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 F: Stations 15-26. Vertical
sections of temperature / salinity / sigma theta.
Figure 4.b. Hydrography Section B to G: Stations 45-40, 32-29.
Figure 4.c. Hydrography Section J to E: Stations 13, 10-01.
Figure 4.d. Hydrography Section A to J: Stations 15-11.
Figure 4.e. Hydrography Section C to F,G: Stations 35, 39, 05, 22, 28.
Figure 4.f. Hydrography Section D to F,G: Stations 27, 25, 03, 36.
This report describes a set of hydrographic measurements obtained 31 January - 4 February 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 second of seven planned 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:
http://ekman.sr.unh.edu/OPAL/CONVEX/
1. Introduction
Click here to read an introduction to the CONVEX program
2. Cruise Narrative.
The R/V Endeavor departed the Naval Station Newport, RI pier at 0800L (1300Z) on 31 January 1997,
crossing Nantucket Shoals enroute to the Gulf of Maine. CTD stations commenced in the southern
Wilkinson Basin (Figure 1.a) at 2053L (0153Z). The Endeavor
SeaBird SBE-911+ instrument package measured pressure, temperature, conductivity, dissolved oxygen,
fluorescense, PAR and light transmission. We paused at the site of the January 1997 mooring (WB-97)
to conduct an acoustic survey, but were unable to find the acoustic release and instrumentation which
had disappeared on 8 January (either because the system had been moved or the 'deck box' we were
using was faulty). The hydrographic survey continued for a total 45 stations arranged in an eight-spoke
wheel (Figure 1.a) to map the presence of water masses during the
1997 winter season. Two drifters were deployed for R. Limeburner (WHOI) at 1229L (1729Z) 1 February near
42° 37.1'N 69° 366'W.
While underway, ship instruments routinely recorded near-surface temperature / salinity (TSAL)
and a weather package provided a continuous records of air pressure, temperature, relative humidity,
wind speed / direction, short / long wave radiation, along with ship's position and movement (IMET).
A RDI 150 KHz Acoustic Doppler Current Profiler (ADCP) recorded ocean current structure along the
ship's path.
The last CTD was completed at 0244L (0744L) on 4 February and the ship headed towards Woods Hole,
MA via the Cape Cod Canal, docking at WHOI at 1250L (1750Z).
2.a. Scientific Party.
F.L. Bub, W.S. Brown, P. Mupparapu, and B. Rogers
2.b. Cruise Photos
Click here to see EN-294 Cruise photos.
GIF photos of the EN-294 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 45 hydrographic stations during
31 January - 4 February 1997 (Figure 1.a).
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 each 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.
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.
Click here for data descriptions, corrections and estimated accuracy/precision
3.d. Data Presentations
The corrected hydrographic data are presented as:
- Station profile plots and property-property diagrams,
- Vertical section contour plots, and
- Horizontal pressure and desnity surface contour plots.
3.d.1. Vertical 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:
- Page A - Station profiles of temperature, salinity, sigma-theta density, stability (N-squared) and a
temperature-salinity diagram. The upper three plots (surface to 100 m deep) 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. These plots are all on the same depth / property
scale for intercomparison. A Brunt-Vaisaila frequency (N-squared) plot indicates water column stability.
- Page B - When data are available, this page shows station profiles of measured dissolved oxygen,
transmissivity, fluorescence (Chl-a), solar irradiance (PAR), as well as computed sound velocity, temperature -
dissolved oxygen, and salinity - dissolved oxygen diagrams.
For each of the CTD stations, page "A" presents a set of profiles
(potential temperature, salinity, sigma-theta) and potential
temperature-salinity diagrams (Figures 01A-45A). 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-45B). Note that during
the first part of the cruise, the dissolved oxygen and PAR sensors were
not working.
3.d.2. Vertical 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.
Point A to F , tracking southeastward through Jeffreys and Wilkinson Basins
(Figure 4.a),
Point B to G , tracking eastward through Massachusetts Bay and Wilkinson
Basin (Figure 4.b),
Point J to E , tracking southward across Wilkinson Basin (Figure 4.c),
Point A to J, tracking northeastward along the 100 m isobath (Figure 4.d),
Point C to F,G, tracking eastward across the southern Wilkinson Basin
(Figure 4.e), and
Point D to F,G, tracking eastward across the southern Wilkinson Basin
(Figure 4.f).
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 EN-294 Cruise data including enroute ADCP, TSAL, navigation, bathymetry and observed weather records
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
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.
DENSITY
SURFACE
(kg/m^3) |
PRESSURE
(dbar) |
POTENTIAL
TEMPERATURE
(deg C) |
SALINITY
(psu) |
| 26.00 sigma theta |
P26.00 |
T26.00 |
S26.00 |
Hydrographic station information for the R/V ENDEAVOR Cruise EN-294 (31 January - 4 February 1997). 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.
