WHP Ref. No.: AR10
Last updated: 6 November 1995

A.	Cruise Narrative

A.1	Highlights

A.1.a	WOCE designation	AR10 
				
A.1.b	EXPOCODE		18HU92053/1 

A.1.c	Chief Scientist		Neil S. Oakey 
				Bedford Institute of Oceanography
				Box 1006
				Dartmouth N.S. B2Y-4A2
				Canada					
				Fax		902 426 3147
			 	Internet	neil@oakey.bio.dfo.ca
				 
A.1.d	Ship			C.S.S. Hudson
	
A.1.e	Ports of call		Halifax, N.S. Canada; Las Palmos, Canary Islands;
				Halifax, N.S. Canada
				 
				 
				 
				 

A.1.f	Cruise dates		5 April, 1993 to 14 May, 1993

A.2	Cruise Summary Information

A.2.a	Geographic boundaries

A.2.b	Stations occupied

At the 46 Fast CTD tracer stations a Seabird CTD was used to obtain 
temperature, salinity and dissolved oxygen profiles to a depth of 
about 350 meters.  Two rosette bottles were fired at each of these 
positions for analyses of salinity, dissolved oxygen, nutrients and 
total carbonate.

At the 65 Full CTD tracer stations a Seabird CTD was used to obtain 
temperature, salinity and dissolved oxygen profiles to a depth of 
about 500 to 700 meters.  Twenty rosette bottles were fired at each of 
these positions for analyses of salinity, dissolved oxygen, nutrients 
and total carbonate.

45 Biology casts, both shallow and deep casts were performed.

66 ESPONDE profiler stations were occupied.  Nearly 1000 profiles were 
obtained with the vertical microstructure profiler. 


3 Cartesian diver deployments
 


A.2.c	Floats and drifters deployed

2 ALFOS floats were deployed.  Floats #76 and #72 were deployed.

A.2.d	Moorings deploued or recovered

A.3	List of Principal Investigators
-------------------------------------------------------------------------------
Name				Responsibility				Affiliation

Neil S. Oakey  		Chief Scientist, Microstructure 	BIO
neil@oakey.bio.dfo.ca	Studies

James Ledwell		Tracer Sampling				WHOI
ledwell@tracer.whoi.edu
	
Tim Duda		 	Cartesian Diver Profiling		WHOI
timd@salsa.whoi.edu
	
Barry Ruddick		Microstructure Studies			Dal U.
barry@phys.ocean.dal.ca
	
Rolf Lueck			TAMI						U. Vic
rolf@george.seaor.uvic.ca
	
Glen Harrison		Carbon, Nitrogen Uptake 		BIO
g_harrison@bionet.bio.dfo.ca		Kinetics
	
Edward Horne		Optical Measurements, Salinity	BIO 
user@bodvax.bio.dfo.ca
	
Paul Kepkay			Dissolved Organic Carbon		BIO
p_kepkay@bionet.bio.dfo.ca
	
Brian Irwin			Total Carbon Dioxide			BIO
b_irwin@bionet.bio.dfo.ca	Oxygen, Nutrients
-------------------------------------------------------------------------------
Institute Abbreviations and Addresses

BIO 		Bedford Institute of Oceanography
		Box 1006
		Dartmouth, N.S., B2Y4A2, Canada

WHOI		Woods Hole Oceanographic Institute
		Woods Hole, MA, 02543 USA

Dal.U.	Dalhousie University
		Halifax, N.S., Canada

U. Vic	University of Victoria
		Victoria, B.C., Canada
 
 
A.4	Scientific Programme and Methods

The North Atlantic Tracer Release Experiment, NATRE, is a contribution 
to the core 3 WOCE study.  The Hudson voyage to the eastern Atlantic 
Basin had as one primary purpose the measurement of vertical mixing 
processes from the study of the vertical spread of a purposeful tracer 
by J. Ledwell of WHOI.  The second primary purpose was the physical 
estimates of mixing made using the vertical profiling instrument 
EPSONDE and other instruments including a free floating profiler 
called the Cartesian diver and a microstructure mooring.  Secondary to 
the NATRE studies biological studies of carbon and nitrogen uptake, 
dissolved organic carbon, primary production, total CO2, and optical 
studies were carried out by scientists of Biological Sciences Division 
who continued their studies in a follow on experiment.   

