Rubicon Foundation Archive (http://rubicon-foundation.org)
COASTAL UPWELLING
UPWELLING OFF
OFF THE
THE CENTRAL
CENTRAL FLORIDA
FLORIDA
COASTAL
ATLANTIC COAST:
COAST: COLD
COLD NEAR·SHORE
NEAR-SHORE WATERS
WATERS DURING
DURING
ATLANTIC
SUMMER
MONTHS
SURPRISE
MANY
DIVERS
SUMMER MONTHS SURPRISE MANY DIVERS
Patrick A.
A. Pitts
Pitts
Patrick
Harbor Branch
Branch Oceanographic
Oceanographic Institution
Institution
Harbor
5600 Old
Old Dixie
Dixie Highway
Highway
5600
Ft.
Pierce,
Florida
34946
U.S.A.
Ft. Pierce, Florida 34946 U.S.A.
Three 5-moll/h
5-month lime
time series
series recorded
recorded simultaneously
simultaneously from study
study
Three
sites located
located at
at 45
45 km
km inlervals
intervals along
along Ihe
the inner
inner conlinental
continental shelf
shelf of
of
sites
Florida's central
central At/omit
Atlantic coast
coast are
are used
used to
to investigate
investigate spatial
spatial and
and
Florida's
temporal characteristics
characteristics of
of the
the region's
region's summer
summer upwelling.
upwelling. Results
Results tend
tend
lemporal
to
support
historical
findings
that
upwelling
along
the
inner
shelf
to support hislorical
Ihal upwelling along Ihe inner shelf
occurs as
as discrete
discrete events
events lasting
lasting on
on the
the order
order 0/
of several
several days
days to
to about
about
occurs
three weeks
weeks during
during which
which time
time water
water temperatures
temperatures may
may decrease
decrease 8°-/2OC
8'-12 OC
three
from the
the seasonal
seasonal norm
norm of
of 28
28'-30
'-30 "C.
OC. The
The upwelling-induced
upwelling-induced lemperalure
temperature
from
anomalies
also
exhibit
patchiness
over
spatial
scales
on
the
order of
of
anomalies also exhibit
over spatial scales on the order
tens of
of kilomelers.
kilometers. Incorporation
Incorporation of
of local
local meleorological
meteorological data
data indicated
indicated
lens
that, at
at best,
best, wind
wind stress
stress played
played aa supplementary
supplementary role
role in
in producing
producing Ihe
the
Ihat,
observed upwelling.
upwelling.
observed
INTRODUCTION
INTRODUCTION
Coastal upwelling,
upwelling, ,the
intrusion of
of cold,
cold, deep,
deep, nutrient-rich
nutrient-rich water
water onto
onto the
the
Coastal
the intrusion
continental shelf,
shelf, is
is aa relatively
relatively common
common seasonal
seasonal phenomenon
phenomenon along
along the
the eastern
eastern
continental
margins of
of the
the Atlantic
Atlantic and
and Pacific
Pacific Oceans.
Oceans. Upwelling
Upwelling in
in these
these regions
regions usually
usually occurs
occurs
margins
throughout
the
year
as
a
result
of
semi-permanent
mid-ocean
high
pressure
centers
throughout the year as a result of semi-permanent mid-ocean high pressure centers
which cause
cause wind-driven,
wind-driven, seaward-directed
seaward-directed Ekman
Ekman transport
transport of
of the
the near-surface
near-surface layers.
layers.
which
The term
term isis most
most familiar
familiar in
in the
the context
context of
of its
its association
association with
with high
high coastal
coastal productivity;
productivity;
The
i.e. high
high plankton
plankton productivity
productivity due
due to
to the
the increased
increased nutrients
nutrients in
in the
the upwelled
upwelled water
water
i.e.
which
supports
commercially
important
fisheries.
Some
of
the
world's
most
productive
which supports commercially important fisheries. Some of the world's most productive
fishing grounds
grounds exist
exist along
along those
those areas
areas off
off the
the west
west coasts
coasts of
of the
the Americas
Americas and
and Africa
Africa
fishing
where upwelling
upwelling isis most
most pronounced.
pronounced.
where
Though upwelling
upwelling results
results in
in good
good fishing,
fishing, scuba
scuba diving
diving during
during upwelling
upwelling
Though
conditions
can
be
very
uncomfortable.
