, 1976;
174

Tintelnot 1995). Most of the modern and relict terrige-
nous sediment are also relatively poor in organic matter
and phosphorites, even where upwelling persits (Sum-
merhayes et al. 1976).
From cluster analysis using several variables (car-
bonate, biogenic opal, C
org
, N
org
, amino acids and water
depth), Jennerjahn and Ittekkot (1997) de®ned six sedi-
ment provinces for the shelf between the Sa
Ä
o Francisco
and Paraõ
Â
ba do Sul rivers. Fine-grained recent silicla stic
sediments from rivers, relatively rich in organic matter
(C
org
1.4%), opal (3.4%), and labile nitrogen-containing
compounds, are only found near the river mouths, while
coarse-grained relict siliclastic sedimen ts, lower in or-
ganic matter (C
org
0.4%) and opal (1.6%), characterize
some areas of the inner shelf between river mouths.
Carbonates in these two provinces reach 11% and 15%,
respectively. Coarse-grained carbonates (83%) poor in
organic matter (C
org
0.3%) dominate the outer shelf.
Fine-grained siliclastic sediments (carbonate 28%, opal
4%, C
org
1.1%) accumu lated in morphological traps at
the upper shelf slope, except for the region between
Salvador (13°S) an d the Abrolhos bank (18°S), charac-
terized by coarse-grained carbonates.
Much of the present sediment distribution can still
be attributed to past proce sses related to sea-level his-
tory. Patches of mud from drowned lagoonal deposits
are found in several places along the shelf. The mud
wedge of the Sa
Ä
o Francisco appears to have been de-
posited in a coastal lagoon during the last sea-level
transgression, and carbonate muds in deeper areas
(40±60 m) of the Abrolhos bank are derived from the
degradation of coral reefs during periods of lower sea-
level stands. Red muds and refractory organic matter
from mangroves, encountered at the shelf edge and
slope o NE Brazil, are considered to have been de-
posited when the sea-level stand was positioned at the
margin about 12,000 yr BP (Jennerjahn et al. this issue;
Arz et al. this issue).
Material transport and sedimentation processes
The seaward transport of land materials can be consid-
ered to be minor as inferred from the rela tively low
sediment yields of the drainage basins and low concen-
trations of suspended matter and predominance of car-
bonate sediments (Milliman 1975). A unique feature of
the east and northeast inner shelf is the lack of well-
de®ned coastal waters, which, in contrast, are found in
the southeast (Castro and Miranda 1998; Mahiques
et al. 1999). River input does not suce to maintain a
detectable freshwater fraction along the coast, even
within the 20-m isobath o most larger river mouths,
due to ecient ¯ushing by tropical surface waters (TSW)
(Ekau and Knoppers 1999). Most materials are retained
nearshore and some ®ner materials that bypass the
phase of initial deposition during plume dispersal are
washed out by TSW. The plumes of the Paraõ
Â
ba do Sul
and Doce rivers, which generally edge to the north or
south along the coast, are readily diluted by TSW within
a maximum of 1.5 km from the river mouths, where
bulk sedimentation of plume suspensates also occurs.
Free-drifting sediment trap experiments along these
river plumes, yielded gross sedimentation rates of SPM
and particulate organic carbon between 38 and
100 g SPM m
)2
d
)1
and 0.9 and 2.9 g Cm
)2
d
)1
and in
waters not aected by the plumes they were lower by a
factor of ®ve (Ba lzer and Knoppers 1996; Carneiro
1998). Material export to the inner shelf from the smaller
mangrove rias in the east (Jennerjahn and Ittekkot 1997;
Leipe et al. this issue; Ovalle et al., this issue) and in the
northeast (Schwambor n et al. 1999; Souza 1999), has
been found to be insigni®cant, in part from ecient in-
ternal recycling of biogenic mat ter.
However, Patchineelam and Smoak (this issue) found
variable and even signi®cant sedimentation rates
Fig. 2 Sediment facies of the East and Northeast Brazil shelves.
