Technical Report UNH-OPAL-1998-004

Convective Overturn Experiment

(Between 09 and 12 January 1998)

F.L. Bub, W.S. Brown, P. Mupparapu, and L.C. Smith

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

This report is maintained as the web page
(Filed 13 February 1998, last update 05 August 1999)

Report Contents.

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


Table 1. Surface Contours of Properties on Pressure and Density Surfaces.

Table 2. CTD Station Information.


Figure 1.a. Cruise Track, CTD Locations and UNH mooring sites. Stations numbered sequentially.

Figure 1.b. Station and mooring locations with Wilkinson Basin bathymetry and water mass analysis region outlined.

Figure 2. Wilkinson Basin mooring configuration showing the Main Buoy (A), thermistor chains (B & C), and guard buoys (D, E & G).

Figure 3.a.. Composite of CTD profiles in Wilkinson Basin. See section 3.d.1 for a description.

Figure 3.b.. Temperature-Salinity Diagram for CTD profiles in Wilkinson Basin.

Figure 4.a. Hydrography Section A to WB to F: Stations 17-13, 03-07. Vertical sections of temperature / salinity / sigma theta.

Figure 4.b. Hydrography Section A to I to WB to G: Stations 17-20, 12-09.


This report describes the hydrographic measurements obtained 9-12 January 1998 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 fifth of seven University of New Hampshire (UNH) cruises aboard the R/Vs ENDEAVOR and OCEANUS as part of this "Convective Overturn Experiment" (CONVEX). This report and these data can be accessed through the RMRP Research Environmental Data and Information Management System (REDIMS) via the WWW address:


1. Introduction.

Click here to read an introduction to the CONVEX program.

2. Cruise Narrative.

The RV Oceanus departed Woods Hole at 0900L on 08 January 1998. We passed through Cape Cod Canal enroute to central Wilkinson Basin in the Gulf of Maine. The first CTD cast was made at 0100Z (0600 L EST) at the mooring site. After surveying the site for botom bathymetry and locations of the existing guard buoys, a second CTD cast occurred at 1120Z prior to buoy deployment. At 1540Z (1030L), we commenced rigging for deployment of the Main Instrumented Buoy "A" (Figure 2). The anchor was released at 1817Z (1317L) at 42 ° 42.08' N 69 ° 38.07' W. We then placed T-Chain "C" at 1952Z (1452L) and Guard Buoy "G" at 2052Z (1552L). The mooring configuration then consisted of the Main Instrumented Buoy (A), two subsurface T-Chains (B and C), and two Guard Buoys (E and G).

A post-deployment CTD at 2040Z was followed by another 18 profiles in the pattern depicted by Figure 1.a. Water samples were drawn for four nutrient sample profiles and 10 CTD salinity calibrations. The final cast occurred at 0726Z 12 January and the Oceanus returned to Woods Hole via Cape Cod Canal and docked the evening of 12 January 1998.

2.a. Scientific Party:

F. L. Bub (Chief Scientist), W. S. Brown, R. Regnier, and B. Strully. Coast Guard observer - M. Brooks. Woods Hole Technician - L. Stein.

2.b. Cruise Photos

Click here to see OC-315 Cruise photos. GIF photos of the OC-315 scientific party and cruise work are included.

3. Data.

3.a. Hydrographic Data Acquisition.

The R/V OCEANUS' SeaBird SBE 911 Plus CTD Profiler was used to measure vertical profiles of electrical conductivity and temperature versus pressure at 22 hydrographic stations during 9-12 January 1998 (Figure 1.a).

Sensors on the CTD were factory calibrated on 9 October 1996. This CTD samples at a rate of 24 scans per second. Salinity profiles were computed from these data using SeaBird software. Additional sensors on the SBE-911 also recorded data for the measurement of dissolved oxygen, water transmissivity, fluorescence (Chl-a), and irradiance (PAR). See Figure 3.a. for a composite of profiles. CTD data acquisition, display and storage were managed by an on-board computer using the SeaBird software package SEASOFT.

At each station, the CTD was lowered at a rate of approximately 30 meters per minute to depths within 5-10 meters of the bottom. Three to eight water samples were collected with a rossette of 5-liter Niskin bottles, and specimens for nutrient and oxygen isotope analyses were gathered. At selected stations, the condutivity of one water sample was determined using the UNH Guildline 8400A Autosal and the corresponding salinities were used to correct salinity values derived from the raw CTD measurements.

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 a summary of 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,
  2. Vertical section contour plots, and
  3. Horizontal pressure and desnity surface contour plots.

3.d.1. Vertical CTD Profile Plots.

