ACCESS NUMBER: 31035 

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, October 19-21, 1999 

CONTRACT NUMBER: 1435-10-99-CA-31035 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Northeastern Gulf of Mexico 

FISCAL YEAR OF PROJECT FUNDING: 1999 

COMPLETION DATE OF REPORT: July 2000 

COST: FY 1999: $86,542 

PROJECT MANAGER: W. W. Schroeder 

AFFILIATION: University of Alabama, Dauphin Island Sea Lab 

ADDRESS: 101 Bienville Boulevard, Dauphin Island, Alabama 36528 

PRINCIPAL INVESTIGATOR: 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 

BACKGROUND: The U.S. Department of the Interior’s 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. 
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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 
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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. 
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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 world’s 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. 
ACCESS NUMBER: 31035 

STUDY PRODUCTS: 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. 168 pp. 
ACCESS NUMBER: 31035