Adapted from Melo et al. (1975) and Summerhayes et al. (1975, 1976)
175

(0.1±0.8 cm yr
)1
) on the inner shelf between the Jeque-
tinhonha and Doce rivers, particul arly around the
Caravelas bank at Abrolhos. The bank is a depositional
area of materials transported by longshore drift, part of
which seem to originate from coastal erosion of the fossil
blus of the Tertiary Barreiras Formation (Dominguez
and Bittencourt 1996; Leipe et al. this issue). The trend
in sea-level rise of 2±4 mm yr
)1
, established for the re-
gion today (Pirazolli 1986; Aubrey et al. 1988), could be
responsible for shore erosion, but direct links have as yet
to be established (Muehe and Neves 1995). It is postu-
lated that cascading of materials alon g the bottom is an
important process governing the transport between
nearshore and inn er shelf waters. The waters of the
entire east coast are prone to signi®cant resuspension,
subsequent advection, and deposition of bottom mate-
rials, due to high wave energy, tidal eects, and rela-
tively strong coastal currents when constrained by
topography (Dominguez and Bittencourt 1996; Leipe
et al. this issue). Gross sedimentation rates during dis-
persal of the Paraõ
Â
ba do Sul and Doce plumes are also
highly aected by resuspended matter (Balzer and
Knoppers 1996; Carneiro 1998).
In spite of the low total and inorganic SPM concen-
trations of the shelf waters (Milliman 1975), ®ne mate-
rials from land are transported to the shelf slope,
particularly o the Sa
Ä
o Francisco, Jequetinhonha, and
Doce rivers (Tintelnot 1995; Jennerjahn and Ittekkot
1997). Clay minerals of the rivers along the northeast,
from Fortaleza to Maceio
Â
, are dominated by illite and
smectite, and along the east, from the Jequetinhonha to
the Paraõ
Â
ba do Sul river mouths, by more than 80% of
kaolinite. Similar signals are found in depos ited mater ial
along the upper shelf slope. At the mid-continental slope
(1240±2400 m depth) o the Abrolhos bank and Doce
river, Masse
Â
et al. (1996) registered signi®cant and
highly variable sediment ¯uxes in 3 cores characterized
by high kaolinite contents derived from the continent.
O the narrow Sa
Ä
o Francisco river shelf, sediment ¯uxes
are linked to the oscillation of river ¯ow. Jennerjahn
et al. (this issue) positioned a sediment trap at 1550 m
depth 50 km o the coast. They registered peak ¯uxes of
amino acids, hexosamines, and carbohydrates coinciding
with the high discharge period of the river. During rising
river ¯ow, the ¯uvial input of nutrients triggered a
bloom of nonbiomineralizing plankton, leading to in-
creased ¯uxes of autochthonous organic matter. Subse-
quently, during and after peak river ¯ow, suspended
matter derived from the river and/or shelf erosion
enhanced ¯uxes of refractory matter associated with
lithogenics.
The mechanisms of across-she lf transport have yet to
be quanti®ed, but cross-shelf currents together with tidal
eects may be signi®cant. Cross-shelf currents at NBC
along the Northeast have been computed to be 0.3±
0.4 m s
)1
, dominated by tidal oscillations, primarily
from the M
2
and S
2
constituents. Semidiurnal tidal el-
lipses are oriented mainly across the isobaths (Castro
and Miranda 1998). Leipe et al. (this issue) found strong
across-channel tidal currents at the outer Abrolhos reefs
and postulated this as being one of the features en-
hancing the across shore exchange of suspended matter
at the site.
