1 Cruise narrative
1.1 Highlights
1.1.1 Expedition
R/V Oceanus 365-41.1.2 Chief scientist
Claudia Schmid1.1.3 Ship
R/V Oceanus1.1.4 Crew
|
Lawrence T. Bearse |
Captain |
|
Courtenay Barber |
Chief mate |
|
Michael J. Conda |
2nd mate |
|
Jeffrey M. Stolp |
Boatswain |
|
Darrell Hanna |
AB |
|
Leonidas Byckovas |
AB |
|
Colin Walcott |
OS |
|
Partick S. Mone |
Chief engineer |
|
Nelson V. Botsford |
Jr. engineer |
|
Marcel Vieira |
Jr. engineer |
|
Christopher Moody |
Steward |
|
Brett Bluestein |
MA |
1.1.5 Ports of call
Fortaleza, BrazilBridgetown, Barbados
1.1.6 Cruise dates
5 March - 25 March 20011.2 Principal Investigators
| Robert Molinari | AOML | molinari@aoml.noaa.gov |
| Claudia Schmid | CIMAS/ AOML | schmid@aoml.noaa.gov |
1.3 Cruise participants
| Steven Eykelhoff | networking | WHOI | |
| Marlos Goes | CTD | Inst. Sao Paulo | |
| Robert Roddy | CTD, oxygen | AOML | roddy@aoml.noaa.gov |
| Kathleen Schact | autosal | Univ. Wash. | |
| Claudia Schmid | Chief scientist | AOML/ CIMAS | schmid@aoml.noaa.gov |
| Derrick Snowden | ADCP, CTD | AOML | snowden@aoml.noaa.gov |
| John Steger | ADCP, CTD | AOML | steger@aoml.noaa.gov |
1.4 Abbreviations and addresses
AOML National Oceanic and Atmospheric AdministrationAtlantic Oceanographic and Meteorological Laboratory
4301 Rickenbacker Cswy, Miami 33149, FL, USA
CIMAS Cooperative Institute of Marine and Atmospheric Science
4600 Rickenbacker Cswy, Miami 33149, FL, USA
WHOI Woods Hole Oceanographic Institution
Woods Hole, MA, USA
1.5 Primary objective
Studying the subtropical cells and the spreading of the Subtropical Underwater1.6 Scientific program and methods
1.6.1 Cruise track
Fig. 1: Map of cruise track of the R/V Oceanus during OC 365/IV in March 2001. P = Palace deployement, D = Surface drifter deployment, + = CTD/LADCP station, X = XBT profile. The isobaths are 1000 and 4000 m.
1.6.2 CTD/LADCP and water sampling
Data from 98 CTD/LADCP/rosette stations are available (Table 1, Fig. 1, station 8 was counted but not done). All stations include LADCP. Water samples for salinity and oxygen were taken throughout the upper 1500m.1.6.3 XBT's deployed
57 XBT with the Mark 12 system (Table 2, Fig. 1).1.6.4 PALACE floats and drifters deployed
5 PALACE (Table 3, Fig. 1).6 drifters (Table 4, Fig. 1).
1.6.5 Underway measurements
Underway measurements included thermosalinograph (TSG) data and the various variables of the Oceanus' IMET system (surface temperature, conductivity, oxygen, meteorological parameters, GPS, ship speed, heading and bathymetry).1.7 Problems with scientific equipment
CTD:The primary conductivity and oxygen sensors failed during the up-cast of station 2. The symptoms were very spiky salinity and oxygen data and the pump indicator showed 10 (which means that the primary pump is off). This seemed to indicate that the pump is the problem. During station 3 the primary conductivity and oxygen sensors failed as expected. The secondary conductivity was OK. Unfortunately the secondary oxygen sensor failed as well. The replacement of the primary conductivity sensor between stations 3 and 4 solved the problems with the secondary oxygen sensor.
Throughout the 35° W section the primary oxygen sensor did not work properly. The oxygen current was reasonable but the oxygen temperature was wrong. A replacement with a backup sensor after CTD station 38 did not solve this problem. In fact the older replacement oxygen sensor did not work at all. The last cast was used as a test of the digitizer in the CTD. The primary oxygen sensor was plugged into a different A/D channel. This did not improve the data in any way. A final test for the digitizer was done on deck. The deck unit was turned on to test two different configurations: (1) The good secondary oxygen sensor was plugged into the A/D channel for the primary sensor and the primary sensor was plugged into the A/D channel for the secondary sensor. (2) The primary and the secondary oxygen sensors were plugged into their original A/D channels. Result: The values for both oxygen sensors were independent of the A/D channel. The primary oxygen sensor had the word display "0 0", and the secondary sensor had a varying word display (order of magnitude "2000 200") in both configurations.
Conclusion: Both oxygen sensors used as primaries are bad (serial # 130433 and 230297). The secondary oxygen sensor is good (serial #230531). The digitizer is working correctly.
