WOCE Line        AR19
Expocode         90AV15_1
Chief Scientist  S. M. Shapovalov/RAS*

Ship             R/V Akademic Sergei Vavilov
Region           North Atlantic

Ports of call    Kaliningrad, Hamburg (Germany), Halifax (Canada)



EXTRACTED FROM:

  Oceanology, Vol. 40, No. 5, 2000, pp. 747-749. Translated from Okeanologiya,
                       Vol, 40, No. 5. 2000 pp. 791-793.
  Original Russian Text Copyright (c) 2000 by Shapovalov, Sokov, Dobrolyubov.
English Translation Copyright (c) 2000 by MAIK "Nauka /Interperiodica" (Russia).

         Cruise 15 of R/V Akademik Sergei Vavilov in the North Atlantic
              under the Auspices of the WOCE International Program

             S. M. Shapovalov*, A. V. Sokov*, and S. A. Dobrolyubov"

*Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia 
**Geographical Department, Moscow State University, Moscow, Russia 

                                                       Received March 16, 2000


SCIENTIFIC PROGRAM AND PRIME OBJECTIVES OF THE EXPEDITION

Cruise 15 of R/V Akademic Sergei Vavilov was carried out in accordance with the 
prior plan of action for 1999 envisaged by the "World Ocean" Federal Program 
affirmed by the Russian Government on August 10, 1998 (resolution no. 919) in 
the framework of the list "Critical Technology of the State Level" affirmed by 
the Governmental Commission on Scientific-Technological Policy on July 21, 1996, 
and the Program of the Department of Oceanology, Physics of Atmosphere, and 
Geography of the Russian Academy of Sciences.

The scientific program of oceanological investigations during cruise 15 of R/V 
Akademik Sergei Vavilov included research into the following areas:

* Distinguishable features of the interaction between the subpolar and 
  subtropical gyres in the North Atlantic.
* Estimating the natural seasonal and low-frequency variability of the 
  thermochaline water structure of the subpolar gyre in the North Atlantic 
  including its deep-sea part.
* Studying the spatial structure of the northern and western deep-sea boundary 
  currents near the eastern and western continental shelves in the North 
  Atlantic,
* Estimating the heat and salt exchange rate between the subpolar and 
  subtropical gyres in the North Atlantic.


FINANCIAL SUPPORT FOR THE EXPEDITION

The major financial source for the expedition was provided by the Ministry of 
Science and Technologies of the Russian Federation for carrying out the prior 
action envisaged by the program "Investigation of World Ocean Nature." In 
addition, the organizing expenses of the expedition were defrayed by the "Long-
Term Variability of the Meridional Water Circulation in the North Atlantic" 
project in the framework of the subprogram "Multidisciplinary Investigations of 
Oceans and Seas, Arctic and Antarctic Regions" of the "Investigations and 
Developments on Priority Lines of Development of Civil Sciences and 
Technologies" Federal Purposive Scientific-Technological Program, direct 
financial support of the expeditions of the Russian Academy of Sciences, and 
INTAS-RFBR 95-0972 grant.


ROUTE OF THE EXPEDITION

The expedition began on October 13, 1999. The ship put out from Kaliningrad on 
October 15 and called at the port of Hamburg (Germany), where scientific 
equipment and a cable-rope for STD probes were loaded. On October 19, the ship 
left Hamburg and on October 23, it reached the observation field. The location 
of the section planned corresponded to the standard section of WOCE A02 (the 
figure). The coordinates of the initial and end points of the section were 
48°16' N, 09°34' W and 43°23' N, 49°32' W, respectively. The last station of the 
section was performed on October 7.  On October 9 the ship called at the port of 
Halifax, where the equipment obtained in Hamburg was unloaded and sent to 
Germany in a container. The scientific team of the expedition, which consisted 
of 14 scientists from the Shirshov Institute of Oceanology, Moscow State 
University, and All-Russia Scientific-Research Institute for Marine Fisheries 
and Oceanography, left the ship for Moscow on November 10.


METHODS AND MEANS FOR MEASUREMENTS AND DATA PROCESSING

The vertical distributions of temperature and salinity were observed with the 
use of an oceanographic MarkIIIC/WOCE CTD probe supplied with an Intelligent 
Rosette Sampling System developed by General Oceanics with 24 Niskin bottle 
samplers 2.5 L in volume.

The offboard unit was provided with an altimeter (BENTHOS 2110 Altimeter) 
designed for determining the location of the set with respect to the bottom. The 
signals from the altimeter were transmitted to the onboard computer in the real 
time mode, which provided the measurements in the vicinity of the bottom.

The equipment for the deep-water hydrological operations was placed at the 
expedition's disposal by the Federal Department of Marine Navigation and 
Hydrography (Bundesamt für Seeschiffahrt und Hydrographie- BSH, Hamburg, 
Germany) under the auspices of the Russian Foundation for Basic Research-INTAS 
joint grant no. 95/0972.

