Eddy Forced Variations in On-And Off-Margin Summertime Circulation along the 1000-M Isobath of the Northern Gulf of Mexico, 2000-2003, and Links with Sperm Whale Distributions along the Middle Slope

• Main Authors: Biggs, D. C, Jochens, A. E, Howard, M. K, Dimarco, S. F, Mullin, K. D, Leben, R. R, Muller-Karger, Frank E, Hu, Chuanmin
• Format: Book Part
• Language: unknown
• Published: Digital Commons @ University of South Florida 2005
• Subjects: Gunter; Sperm whale
• Online Access: https://digitalcommons.usf.edu/msc_facpub/1124; https://doi.org/10.1029/161GM06

In summers 2000-2003, NOAA Ship Gordon Gunter and TAMU R/V Gyre dropped XBTs and logged ADCP data while carrying out visual and passiveacoustic surveys for sperm whales along the 1000-m isobath of the northern Gulf of Mexico. The ships also made CTD casts, particularly when/where the XBT and ADCP data indicated the ships were passing into or out of anticyclonic and/or cyclonic slope eddies. The fine-scale resolution of the ship surveys, when combined with the meso-scale resolution of remote sensing surveys of sea surface height and ocean color, document the summer-to-summer variability in the intensity and geographic location of Loop Current eddies, warm slope eddies, and areas of cyclonic circulation over this middle slope region of the northern Gulf of Mexico. These variations forced striking year-to-year differences in the locations along the 1000-m isobath where there was on-margin and off-margin flow, and in locations where sperm whales were encountered along the 1000-m isobath. For example, when there was on-margin flow into the Mississippi Canyon region in early summer 2003, sperm whales were very rarely seen or heard there. In contrast, later that summer and during other summers when flow was along-margin or off-margin there, sperm whales were locally abundant. In this report we describe how eddy-forced variations in on-margin and off-margin flow changed the meso-scale circulation along the 1000-m isobath, and we show that most sperm whales were encountered in regions of negative SSH and/or higher-than-average surface chlorophyll.