CTD Hydrocasts were performed with a Sea-Bird SBE 911/917 plus CTD mounted near the base of a Niskin 24 Bottle Rosette.
|Created||September 18, 2015|
|Modified||August 19, 2016|
|State||Final no updates expected|
CTD data from KN223 in the western North Atlantic.
CTD Hydrocasts were performed with a Sea-Bird SBE 911/917 plus CTD mounted near the base of a Niskin 24 Bottle Rosette. The CTD instrumentation included Conductivity (S/N 2147 & 2768), Temperature (ITS-90, S/N 4195 & 4252), Pressure (S/N 63505 SBE090462), Oxygen (SBE 43, S/N 0264), Fluorescence (Wetlab ECO-AFL/FL, S/N FLNTURTD-304), and Beam Transmission (Chelsea/Seatech/Wetlab CStar, S/N CST-1118DR). Processing firmware is SBE11plus v 5.
At each station, a hydrocast was conducted with a rosette carrying 24 10-L Niskin bottles. The rosette was instrumented with sensors for conductivity, temperature, pressure, oxygen, fluorescence, and beam transmission, as listed above. The downcast was conducted at 30 m per minute in the upper 100 m and increased to 60 m per minute to a maximum depth of ~5 m above the seafloor (based on altimeter data). Features were selected from the downcast data for sampling on the upcast. These features included oxygen minimum layer(s), chlorophyll maximum layer(s), and the thermocline. In addition, standard depths of bottom, 50 m above bottom, 5000 m, 4000 m, 3000 m, 2000 m, 1500 m, 1000 m, 300 m, 200 m, 100 m, 50 m, 10 m, and surface were sampled.
The vent plugs were removed and replaced with t-fittings. A ring of plastic tubing (1/4″ inner diameter) was used to construct a manifold to deliver pressure to each Niskin bottle. Each bottle was connected individually to the manifold to prevent any potential mixing between bottles. The compressor was connected to the initial t-valve in the series and the final t-valve was plugged. The compressor was set to 8 – 10 psi.
Cylindrical, 0.2 um retention membrane filters (Sterivex) were attached to the petcock valve of the Niskin bottles with 1/4″ tubing (Fig. 8). The valves were opened and the water was pushed through the filters with the compressed air. The filtration rate is ~200 mL per minute. When the water stopped dripping through the filter, the filters were removed, capped at both ends, placed into freezer boxes and stored at -70 degrees C in the main lab freezer.
The CTD data were processed with Seasave v. 7.21k.
– Modified parameter names to conform with BCO-DMO naming conventions;
– Obtained lat_start, lon_start, date_start, and time_start from the CTD file headers;
– Converted lat and lon to decimal degrees;
– Added ISO_DateTime_Start column.
Latitude at start of cast.
latitude at start time of measurement; in decimal degrees (negative denotes South)
Longitude at start of cast.
longitude at starting time of measurement (west is negative), in decimal degrees
date sampling starts such as YYYYMMDD
starting time of observation, GMT time, 24 hour clock
Date/Time (UTC) ISO formatted
This standard is based on ISO 8601:2004(E) and takes on any of the following forms:
2009-08-30T09:05:00[.xx] (local time)
2009-08-30T14:05:00[.xx]Z (UTC time)
The dashes and the colons can be dropped.
The T can also be dropped "by mutual agreement", but one needs the trailing Z if the time is UTC.
2009-08-30T14:05:00[.xx]Z (UTC time)
Pressure. Originally named 'PrDM'.
water pressure at measurement; depth reported as pressure; positive number increasing with water depth
Conductivity. Units and collection methods may vary. Often reported in Siemens/meter.
When used in a JGOFS/GLOBEC project this is the conductivity in Siemens/meter for the primary conductivity sensor on a CTD.
conductivity, from the CTD 'secondary sensor', usually reported in Siemens/meter. Depending on input source may have a variety of names.
dissolved oxygen concentration
Fluorescence. Indirect measure of pigment concentration.
Units and collection method may vary. Units often reported in milligrams/meter^3 (mg/m3) or micromoles per liter (ug/L). Sometimes reported after being calibrated against extracted pigment concentrations.
In JGOFS/GLOBEC projects fluorescence is measured from CTD instrument sensor.
light transmission, as percent
Turbidity is the cloudiness or haziness of a fluid caused by individual particles
Depth. Originally named 'DepSM'.
Observation/sample depth below the sea surface. Units often reported as: meters, feet.
When used in a JGOFS/GLOBEC dataset the depth is a best estimate; usually but not always calculated from pressure; calculated either from CTD pressure using Fofonoff and Millard (1982; UNESCO Tech Paper #44) algorithm adjusted for 1980 equation of state for seawater (EOS80) or simply equivalent to nominal depth as recorded during sampling if CTD pressure was unavailable.
salinity, calculated from the CTD 'primary sensors' of conductivity and temperature, Practical Salinity Scale (PSS-78), dimensionless. Depending on the input source, salinity from the primary sensors can have a variety of names i.e. s0, s00, sal0, sal00.
sound velocity in sea water, in meters/second
|Steven L. D'Hondt||University of Rhode Island (URI-GSO)|
|Robert Pockalny||University of Rhode Island (URI-GSO)|
|Arthur J. Spivack||University of Rhode Island (URI-GSO)|
|Shannon Rauch||University of Rhode Island (URI-GSO)|
|Shannon Rauch||Woods Hole Oceanographic Institution (WHOI BCO-DMO)|
BCO-DMO Project Info
|Project Title||North Atlantic Meridional Circulation during the Last Glacial Maximum: Density Structure and Pre-formed Nitrate: Phase I|
|Acronym||AMOC Last Glacial Max|
|Created||September 18, 2015|
|Modified||September 18, 2015|
Description from NSF award abstract:
The large-scale conveyor-belt-like circulation of the Atlantic Ocean (the Atlantic Meridional Overturning Circulation, or AMOC) significantly affects climate via its heat flux and its impact on atmospheric carbon dioxide levels. A number of lines of evidence suggest that the structure of the circulation was different during the last ice age, however these reconstructions are indirect. Sedimentary pore waters in the deep sea preserve ancient seawater, and offer the possibility of more directly documenting how AMOC of the last glacial maximum differed from that of the present.
This project, led by a team of researchers from the University of Rhode Island, will address these fundamental questions about the links between ocean circulation and climate change. Specifically, funding supports a month-long research expedition to collect long sediment cores along a transect between Puerto Rico and New England. Coring sites would range in depth from 1 to more than 5 km. Coring targets will be chosen with a combination of multibeam swath bathymetry, seafloor backscatter, and CHIRP sub-bottom seismic data. The team would analyze the composition (chloride, dissolved oxygen, and nitrate concentrations) of pore waters in the recovered sediments shipboard to detect the relict signal of deep water chemistry during the last glacial maximum. These measurements will allow the researchers to directly test the influence of glacial circulation on climate (via the pre-formed nitrate content of deep and intermediate water in the LGM North Atlantic). The expedition will include several graduate and undergraduate students, offering a valuable training activity and a strong educational experience.