Boundary Currents and Their Effect on Carbonate Sedimentation

Boundary Currents and Their Effect on Carbonate Sedimentation


An exercise in using satellite
-
derived oceanographic data
products
(SST) to interpret
carbonate depositional patterns on the southwest Florida shelf


Objective
s
: To access web available

AVHRR d
ata sets

and create annual

running movies
of SST patterns in the Gulf of Mexico. Specifically, identify and interpret the effects of
Loop Current variability and its potential control on the nature of carbonate deposits
under its influence.


Note
: Would al
so
be useful to
include
SeaWifs
(chlorophyll
a

proxy)
imagery

for this
exercise.


AVHRR

(Advanced Very High Resolution Radiometer): Broad
-
band scanner that senses
in the visible, near
-
infrared, and thermal infrared portions of the electromagnetic
spectrum.

Sensor carried on NOAA’s Polar Orbiting Environmental Satellites (POES)
first launched in 1978.

Web reference: NOAA National Data Centers, NGDC

www.ngdc.noaa.gov/seg/globsys/avhrr.shtml


In
troduction

to study area


Introduction

to western boundary currents and Loop Current


AVHRR data shown in today’s class presentation:



Images downloaded from the Institute for Marine Remote Sensing Website at the
University of South Florida (http://imars.us
f.edu/)



Individual images represent three day composites.



Images have dimensions of 512 x 512 pixels at a spatial resolution of 2.8 x 4.1 km



Years 1994 and 2000 are chosen for analysis (five images/month)



Temperature scale ranges from 29
°

C (reds and yello
ws) to 23
°
C (purple)



Star symbol (*) marks a reference point to be considered during visual animations


Applications

(Part I)
: Run
SST
video animations for 1994 and 2000


Questions



What are your general observations of SST in Gulf of Mexico thr
oughout an

annual cycle?



Is the Loop Current identifiable?



If so, what are the temperature characteristics of the Loop Current as compared to
shelf and coastal waters to the east?



Does the degree of Loop Current intrusion northward into the Gulf of Mexico
vary on an

annual basis?



Are there time periods where SST is uniformly warm across the Gulf of Mexico?
If so, what season(s) do you think this corresponds to?



During times of SST uniformity, is the Loop Current still present?



Is the star symbol (*) encompassed by or

at least closely bordered by Loop
Current waters?



What do grey areas represent on SST images?


Summary of Results
: For ~8 months o
f each

year

analyzed
, a distinct oceanographic
boundary is present on the southwest Florida shelf separating warm, Loop Curre
nt
-
derived waters from cooler shelf waters to the east. During the remaining months, SST is
uniformly warm across the area of study. Further, the region marked by star symbol (*) is
encompassed by these warm surface waters throughout the year.



Applicatio
ns (Part II)
: Given the following information concluded from previous
research, answer the
question

below.


Satellite imagery of ocean color (SeaWifs) (chlorophyll
a

proxy) in the Gulf of Mexico
reveals a similar oceanographic gradient, wherein Loop Curren
t waters are nutrient
depleted (oligotrophic) and shelf waters to the east contain increasingly higher
concentrations of chlorophyll
a
.


Phototransmissometer measurements
, light sensors,

and visual observations using ROV
video and manned submersible trans
ects reveal extremely high water clarity from surface
to depth in the region of the star symbol (*).


The seafloor beneath the star symbol (*) is characterized by extensive, hermatypic coral
reef development in water depths ranging from 65
-
75 m.
This biost
romal reef system
extends ~30 km in length and is nucleated on a series of late Pleistocene paleoshoreline
deposits. Primary reef constituents (requiring light for survival) include hermatypic plate
corals, leafy green algae, coralline red algae, calcareou
s green algae, and benthic
foraminifera with photosynthetic algal symbionts.


Question



Given what you know about conditions necessary for coral reef development and
the information above (including AVHRR SST data), explain the presence of this
anomalous d
eep
-
water reef system on the outer
-
ramp of the southwest Florida
platform?


Summary of Integrated Results
:
The impingement of the Loop Current on the
southwest Florida shelf provides
a critical control for deep
-
water, hermatypic coral reef
development by p
roviding
warm,
clear, low nutrient waters to this region.


Questions for Further Consideration
:



Are two years worth of SST data sufficient enough to conclude that the Loop
Current
persistently

bathes the location of coral reef growth?



What is the primary l
imitation in using satellite data products to infer controls on
deep
-
water coral reef development?