ACCESS NUMBER: 30501 

STUDY TITLE: Ship of Opportunity Hydrographic Work in the NW Gulf of Mexico 

REPORT TITLE: Ship of Opportunity Hydrographic Data from the NW Gulf of Mexico 

from R/V Gyre Cruises 94G-11 and 95G-01 

CONTRACT NUMBER: 14-35-0001-30501 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREAS: Western, Central, and Eastern Gulf of Mexico 

FISCAL YEARS OF PROJECT FUNDING: 1990, 1991, 1992, 1993, 1994, 1995 

COMPLETION DATE OF REPORT: September 1995 

COSTS: FY 1990: $40,200; FY 1991: $40,000; FY 1992: $40,000; FY 1993: 

$40,000; FY 1994: $40,000; FY 1995: $40,000 

CUMULATIVE PROJECT COST: $240,000 

PROGRAM MANAGER: D.C. Biggs 

AFFILIATION: Texas A&M University (TAMU) 

ADDRESS: Department of Oceanography, TAMU, College Station, TX 77843-3146 

PRINCIPAL INVESTIGATOR: D. C. Biggs 

KEY WORDS: Western Gulf of Mexico; Central Gulf of Mexico; Eastern Gulf of Mexico; 

Loop Current; eddies; rings; LATEX; ship of opportunity; hydrographic data; CTD; XBT; 

nutrients; salinity; oxygen; chlorophyll; dynamic topography; geostrophic transport 

BACKGROUND: In September 1989, the U.S. Minerals Management Service (MMS) 

and the Department of Oceanography of Texas A&M University (TAMU) entered into a 

4-year Cooperative Agreement 14-35-0001-30501 for TAMU Marine and Electronics 

Technicians to collect CTD, XBT, and other Ship of Opportunity Program (SOOP) 

hydrographic data from the Gulf of Mexico, as sciences/station schedules allowed, while 

they were at sea on research cruises. SOOP hydrographic data were collected on 11 

cruises from Nov 1989 - Apr 1992 in the Western, Central, and Eastern Gulf of Mexico 

prior to the start of fieldwork for the Texas-Louisiana Shelf Circulation and Transport 

Processes Study (LATEX), and SOOP data collection was continued on 12 more 

cruises from May 1992 - Sep 1993 separately but concurrent with cruises fielded by 

LATEX. This MMS-TAMU SOOP Cooperative Agreement 14-35-0001-30501 was 

continued and extended twice: (1) for a fifth field year from Oct 94 - Jun 95 to allow 

data to be collected concurrent with the final LATEX field work, and subsequent to 

LATEX in 1995 in cooperation with Mexican Navy survey work in the Yucatan Channel. 
ACCESS NUMBER: 30501 

OBJECTIVES: (1) To collect XBT, CTD, and bottle data as science/station schedules 

allowed from deepwater and continental margin environments of the Western Gulf of 

Mexico in order to extend the existing knowledge of seasonal and geographic variability 

there; (2) to extend this hydrographic data collection into the Central and Eastern Gulf of 

Mexico, on transits of opportunity through these regions while research vessels 

deadheaded between Galveston, Texas, and the Straits of Florida or Yucatan Channel; 

and (3) to compare differences in sea surface height and other hydrographic 

characteristics of "young" Loop Current eddies encountered in the Central Gulf with 

those of "old" eddies in the Western Gulf of Mexico. 

DESCRIPTION: TAMU technicians made 373 CTD casts and 271 XBT drops of 

opportunity during 22 cruises of R/V Gyre and 1 cruise of R/V Powell between Oct 1989 

and Sep 1993 (Fig. 1). The data were collected during NSF-, Navy-, and DOEsponsored cruises, as well as during cruises dedicated to State-sponsored graduate 

training and research, and to oil and gas industry sponsored piston coring. In addition, 

23 CTD casts were made from an offshore gas production platform owned by Mobil 

Exploration & Production USA at 27°54.2'N, 93°34.4'W in lease block HIA-389 during a 

3-week period in summer 1991. TAMU Technical Report 93-09-T is a synopsis of these 

first 4 years of MMS-TAMU SOOP work (Biggs, 1993). 

TAMU technicians made 130 CTD casts and 329 XBT drops of opportunity during 11 

cruises of R/V Gyre, 1 cruise of R/V Powell, and 1 cruise of B/O Antares between Oct 

1993 and Jun 1995 (Fig. 2). The data collection from Gyre and Powell was again done 

during federally-sponsored cruises, as well as during cruises for State-sponsored 

graduate training and research, and for oil and gas industry sponsored piston coring. 

MMS-sponsored Ship Of Opportunity Program hydrographic data collection was 

completed in June 1995, with a 2-ship hydrographic survey of Eddy Zapp, the Loop 

Current, and the Yucatan Channel carried out by R/V Gyre from TAMU in cooperation 

with B/O Antares from the Direccion General de Oceanografia naval (DGON) of the 

Mexican Navy. 

All these CTD and XBT casts of opportunity were made in addition to those done on 10 

hydrographic cruises made Apr 1992 - Nov 1994 for the Texas-Louisiana Shelf 

Circulation and Transport Processes study (Dr. W.D. Nowlin, Jr., P.I.). 