Sedimentation during the Holocene
During lower sea-level stands, particularly 12,000 yr BP,
most of the shelf was exposed, and it is conceivable that
river input and mangroves at the shelf edge exported
materials directly to the Northeast shelf slope (Tintelnot
1995; Ittekkot and Jennerjahn 1997; Arz et al. this is-
sue). The results of Masse
Â
et al. (1996) support this for
the Abrolhos bank slope. Arz et al. (this issue) provide
evidence for short-term variations in sediment compo-
sition related to changes in the input and deposition of
terrigenous material controlled by sea level and the
climate during the last 22,000 yr along the northeast
continental margin. The prime objective was to detect
short-term deglacial climatic signals in the northeast
Brazil climatic province, which is sensitive to changes in
the equatorial wind ®eld and the hydrography of the
adjacent ocean. Sedimentation proce sses on the upper
continental slope, in turn, are strongly in¯uenced by the
continental climate. Detailed
14
C MAS data and isotope
stratigraphies revealed sedimentation rates of up to
100 cm per 1000 yr. Periods of increased terrigenous
input related to more humid conditions in the hinterland
were 18.5±15.5, about 14.2, and 12.7±11.2 cal. kya. The
youngest period of increased terrigenous sedimentation
coincides with the Younger Dryas (YD) climatic rever-
sal. The four sediment cores from the upper co ntinental
slope o NE Brazil are comprised of relati vely undis-
turbed and high-resolution sediments, providing valu-
able information for the detection of short-term climatic
variations. The well-de®ned stratigraphies of the cores
and comparisons with results from other regions
(e.g.,West Africa, West African and Equatorial upwel-
ling areas) support the fact that the recorded humid
events are nearly synchronous to the Northern Hemi-
sphere YD signal.
Summary
Earlier studies and results of JOPS-II included in this
short review have shown that the northeastern and
eastern shelves up to until the Abrolhos bank are similar
and may be considered as one unique system, governed
by little material input from land, extremely oligotrophic
western boundary currents, and carbonate sediments. In
contrast, the sector of the east Brazil shelf from the
Abrolhos bank to Cape Sa
Ä
o Tome
Â
exhibits diverse
physical, sedimentological, and biogeochemical features,
generated by the impact of its topography upon the
southwestward ¯owing Brazil Current and the deeper
northward ¯owing South Atlantic central waters. Most
materials derived from rivers and coastal erosion seem
176

to be retained in nearshore waters, and bypassed mate-
rials are readily washed out by the oceanic currents. Fine
suspensates from land reach the shelf edge and upper
shelf slope along the entire margin. Little information
still exists on biogeochemical and modern material
transport processes, but some features of nearshore and
oshore material transport and, particularly, of ho-
locene sedimentation related to climatic and sea-level
changes, are now better known.
Acknowledgments All colleagues, the ship's crew of RV Victor
Hensen and ocials, are greatly acknowledged for their long-term
cooperation during the Brazilian±German JOPS endeavor. The
Ministries of Science and Technology of Brazil (MCT) and Ger-
many (BMBF) and the Ministry of the Environment (MMA) of
Brazil ®nanced the JOPS campaigns. Scholarships were rewarded
from both sides to PhD and MSc students, without whose help
much of the work would not have been feasible. B. Knoppers and
A. G. Figueiredo are research scholars of the National Council for
the Development in Science and Tecnology (CNPq) of Brazil.
Gesse
Â
Mendes de Souza and Hugo Sardenberg made the ®gures.
References
ANEEL (1998) Ageà ncia Nacional de Energia Ele
Â
trica. Internet
source: http://www.aneel.gov.br
Angulo JA and Lessa GC (1987) The Brazilian sea-level curves: A
critical review with emphasis on the curves from Paranagua
Â
and
Canane
Â
ia regions. Marine Geology 140: 141±166
Asmus HE (1984) Geologia da margem continental brasileira. In:
Schobbenhaus C, Campos DA de, Derze GR, and Asmus HE
(Eds.), Geologia do Brasil. Brasil, Departamento Nacional da
ProducË a
Ä
o Mineral (DNPM), pp 443±472
Aubrey DG, Emery KO, and Uchupe E (1988) Changing coastal
levels of South America and the Caribbean region from tide
gauge records. Tectonophysics 154: 269±284
Balzer W and Knoppers B (1996) Transport mechanisms of bio-
geneous material, heavy metals and organic pollutants in east
Brazilian waters, large scale investigations. In: Ekau W,
Knoppers BA (Eds.), Sedimentation Processes and Productivity
in the Continental Shelf Waters o East and Northeast Brazil.