Often,
surface
water
is
colder
during
summer
than
conditions can be very uncomfortable. Often, surface water is colder during summer than
in
winter,
prompting
divers
to
wear
thick
wetsuits
or
even
drysuits
to
ward
off
the
cold.
in winter, prompting divers to wear thick wetsuits or even drysuits to ward off the cold.
Also, upwelling
upwelling can
can cause
cause substantial
substantial changes
changes ill
ir water
water clarity
clarity due
due to
to changes
changes in
in
Also,
population densities
densities of
of phytophyto- and
and zooplankton.
zooplankton.
population
Though more
more often
often associated
associated with
with the
the west
west C03l>tS
coasts of
of continents,
continents, upwelling
upwelling is
is not
not
Though
limited
to
these
environments.
The
Atlantic
coast
of
Florida
is
one
of
the
relatively
few
limited to these environments. The Atlantic coast of Florida is one of t.he relatively few
east-coast regions
regions which
which experiences
experiences well-defined
well-defined and
and recurring
recurring seasonal
seasonal upwelling.
upwelling.
east-coast
Upwelling has
has been
been documented
documented as
as far
far back
back as
as 1944
1944 when
when Green
Green reported
reported anomalously
anomalously
Upwelling
low surf
surf temperatures
temperatures off
off central
central Florida
Florida during
during lhe
the months
months of
of June,
June, July
July and
and August.
August.
low
Taylor
and
Stewart
(1957)
conducted
a
more
comprehensive
study
using
a
larger
Taylor and Stewart (1957) conducted a more comprehensive study using a larger
99
Rubicon Foundation Archive (http://rubicon-foundation.org)
Diviqe,
Science ...1993
Diving for Science...
/993
temperature data base and mean monthly winds. Their measurements showed that the
thermal effects of coastal
thermal
coastal upwelling were most apparent during mid summer months and
confined to the coastline between 27'-30°N
27°_300 N. They postulated that seasonal wind stress
stress
acting on shelf waters
waters was the dominant
force driving
upwelling. Lemming
dominant force
driving the observed
observed upwelling.
(1979) combined current and wind data with temperature data to focus
focus on the acrossacrossfrom the coast to the shelf break off Cape Canaveral. His
shelf aspect of upwelling from
results supported the hypothesis of upwelling as a response to local wind forcing.
Studies by Smith
Smith (1981, 1982),
1982), however, indicated that wind stress
stress probably plays a
secondary or supporting role in driving coastal upwelling in this region. His results
showed inner shelf near-bottom temperatures were not significantly correlated with
showed
stress.
longshore or the cross-shore component of the wind stress.
either the longshore
The purpose of this paper is primarily to document the temporal and spatial
chara.cteristics of upwelling over the inner continental shelf off the central Florida
characteristics
Atlantic
sites.
Atlanric coast using temperature data recorded simultaneously from
from three study sites.
The study,
study, also, re-examines the role that wind stress
stress might be playing in initiating or
terminating
tenninating upwelling in this region.
DATA AND METHODS
METHODS
film-recording thermographs (Environmental
(Environmental Devices Corporation, Type
Three film-recording
109),
accurate
to
±0.2'C
were
positioned
just above
above the bottom
109),
±O.2°C,
bollom at study sites located
located
along the 10
10 m isobath over the inner continental shelf. Stations were spaced
approximately 45
27'45'N (Figure 1).
45 km apart between latitudes 26O55'N
26°55'N and 27°45'N
I). Water
temperatures were recorded bihourly from
from May 24 through October 31, 1983.
1983. The three
temperature records were plotted versus time providing information on temperature
fluctuations over time scales ranging from days to months. Comparisons
Comparisons of temperature
temperature
fluctuations
variations between sites allowed characterizations over spatial
spatial scales on the order of
of
tens
kilometers.
tens of kilometers.
Wind speeds
speeds and direcrions,
directions, recorded
recorded hourly at the Vero Beach Municipal
Municipal Airport
approximately 10
10 km southwest of the northernmost study site, were obtained for the
approximately
same time period. As the airport is about 66 km inland, wind speeds were increased to
better
(Hsu, 1981).
1981). Wind data were converted to
beller approximate over-water conditions (Hsu,
wind stress vectors by the method described by Wu (1969) for moderate wind speeds.
speeds.
