Northeast Fisheries Science Center Reference Document 05-03
Description of the 2004 oceanographic conditions
on the northeast continental
shelf
by Maureen H. Taylor, Cristina Bascuñán, and James
P. Manning
National Marine Fisheries Serv., Woods Hole Lab., 166 Water St., Woods
Hole, MA 02543
Print
publication date April 2005;
web version posted April 12, 2005
Citation: Taylor MH, Bascuñán C, Manning JP. 2005. Description of the 2004 oceanographic
conditions on the Northeast Continental Shelf. US Dep Commer, Northeast Fish Sci Cent
Ref Doc. 05-03; 92 p.
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ABSTRACT: A summary of hydrographic observations for 15 surveys on the northeast
continental shelf during 2004 is presented. Distributions of CTD
stations, surface and bottom temperature, salinity, and anomalies are
portrayed. The average surface and bottom temperatures and salinities
have been calculated in five geographic regions over the northeast
continental shelf: western Gulf of Maine (GOMW), eastern Gulf of Maine
(GOME), Georges Bank (GB), northern Middle Atlantic Bight (MABN) and
southern Middle Atlantic Bight (MABS). Time series plots from various
shipboard environmental sensors are included if available.
Hydrographic data collected
during 2004 were sorted into six 2-month time bins to provide the best
spatial coverage used in the averaging method. A comparison of the
computed areal average temperature and salinity data for 2004 with
the MARMAP reference
values indicate that the majority of the shelf experienced relatively cold
bottom temperatures and fresher salinities in all regions during the majority
of the observations made during the year.
INTRODUCTION
The Northeast Fisheries Science Center (NEFSC) conducts several different
surveys off the northeast continental shelf each year. Complete coverage
of the shelf (Cape Hatteras to the Gulf of Maine) occurs during the spring
and fall bottom trawl surveys and during some of the Ecosystem Monitoring
cruises. Station coverage on other cruises throughout the year varies.
Temperature and salinity observations from 15 NEFSC surveys conducted
during 2004 are summarized and presented in this report. Cruise operation
summaries are presented for all cruises. Distribution plots of surface
and bottom temperature, salinity, and anomalies are contoured where sufficient
data are available. Areal average temperature and salinity and the corresponding
anomalies also are presented for the five different regions on the shelf
and for 6 time periods throughout the year. The data are presented chronologically
in atlas form. Environmental data from the SCS system (Shipboard Computing
System) are presented as time series figures for each leg of a cruise. No
attempt has been made here to rigorously analyze the data or discuss
in detail individual observations from the cruises.
DATA AND
METHODS
All raw Profiler data were processed using the Seabird manufactured
software: DATCNV, FILTER, ALIGNCTD, BINAVG, DERIVE, and ASCIIOUT to produce
1 decibar averaged ASCII files. The data were edited, cleaned, and converted
to a standard 80-column ASCII formatted cruise file and were archived
in ORACLE tables and in the NEFSC anonymous FTP account (ftp://ftp.wh.whoi.edu/pub/hydro).
Station distributions and horizontal contour plots of the surface and
bottom temperature, salinity, and temperature anomaly were prepared for
each survey if coverage was sufficient. In addition, all the hydrographic
data were combined and sorted into 2-month time bins. Areal average
temperatures and salinities were then calculated for the six time periods
and for the five regions of the northeast continental shelf shown in
Figure 1a: western and eastern Gulf of Maine (GOMW, GOME), Georges Bank
(GB), and the northern and southern Middle Atlantic Bight (MABN, MABS). Station
distributions for each time period are shown in Figure
1b. Anomalies
for the temperature and salinity observations were determined relative
to reference values, using the method described by Holzwarth and Mountain
(1990) as modified by Mountain et al. (2004). The areal averaging was
also done using the method described in Holzwarth and Mountain (1990)
as modified by Mountain et al. (2004). The areal averages and anomalies
were plotted against the calendar mid-date of all observations within
each of the six time periods. Areal averages and anomalies were also
calculated by cruise and are listed in Tables 4 and 5.
RESULTS
The NEFSC cruises that are included in this report are listed in Table
1. A summary of each cruise is described in Appendix
A and includes
information on the type of cruise, its objectives, dates, the number
of hydrographic stations, type(s) of instruments used, salinity calibration
value, and notes pertaining to instrument performance. No salinity
correction was applied to the cruise data if the mean salinity offset
was less than +/- 0.01 psu.