SIGNIFICANT CONCLUSIONS: The TAMU-SOOP hydrographic data document 

these is a strong positive correlation between the depth of the 15°C isotherm (x) and the 

dynamic height relative to a reference level of 800 db (y): y = 0.26x + 54 (r2

 = 0.93). 

There is also a strong positive correlation between the sea surface height (SSH) 

anomaly of the Loop Current and the eddies it shed 1989-1995 (x) and the geostrophic 

transport (y) : y = 0.42x - 0.7 (r2

 = 0.95). 

STUDY RESULTS: In general, most of the TAMU-MMS SOOP CTD stations of 

opportunity are concentrated on the LATEX shelf in the NW Gulf of Mexico, in particular 

along transects off Galveston and off Corpus Christi, Texas, which were revisited as 
ACCESS NUMBER: 30501 

part of the Texas Institutions Gulf Ecosystem Research initiative (Biggs, 1990). In 

contrast, most of the TAMU-MMS SOOP XBT stations are seaward of the LATEX shelf. 

Those over deep (>2 km) water were dropped during basin wide transits of opportunity 

to/from Galveston and the Straits of Florida and the Straits of Yucatan. These transits 

of opportunity crossed Quiet Eddy (Oct 90), Eddy Triton (Oct 91), and Eddy Zapp (Jun 

95). When Quiet Eddy reached the western Gulf, it was revisited in Mar 1991 during a 

follow-up cruise that was fielded as part of the TAMU-Mexico cooperative program 

Analysis Multidiciplinario de Investigaciones en el Golfo Occidental (AMIGO). Two 

other cruises in the western Gulf revisited Eddy Triton in May-Jun 1992 (biggs et al., 

1994). AMIGO/TIGER cruises also surveyed the companion cylonic eddies that appear 

to be created when these Loop Current rings experience the shoaling topography of the 

western Gulf and transfer mass/vorticity to the adjacent slope water (Biggs et al., 1991). 

Hydrographic data collected by TAMU-SOOP field programs are of interest for data 

assimilation into general circulation models of the northern Gulf of Mexico and for 

ongoing studies of the Loop Current and the eddies that shed from it (Biggs, 1992; 

Biggs et al., 1996). A synthesis of TAMU-SOOP hydrographic data with CTD + XBT 

data collected by the GulfCet program (Dr. R.W. Davis, P.I.) and AXBT data collected 

by the LATEX Eddy program (Dr. T.J. Berger, P.I.) is underway to allow us to better 

understand the processes by which Loop Current eddies "spin down" in the western 

Gulf of Mexico. Since the launch of TOPEX/Poseidon in Fall 1992, this synthesis has 

been used to provide "sea truth" verification of TOPEX altimetry in the Gulf of 

Astrodynamics Research (Leben et al., 1993). Presentations were given by Biggs, at 

meetings of AGU and IUGG; abstracts of these presentations are published in EOS 

Trans. AGU, and several cooperatively authored manuscripts are in preparation for J. 

Geophys. Res. 

STUDY PRODUCTS: The Oct 89 - Jun 95 hydrographic data were published as a 

series of 28 TAMU technical reports, each released 1-2 months after each cruise of 

opportunity. The XBT, CTD, and bottle data archived in these reports were also shared 

in digital format with NOAA's National Oceanographic Data Center (NODC) as LATEX 

supplement code 0215. Citation information for the 28 reports is provided as Appendix 

1. A useful synopsis of the first 18 reports is: 

Biggs, D.C. 1993. A -synopsis of hydrographic data from the TAMU Ship of 

Opportunity 

Program: XBT, CTD, and bottle data collected from the Gulf of Mexico November 1989 

- September 1993 by the Technical Support Services Group, TAMU. Technical Report 

93-09-T, TAMU Dept. of Oceanography. 40 pp. 

OTHER STUDY PRODUCTS: 

Biggs, D.C. 1990. The Texas Institutions Gulf Ecosystem Research initiative: Multiyear, repeated hydrographic surveys in the NW Gulf of Mexico continental shelf and 

slope, pp. 175-181. In Proceedings, 10th Annual Information Transfer Meeting, U.S. 
ACCESS NUMBER: 30501 

Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New 

Orleans, LA. OCS Study MMS 90-0027. 

Biggs, D.C. 1992. Nutrients, plankton, and productivity in a warm-core ring in the 

western Gulf of Mexico. J. Geophys. Res. 97(C2): 2143-2154. 

Biggs, D.C., M.M. Crawford, D. Salas de Leon, O. Salas Flores, and S. Escoto Hidalgo. 

1991. A United States-Mexico cooperative study of a cold-core ring in the western Gulf 

of Mexico, PP. 374-380. Proceedings, 11th Annual Information Transfer Meeting. U.S. 

Dept. of the Interior, Minerals Mgmt. Service, Gulf of Mexico OCS Region, New 

Orleans, LA. OCS Study MMS 94-0061. 

Biggs, D.C., G.S. Fargion, P. Hamilton, and R.R. Leben. 1996 (in review). Cleavage of 

a Gulf of Mexico Loop Current eddy by a deep water cyclone. J. Geophys. Res., 

manuscript WSB-0381; submitted 3/23/95; revised and resubmitted 1/15/96. 

Leben, R.R., G.H. Born, D.C. Biggs, D.R. Johnson, and N.D. Walker. 1993. 

Verification of TOPEX altimetry in the Gulf of Mexico. TOPEX/Poseidon Research 

News, 1: 3-6.