WOCE Line:        AR19
WOCE ExpoCode:    06GA350_1
Cruise Plan:      Gauss Cruise No. 350/1

Expedition:       MEridional TRAnsports in the North Atlantic (MeTRaNA)

Ship:             FS Gauss, DBBX, 
                  L.o.a 68.9 m, 1599 GRT, 
                  Inmarsat 3218 111210
                  email: science.gauss@bsh.d400.de
Ports:            Hamburg, Germany  via Horta, Azores   to St. John´s, Canada
                  Eastbound St John´s via great circle to Irish shelf - Hamburg
Dates:            06 May 2000 - 05 July 2000

Chief Scientist:  K. Peter Koltermann 
                  Bundesamt für Seeschiffahrt und Hydrographie
                  POB 30 12 20
                  D-20305  Hamburg
                  Germany
                  Tel:      49-40-3190 3540
                  FAX:      49-40-3190 5000
                  Internet: koltermann@bsh.d400.de



Overview

We plan to run the WOCE repeat section AR19 in the North Atlantic Ocean again 
along nominally 48( N to WHP one-time survey standards in June 2000. The section 
runs from the Irish Shelf at 49( 10'N, 10(W along the track of the Hudson 1982 
cruise and essentially the Discovery track of 1957 to 47(N, 27(W, continuing to  
42(N, 45(W and cutting onto the Newfoundland Shelf to 43( 30'N, 50(W. The latter 
part parallels the former BIO mooring array. This section essentially follows 
the zero wind stress line, separating the subpolar from the subtropical gyre. 
This track has been worked with identical station positions before in 1993 
(Gauss 226), 1994 (Meteor M30/2 to full WHP one-time standards), in June 1996 
(FS Gauss 276) and in June 1997 (Meteor M39/3) and in June 1998 (Gauss G316/1).

The section is to quantify the changes in water mass properties and 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. It will be used to determine the Meridional Overturning 
Circulation MOC in the Atlantic. 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, nutrients and oxygen content. These data will be used to estimate 
geostrophic velocities and transports, and to map properties, mainly nutrient 
distributions, 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 (G226/2), Meteor M30/2 in October 1994 and Meteor M39/3 in June 
1997 as A2 and as AR19 with FS Gauss in May/June 1996 (G276/1) and June 1998 
(G316/1). In the context of previous occupations since 1957 (IGY) this data will 
provide another estimate of the MOC at this latitude. Its variations have shown 
a systematic pattern and appear to be linked to large-scale changes in the 
forcing and water mass modifications. A close linkage to changes in the NAO 
index have recently been published by Lorbacher (2000).

Measurements planned include ca. 85 CTD-stations with a Neil Brown MkIIIb CTDO 
and water samples with a GO 24x10 l rosette system at 24 levels. Samples will be 
analysed 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. A l-ADCP will be deployed on each cast to 
measure the vertical profile of velocity.

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. 

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 service of two full-depth moorings west of the 
Mid-Atlantic Ridge at sites occupied from 1993 to 1995 and since 1996. All 
moorings will be recovered in the summer of 1998. Also seven profiling floats, 
APEX will be deployed across and in the vicinity of the moorings, re-seeding 
previous sites.

Gauss will again work a hydrographic section following the great circle between 
Flemish Cap and Porcupine Bank on the Irish shelf on the eastbound voyage. The 
specifications follow the AR19 details. The previous coverage was in 1998 with 
Gauss on G316/2.


Scientific Goals

Besides providing estimates of the water mass characteristics, their spreading 
paths and mixing history as a snap-shot in early summer of 1997, the data from 
this cruise are to be compared with historical 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 48(N that continued with this 
re-occupation with FS Meteor M39/3 in June 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 140 almost monthly repeats since June 1988, resolving monthly to 
annual changes.

The previous 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 1000 m. The 1998 data indicate that this invasion has slowed down. But the 
winter 1999/2000 SST in the eastern North Atlantic are again anomalously warm, 
compared to long-term climatologies.

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 Scripps 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 responsibilities

The major groups involved in this WHP programme are the BSH/CTD - group, a BSH 
underway sampling group. Oxygen and nutrients measurements as well as CO2-
sampling to JGOFS standards will be done as a joint operation by a group from 
IfM Kiel.

Persons to contact are besides the chief scientist:

               Principal Investigators
----------------------------------------------------------
CTD operation            K.P. Koltermann/G.Stelter; BSH
CTD processing           H. Mauritz, BSH
L-ADCP                   G. Stelter, BSH
ADCP                     K. Jancke, BSH
salinity                 P. Einfeld, BSH
oxygen                   H. Johannsen/IfMK, F. Schmiel/BSH
nutrients                H. Johannsen/IfMK 
underway measurements    G. Stelter, BSH
moorings                 K.P. Koltermann, H. Giese /BSH
XBT                      A. Sy, BSH
CO2                      C. Neill, H. Lüger, IfMK
N15-sampling             H. Lüger, IfMK
          
                Cruise participants
----------------------------------------------------------
Peter Koltermann (BSH)   chief scientist
Gerd Stelter (BSH)       data quality, operations
Petra Einfeld (BSH)      salinity 
Gerd Stelter (BSH)       CTD/rosette electronics
Holger Giese (BSH)       moorings, moored instruments
Heiko Mauritz (BSH)      CTD processing
Hergen Johannsen (IfMK)  nutrients
Franziska Schmiel (BSH)  oxygen
Heike Lueger (IfMK)      CO2-components
Craig Neill (IfMK)       CO2-components
Ilse Gottschalk (BSH)    hydro watch
Victor Gouretski (IfMK)  hydro watch
Katja Lorbacher (BSH)    hydro watch
Helmut Rick (BSH)        hydro watch


Associated work

Moorings

Full-depth moorings will be serviced 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-K1     46 20N     30 00W    3200 5cm,4seacats  Koltermann
deploy June 2000
recover Jun 01
3 Tempchains
                                                  
BSH-K3     45 20N     33 08W    3900 5cm,4seacats  Koltermann
deploy June 2000
recover Jun 01
3 Tempchains



P-ALACE

Across and west of the Mid-Atlantic Ridge  seven APEX floats will be deployed at 
1500 m depth according to the specifications and as part of the North Atlantic 
Float Programmes.


CO2-sampling

A complete suite of samples for determining the components of the CO2-system 
will be collected and analysed on board (D. Wallace, IfMK). Previous work on 
this section in 1994 (M30/2) and 1997 (M39/3) has shown a considerable 
variability that seem to be intimately associated with the observed changes in 
the meridional overturning circulation MOC.

N-15 sampling

On an experimental basis water samples will be collected to investigate the role 
of nitrate fixation of the role of the N-budget in the North Atlantic (GKSS, 
Voss).  N15-isotope pattern of nitrate will be investigated for the subtropical 
part of the North Atlantic where it can be assumed that the N2-fixation is 
underestimated.
