echnical Summary : MMS Publication 2000-074
Physical/Biological Oceanographic Integration
Workshop for the DeSoto Canyon and Adjacent Shelf
BACKGROUND: The U.S. Department of the
Interiors Minerals Management Service (MMS) conducts all leasing and resource
management functions on the Outer Continental Shelf. The MMS sponsors scientific research
to effectively manage and protect the environment. While MMS has sponsored substantial
oceanographic studies in the northeastern Gulf, demand for scientific information
continues to be high. Recently completed, and ongoing, MMS studies in the Northeastern
Gulf also suggest that more integration is needed between the biological and physical
oceanographic disciplines.
From the perspective of information needs concerning any future OCS activities, the
geographic area of interest for this workshop is defined as an area encompassing the
western portion of the Florida panhandle westward into the Alabama and Mississippi and
includes the DeSoto Canyon and adjacent areas going into deeper waters. This geographic
area, of course, cannot be studied by itself, it must include the influences from coastal
bays and estuaries, as well as the offshore currents including the Loop Current and eddies
impinging on the continental shelf.
OBJECTIVES: 1) To synthesize physical,
geological, chemical and biological oceanographic information of the DeSoto Canyon and
adjacent shelf area; 2) Identify the critical components and processes which need to be
delineated, measured and modeled in order to understand the important physical and
biological phenomena that occur in the DeSoto Canyon and adjacent continental shelf
region; 3) Identify significant knowledge and/or data gaps germane to these components and
processes; and 4) formulate recommendations for research elements, based on the results
from items 1) and 2).
DESCRIPTION: The Northeastern Gulf of
Mexico continental shelf is an ecologically heterogeneous marine ecosystem. The shelf
region is bounded onshore by a number of estuaries and bays acting as nutrient sources and
serving as fertile nursery areas. Offshore, the DeSoto Canyon, an area serving as an
important fisheries ground and upwelling site, dominates the shelf. The health of the
shelf ecosystem depends on physical habitat, environmental and climatic factors, nutrient
availability, and oceanographic processes. These physical processes link the biotic
components of the ecosystem. Hydrographic and sedimentological information suggest an
east-west change of water column nutrients and physico-chemical properties near Cape San
Blas; however, the information available is not enough to elucidate and characterize this
change. Ongoing oceanographic studies in this region will provide a comprehensive and
synoptic data set that can help prove this transition or provide an alternative paradigm.
Ongoing biological studies suggest a number of data gaps that need investigating. This
includes levels of production, taxonomic and trophic structure of coastal and shelf
communities, coupling between water column and benthic communities, impacts of freshwater
on shelf ecosystems, impacts of catastrophic events, and status and trends in fisheries
resources and management.
To assess our state of knowledge for the area and to address the issue of additional
information needs, particularly that of the integration of any future data collection and
analysis efforts, a workshop was sponsored by the MMS and co-hosted by The University of
Alabama and the Dauphin Island Sea Lab. This workshop brought together experts who
summarized what was known about the area; determined critical issues; and provided input
to the design of an integrated physical and biological study.
SIGNIFICANT CONCLUSIONS: Study questions
recommended by Working Group I: 1) Physical processes create or enhance biological
anomalies. Can they be used to help find or forecast them? 2) Are the surface and bottom
Ekman layers responsible for across-shelf transport of substances and/or larvae? 3) What
is the relative importance of nutrient derived from terrigenous/riverine versus deepwater
upwelling sources? Is the water chemistry of the shelf different than in deepwater? 4) Are
there spatial and temporal differences in the trophodynamic (energy/food transfer)
processes in the area of interest? 5) Are benthic habitats stable over space and time? 6)
Are there specific areas that are consistently important for fish spawning and
recruitment? Is there a relationship between the distribution of certain species and
spawning? Can current patterns and water mass movement predict the distribution and
abundance of fish larvae? 7) Is there a relationship between sediments or current flow and
fish species life history requirements such as essential fish habitat and recruitment? 8)
Does primary and/or secondary production vary spatially and/or temporally? 9) What
catastrophic phenomena occur in the area? Do these catastrophic phenomena (e.g.,
hurricanes) have the potential to impact fishes and benthic organisms? How important are
these effects? 10) Can marine reserves serve as a useful tool in evaluating the impacts of
activities in the area such as fishing and potential OCS activities? Do OCS activities
significantly affect natural processes in the study area over some space and time scales?