It should be noted that the current Hudson voyage was a continuation 
of the study started on the Woods Hole Vessel, the R/V Oceanus from 26 
October to 19 November, 1992 on which Oakey was chief Scientist.


Summary of Mission Along with Comparison with a Previous 
Cruise 	 The North Atlantic Tracer Release Experiment, NATRE, is a 
study of the rate of mixing in the eastern Atlantic carried out by a 
group of scientists from the United States, the United Kingdom and 
Canada as a part of the international WOCE Core Project 3 study.  
Diapycnal mixing is integral to the dynamics of ocean circulation; the 
temperature and salinity of water masses are altered by diapycnal 
mixing, and this affects the pole ward transport of heat by the 
circulation.  Knowing the magnitude and the mechanisms causing mixing 
is important to developing better models of ocean circulation.  NATRE 
was planned as part of WOCE Core Project 3 to be the first direct 
measurement of the diapycnal mixing rate in the main thermocline of 
any ocean basin.  The essence of this experiment was to release a 
chemically inert, easily measurable tracer on a target isopycnal 
surface, and to measure the subsequent tracer dispersion over the 
following year. Observations of turbulence and microstructure were 
part of the tracer experiment in order to understand the mixing 
processes that occur.  This understanding is needed so that the 
results for the tracer can be applied appropriately and confidently to 
heat, salt, and density, and extrapolated from the experimental sites 
to the global ocean.  NATRE provided an outstanding and unique 
opportunity to test the concepts, models and methodologies presently 
used to study mixing, and to refine them further, by comparison with 
direct measurements of diapycnal spreading rates of a tracer. 

The NATRE experiment started in the spring of 1992 when Dr. Jim 
Ledwell and his group from WHOI on the R/V Oceanus injected 139 kg of 
sulpher hexafluoride at a depth of approximately 300 meters in an area 
of about 20x20 km in the Canary Basin.  This patch of tracer diffused 
vertically and moved horizontally over the months to follow and 
various surveys explored this evolution, allowing us to deduce the 
rate of mixing or the vertical diffusivity in this region of the 
ocean.  In the month after the injection Ledwell and Dr. Andy Watson 
from the UK explored the initial distribution from the UK ship the RRS 
Darwin.  The patch had increased to about 50 km across and had 
thickened vertically consistent with a vertical diffusivity of order 
10-5 m2/s.  In October through November, Ledwell and Watson explored 
the evolution of the dye patch during two cruises on the R/V Oceanus. 
They found about 35% of the original tracer in a narrow (10 to 20 km 
wide) band about 350 km long.  Their measurements in the vertical 
yielded a vertical diffusivity of 1.1x10-5 m2/s.  During the second of 
these cruises Oakey and his group joined the R/V Oceanus and surveyed 
the area using EPSONDE, a vertically profiling microstructure 
instrument.  A report of this experiment is included at the end of 
this report on the Hudson 92053 voyage. 

The final surveys of the NATRE study were done in the spring of 1993 
using the CSS Hudson (cruise 92053) and the RRS Darwin.  Along with 
its other studies, the CSS Hudson gathered water samples using a CTD 
with a rosette sampler for analysis by Ledwell and his group from 
WHOI.  About 115 CTD tracer stations were done to delineate the extent 
of the tracers horizontal dispersion including about 60 full profiles 
to examine the vertical diffusion of the tracer.  The RRS Darwin, 
devoted only to the tracer studies obtained over 160 full tracer 
profiles.  It is estimated that all of the tracer released in the 
spring of 1992 has been accounted in the survey a year later and that 
the tracer can be found spread over an area of about 500 km by 700 km 
and has increased in thickness due to vertical mixing from a few 
meters to about 30 meters.  These measurements are consistent with the 
above estimates of vertical mixing but indicate that the rates over 
the winter were higher than during the summer, about 1.8x10-5 m2/s.