The salinity analysis in the water samples was performed on board the ship with 
the use of a Guideline. AUTOSAL 8400 salinometer. The amount of dissolved oxygen 
was determined by the Winkler method modified at the Shirshov Institute of 
Oceanology, RAS. The concentration of silicates, phosphates, and nitrites was 
determined with the KFK set. Silicates were determined by the Korolev method. 
Phosphates were determined by the Morphy-Riley method modified by Sugawara, and 
nitrites were determined by the Bendschneider-Robinsonson method.


EXTENT OF THE WORK

In total, 58 deep-sea hydrological stations were carried out. Among them, 21 
stations were carried out in the eastern basin and 37 stations were performed in 
the western one. The following observations were performed at each deep-sea 
hydrological station.

* Recording the vertical distributions of temperature, electric conductivity, 
  and content of dissolved oxygen.
* Sampling water at several levels for the subsequent laboratory determination 
  of salinity, dissolved oxygen, silicates, and phosphates.
* Measurement of air temperature, velocity, and wind direction, as well as 
  observations of the sea surface condition.


PRELIMINARY SCIENTIFIC RESULTS

To reveal the climatic variability of the thermohaline water structure, the 
expeditionary data were compared with the data obtained in this section by 
German oceanologists during 1993-1998 and placed by them at our disposal during 
our visit to Hamburg. To estimate the intensity of mass, heat, and salt transfer 
across the plane of the section, we used the method described in [1]. As a 
reference surface, we used the isopycnal _2000, and the total flow was presented 
as a superposition of geostrophic, Ekman's, and barotropic (determined from the 
Sverdrup relationship) currents. The integral mass transfer across the section 
plane by each of the components was assumed to he zero (the location of the 
reference isopycnal surface varied depending on this condition).


The major conclusions made on the basis of the data analysis are the following.

1. The climatic change of the characteristics of the Labrador water mass (LWM) 
   core in the North Atlantic is found to be proceeding. In the Western Basin, 
   from 1993 to 1996, a sharp drop of the LWM temperature has been observed 
   without significant variations in salinity.  Since 1996, the temperature and 
   salinity of the LWM have been increasing. From 1996 to 1999, the temperature 
   and salinity has increased on average by O.1€C and 0.02”, respectively. This 
   process is an isopycnic one. In the Eastern Basin, the general tendency of 
   variability of the LWM characteristics is the same. The temperature of the 
   LWM core, however, had begun to increase here only since 1998, and salinity 
   variations are less important.

2. The time of propagation of the LWM from the source up to 48°N was determined 
   on the basis of the known heating and salinating characteristics of the LWM 
   in the Labrador Sea since 1994 [3]. For the region of the western deep-sea 
   boundary current (WDBC) and the eastern slope of the Mid-Atlantic Ridge, this 
   interval is two and four years, respectively. These values precisely 
   correspond to the travelling velocities of the climatic signal in the LSW 
   layer calculated previously within the frames of the project.

3. Stable desalination and cooling of the deep-water layer occurred in the 
   Western Basin of the Northern Atlantic along 48°N from 1993 to 1999. This is 
   best pronounced in the Northeastern deep-sea water mass (NWDM) layer entering 
   the Western Basin through the Charlie-Gibbs Fracture Zone. The cooling of the 
   core of NWDM reaches 0.3°C in the WDBC and 0.2°C near the western slope of 
   the Mid-Atlantic Ridge. The corresponding values of desalination are 0.015 
   and 0.01”. The desalination and cooling of the deep-sea water are slightly 
   less pronounced in the Northwestern deep-sea water mass, the source for which 
   is the intermediate water of Arctic origin entering the North Atlantic 
   through the Denmark Strait threshold.

4. In comparison with 1997-1998, marked changes in T,S characteristics of the 
   Mediterranean water is found in the eastern basin of the North Atlantic. The 
   temperature and salinity of the core cast of the Mid-Atlantic Ridge have 
   increased by 0.5°C and 0.15”, respectively. One of the possible reasons is 
   the reduction of the northward transport of Mediterranean water due to the 
   reconstruction of the circulation in mid-latitudes.

5. Calculations of the mass and heat transfer across the plane of the zonal 
   section for the principal water masses show that the maximum intensification 
   of the meridional thermohaline circulation occurs in 1999 in comparison with 
   previous years: the southward deep sea water flow and the northward heat flux 
   were more intensive than their mean climatic values by 20%. Thus, the heat 
   flux in the autumn of 1999 achieved 0.75 PW, which is by 0.12-0.15 PW greater 
   than the mean value.


REFERENCES

1. Koltermann, K.P., Sokov, AX, Tereschenkov, V.P., Dobrolyubov, S.A., 
   Lorbacher, K., and Sy, A., Decadal Changes in the Thermohaline Circulation of 
   the North Atlantic, Deep-Sea Research II, 1999, vol. 46, nos. 1-2, pp.109-
   138.

2. Saunders, P.M., The Accuracy of Measurements of Salinity, Oxygen, and 
   20448.

3. Sy, A., Rhein, M., Lazier, J., Koltermann, KR, Meincke, J., Putzka, A., and 
   Bersch, M., Surprisingly Rapid Spreading of Newly Formed Intermediate Waters 
   Across the North Atlantic Ocean, Nature, 1997, vol. 386, pp. 675-679.