Wind stress
stress vectors were then decomposed
decomposed into longshore (170°-350°)
(170'-350') and cross-shore
cross-shore
components for comparison with temperature records. Only the longshore components
components
components
were used in this study.
study. Due to the broadening of the continental shelf in the northward
orientation utilized in the analysis is a compromise
compromise
direction in this region, the longshore
longshore orientation
between the 160°-340
160°_340° orientation of the coastline and the nearly north-south
orientation of the 100
100 m isobath. Before comparison with temperature records, wind
stress was smoothed to remove the seabreeze
seabreeze and other high-frequency
high~frequency fluctuations
stress
using an exponential filter that only integrated past wind stress events. Thus, the filter
emphasized the most recent wind stress but incorporated to a lesser extent winds
recorded earlier.
earlier.
100
Rubicon Foundation Archive (http://rubicon-foundation.org)
PillS: CoastaL
CentraL Florida Atlantic
Allantic Coast
Coast
Pitts:
Coastal Upwelling
Upwelling OjJlhe
Offthe Central
,
\
\,
\
\,
\,
\
i
i
i
\.
;
\1
;
,
i
Figure 1. Study
Study area on the Atlantic shelf of central Florida. Triangles represent
locations of thermographs, the square shows the location of the Vero Beach
Municipal Airport, and hatched
100m isobaths.
hatched lines
lines indicate 20m and 100m
RESULTS
A composite of temperatures
study sites is shown in Figure
temperatures recorded at the three study
2. Upwelling was most apparent in the temperature record from the northernmost study
site (Station 1,
dominant feature in the plot is the upwelling event occurring
site
I, Fig. 2a). The dominant
from August 8-21
8-21 during which time water temperatures were 5-7°C
5-7OC below the seasonal
seasonal
28°_30°C. During the 2 week event there were occasions when water
norm of 28O-30°C
temperature increased briefly,
seaward retreating of cold
brieDy, probably reflecting
reDecting a temporary seaward
water.
water. Two periods of relatively low temperatures near the beginning of the record and
another during the third week of September are probable indications of upwelling.
another
upwelling.
Station 2 (Fig. 2b) shows a similar but somewhat more erratic
The record from Station
pattern when compared to Station 1.
I. The midAugust event is apparent as well
well as the
short-lived decreases observed near the beginning of the record and during the third
week of September. However, there are several distinct differences between the two
records. The mid-August event that dominates the top plot is not as prominent in the
seasonal highs several days earlier at
record from
from Station 2. Temperatures returned to seasonal
Station 2. Also, there were indications of upwelling or the initiation of upwelling during
Station
Station 2 that do not appear in the more northern
several time periods at Station
nonhern record; namely,
namely.
during the first
first and fourth weeks of July when temperatures decreased 3-4OC
3-4°C for 4-5
days.
tOt
Rubicon Foundation Archive (http://rubicon-foundation.org)
Divingfor
forScience
Science......1993
1993
Diving
31.0
30.0'0.
29.0.-. 29.0
-u
ww
5
~
a::
LiJ
~
2 8 - 027.0-
27.0
26.
a
2 25.0
2 5 - 0 wIll ~
2-4.0
23.023.0
25
25 -44
14
14 24
24
.JtJ"(
JUNE
~4
22
1.0:
J 23
12 22
2 2 2:2 12
1 2 22
14 2<1
24 33 113
2 3 2:2 12
SEPT
OC T
AUC
S(P1
oel
AUG
I1
.JULY
JULY
'0 .
.~O.
24
2.0:
33
1 3 23
2 3 33 13
1 3 23
2 3 22
13
JUNE
JULY
JUN(
JULY
122
\2
222
AUG
.we
21
11 1111 21
SEPT
S(P1
I1
1 1 21
21 31
31
11
OC T
OCT
31.0
30.0
29.0
u
<-
'8.
l;!
27.0
::>
''""
26.0
W
2:5.0
,-w
".
/hf~~j1r
IIIf1
~\
I
23.0
(c)
~~~\
,
i
22.0
,>2
1 . 0 i i 1 1 1 1 1 i l 1 1 1 1 1 1 1
7 4 J3 13
13 23
2 3 33 13
13 2 3 <2 12
12 22
22 I1 II
1 1 :1
21 11 I1 I1 :!21I
aei
S[PI
JUNE
JULY
AUG
SEPT
OC T
JUlT
Jut/(
"
n
'u.
1
31
31
Figure 2.
