RRS Discovery D308

Cruise summary report

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Cruise Info.

Ship name (ship code)

RRS Discovery (74E3)

Cruise identifier

D308

Cruise period

2006-07-24 — 2006-08-15

Status

Completed

Port of departure

St. John's, Canada

Port of return

St. John's, Canada

Purpose

Research

Objectives

RRS Discovery cruise 308 was the fourth field campaign of the project RAPID-WAVE (West Atlantic Variability Experiment), funded by the NERC Rapid Climate Change thematic programme (RAPID).

RAPID-WAVE aims at investigating how signals associated with changes in the Atlantic meridional overturning circulation propagate along the Atlantic deep western boundary current. As part of the project, two cruises took place in 2004. In the first one, a line of 6 Bottom Pressure Recorders (BPR) was deployed in an operation area approximately located at 36.5 N 67.5 W. In the second one, two additional lines of 6 BPRs and 5 CTD moorings each were deployed on the continental shelf break approximately south of St. Johns and southeast of Halifax, respectively.

The aim of D308 was to recover and redeploy the BPRs and moorings deployed in 2004 along the St. Johns and Halifax lines. In conjunction with the recovery/redeployment operations, CTD casts were planned to be carried out and to include helium, tritium and oxygen sampling (for calibration of the CTD oxygen sensor). Measurement of tritium-helium ratios provides estimates of ventilation age up to about 20 year and is therefore very useful for inferring timescales of water-mass age and tracer transport by the Atlantic deep western boundary current.

The cruise encountered mixed success as regards the recovery of instruments: only 50% of the BPRs and 20% of the moorings could be retreived. All planned CTD casts and sampling operations were completed.

Chief scientist

Miguel Angel Morales Maqueda (Proudman Oceanographic Laboratory)

Project

Rapid Climate Change (RAPID)

Coordinating body

Natural Environment Research Council

Cruise report

(4.97 MB)

Ocean/sea areas

General

North West Atlantic Ocean (limit 40W)

Specific

Continental slope southwest of Grand Banks, and continental slope southeast of Nova Scotia

Track charts

(0.02 MB)

Measurements

Physical oceanography

Surface measurements underway (T,S)

Quantity: activity duration in days = 21
Description: The Discovery "surfmet" package was switched on for the duration of the cruise, providing thermosalinograph measurements (sea surface temperature, conductivity, fluorescence, beam transmission) and meteorology measurements (barometric pressure, wind speed & direction, air temperature, humidity, photosynthetically-active radiation and total incidence radiation). True wind speed and direction (rather than relative to ship) were derived, and uncalibrated sea surface salinity.

CTD stations

Quantity: number of stations = 2
Description: CTD stations conducted with UKORS SeaBird 911+ instrument:- Test site: 25/7/06, 20:33Z, to 550 m, 43 43.1N 052 14.0W Test site: 27/7/06, 22:03Z, 3150m depth, 42 54.3N 52 28.8W For each of these stations, two 300kHz LADCPs (downward and upward-looking), an oxygen sensor, a fluorometer, a transmissometer, a back scatter sensor and an altimeter were fitted on the CTD frame

CTD stations

Quantity: number of stations = 6
Description: CTD stations conducted with UKORS SeaBird 911+ instrument:- Site A0: 29/7/06, 03:53Z, 1770m depth, 43 15.7 N, 52 11.2 W Site A1: 28/7/06, 22:59Z, 2205m depth, 43 13.4 N, 52 16.5 W Site A2: 28/7/06, 18:08Z, 2785m depth, 43 07.9 N, 52 23.6 W Site A3: 11/8/06, 21:52Z, 3150m depth, 42 55.7 N, 52 28.5 W Site A4: 12/8/06, 14:57Z, 3630m depth, 42 39.9 N, 52 38.7 W Site A5: 12/8/06, 09:35Z, 4080m depth, 42 29.1 N, 52 50.2 W For each of these stations, two 300kHz LADCPs (downward and upward-looking), an oxygen sensor, a fluorometer, a transmissometer, a back scatter sensor and an altimeter were fitted on the CTD frame

CTD stations

Quantity: number of stations = 8
Description: CTD stations conducted with UKORS SeaBird 911+ instrument:- Site B0: 01/8/06, 06:40Z, 1710m depth, 43 00.3 N, 60 55.4 W Site B1: 06/8/06, 14:38Z, 2180m depth, 42 55.4 N, 60 51.9 W Site B2: 01/8/06, 23:09Z, 2680m depth, 42 49.4 N, 60 46.3 W Site B2, 06/8/06, 11:47Z, 2660m depth, 42 50.0 N, 60 46.7 W Site B3: 04/8/06, 22:42Z, 3310m depth, 42 38.4 N, 60 41.0 W Site B4: 06/8/06, 21:49Z, 3660m depth, 42 25.7 N, 60 26.2 W Site B5: 04/8/06, 02:23Z, 4100m depth, 42 13.1 N, 60 16.6 W Site B5: 08/8/06, 00:36Z, 4020m depth, 42 15.1 N, 60 18.0 W For each of these stations, two 300kHz LADCPs (downward and upward-looking), an oxygen sensor, a fluorometer, a transmissometer, a back scatter sensor and an altimeter were fitted on the CTD frame Note that two CTD casts were carried out on site B2. The second one was needed to collect a near bottom sample that was omitted in the first cast. No other bottle samples were taken in this second cast. Note that two CTD casts were carried out on site B5. The second cast was made in order to calibrate the SBE37 instruments to be deployed in the UKORS moorings. No water samples were taken in this second cast.

CTD stations

Quantity: number of stations = 3
Description: CTD stations conducted with UKORS SeaBird 911+ instrument:- Site C1: 09/8/06, 21:52Z, 4560m depth, 41 48.0 N, 60 00.0 W Site C2: 10/8/06, 18:08Z, 4760m depth, 41 57.3 N, 56 34.0 W Site C3: 11/8/06, 11:37Z, 4910m depth, 42 06.0 N, 53 09.3 W

Geochemical tracers (eg freons)

Quantity: number of stations = 19
Description: Helium and tritium tracer samples were drawn from Niskin bottles on above CTD casts. Samples will be shipped back to UK. Between 11 and 16 helium/tritium samples were drawn from each cast. Six oxygen samples were also taken per cast for calibration of the oxygen sensor.

Chemical oceanography

Oxygen

Meteorology

Incident radiation

Routine standard measurements

Geology and geophysics

Single-beam echosounding

Quantity: activity duration in days = 21
Description: The Simrad EA500 single-beam echosounder was switched on for the duration of the cruise. Corrected depth was calculated using Carter tables. Some manual cleaning of this data was done routinely.

Moorings, landers, buoys

Physical oceanography