Individual profiles may be viewed via Table 2. A composite of all CTD profiles is shown as Figure 3.a and an expanded T-S diagram as Figure 3.b. Data are presented on two pages per station:

3.d.2. Vertical Hydrographic Sections.

Potential temperature, salinity, and sigma-theta sections for the following transects are presented. Each plot spans 200 km and horizontal scales are preserved. Contour intervals are indicated on plots. The CTD station numbers are shown along the top horizontal axis and the ocean bottom (based on depths at CTD stations) is shaded.

3.d.3. Horizontal Pressure and Density Surfaces.

Contoured surfaces may be accessed via Table 1. Contours of temperature, salinity and density fields on the 5, 25, 50, 100, 150 and 200 dbar pressure surfaces (equivalent to depth in m) and the sigma theta 26.00 density surface (mid water column) are presented for information. The 5 m field is the mean of the 0-10 m layer. Dynamic height fields indicate geostrophic shear. Cyan regions show where the ocean bottom is shallower than the plotted surface. CTD profiles at the red dots (x indicates no data). Wilkinson Basin mooring marked by the wheel. Red lines bound region of the CONVEX water mass analyses. Plotted contour intervals, along with data extrema and search epsilon, are indicated in captions.

3.d.4. Data Files.

Profiles can be made available as (a) ASCII files upon request to frank.bub@unh.edu. Upon final quality control, we will provide (b) JGOFS default files through a ftp site.

Other OC-315 Cruise data including enroute ADCP, TSAL, navigation, bathymetry and observed weather records will also be made available upon further processing.

4. Acknowledgements

The valuable work of Ken Morey, Dan Howard and Karen Garrison resulted in the successful deployment of the Wilkinson Basin Buoy and hydrographic survey. We appreciate the efforts of Captain Bearse and crew of R/V OCEANUS as they helped us conduct this field program. We are grateful for the help provided by T. Loder and A. Wang / V. Pilon in processing the bottle salinities.

F. Bub, W. Brown, and P. Mupparapu are supported by NSF Grant OCE-9530249.

5. References.

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. Surface Contours of Water Properties.

These fields are briefly described in section 3.d.3. Pressure (P), Temperature (T), Salinity (S), Density (D), and Dynamic Height (DH) are contoured at the specfied pressure or density levels.


(deg C)

(cm, ref surface)
05 dbar T05 S05 D05 X X X
25 dbar T25 S25 D25 X X X
50 dbar T50 S50 D50 X X X
100 dbar T100 S100 D100 DH100
150 dbar T150 S150 D150 DH150
200 dbar T200 S200 D200 X X X


(deg C)

26.00 sigma theta P26.00 T26.00 S26.00

Table 2. CTD Profile Plots.

Hydrographic station information for the R/V OCEANUS Cruise OC-315 (09 - 12 January 1998). Position, depth, date, and time are for the bottom of the cast. Profiles, which are described in section 3.d.1, may be viewed by clicking on ##A or ##B. See Figure 1.a for station locations.
 CTD station    Latitude    Longitude   Water Depth  Time     Date
   number      (deg min N)  (deg min W)  (meters)    (Z)   (DD/MM/YY)

01A   01B       42.7052      69.6415       270       0122   10/01/98
02A   02B       42.6988      69.6338       265       1130   10/01/98
03A   03B       42.7002      69.6357       265       2040   10/01/98
04A   04B       42.5268      69.4137       235       2248   10/01/98
05A   05B       42.3527      69.1927       240       0036   11/01/98
06A   06B       42.1763      68.9677       157       0225   11/01/98
07A   07B       41.9990      68.7477       140       0401   11/01/98
08A   08B       42.2462      68.7463       205       0546   11/01/98
09A   09B       42.4955      68.7467       185       0736   11/01/98
10A   10B       42.5670      69.0457       170       0914   11/01/98
11A   11B       42.6343      69.3395       210       1049   11/01/98
12A   12B       42.7037      69.6307       265       1238   11/01/98
13A   13B       42.7985      69.8230       240       1846   11/01/98
14A   14B       42.8990      70.0012       140       2013   11/01/98
15A   15B       42.9983      70.1997       170       2136   11/01/98
16A   16B       43.0723      70.3488       110       2245   11/01/98
17A   17B       43.2000      70.4883       031       2357   11/01/98
18A   18B       43.1185      70.1400       140       0133   12/01/98
19A   19B       43.0875      69.7813       165       0311   12/01/98
20A   20B       42.8933      69.7083       175       0430   12/01/98
21A   21B       42.6970      69.6290       270       0550   12/01/98
22A   22B       42.5468      69.8160       255       0726   12/01/98