Colorado Center for Astrodynamics Research

Introduction

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Example Survey Design: GulfCet 2001

From 17 March - 3 April 2001, marine mammal researchers from NOAA-NMFS Pascagoula Laboratory searched for sperm whales along the continental margin in the eastern Gulf of Mexico, on a cruise aboard NOAA Ship Gordon Gunter. The cruise departed from Key West FL and generally followed the 1000 m isobath of the West Florida Escarpment from west of the Dry Tortugas to Pascagoula, Mississippi.

The scientists focused their search on the Tortugas Gyre, a region which historical temperature and salinity data show is a mesoscale area of cyclonic circulation that is often present seaward of the shelf-slope break west of the Dry Tortugas. The first of the composite images (March 14: 3 day composite SST with SSH overlay) was faxed to the researchers a few days before the cruise sailed from Key West. In this oceanographic habitat analysis, the Tortugas Gyre is visible as a local low in SSH that corresponds to a region of SST that is cooler by 1-2° C than the adjacent continental margin. The 5-point star that is superimposed on the SST and altimetry isopleths shows the locations for 21 XBT drops that we recommended be made to resolve the geometry of major and minor axis of the feature (i.e.,to provide fine-scale spatial information to determine if cyclone was elliptical rather than circular in shape).

The marine mammal researchers completed two of the four lines of XBTs that we recommended they make in the Tortugas Gyre. They stopped the ship as well to make CTD casts at SE corner, NW corner, and in the interior of the star.

This Tortugas Gyre and a cold-core ring (CCR) to the north that was about the same size and intensity (in terms of its SSH anomaly) were the most prominent regions of cyclonic circulation present along the West Florida Escarpment from mid-March to early April 2001. Two additional habitat analysis (March 22: 3 day composite SST with SSH overlay, and March 30: 3-day composite SST with SSH overlay) show that these features in approximately the same spatial locations throughout the time that the ship was at sea. The habitat analyses show the location for a second 5-point star survey that we recommended be done to resolve the geometry of the CCR to the north. However, weather offshore during the second half of the cruise was blustery and seas were white-capped, making it difficult for the marine mammal researchers to search efficiently for sperm whale "blows". Under these conditions, a survey of for sperm whales in the CCR to the north of the Tortugas Gyre would have been inefficient, and a star survey of the CCR would have put the vessel "in the troughs" for long runs on E-W and/or SE-NW vessel headings. So, for the rest of the cruise the ship followed the 1000 m isobath north from the Tortugas Gyre to the ship's home port of Pascagoula. XBTs were dropped at regular intervals along the 1000 m isobath, and sperm whales were seen to the north of as well as in the Tortugas Gyre.

Data processing for the habitat analysis and recommendations for star surveys were done cooperatively by Robert Leben (CCAR) and Douglas Biggs (TAMU). For more information, contact Dr. K. D. Mullin, who served as NMFS Chief Scientist for this Gordon Gunter cruise (Keith.D.Mullin@noaa.gov) .

This page was last updated on Monday April 9, 2001.