2. Time-plots
Time-plots of bihourly,
bihourly, near-bottom
near-bottom temperatures
temperatures (in
(in °C)
OC) recorded
recorded at
at Figure
1
(a),
Station
2
(b)
and
Station
3
(
c
)
,
May
24
to
October
31,
1983. Station
Station
(a), Station
(b) and Station
(c),
24
October
1983.
102
Rubicon Foundation Archive (http://rubicon-foundation.org)
Pitts:
Pitts:Coastal
CoastalUpwelling
UpwellingOff
Offthe
theCentral
CentralFlorida
FloridaAtlantic
AtlanticCoast
Coast
The temperature
temperature record
record from
from the
the southernmost
southernmost study
study site
site (Station
(Station 3;
3; Fig.
Fig. 2c)
2c)
The
reveals
reveals aasomewhat
somewhatdifferent
differentpattern
pattern than
than those
thoseobserved
observedatat the
themore
morenonhem
northernlocations.
locations.
Mid-August
becharacterized
characterizedby
by short-lived
short-liveddecreases
decreasesof
of 2-5°C
2-5OC lasting
lasting
Mid-Augusttemperatures
temperaturescan
canbe
only
only 3-4
3-4days
days (possibly
(possibly indicating
indicating the
the beginning
beginning of
of upwelling)
upwelling) followed
followed by
by aa return
return to
to
temperaturesapproaching
approachingseasonal
seasonalhighs.
highs. The
Thestrongest
strongestindication
indicationof
of upwelling
upwelling occured
occured
temperatures
during
during the
the second
second week
week of
of June
June when
when temperatures
temperatures decreased
decreased from
from over
over 27°C
27OC to
to less
less
than
than 22°C.
22OC. AA decrease
decrease inin temperatures
temperatureswas
was observed
observed atatthe
the other
other two
two study
study sites
sitesduring
during
this
thissame
sametime
timeperiod
period but
butititwas
wasnOl
notas
asdramatic.
dramatic.
(J)
(J)
0.4
w
0:0
(a)
0.2
t-
(J)~
ON
0.0
zE
-()
~"en -0.2
W'"
o:oc
0>- -0.4
I'::;'
(J)
-0.6
()
z
-0.8
0
--'
32
(b)
30
w
o:o~
::::>u
t-en 28
<t",
0:0",
w~
0..'" 26
:2'"
w.::;.
t-
24
22 -\"'-"'T""""'T""""'1'=t='''''''''l''''''l''''"''1'''"'''l''"''''~t='''l''
1 7 11 15
15 29
29
, 144 28
20 35 17
28 11
1 1 25
25 99 2,3
25 66 20
0CT
SEP
MAY
JUN
JUL
AUG
MAY
JUN
JUL
AUG
SEP
OCT
Figure 3.3. Composite
Composite time·
time-plots
of exponentially-filtered,
exponentially-filtered,longshore
longshorewind
wind stress,
stress, in
in
Figure
plots of
O C , (b)
dynesIcm2, (a)
(a) and
and near-bottom
near-bottom temperatures,
temperatures, in
in °C,
(b) recorded
recorded May
May 24
24 to
to
dynes/cm2,
October
31,1983.
Positive
values
in
the
top
plot
indicate
upwelling-favorable
winds.
October 31, 1983. Positive values in the top plot indicate upwelling.ravorable winds.
composite of
of the
the exponentially-filtered,
exponentially-filtered, longshore
longshore component
component of
of wind
wind stress
stress
AA composite
plotted against
against time
time and
and the
the near-bottom
near-bottom water
water temperatures
temperatures recorded
recorded atat Station
Station I1are
are
plaued
shown inin Figs.
Figs. 33
3a and
and 3b,
3b, respeclively.
respectively. Positive
Positive values
values inin the
the upper
upper plot
plot indicate
indicate
shown
longshore wind
wind stress
stress to
to the
the north
north which
which isis upwelling
upwelling favorable.
favorable. Results
Results show
show aa
longshore
recurrenceof
of upwelling-favorable
upwelling-favorablewind
wind stress
stress roughly
roughly every
every two
two weeks
weeks throughout
throughout the
the
recurrence
study period.
period. However,
However,only
only one
one of
of the
the inner-shelr
inner-shelf upwelling
upwelling episodes
episodes recorded
recorded nearby
nearby
study
corresponds in
in time
time to
to aa period
period of
of upwelling-favorable
upwelling-favorable wind
wind stress
stress (arrows).