Are these effects localized, positive or negative?
Studies recommended by Working Group II: 1) Biological-Physical Processes East of the
DeSoto Canyon Out to 500m. The first element of this proposed study is a comprehensive
topographical survey of the sea floor to locate hard bottom sites using acoustic mapping
techniques. The study would feature several cross-shelf transects of fixed moorings
creating a mooring array, as well as oceanographic stations to gather biological and
physical data. Seasonal changes in water quality and nutrients; variation in the megafauna
of the hard bottom areas; and variation of the infauna at the soft bottom areas are key
issues. The processes which need to be described are: local circulation, carbon fluxes,
import/export of carbon, transport of nutrients between the shelf and deeper waters,
fluxes of nutrients in response to upwelling and eddies, and impacts of storms on benthic-
and water column-dwelling organisms. 2) Trophic Dynamics of a "Small" Site West
of the DeSoto Canyon. The purpose of this study would be to couple biological and physical
processes on a local scale. A small study site would be located between the 40 m isobath
and the 100 m isobath on the western flank of the DeSoto. The area would include both a
pinnacle and other low relief features along with the surrounding sand bottom. The site
would be in a region previously studied and for which there are historical data. The
research plan would require 2 current meters on a mooring to measure the circulation
around a pinnacle. Stable isotope measurements would be made to assess trophic linkages
between the water column and benthic organisms. 3) Biological-Physical Processes West of
the DeSoto Canyon Down to 1000 m. This study plan is very similar to that of
Recommendation 1 and would feature several cross-shelf transects of fixed moorings, that
create a mooring array. Also oceanographic stations would gather biological and physical
data such as seasonal changes in water quality and nutrients, variation in the megafauna
of the hard bottom areas, and variation of the infauna at the soft bottom areas. These
measurements would provide information on the local circulation, import/export of carbon,
transport of nutrients between the shelf and deeper waters, and the fluxes of nutrients in
response to the presence of upwelling, eddies, and Loop Current rings. Information on the
impacts of storms on organisms within the water column and benthos could also be measured
by means of the oceanographic stations. 4) Biological-Physical Processes in Eddy-Pairs.
This study is to sample the periphery of eddy-pairs and observe the edge effects such as
productivity, fish/larval transport, plankton, and recruit of marine mammals. It is
designed as a response team effort that would go into action by the occurrence of an eddy
pair over the slope as revealed by remote sensing. If an eddy pair is detected then
shipboard measurements would be made to locate the edges of the eddies. No moorings would
be used for this study. Rather, shipboard sampling would be conducted as well as
collection of visual and acoustic data for marine mammals. Aircraft would be used for
physical measurement of the water column.
Studies recommended by Working Group III. 1) A study of the deep biology and its
correlation with deep currents in the 181-Sale Area. In the deep, southern portion of the
181-Sale Area (approximately the regions deeper than 1000 m) it is known that the Loop
Current and the rings it sheds exist there for many months of the year and for comparably
long-duration periods they are absent. Do the Loop Current and its rings extend to the
bottom? If so, how do the near-bottom biota respond to extended periods of a strong flow
followed by comparable periods of quiescent flow? 2) A continental shelf upper
slope upwelling study. It is evident from several presentations that upwelling occurs
frequently in the northern region of the study area. It is also evident from studies of
upwelling in other regions of the worlds oceans that high levels of biological
activity are associated with upwelling events. The objectives of the study would be (1) to
better understand the wind-induced upwelling in the region, and (2) to assess the effect
the DeSoto Canyon has on enhancing upwelling and the associated increased biological
activity.