Table 2 lists
the surface and bottom areal average temperatures and temperature anomalies
that were calculated for each of the five regions. Table
3 lists the surface and bottom areal average salinity and salinity
anomalies for the same five regions. For most cruises, the areal averages
and anomalies could not be calculated for all regions due to limited
station
coverage. Combining all the hydrographic data from all NEFSC programs
and ships provided a better chance of adequate spatial and temporal coverage
within the regions of the northeast continental shelf. In some cases
however, a simple average (not an areal weighted mean) was determined
for the observations in the region; these values are indicated in Tables
2 - 4 with a flag value of '1'. The standard deviations are also listed. SDV1
indicates how well the calculated anomaly represents the true regional
average anomaly. SDV2 is an indicator of how closely the areal average
matches the anomaly at any particular location within that region (see
Holzwarth and Mountain, 1990 for further explanation of SDV1 and SDV2).
Figures 2 - 3 present the
time series of surface and bottom average temperature/salinity and temperature/salinity
anomaly for each region. Cruises
having less than 10 observations were not included in the time series
figures. We were not able to resolve small-scale, localized events because
of the regional averaging method used in this report. Station positions
and distributions of surface and bottom temperature, salinity, and anomalies
for the different cruises are presented in Figures 4
- 55. Contour distribution
figures were not prepared for some of the cruises because of poor station
coverage. In addition, contour levels are not always consistent for
a variable within a cruise. Contour distributions have been routinely
produced for the scallop survey although the station coverage for this
survey does not provide sufficient spatial coverage to allow one to produce
realistic broad-scale hydrographic distributions of the MAB and Georges
Bank regions. Environmental time series plots from shipboard sensors
(SCS data) are included in Appendix B. Further information about this
data may be obtained at http://www.wh.whoi.edu/~jmanning/foi/alongtrack.html.
DISCUSSION
The bottom temperature anomaly time series (Figure
2) indicates that
the bottom temperatures of the entire northeast continental shelf were
colder (= 1°C) for much of the year. Similarly, the salinity
anomaly pattern displayed in Figure 3 indicates that the shelf region
was also fresher than the MARMAP reference annual cycle. The salinity
anomaly time series suggests a pattern of increasing freshness in the
Georges Bank and Gulf of Maine regions with the year ending with these
regions having salinity values approximately 0.5 fresher than the reference
period. The air temperatures during January 2004 were approximately
6 degrees below average in the northeast region every day for the month
(Northeast Regional Climate Center, 2004), and the cold atmosphere likely
contributed to the colder bottom temperatures observed on the northeast
continental shelf during much of the year. The fresher surface and bottom
salinities suggest an increase in cold, fresh scotian shelf water entering
the eastern Gulf of Maine and being advected during the year 'downstream' into
the Georges Bank and MAB regions.
REFERENCES
Holzwarth, T.J. and D. Mountain. 1990. Surface and bottom temperature
distributions from the Northeast Fisheries Center spring and fall bottom
trawl survey program, 1963-1987. Woods Hole, MA: Northeast Fisheries
Center. Reference Document 90-03. Available from: Information Services
Section, NMFS/Northeast Fisheries Science Center, Woods Hole, MA 02543
Manning, J.P. (2004). NEFSC Scientific Computer System (SCS) Alongtrack
Data Processing. http://www.wh.whoi.edu/~jmanning/foi/alongtrack.html (10 Dec 2005).
Mountain, D.G., M.H. Taylor and C. Bascuñán. 2004. Revised Procedures
for Calculating Regional Average Water Properties for Northeast Fisheries
Science Center Cruises. Woods Hole, MA: Northeast Fisheries Center. Reference
Document 04-08. Available from: Information Service Section, NMFS/Northeast
Fisheries Science Center, Woods Hole, MA 02543.
Northeast Regional Climate Center, Cornell University. Seasonal Climate
Summary Tables. http://met-www.cit.cornell.edu/ (10 January 2005).
Taylor, M. H. and Bascuñán, C. 2000. CTD Data Collection on Northeast
Fisheries Science Center Cruises: Standard Operating Procedures. Northeast
Fisheries Science Center Reference Doc. 00-11; 28 p. Available
from: National Marine Fisheries Service, 166 Water St., Woods
Hole, MA 02543.