(arrows). The
The
corresponds
pronounced 2-week
2-week event
event recorded
recorded inin mid-August
mid-August occurred
occurred when
when wind
wind stress
stress isis very
very
pronounced
103
Rubicon Foundation Archive (http://rubicon-foundation.org)
for Science
Science...J993
...I 993
Diving for
weak
weak and
and out
out of
of the
the northern
northern quadrant;
quadrant; clearly
clearly aa situation
situation unlikely
unlikely to
to produce
produce
upwelling
upwelling via
via Ekman
Ekman transport.
transport. Also,
Also, the
the upwelling
upwelling episode
episode recorded
recorded during
during the
the third
third
week
week of
of September
September at
at all
all three
three study
study sites
sites corresponded
corresponded in
in time
time with
with strong
strong winds
winds from
from
the north;
north; again,
again, wind
wind conditions
conditions very
very unfavorable
unfavorable for
for upwelling.
upwelling.
the
DISCUSSION
DISCUSSION
The time
time series
series recorded
recorded at
at the
the three
three study
study sites
sites show
show temporal
temporal upwelling
upwelling patterns
patterns
The
similar
pub!. data).
similar to
to those
those observed
observed historically
historically from
from this
this region
region (Smith;
(Smith; 1981,
1981, un
unpubl.
data). The
The
major
major event
event recorded
recorded at
at Station
Station I1 in
in mid-August,
mid-August, when
when intruding
intruding water
water decreased
decreased
temperatures
temperatures 5°_6°
5O-6O from
from aa seasonal
seasonal norm
norm of
of 28°_30°
28'-30' for
for approximately
approximately two
two weeks,
weeks, is
is
typical.
typical. The
The more
more temporary
temporary episodes
episodes recorded
recorded at
at al1
all three
three sites
sites isis common.
common. The
The weaker
weaker
indications
indications of
of upwelling
upwelling observed
observed at
at the
the two
two more
more southerly
southerly study
study sites
sites may
may stem
stem from
from
their being
being on
on the
the southern
southern extreme
extreme of
of the
the geographical
geographical range
range of
of documented
documented upwelling
upwelling
their
off
off the
the east
east coast
coast of
of Florida.
Florida.
Upwelling
Upwelling events
events in
in this
this region
region are
are not
not only
only ephemeral
ephemeral but
but appear
appear to
to be
be spatially
spatially
patchy; that
that is,
is, the
the occurence
occurence of
of upwelling
upwelling at
at one
one location
location isis not
not necessarily
necessarily indicative
indicative
patchy;
of upwelling
upwelling at
at another
another location
location only
only aa few
few tens
tens of
of kilometers
kilometers away.
away. This
This point
point isis best
best
of
exemplified by
by the
the onsel
onset of
of upwelling
upwelling twice
twice during
during the
the month
month of
of July
July alat Station
Station 22 while
while
exemplified
there was
was little
little indication
indication of
of significant
significant temperature
temperature changes
changes at
at sites
sites only
only 45
45 km
km to
to the
the
there
north and
and south
south during
during the
the same
same time
time period.
period. Alternately.
Alternately, the
the temperature
temperature records
records
north
indicate
indicate that
that aa given
given episode
episode can
can be
be widespread
widespread geographically,
geographically,as
as indicated
indicated by
by the
the midmidAugust event
event that
that affected
affected all
all three
three study
study sites;
sites; however.
however, none
none of
of the
the sites
sites experienced
experienced
August
the sarne
same degree
degree of
of upwelling.
upwelling.
the
Studies by
by Smith
Smith (1981,
(1 981, 1982,
1982, 1983)
1983) have
have shown
shown that
that at
at aa given
given latitude
latitude lhe
the
Studies
entire shelf
shelf may
may not
not be
be involved
involved in
in shoreward
shoreward excursions
excursions of
of cool
cool water.
water. "Tongues"
"Tongues" of
of
entire
cool waler
water may
may only
only reach
reach the
the mid-shelf
mid-shelf or
or outer-shelf
outer-shelf regions,
regions, especially
especially funher
further north,
north,
cool
where lhe
the shelf
shelf becomes
becomes significantly
significantly broader.
broader. As
As the
the present
present study
study was
was confined
confined to
to lhe
the
where
nearshore areas
areas of
of the
the inner-shelf,
inner-shelf, there
there were
were probably
probably intrusions
intrusions of
of cool
cool water
water onlO
onto the
the
nearshore
outer- or
or mid-shelf
mid-shelf areas
areas during
during the
the study
study period
period that
that would
would not
not have
have been
been recorded
recorded by
by
oulerour thermographs.
