HYDROGRAPHIC SURVEY REPORT

Convective Overturn Experiment
(CONVEX)

R/V ENDEAVOR Cruise EN-300
[18-19 May 1997]


F.L. Bub and W.S. Brown

Ocean Process Analysis Laboratory (OPAL)

Institute for the Study of Earth, Ocean and Space
Department of Earth Sciences
University of New Hampshire
Durham, NH 03824

Research Sponsored by the National Science Foundation

(08 April 1998, update 27 April 1998)

Contents

Contents

0. Abstract
1. Introduction
2. Cruise Narrative
3. Data
3a. Data Acquisition
3b. Processing
3c. Corrections
3d. Presentations
4. Acknowledgements
5. References

Tables

Table 1. CTD Station Information

Figures

Figure 1. Jeffrey's Basin 1997 mooring configuration.

Figure 2. CTD salinity correction plots.

Appendix Figures

Individual profiles at each hydrographic station are presented on 2 pages:

Page A: Station profiles of temperature, salinity, sigma-theta density, stability (N-squared) and temperature-salinity diagram (top 3 panels show surface layer profiles at higher resolution, remainder are all on the same depth /property scale for intercomparison).

Page B: Station profiles of dissolved oxygen, transmissivity, fluorometer (Chl-a), irradiance (PAR), temperature-dissolved oxygen and salinity-dissolved oxygen diagrams when observed.

Abstract

This report describes a set of hydrographic measurements obtained 18-19 May 1997 as part of the NSF-supported "Observational / Modeling Study of Wintertime Convection and Water Mass Formation" in the western Gulf of Maine (GOM). Herein we document the third of seven planned University of New Hampshire (UNH) cruises aboard the R/Vs ENDEAVOR and OCEANUS as part of this "Convective Overturn Experiment" (CONVEX) (see Bub et al., 1997a). This report and these data can be accessed via the WWW address:

http://ekman.sr.unh.edu/OPAL/CONVEX/

1. Introduction

Click here to read an introduction to the CONVEX program

2. Cruise Narrative

The RV Endeavor was underway from the University of Rhode Island Graduate School of Oceanography pier, Narragansett, RI at 0040L (0540Z). She passed through the Cape Cod Canal enroute to Jeffreys Basin. After a survey of bathymetry at the site, an oceanographic mooring (JB-97, Figure 1) was placed at 1823L (2223Z) near 43 00.12N 70 09.50W. The deployed instrument string included temperature and conductivity sensors at nominal depths of 10, 30, 60 and 100 m, 14 thermistors at 10 m intervals between 2 and 132 m, and an upward looking acoustic doppler current profiler (ADCP) at 132 m depth (Figure 1). A CTD profile using the Endeavor SeaBird SBE-911+ (measuring pressure, temperature, conductivity, dissolved oxygen, fluorescense, PAR and light transmission) was observed and the ship headed home. While underway, ship instruments routinely recorded near-surface temperature / salinity and a weather package (IMET) provided a continuous records of air pressure, temperature, relative humidity, wind speed / direction, short / long wave radiation, along with ship's position and movement. A RDI 150 KHz ADCP recorded ocean current structure along the ship's path. Two drifters were launched for R. Limeburner at 0021L (0521Z) off Race Point, MA at 42 10.06N 70 10.30W. After passing through Cape Cod Canal, RV Endeavor returned to GSO at 1300L (1700Z). Postlog: The JB-97 mooring was recovered aboard the UNH RV Gulf Challenger on 14 June 1997. Due to conducting cable failure, the temperature and conductivity data were not recoverable. The internally recorded ADCP data have been recovered and analyses are in progress.

2.a. Scientific Party:

W. Brown (Chief Scientist), F. Bub, K. Morey, K. Garrison, P. Mupparapu, and T. Orvash (URI Marine Technician).

2.b. Cruise Photos

Click here to see EN-300 Cruise photos. GIF photos of the EN-300 scientific party and cruise work are included.

3. Data

3.a. Hydrographic Data Acquisition

The R/V ENDEAVOR's SeaBird SBE 911 Plus CTD Profiler was used to measure vertical profiles of electrical conductivity and temperature versus pressure at 01 hydrographic station during 18 - 19 May 1997. Sensors on the CTD were factory calibrated on 9 October 1996. This CTD sampled at a rate of 24 scans per second. Salinity profiles were computed from these data. Additional sensors on the SBE-911+ also recorded data for the measurement of dissolved oxygen, water transmissivity, fluorescence (Chl-a), and irradiance (PAR). Data acquisition, display and storage were managed by an on-board computer using the SeaBird software package SEASOFT.