The largest program carried out on the April-May Hudson 92053 survey 
was an extensive set of microstructure and turbulence measurements.  
Nearly 1000 profiles to greater than 360 meters depth were obtained 
with the vertical microstructure profiler, EPSONDE.  These 
measurements will be used along with the 825 profiles last November on 
the R/V Oceanus to estimate vertical mixing rates and explore the 
mechanisms which are important in the vertical dispersion of dye.  
These mixing studies are part of the WOCE NSERC collaboration between 
Oakey and Dr. B. Ruddick of Dalhousie.  This is the largest set of 
data collected with this instrument and represents nearly 700 km of 
sampling of the fluctuations of temperature and velocity fluctuations 
in the ocean sampled at about 3 mm intervals, about 3 gigabytes of 
data!  The challenge is whether we get the correct answer which has 
been obtained from the tracer studies.  Preliminary results indicate 
that our results are consistent.

Other studies were done on Hudson 92053 as well.  A group from the 
University of Victoria led by Dr. R. Lueck deployed and recovered a 
mooring designed to measure the intensity of mixing at a fixed site 
over a period of several weeks using a variety of microscale and 
larger scale sensors.  Several deployments of an instrument called a 
Cartesian Diver were also carried out successfully.  This instrument 
floated freely measuring vertical profiles of velocity and 
microstructure from which mixing processes can be explored. 	 To 
take advantage of the transit to the eastern Atlantic scientists from 
Biological Oceanography, BSB participated in the survey with extensive 
biological studies.  They continued their experiment in the following 
experiment.

The ship left Halifax on Monday, 5 April, 1993 en route to the 
position 32o16'N, 34o08'W where a surface mooring buoy which had 
broken from a Scripps/WHOI mooring was recovered.  Tracer surveys were 
started south from here to approximately 25o30'N, 34o08'W then east to 
near the site of a mooring central to the experiment at 25o30'N, 
29oW.  The ship track is shown in Figure 1.  A mooring was placed in 
this region by the group from University of Victoria headed by Lueck, 
the first deployment of the Cartesian diver was done and coordinated 
tracer and EPSONDE surveys started.  These continued until 18 April 
when the program was interrupted by a medical emergency that required 
taking the Chief Mate to Las Palmos.  We returned to the site of the 
experiment on 23 April and continued sampling until the end of the 
study on 12 May allowing time for the transit to Las Palmos where the 
expedition terminated on May 14, 1993.  


 
A.5	Major Problems and Goals not Achieved


A.6	Other Incidents of Note

A.7	List of Cruise Participants

Name				Responsibility			Affiliation
-------------------------------------------------------------------------------
Neil S. Oakey  		Chief Scientist, Microstructure 	BIO
				Studies
James Ledwell		PI, Tracer Sampling			WHOI
Gary Stanbrough		Technician, Tracers			WHOI
Brian Guest			Technician, Tracers			WHOI
Tim Duda		 	Cartesian Diver Profiling		WHOI
Barry Ruddick		Microstructure Studies			Dal U.
Dave Walsh			Post Doc, Microstructure		Dal U.
James Burke			Student, Microstructure			Dal U.
Nauzer Kalyaniwalla	Student, Microstructure			Dal U.
Rolf Lueck			PI, TAMI					U. Vic
Rick Hudson			Engineer, TAMI				U. Vic
Don Newman			Engineer, TAMI				U. Vic
Robert Ryan			Technician, Microstructure		BIO
Jennifer Hackett		Technician, Microstructure		BIO
Liam Petrie			Technician, Microstructure		BIO
Edward Verge		Technician, Microstructure		BIO
Glen Harrison		PI, Carbon/Nitrogen Uptake Kinetics	BIO
Edward Horne		PI, Optical Measurements		BIO 
Brian Fraser		Technician, Optical Measurements	BIO
Paul Kepkay			PI, Dissolved Organic Carbon		BIO
Brian Irwin			PI, Total Carbon Dioxide		BIO
-------------------------------------------------------------------------------