thermographs. In
In addition,
addition, Smith's
Smith's studies
studies have
have shown
shown aa highly
highly stratified
stratified water
water
our
column across
across the
the enlire
entire shelf
shelf during
during times
times of
of aa fully
fully developed
developed upwelling
upwelling episode.
episode..
column
Surface temperatures
temperatures may
may be
be atat or
or near
near seasonal
seasonal highs
highs of
of 28°_30°
28'-30' during
during those
those limes
times
Surface
while aa strong
strong themlocline
thermocline exists
exists in
in the
the mid
mid to
to lower
lower levels.
levels.
while
The idea
idea of
of wind
wind stress
stress as
as aa primary
primary mechanism
mechanism for
for driving
driving the
the observed
observed
The
upwelling during
during the
the study
study period
period isis not
not supported
supported by
by the
the dala.
data. This
This finding
finding isis in
in
upwelling
contrast with
with results
results from
from some
some studies
studiesconducted
conducted in
in the
the same
same geographical
geographical area
area (Green.
(Green,
contrast
1944; Taylor
Taylor and
and Stewart,
Stewart, 1957;
1957; Lemming,
Lemming, 1979).
1979). However,
However, Smith
Smith (1981)
(1981) showed
showed
1944;
coherence
values
computed
between
wind
stress
and
bottom
temperatures
to be
be
coherence values computed between wind stress and bottom temperatures to
generally well
well below
below the
the 95%
95% confidence
confidence limit.
limit, particularly
particularly over
over the
the longer
longer time
time scales
scales
generally
usually associated
associated with
with meteorological
meteorological forcing.
forcing. Results
Results described
described here
here indicate
indicate that
that only
only
usually
one of
of the
the observed
observed upwelling
upwelling intrusions
intrusions corresponded
corresponded in
in time
time with
with upwelling-favorable
upwelling-favorable
one
wind stress
stress and
and several
several events,
events, notably
notably the
the pronounced
pronounced mid-August
mid-August episode,
episode, occurred
occurred
wind
under wind
wind conditions
conditions unfavorable
unfavorable lO
to upwelling.
upwelling. ItIt isis noteworthy,
noteworthy, however,
however, that
that wind
wind
under
stress was
was upwelling-favorable
upwelling-favorableat
at aperiodic
aperiodic intervals
intervals for
for approximately
approximately half
half of
of the
the study
study
stress
period and
and itit isis likely
likely that
that wind
wind plays
plays aa supporting
supporting role
role in
in driving
driving the
the observed
observed
period
upwellings.
upwellings.
An alternate
alternate mechanism
mechanism for
for producing
producing upwelling
upwelling in
in this
this region
region was
was postulated
postulated by
by
An
104
Rubicon Foundation Archive (http://rubicon-foundation.org)
PillS: Coastal Upwelling
Cerural Florida Atlantic
AtLamie Coast
Pitts:
Upwelling Offthe
Offthe Central
Smith
Smith (1981, 1982).
1982). He suggested that the local upwelling may be a response to
meandering of the Florida Current.
Current. According to this hypothesis, during those times
when the Horida
Florida Current meanders to the west and contacts the continental
continental shelf, local
geostrophy temporarily deteriorates leaving a shorewarddirected pressure gradient in
the benthic boundary layer. Onshore movement near the bottom then advects cooler
water onto the shelf. The hypothesis is supported by several lines of evidence.
Meandering of the Florida Current streamlines has been documented using satellite
1979) and by drogue
imagery (Vukovich et.al., 1979)
drogue measurements (Chew and Berberian,
1970;
1970; Richardson et.al., 1969).
1969). These meanders characteristically have wavelengths of
100-200 km.
of Florida
km. An amplitude of 5 km was reported for a meander in the Straits of
100-200
(Chew and Berberian, 1970).
1970). It is not clear how the meanders are generated, but low1-2 weeks have been correlated with
frequency variations in flow over time scales of 1-2
wind stress (DAing
( ~ A i net.al.,
~
1977). Studies
Studies have shown a statistically significant
1977).
relationship between longshore currents and temperature; as longshore motion
days (Smith,
(Smith, 198
1981).
increased, water temperature decreased
decreased within 1-3
1-3 days
1).