Cruise Report and First Results of the Brazilian German Pro-
ject JOPS-II (Joint Oceanographic Projects). Bremen: Centre
for Tropical Marine Ecology, pp 9±25
Bessa MF and Paredes J.F (1990) Transporte do carbono e do
nitrogeà nio orgaà nico e inorgaà nico dissolvidos pelo Rio Sa
Ä
o
Francisco, Brasil, durante um ano hidrolo
Â
gico (1984±1985).
Geochimica Brasiliensis 4: 17±31
Beurlen K (1961) O Turoniano marinho do nordeste do Brasil.
Boletim da Sociedade Brasiliera de Geologia 10(2): 39±52
Beurlen K (1962) O desenvolvimento peleogeogra
Â
®co do Oceano
Atlaà ntico Sul. Recife: Universidade de Recife, Gabinete de
Estratigra®a e Arquivo Geolo
Â
gico 2: 21±36
Brandini FP, Lopes RM, Gutseit KS, Spach HL, and Sassi R
(1997) Planctonologia na plataforma continental do Brasil:
Diagnose e revisa
Ä
o bibliogra
Â
®ca. Brasõ
Â
lia, Ministe
Â
rio do Meio
Ambiente dos resursos hõ
Â
dricos e da Amazoà nia legal (MMA),
Comissa
Ä
o Interministerial para os recursos do Mar (CIRM),
FundacË a
Ä
o de Estudos do Mar (FEMAR), 196 pp
Carneiro M.E (1998) Origem, transporte e destino de mate
Â
ria
biogeà nica e hidrocarbonetos no estua
Â
rio do Rio Paraõ
Â
ba do Sul.
Unpublished PhD thesis. Nitero
Â
i, Departamento de Geoquõ
Â
-
mica, Universidade Federal Fluminense, 137 pp
Castro BM and Miranda LB (1998) Physical oceanography of the
western Atlantic contiental shelf located between 4°N and 34°S.
In: Robinson AR and Brink KH (Eds), The Sea, Vol. 11: pp
209±252, New York: John Wiley & Sons
Cruz O, Coutinho PN, Duarte GM, Gomes AMB, and Muehe D
(1985) Brazil. In: Bird ECF and Schwartz ML (Eds.),
The World's Coastline. New York: Van Nostrand Reinhold, pp
85±91
Dietz RS (1961) Continent and ocean basin evolution by spreading
of the sea ¯oor. Nature 190: 854±857
Dietz RS and Holden JC (1970) Reconstruction of Pangea: Break
up and dispersion of continents, Permian to present. Journal of
Geophysical Research 75: 4939±4956
Dominguez JML and Bittencourt AC (1996) Regional assessment
of long-term trends of coastal erosion in northeastern Brazil.
Anais Academia brasileira de Cieà ncias 68: 355±371
Ekau W and Knoppers BA (1996) (Eds.) Sedimentation Pro-
cesses and Productivity in the Continental Shelf Waters o
East and Northeast Brazil. Cruise Report and First Results
of the Brazilian German Project JOPS-II (Joint Oceano-
graphic Projects). Bremen: Centre for Tropical Marine Ecology,
151 pp.
