WOCE Line:        AR19
EcpoCode:         06GA276_2

Cruise Plan       Gauss cruise Nr. 276
Expedition:       MEridional TRAnsports in the North Atlantic (METRANA 96)
Ship:             FS Gauss, DBBX, L.o.a 68.9 m, 1599 GRT, Inmarsat 3218 111210
Ports:            Hamburg to Halifax, NS, Canada to Hamburg, Germany
Dates:            04 May 1996 - 02 Jul 1996
Chief Scientists: K. Peter Koltermann (westbound),
                  Alexander Sy (eastbound)
                  Bundesamt f Seeschiffahrt und Hydrographie
                  D-2000  Hamburg 20305
                  Germany
                  Tel: 49-40-3190 3540
                  FAX: 49-40-3190 5000
                  Email: KoltermannOo bsh.d400.de
                  Email: Sy@ bsh.d400.de

OVERVIEW

We plan to work the WOCE section AR19 in the repeat mode AR19 in the North 
Atlantic Ocean again along nominally 48 N to WHP standards with a reduced 
parameter set in May-June 1996. The section will run from the Irish Shelf at 49 
10'N, 10W along the track of the Hudson 1982 cruise and essentially the 
Discovery track of 1957 to 47N, 27W, continuing to 42N, 45W and cutting onto the 
Newfoundland Shelf to 43 30'N, 50W. The latter part parallels the former BIO 
mooring array. This track has been worked before in 1993 (Gauss 226) and 1994 
(Meteor M30/2).

The section is to measure the northward flow of the North Atlantic Current and 
the southward recirculation in the Eastern Basin. The southward flow of the 
Western Boundary Current and the boundary current regimes on both sides of the 
Mid-Atlantic Ridge (MAR) are to be well resolved. The cruise aims to improve the 
scientific knowledge of the distribution and sources of water masses, and their 
flows, velocities and patterns by obtaining high-accuracy measurements of 
temperature, salinity and oxygen content. These data will be used to estimate 
geostrophic velocities and transports, and to map properties, mainly nutrient 
distribution, to deduce the circulation over the entire depth, particularly of 
the deep basins. Previous recent occupations have been with Gauss 226 in July 
1993 as AR19 and Meteor M30/2 in October 1994 as AR19.

Measurements planned include ca. 85 CTD-stations with a Neil Brown MkIIIb CTDO 
and water samples with a GO 24xlO I rosette system at 24 - 36 levels. Samples 
will be analyzed on board for salinity, oxygen and nutrients (silicate, nitrate, 
nitrite and phosphate). Duplicate samples for salinity will be drawn at random 
for parallel analysis on board and ashore. In addition 18O-samples will be drawn 
essentially from all samples.

Hydrographic stations are planned at nominally 30 nm station spacing, with 
closer spacing over changing topography (500 m depth steps) and slightly larger 
spacing over abyssal plains (50 nm) if time becomes a constraint. All stations 
will be run to within 5 - 10 m from the sea floor. At most stations a pogo float 
will be used to measure the depth-averaged current.

Underway measurements will include bathymetry with a Parasound system, sub-
surface temperature and salinity from the sea-water supply and standard 
meteorological observations including a prototype of a rain-gauge to WMO 
standards. In addition deep XBTs will dropped between stations to improve the 
resolution of the temperature structure.

Ancillary work will include the deployment of two full-depth moorings west of 
the Mid-Atlantic Ridge at sites previously occupied from 1993 to 1995. All 
moorings will be turned around in 1997 unless a ship can be found to do so in 
1998.

SCIENTIFIC GOALS

Besides providing estimates of the water mass characteristics, their spreading 
paths and mixing history as a snap-shot in late spring of 1996, the data from 
this cruise are planned to be compared with historic data sets and recent 
repeats to determine long-term changes of these properties. The North Atlantic 
being the most active ocean it subsequently shows the better signal-to-noise 
ratio of these changes on time-scales of years to decades. Furthermore, the 
transport estimates from the DWBC array and other current meter arrays will be 
used to calculate the meridional transports of heat, salt and freshwater through 
this section and their changes. We also aim at describing the property transfer 
at intermediate and greater depths, between the western and eastern basins, 
either through boundary currents or spillover across the MAR.

The repeats since 1993 are part of a long-term assessment of changes in the 
transports of heat, salt and fresh-water through 48N that will continue until 
the re-occupation with FS Meteor M39/2 in July 1997 as part of the WOCE - ACCE. 
While the full-depth hydrographic sections will look at changes at time-scales 
of years and longer, an on-going XBT/XCTD programme on AX3 has already built up 
more than 100 monthly repeats since June 1.988, resolving monthly to annual 
changes.

The recent data have shown a massive invasion of newly formed LSW into the 
Northwestern Atlantic that has continued into the Northeastern Basin in 1994. 
Core properties, particularly temperature, density and core layer depth have 
changed dramatically from known estimates, suggesting a close coupling to the 
new LSW production phase in the Labrador Sea. The repeats in the 1990s also 
suggest a cooling of the bottom layers and a warming and salinification of the 
top IWO m.

By using forcing fields for momentum, fresh-water and heat exchange with the 
atmosphere from ECMWF products, we hope to resolve changes of the North Atlantic 
transports in relation to changes in these forcing fields.

DATA

Data storage and distribution information can be obtained at all time from the 
WOCE Hydrographic Programme Office at the Woods Hole Oceanographic Institution 
and from the Chief Scientist. Cruise information and information about the 
status of the data will be made available through the WOCE Data Information Unit 
WOCE DIU.

CRUISE PARTICIPANTS AND RESPONSIBILITIES

The major groups involved in this WHP repeat programme are the BSH/CTD - group, 
the BSH oxygen group, BSH nutrient group and a BSH underway sampling group. 
Oxygen isotopes will be sampled for Karen Heywood of the University of East 
Anglia, UK.

PERSONS TO CONTACT ARE BESIDES THE CHIEF SCIENTISTS:

CTD operation            K.P. Koltermann/G. Stelter
CTD processing           H.J. Weichert/H.K. Mauritz
salinity                 A. Frohse
oxygen                   I. Köper/F. Schmiel
nutrients                R. Kramer
sounding and navigation  BSH surveying group  
underway measurements    M. Stolley, A. Sy  
mooring                  K.P. Koltermann
XBT/XCTD                 A. Sy
Delphin                  A. Schulz/R. Rasmus

ASSOCIATED WORK

Full-depth moorings will be deployed at two sites west of the MAR where previous 
deployments from 1993 - 1995 have shown the need to continue the time series.

Code    latitude longitude  sounding  levels         PI
---------------------------------------------------------------
BSH-Kl    46 20N 30 OOW     3200      5cm, 4seacats  Koltermann 
   deploy June 1996                   3 Tempchains
   recover Jul 97
BSH-K3    45 20N 33 08W     3900      5cm, 4seacats  Koltermann
   deploy June 1996                   3 Tempchains
   recover Jul 97


AX3

RV Gauss will be working the AX3 section on the eastward leg from June 13 to 
July 2, 1996. AX3 has been in operation almost monthly since June 1998 with 
ships- of- opportunity. In addition to the high-density XBT work XCTDs will be 
deployed and several intercalibration stations for CTD/XCTD will be run.

C02-surface sampling will be done and an undulating vehicle (Delphin) will be 
towed eastward to measure the temperature, salinity and fluororescence 
distributions of the top 100m.