Biological studies
Biological
studies have shown that upwelling off the Florida coast not only has a
profound effect on the local hydrography, but influences the distribution and
abundance of the biota as well. Green (1979) described differences in phytoplankton
across
across the shelf at times before and after the onset of upwelling. Others (Atkinson et.al.,
1978; Paffenhifer,
Paffenhtfer, 1983)
1983) have shown high chlorophyll and dense phyto- and
1978;
zooplankton populations resulting from
from shoreward
near-bottom
shoreward transport of nutrients at near-bottom
levels during Gulf Stream
intrusions onto the Florida shelf.
levels
Stream intrusions
shelf. Yoder (1983), working over
the southeastern U.S. continental shelf between Cape Canaveral and South Carolina,
estimated that as much as 90% of the region's outer shelf primary productivity occured
estimated
during upwelling and, thus, upwelling is the dominant process affecting primary
productivity at this location. Furthermore, the ecological impacts of
of upwelling are
probably enhanced by the role it plays as a crossshelf exchange mechanism.
mechanism. Dissolved
and suspended material
material (e.g. nutrients, plankton and possibly larvae of commercially
important species)
species) can be transported the entire width of the continental
continental shelf.
Regardless
of the effects,
effects, the data reported here and results from
studies
from previous studies
Regardless of
continental shelf in this region occurs
occurs as
clearly indicate that upwelling over the inner continental
discrete events lasting on the order of severa]
several days to approximately three weeks.
During these events water temperatures typically decrease,
decrease, at least temporarily,
temporarily. to values
more characteristic of late spring or early winter conditions. The upwelling-induced
anomalies are limited not only temporally, but spatially
spatially as well, with little or
temperature anomalies
no apparent pattern. There is no clear indication that upwelling events occur
simultaneously at two or three locations
consistently or that they move in a northerly or
locations consistently
simultaneously
southerly direction.
direction. The available data from
southerly
from this study do not support the concept that
wind stress
stress plays a major role in driving upwelling in this region,
although it is likely that
region, although
stress plays a supplementary role in these events.
events.
wind stress
ACKNOWLEDGEMENTS
I thank Ms. Elizabeth Smith
Smith and Dr. Ned P. Smith
Smith for collecting the temperature
temperature
Special acknowledgement to Dr. Smith for his help with data analysis and
data. Special
manuscript suggestions.
suggestions.
105
Rubicon Foundation Archive (http://rubicon-foundation.org)
Diving/or Science...
/993
Science.. .I993
LITERATURE CITED
CITED
LITERATURE
Atkinson, L.P., G.-A. Paffenhifer,
PaffenhTfer, and
and W.
W. M.
M. Dunstan.
Dunstan. 1978.
1978.The
The chemical
chemical and
and biological
biological effect
effect
Atkinson,
of
a
Gulf
Stream
intrusion
off
St.
Augustine,
Florida.
Bull.
Mar.
Sci.
28(4):667-679.
of a Gulf Stream intrusion off St. Augustine, Florida. Bull. Mar. Sci. 28(4):667-679.
Chew, F., and
and G.
G. Berberian.
Berberian. 1970.
1970. Some
Some measurements
measurements of current
current by shallow
shallow drogues
drogues in
in the
Chew,
Florida Current.
Current. Limnology
Limnology and
and Oceanography.
Oceanography. 15:88-99.
15:88-99.
Florida
~ A i nW.O.,
~ , C.N.
C.N. Mooers
Mooers and
and T.N. Lee.
Lee. 1977.
1977.Low·frequency
Low-frequency variations
variations in
in the
the Florida
Florida Current
Current
DAing,
and relations
relations to
to atmospheric
atmospheric forcing
forcing from
from 1972
1972to
to 1974.
1974. J.J. Mar.
Mar. Res
Res.,
35:129-161.
and
.. 35:129-161.
Green, C.
C. 1944.
1944.Summer
Summer upwelling
upwelling--northeast
coast of
of Florida.
Florida. Science.
Science. 100:546-547.
100:546-547.
Green,
northeast coast
n
Green, D.W.
D.W. 1979.
1979. The
The distribution
distribution of phytoplankton
phytoplankton in
in the
the shelf
shelf waters
waters between
between Ft.
Ft. Pierce
Pierce and
and
Green,
Cape
Canaveral
(Florida).
Unpubl.
M.S.
Thesis,
Fla.
Inst.
Technol.,
Melbourne.
64
pages.
Cape Canaveral (Florida). Vnpub!.
Thesis, Fla. Inst. Techno!., Melbourne. 64 pages.