Ekau W and Knoppers BA (1999) An introduction to the pelagic
system of the East and Northeast Brazilian shelf. Archive of
Fishery and Marine Research 47(2/3)
Eletrobra
Â
s (1992) Diagno
Â
stico das condicË o
Ä
es sedimentolo
Â
gicas dos
principais rios Brasileiros. Technical Report. Rio de Janeiro:
Eletrobra
Â
s, 100 pp
Eletrobra
Â
s (1998) Relato
Â
rio anual do GTIB. Grupo de Trabalho de
InformacË o
Ä
es Ba
Â
sicas para o Planejamento da ExpancË a
Ä
o e Ge-
racË a
Ä
o. Technical Report. Rio de Janeiro: Eletrobra
Â
s, 118 pp
Emery KO and Uchupi E (1994) The Geology of the Atlantic
Ocean. New York: Springer Verlag, 1050 pp
Evans DL, and Signorini SR (1985) Vertical structure of the Brazil
Current. Nature 315: 48±50
Gaeta AS, Lorenzetti JA
Â
, Miranda LB, Susini-Ribeiro SMM,
Pompeu M, and De Araujo CES (1999) The Victoria Eddy and
its relation to the phytoplankton biomass and primary pro-
ductivity during the austral fall of 1995. Archive of Fishery and
Marine Research 47(2/3)
GERCO-PNMA (1996) Macrodiagno
Â
stico da zona costeira do
Brasil na escala da unia
Ä
o. Gerenciamento Costeiro, Programa
Nacional do Meio Ambiente. Brasõ
Â
lia, Ministe
Â
rio do Meio
Ambiente (MMA), 280 pp
Guerra HT (1962) O litoral Atlaà ntico. Paisagens do Brasil. Rio de
Janeiro: Instituto Brasileiro de Geografõ
Â
a e Estatistica (IBGE),
456 pp
Herz R (1991) Manguezais do Brasil. Sa
Ä
o Paulo: Instituto Ocean-
ogra
Â
®co, Universidade de Sa
Ä
o Paulo, SP, 227 pp
Jennerjahn TC, and Ittekkot V (1997) Organic matter in sediments
in the mangrove areas and adjacent contiental margins of
Brazil: I. Amino acids and hexosamines. Oceanologica Acta
20(2): 359±369
Lacerda LD, De Arau jo DSD and Maciel NC (1993) Dry coastal
ecosystems of the tropical Brazilian coast. In: Maarel E vd (Ed.),
Ecosystems of the World 2B. Amsterdam: Elsevier, pp 477±493
Lea
Ä
o ZMAN (1996) The coral reefs of Bahia: Morphology, de-
struction and the major environmental impacts. Anais Acade-
mia Brasileira de Cieà ncias 68(3): 439±452
Mabesoone JM and Coutinho PN (1970) Litoral and shallow
marine geology of northern and northeastern Brazil. Recife,
Universidade Federal de Pernambuco. Trabalhos Ocean-
ogra
Â
®cos 12: 1±214
Mahiques MM de, Mishima Y and Rodrigues M (1999) charac-
teristics of the sedimentary organic matter on the inner and
middle continental shelf between Guanabara Bay and the Sa
Ä
o
Frabcisco do Sul, south-eastern Brazilian margin. Continental
Shelf Research 19(6): 775±798
Martin L, Suguio K, Flexor J-M, Dominguez JML, and Bitten-
court ACSP (1996) Quaternary sea-level history and variation
in dynamics along the central Brazilian coast: consequences and
coastal plain construction. Anais Academia brasileira de
Cieà ncias 68(3): 303±354
Martins LR, and Coutinho PN (1981) The Brazilian continental
margin. Earth Science Review 17: 87±107
177

Masse
Â
L, Fauge
Â
res JC, Pujol C, pujos A, Labeyrie LD, and Bernat
m (1996) sediment ¯ux distribution in the Southern Brazil Basin
during late Quaternary: The role of deep-sea currents. Sedi-
mentology 43: 115±132
Maxwell AE, von Herzen RP et al (1970) Initial reports Deep Sea
Drilling Project, Washington, DC: US Government Printing
Oce Vol. 3
Melo U, Summerhayes CP, and Ellis JP (1975) Salvador to Vito
Â
ria,
Southeastern Brazil. In: Upper Continental Margin Sedimen-
tation o Brazil. Stuttgart: Contribution to Sedimentology 4:
78±116
Milliman JD (1975) A Synthesis. In: Upper Continental Margin
