This data report presents a description of the field program and instrumentation, an overview of the data through summary plots and statistics, and the data in NetCDF and ASCII format for the period December 1989 through December 2002. The objective of this report is to make the data available in digital form, and to provide summary plots and statistics to facilitate browsing of the long-term data set
These data have been edited to remove wild points and data recorded when the instruments were out of the water before and after deployment.
Biological fouling often degrades light transmission data after several months of deployment. Organisms grow on the transmissometer lenses and gradually block light transmission, which results in a gradual upward drift of the beam attenuation coefficient. This drift occurs more quickly and is more severe at shallower depths. The attenuation data plots have not been corrected for biological fouling and should be interpreted with care.
Tripod salinities in 1989 - 1996, were erroneously low by as much as one psu by the end of the 4-month deployments, due to fouling of the conductivity cells. Tripod conductivity data was apparently affected by a slow, gradual build-up of a biological film on the electrodes and also occasional sudden depositions of a significant volume of material (possibly sediments) inside the measurement volume of the conductivity cell. In June 1996 (mooring 470), Seabird pumps were added to the MIDAS to flush the conductivity cell prior to making a measurement, reducing the affect of deposits on the conductivity measurements. The salinity data should be used and intepreted with care.
Brad Butman was the Principal Investigator (PI) for the physical oceanographic observations. Mike Bothner was chief scientist on the USCG cruises and PI for the sediment trap observations. Fran Lightsom managed the time-series data processing and archive. William Strahle, Marinna Martini, and Jon Borden oversaw the preparation and deployment of the physical oceanographic instrumentation. Soupy Alexander wrote most of the Matlab scripts, made all of the plots and calculations, and assembled the data report.
We thank the Captains and crews of the U.S. Coast Guard Cutters WHITE HEATH and MARCUS HANNAH for their outstanding logistical support for this measurement program. The USGS and the USCG safely conducted over 40 cruises to deploy and recover hundreds of individual instruments on over 100 moorings to obtain this long-term data set. Bob Barton, Dan Blackwood, Jon Borden, Michael Casso, Jessica Cote, Ray Davis, Peter Gill, Joe Newell, Carol Parmenter, Andre Ramsey, Rick Rendigs, and Richard Signell carried out the work at sea, ashore and in the laboratory. Rick Rendigs, Dan Blackwood, Larry Ball, Steve Cross, and Ken Parolski aided in the successful recovery of several bottom tripod systems by diving when the primary recovery system failed. Dann Blackwood took most of the photographs shown in this report. Mike Connor, Ken Keay, Wendy Leo, Mike Mickelson, and Andrea Rex provided encouragement and support from MWRA. Frank Marachi, Captain of the fishing vessel CHRISTOPHER ANDREW, provided assistance and valuable local knowledge on a number of cruises.
Instruments to measure current, temperature, salinity, bottom pressure, light transmission, suspended matter, and to photograph the sea floor have been deployed at Site A from 1989 to 2002. Instruments to measure current, temperature and suspended matter were deployed at Site B from 1997 to 2002.
In addition to the time-series physical observations, sediment traps were deployed at both Sites A and B. The data they collected are used to estimate the relative amount of suspended sediment falling through the bottom water, to link variations in the trapping rate with changes in oceanographic conditions, and to determine the chemical and physical properties of the trapped sediment. Traps collected samples during storm and non-storm periods and during seasonal cycles in primary productivity, providing information on the nature and amounts of material in transport under different oceanographic conditions. The sample suite was also designed to monitor any changes in contaminant concentrations of trapped material since 1989 and especially since the start of the Massachusetts Bay Outfall. Outfall-related changes in chemistry are expected to be detected earlier and more intensively in trapped suspended sediment than in the surficial bottom sediments because trapped sediments are immediately isolated. In contrast, particles falling on the sea floor can be mixed downward by benthic organisms and diluted by older particles from below the water-sediment interface.
Instrumentation was recovered and replaced at each site 3 times each year (typically in February, June and September). The moorings at Site A and Site B were deployed and recovered using the U.S. Coast Guard Cutter WHITE HEATH between 1989 and 1998, and the U.S. Coast Guard Cutter MARCUS HANNAH between 1998 and 2002. Additional instrument deployments and recoveries in emergencies and to test gear were accomplished using the fishing vessel CHRISTOPHER ANDREW.
DATA PROCESSING
Data processing was conducted using the WHOI Buoy Group Data Processing System and a WHOI-USGS Oceanographic Data Processing System. The Buoy System runs on VAX VMS computers and stores data in a VMS data format. The more recent WHOI-USGS //www.mathworks.com/) on all computers that have Matlab software, and keeps data in EPIC standard NetCDF files //www.pmel.noaa.gov/epic/). For compatibility, the older Buoy Format data files have been translated to EPIC NetCDF.
In either data processing system, after data were decoded and calibrated, they were carefully checked for instrument malfunctions and then edited. The beginning and end of each data series were truncated and wild points deleted. Short data gaps (less than about 8 data values, which is half an hour for VMCMs and Seacats and an hour for tripods) were filled by linear interpolation. The data were carefully checked at each stage of processing. After editing, the basic version of the data file includes all variables recorded at the basic sampling interval. An hour-averaged data file and a low-pass filtered data file were created from the basic version. The low-pass filter essentially removes all fluctuations having periods shorter than 33 hours. Low-pass filtered data were subsampled every 6 hours.