The tripping of the Niskin bottles proved to be unreliable (stations 5-7). While checking the connections at the CTD between stations 7 and 8 unit a pin broke of off the plug to the rosette. The pin was corroded through. It was decided to skip two stations of the high-density section (station 8 was already numbered, but no cast was done). The repairs took about two hours. Afterwards the tripping of the bottles was much more reliable. Towards the end of the cruise the tripping of the bottles started to get more random.
ADCP:
The shipboard 300 kHz ADCP was not working until 8 March in the evening. The
software problem could finally be solved with the help of a technician at WHOI.
1.8 Other incidents of note
Condensation in the radar lead to delay of departure by seven hours until 16:00 pm on 6 March.
2.1 CTD/LADCP/rosette
A CTD with two sensors of temperature, conductivity and oxygen was used. 10 Niskin bottles were available. Water samples for oxygen and salinity were taken after each cast. These samples were analyzed on board and the resulting data will be used for the insitu calibration of the conductivity and oxygen sensors.The LADCP is a RDI Broadband 150 kHz ADCP.
2.2 XBT
The Mark 12 system was used to achieve a higher resolution of the temperature field.2.3 Vessel-mounted ADCP
The data from two vessel-mounted ADCPs were recorded throughout the survey. The used instruments are a RDI Broadband Ocean Surveyor 38 kHz ADCP and a RDI Narrowband 150 kHz ADCP. Combining the data from the two ADCPs will result in velocity profiles over the upper nearly 1000 m with a higher resolution in the upper 350-400 m.2.4 PALACE float deployments
The PALACE floats were programmed to surface after 10 day long periods of submerged drift to take pressure-temperature profiles. After an 18 hour long surface period, during which they transmit their data, they go back to their target pressure of 1000 dbar. The instruments were launched after selected CTD casts.2.5 Drifter deployments
Each surface drifter was launched together with a PALACE float. The drifters measure the sea surface temperature and they are tracked by ARGOS. Their drogue is at 15 m.2.6 Underway measurements
Underway measurements included thermosalinograph (TSG) data and the various variables of the Oceanus' IMET system (surface temperature, conductivity, oxygen, meteorological parameters, GPS, ships speed, heading and bathymetry).3 Preliminary analysis
Preliminary data products generated on the R/V Oceanus are presented. The hydrographic sections show the major water masses (Figs.2, 3, 5-7, 9-11, 13-15, 17) and the flow field from the ADCPs (Figs. 4, 5, 8, 9, 12, 13, 16, 17).
The water masses in the upper 1500 m of the tropical Atlantic are the Tropical Surface Water (TSW), the Subtropical Underwater (SUW), the Central Water (CW), and the Antarctic Intermediate Water (AAIW).
One major goal of this cruise is to improve the understanding of the spreading of the SUW. This water is characterized by a salinity maximum in the upper 150m of the water column. The maximum is strongest near the equator (Fig. 18). It is weakening towards the north before it strengthens again. Between about 2°N and 5°N the salinity maximum shows only small changes of its strength. The sections at the four longitudes indicate an increase of the salinity in the SUW near the equator. The maximum salinity north of 5°N does not change as much as the maximum salinity near the equator between 35°W and 41°W. From 41°W to 44° W this maximum strengthens as much as the maximum south of 3°N.
Between 500 and 1000 m the AAIW is found. It is characterized by a low salinity, which increases slightly towards the north (Figs. 2, 6, 10, 14). Salinity values below 34.6 reach north beyond 6°W at all longitudes except 44°W. At 44°W the 34.6 isohaline terminates at 6°N.
The strongest oxygen signal is the broad minimum centered near 500m at the upper boundary of the AAIW (Figs. 3, 7, 11, 15). The lowest values are observed near the northern end of the section. The oxygen concentration in this minimum layer increases from east to west.
The temperature sections at 38°W and 44°W show a deepening of the 13°C to 5°C isotherms and a shoaling of the thermocline at 3°N and 4°N, respectively (Figs. 6 and 14). Similar patterns are also found in other sections: Between 38°W and 35°W (Fig. 5). At 41°W (Fig. 10). Between 38°W to 41°W (Fig. 9).
The ADCP and LADCP sections show the alternating zonal currents characteristic for the tropical Atlantic (Fig. 4, 5, 8, 9, 12, 13, 16). The velocity maximum of the Equatorial Undercurrent (EUC) coincides with the salinity maximum of the STUW. This highest salinity STUW is flowing east (Fig. 18). The STUW with the lowest salinity and also the more saline STUW to the North are flowing west in the northern branch of the South equatorial current.
4 Acknowledgements
We want to thank the officers and crew of the R/V Oceanus as well as the personnel at WHOI. Their expertise and high motivation were important for the successful completion of our work program. The excellent work of the WHOI technician, the AOML personnel and the Brazilian scientist made it possible to obtain a high quality data set. The help and instructions from employees in Miami before and during the cruise are much appreciated. The cruise was sponsored by AOML.