Sedimentation o Brazil. Stuttgart: Contribution to Sedi-
mentology 4: 151±175
Muehe D and Neves C (1995) The implications of sea-level rise on
the Brazilian coast: A preliminary assessment. Journal of
Coastal Research, Special Issue 14: 54±78
Nimer E (1972) Climatolgia da regia
Ä
o Nordeste do Brasil. Revista
Brasileira de Beogra®a 34(2): 3±51
Paiva MP (1997) Recursos pesqueiros estuarinos e marinhos do
Brasil. AvaliacË a
Ä
o do potencial sustenta
Â
vel de recursos vivos na
zona econoà mica exclusiva. Fortaleza: Universidade Federal do
Ceara
Â
, 286 pp
Peterson RG, and Stramma L (1991) Upper-level circulation in the
South Atlantic Ocean. Progress in Oceanography 26: 1±73
Pirazolli PA (1986) Secular trends of relative sea-level (RSL)
changes indicated by tide-gauge records. Journal of Coastal
Research, Special Issue 1: 1±26
Schmid C, Scha
È
fer H, Podesta
Â
G, and Zenk W (1995) The Vito
Â
ria
Eddy and its relation to the Brazil Current. Journal of Physical
Oceanography 25(11): 2532±2546
Schwamborn R, Voss M, Ekau W, and Saint-Paul U (1999) Stable
isotope composition of particulate organic matter and zoo-
plankton in northeast Brazilian shelf waters. Archive of Fishery
and Marine Research 47 (2/3)
Silveira ICA, Miranda LB, Evans DL, Stevenson MR, and In-
ostroza HM (1994) On the origin of the North Brazil Current.
Journal of Geophysical Research 99(C11): 22501±22512
Silveira JDA (1964) Morfologia do litoral. In: Azevedo A (Ed.),
Brasil a terra e o homen. Sa
Ä
o Paulo, Companhia Editora
Nacional, pp 253±305
Souza FL de (1999) O metabolismo e balancË o de massa do estua
Â
rio
do rio Piauõ
Â
, Sergipe. Unpublished PhD thesis. Nitero
Â
i: Depart-
amento de Geoquõ
Â
mica. Universidade Federal Fluminense, 91 pp
Stramma L, Ikeda Y, and Peterson RG (1990) Geostrophic
transport in the Brazil Current region north of 20°S. Deep-Sea
Research 37(12): 1875±1886
Suguio K, Martin L, Bittencourt ACSP, Dominguez JML, Flexor
JM. and Azevedo AEG (1985) Flutuaca
Ä
es do nivel relativo do
mar durante o Quaterna
Â
rio Superior ao longo do litoral bras-
ileiro e nas implicacË o
Ä
es na sedimentacË a
Ä
o costeira. Revista
Brasileira de Geocieà ncias 15(4): 273±286
Summerhayes CP, Coutinho PN, FrancË a AMC, and Ellis JP (1975)
Salvador to Fortaleza, North-eastern Brazil. Contribution to
Sedimentology 4: 44±77
Summerhayes CP, De Melo U, and Barretto HT (1976) The in-
¯uence of upwelling on suspended matter and shelf sediments
o southeastern Brazil. Journal of Sedimentary Petrology 46(4):
819±828
Tintelnot M (1995) Transport and deposition of ®ne-grained sed-
iments on the Brazilian continental shelf as revealed by clay
mineral distribution. Unpublished PhD thesis. Heidelberg:
University of Heidelberg, 294 pp
Tomazelli LJ, and Villwock JA (1996) Quaternary geological evo-
lution of Rio Grande do Sul coastal plain, Southern Brazil.
Anais Academia brasileira de Cieà ncias 68(3): 373±382
Travassos P, Hazin F, Zagaglia J, Rocha RA, and Schober J (1999)
Thermohaline structure around seamounts and islandas of
NortheastBrazil. Archive ofFishery and Marine Research 47(2/3)
Van Andel TH, Thiede J, Sclater JC, and Hay WW (1977) Depo-
sitional history of the South Atlantic ocean during the last 125
million years. Journal of Geology 85: 651±698
Walsh JJ (1988) On the Nature of Continental Shelves. San Diego:
Academic Press 520 pp
Wells, S.M. (Ed.) (1988) Coral Reefs of the World. Vol. 1: Atlantic
and Eastern Paci®c. Paris: IUCN/UNEP, 370 pp
178