STUDY RESULTS: The workshop included the
following presentations: Marine Meteorology and Air-Sea Interaction Over the DeSoto Canyon
and Adjacent Shelf - A Summary; Shelf Hydrography Over the Northeastern Gulf of Mexico;
DeSoto Canyon Circulation and Exchange; Some Remarks About Currents on the Continental
Shelf in Relation to Their Relevance to Cross-shelf Transport; Surface Sediments of the NW
Florida Inner Continental Shelf: A Review of Previous Results, Assessment and
Recommendations; Shelf Nutrient Chemistry - The Gulf of Mexico; Shelf Hard Bottom
Habitats; Benthic Macroinfauna of the Northeastern Gulf of Mexico OCS, Near DeSoto Canyon;
Northeastern Gulf of Mexico Coastal and Marine Ecosystem Program: Ecosystem Monitoring,
Mississippi/Alabama Shelf; Introduction and Overview; Regional Fisheries; Ship and
Satellite Studies of Mesoscale Circulation and of Zooplankton and Micronekton Stock in
Sperm Whale Habitats in the NE Gulf of Mexico During GulfCet II; Estuaries and Coastal
Habitats; and Linkages.
The members of each working group were asked to utilize the information syntheses
provided by the speakers, combined with their own expertise, to: 1) identify the critical
components and processes which need to be delineated, measured and modeled in order to
understand the important physical and biological phenomena that occur in the DeSoto Canyon
and adjacent continental shelf region; 2) identify significant knowledge and/or data gaps
germane to these components and processes; and 3) formulate recommendations for research
elements, based on the results from items 1) and 2). These discussions would then be used
to assist MMS in designing an integrated physical and biological study to complete the
Northeastern Gulf of Mexico Physical Oceanography Program and the Northeastern Gulf
of Mexico Coastal and Marine Ecosystem Program.
STUDY PRODUCT(S): Schroeder, W. W. and C.
F. Wood (Eds.) 2000. Physical/Biological Oceanographic Integration Workshop for the DeSoto
Canyon and Adjacent Shelf: October 19-21, 1999. OCS Study MMS 2000-074. U.S. Department of
the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA.
Contract No. 1435-10-99-CA-31035. 163 pp. + app.
STUDY TITLE: Physical/Biological
Oceanographic Integration Workshop for the DeSoto Canyon and Adjacent Shelf
REPORT TITLE: Physical/Biological
Oceanographic Integration Workshop for the DeSoto Canyon and Adjacent Shelf
CONTRACT NUMBER(S): MMS
1435-10-99-CA-31035
SPONSORING OCS REGION: Gulf of Mexico
APPLICABLE PLANNING AREA(S): Northeastern
Gulf of Mexico
FISCAL YEAR(S) OF PROJECT FUNDING: 1999
COMPLETION DATE OF REPORT: July, 2000
COST(S): FY 1999: $86,542
PROJECT MANAGER(S): W. W. Schroeder
AFFILIATION: University of Alabama,
Dauphin Island Sea Lab
ADDRESS: 101 Bienville Boulevard, Dauphin
Island, Alabama 36528
PRINCIPAL INVESTIGATOR(S): W. W. Schroeder
KEY WORDS: Northeastern Gulf of Mexico;
DeSoto Canyon; workshop; integration; continental shelf; deepwater; meteorology;
hydrography; circulation; nutrient chemistry; sediments; hard-bottom; habitats; benthos;
zooplankton; fisheries; estuaries
Report Availability and ESPIS
Copies of the technical report for this study are available through the:
Minerals Management Service
Public Information Office
1201 Elmwood Park Boulevard
New Orleans, Louisiana 70123-2394
(504) 736-2519 (local) or 1-800-200-GULF
Copies of many of the Environmental Studies Program reports and pertinent Technical
Summaries are available through the Environmental
Studies Program Information System (ESPIS)