Hsu, S.A.,
S.A., 1981.
1981.Models
Models for
for estimating
estimating offshore
offshore winds
winds from
from onshore
onshore meteorological
meteorological instruments.
instruments.
Hsu,
Boundary-layer
Boundary-layer Meteorology,
Meteorology, 20:34
20:34I-351.
1-351.
Lemming, T.
T. 1979.
1979. Observations
Observations of
of temperature,
temperature, current
current and
and wind
wind variations
variations off
off the
the central
central
Lemming,
easterncoast
coast of
of Florida
Floridaduring
during 1970
1970and
and 1971.
1971.NOAA
NOAA Tech.
Tech. Memorandum
Memorandum NMFS-SEFC-6.
NMFS-SEFC-6.
eastern
Paffenhifer, G.-A.
G.-A. 1980.
1980.Vertical
Vertical zooplankton
zooplankton distribution
distribution onthe
onthe northeastern
northeastern Florida
Florida shelf
shelf and
and its
its
Paffenhifer,
Plankton Res.
Res. 5(
5(1):
15-33.
relation to
to temperature
temperature and
and food
food abundance.
abundance. J.J. Plankton
relation
I): 15-33.
Richardson, W.S., W.J.
W.J. Schmitz
Schmitz Jr.
Jr. and
and P.P.
P.P. Niiler.
Niiler. 1969.
1969. The
The velocity
velocity structure
structure of
of the
the Florida
Florida
Richardson,
Current from
from the
the Straits
Straitsof
of Florida
Florida to
to Cape
Cape Fear.
Fear. Deep-Sea
Deep-sea res.,
res., 16(Supp!.):225-231.
16(Suppl.):225-231.
Current
Smith, N.
N. 1981.
1981. An
An investigation
investigation of
of seasonal
seasonal upwelling
upwelling along
along the
the Atlantic
Atlantic coast
coast of
of Florida.
Florida.
Smith,
Ecohydrodynamics,J.e.I.
J.C.J. Nihoul,
Nihoul, Ed.,
Ed., Elsevier,
Elsevier, 79-98.
79-98.
Ecohydrodynamics,
Smith, N.
N. 1982.
1982. Upwelling
Upwelling in
in Atlantic
Atlantic shelf
shelf waters
waters of
of South
South Florida.
Florida. Florida
Florida Sci.,
Sci., 45:
45:125-138.
125-138.
Smith,
N. 1983.
1983.Temporal
Temporal and
and spatial
spatialcharacteristics
characteristicsof
of summer
summerupwelling
upwelling along
along Florida's
Florida's Atlantic
Atlantic
Smith, N.
Smith,
shelf. J.J. Phys.
Phys. Oc.
Oc. 13(9):1709·1715.
13(9):1709-1715.
shelf.
Geophys.
Taylor, C.,
C., and
and H.
H. SteWaI1.
Stewart. 1958.
1958.Summer
Summer upwelling
upwelling along
along the
the east
east coast
coast of
of Florida.
Florida. I.J. Geophys.
Taylor,
Res.,
Res., 64:33·39.
64:33-39.
F., B.
B. Crissman,
Crissman, M.
M. Bushnell
Bushnell and
and W.
W. King.
King. 1979.
1979.Gulf
Gulf Stream
Stream boundary
boundary eddies
eddies off
off
Vukovich, F.,
Vukovich,
the east
east coast
coast of
of Florida.
Florida. J.J. Phys.
Phys. Oceanogr.,
Oceanogr., 9:
9:1214-1222.
1214-1222.
the
Wu, J.J. 1969.
1969.Wind
Wind stress
stress and
and surface
surface roughness
roughness atat air-sea
air-sea interface.
interface. J.J. Geophys.
Geophys. Res.,
Res., 74:44474:444Wu,
455.
455.
Yoder, J.A.,
J.A., L.P.
L.P. Atkinson,
Atkinson, S.S.
S.S. Bishop,
Bishop, E.E.
E.E. Hofmann,
Hofmann, and
and T.N.
T.N. Lee.
Lee. 1983.
1983. Effect
Effect of
of
Yoder,
upwelling on
on phytoplankton
phytoplankton productivity
productivity on
on [he
the outer
outer southeastern
southeastern United
United States
States continental
continental
upwelling
shelf.Continental
ContinentalShelf
Shelf Res.
Res. 1(4):385-404.
1(4):385-404.
shelf.
106