At the station, the CTD was lowered at a rate of approximately 30 meters per minute to depths within 5-10 meters of the bottom. Two to six water samples were collected with a rossette of 5-liter Niskin bottles, and specimens for nutrient and oxygen isotope analyses were gathered. For each station, the conductivity of one water sample was determined using ENDEAVOR's Guildline 8400A Autosal and the corresponding salinities was used to correct salinity values derived from the raw CTD measurements ( Figure 2).

3.b. Data Processing

The CTD data were processed using a series of SeaBird SEASOFT programs (listed in parentheses) in which:

a. Raw hexidecimal CTD output is converted into engineering units (DATCNV). Only downcast data were used to produce station profiles. Bottles samples were taken during upcasts and average CTD data at each bottle depth were stored (ROSSUM).

b. Noise contamination greater than 2 standard deviations from 50 point sections was removed (WILDEDIT). In addition, CTD downcast data associated with downward velocities of less than 25 cm/s (due to looping) were discarded (LOOPEDIT).

c. Data were filtered to ensure consistent response times using a low pass filter with time constant 0.15 sec (FILTER).

d. Data were averaged into 1 decibar (dbar) bins (BINAVG) to produce profiles of temperature, salinity, etc., versus pressure from the unequally-spaced cast data from each station.

e. These profile data were stored as ASCII files on floppy disks for post-processing and plotting.

3.c. Data Descriptions, Corrections and Estimated Accuracy/Precision

Click here for data descriptions, corrections and estimated accuracy/precision

3.d. Data Presentations

The corrected hydrographic data are presented as:

(1) Station profile plots and property-property diagrams; and

(2) Vertical section contour plots.

3.d.1. Vertical Profile Plots:

For each of the CTD stations, page "A" presents a set of profiles (potential temperature, salinity, sigma-theta) and potential temperature - salinity diagrams (Figure 01A). The upper surface to 125 m deep plots represent zoomed details of water property structure in the main thermocline (halocline, pycnocline) zone (horizontal scales vary). The middle plots present these water property structures for the entire water column (scales are fixed to facilitate). A Brunt-Vaisaila frequency (N-squared) plot indicates water column stability.

On page "B" are presented CTD station profiles of measured dissolved oxygen, transmissivity, fluorometer (Chl-a), irradiance (PAR), as well as computed sound velocity, temperature-dissolved oxygen, and salinity-dissolved oxygen diagrams (Figures 01B). Note that during the first part of the cruise, the dissolved oxygen and PAR sensors were not working.

3.d.2. Data Files

Preliminary profiles can be made available immediately as (a) ASCII files upon request to Frank.Bub@unh.edu. Upon final quality control, we will provide (b) JGOFD default files through an ftp site. Other EN-300 Cruise data including enroute ADCP, TSAL, navigation, bathymetry and observed weather records. These will also be made available upon further processing.

4. Acknowledgements

The invaluable assistance of Karen Garrison, Susan Becker, Steve Gaudreau, Glenn Rice, and Greg Young resulted in an extremely successful hydrographic survey. We appreciate the efforts of Captain Tyler and crew of R/V ENDEAVOR, and URI ocean technician Jan Szelag, as they helped us conduct this field program. We are also grateful for the help provided by T. Loder and S. Becker in processing the bottle salinities. F. Bub, W. Brown, and P. Mupparapu are supported by NSF Grant OCE-9530249.

5. References

Bub et al., 1997a, Hydrographic Survey Report, R/V Endeavor EN-291 CONVEX Cruise # 1, UNH/OPAL, Durham, NH, January 22, 1997, accessable via http://ekman.sr.unh.edu/OPAL/CONVEX/EN291/en291_report.html.

Fofonoff, N. P. and R. C. Millard Jr., 1983. Algorithms for compilation of fundamental properties of seawater, UNESCO Technical Papers in Marine Science, no. 44. UNESCO, Paris, France, 53 pages.

Garrison, K. M. and W. S. Brown, 1989. Hydrographic survey in the Gulf of Maine July-August 1987, UNH Tech. Rpt. No. UNHMP-T/DR-SG-89-5, Univ. of NH, Durham, NH.

Morgan, P. P., 1994, SEAWATER Software Version 1.2b, CSIRO Division of Oceanography, Hobart, AUS.

TABLE 1

CTD station information for the R/V ENDEAVOR Cruise EN-300 (18-19 May 1997). Profiles, as described above (3.d.), may be viewed by clicking on A or B.
 CTD station   Latitude     Longitude  Water Depth  Time      Date
   number      (deg min N)  (deg min W)  (meters)    (Z)   (DD/MM/YY)
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