2015-2016 USAP Field Season
The Drake Passage high-density XBT program
Dr. Janet Sprintall
Scripps Institution of Oceanography
Project Web Site:
Supporting Stations: ARSV Laurence M. Gould
The objective of the eXpendable BathyThermograph (XBT) program is to measure the seasonal to interannual variability of upper-ocean temperature and geostrophic transport through the Drake Passage. Closely spaced XBT (temperature) measurements are collected underway on six to eight Drake Passage crossings of the ARSV Laurence M. Gould (LMG) per year. The project has been ongoing since 1996. With the multi-year time series, researchers have observed substantial variability in circulation, transport, and water properties on time scales from seasonal to interannual, and spatial scales from mesoscale eddies to the Antarctic Circumpolar Current cores.
Field Season Overview
Underway XBT and XCTD measurements are requested on the six L.M. Gould cruises during the FY2015 season. However, the R/V Laurence M. Gould Operating Schedule published 12 March 2015 does not as yet account for the full 2015-2016 field season.
The PI would like to sample on LMG15-08 (southbound)
and select an additional five (5) cruises during a later date when the LMG schedule is more defined.
In general, my XBT/XCTD sampling plan objective is to schedule sampling on the LMG approximately every 2 months, but this is not always possible. Approximately 70 XBTs are dropped per crossing. The XBTs are loaded and launched using the SIO automatic XBT launcher and associated software that automates the collection of the XBT profiles. The SIO system drops an XBT probe at pre-specified locations, and prompted by the GPS location. The XBT system should be solely dedicated for the use of the XBT program.
During this season, we will continue the transition to the Windows 7 OS and work at compatibility with the Amverseas communication with Iridium. This could potentially require a port call by the Marine Technician Mr. Glenn Pezzoli (or an equivalent personnel from within the XBT laboratory group) to confirm that the system is operating correctly, although the shipboard personnel have been extremely helpful and diligent in helping with this upgrade.
Any problems that arise in any part of the system should be referred to Janet Sprintall (email@example.com), Glenn Pezzoli (firstname.lastname@example.org), and Lucian Parry (email@example.com).
We request 11 TSK XCTDs be dropped per XBT sampling cruise, at every half degree between 55.5S and 60S (i.e. 55.5S, 56S, 56.5S, 57S, 57.5S, 58S, 58.5S, 59S, 59.5S, 60S, 60.5S). This means that each XBT/XCTD sampling cruise should have a box of XCTDs on board (12 probes), and 1 probe is to be used as a spare in case of failure of one of the 11 probes.
Salinity bottle samples will be collected at each XCTD deployment. This bottle data will be used to calibrate the XCTD and underway thermosalinograph (TSG) data. Offsets between the bottle salt data and the TSG can be significant, and this is one way of determining the offset. The offset between two salinities is lowered when the TSG is cleaned before the crossing, and we would request this occur on each XBT/XCTD transect.
To undertake the XBT/XCTD sampling, we request the support from 1-2 Rathyeon personnel for set-up and loading the XBT probes in the launcher, the XCTD deployments, and the collection of salinity bottle samples. XBT/XCTD log sheets should note bottom depth < 800 m, and probe success or failures. All data and log sheets to be downloaded to CD and sent to PI Sprintall upon cruise completion. We also request TSG, met and navigation data from each cruise be sent on CD via US mail.