RRS James Clark Ross JR20091118 (JR195, JR198)

Cruise summary report

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Cruise Info.

Ship name (ship code)

RRS James Clark Ross (74JC)

Cruise identifier

JR20091118 (JR195, JR198)

Cruise period

2009-11-18 — 2009-11-27

Status

Completed

Port of departure

Stanley, Falkland Islands (Malvinas)

Port of return

Rothera, Antarctica

Purpose

Research

Objectives

The objective of the cruise was to perform a CTD section across Drake Passage (Figure 1.1), repeating measurements made during previous research cruises for the purpose of long-term monitoring. Drake Passage is the narrowest passage through which the Antarctic Circumpolar Current (ACC) flows, and thus is a convenient location for making measurements across the entire ACC. A repeat hydrographic section across Drake Passage (SR1) was established by the World Ocean Circulation Experiment and first occupied by the R/V Meteor in 1990. Subsequently, the section was moved eastwards to lie on a satellite ground track with the northern end on the south side of Burdwood Bank, south of the Falkland Islands, and the southern end off Elephant Island at the tip of the Antarctic Peninsula. This revised section location was designated SR1b and was first occupied by the R/V Polarstern in 1992 and by RRS Discovery the same year using SeaSoar only. It has since been occupied 15 times by the UK at nearly one section per year on the RRS James Clark Ross (two exceptions: 1995 and 1998).

The objective of this section is to look at changes on interannual to decadal scales. The key objectives for the JR195 CTD section across Drake Passage are:

(i) to determine the interannual variability of the position, structure and transport of the Antarctic Circumpolar Current (ACC) in Drake Passage;
(ii) to examine the fronts associated with the ACC, and to determine their positions and strengths;
(iii) by comparing geostrophic velocities with those measured directly (by the lowered ADCP), to determine the size of ageostrophic motions, and to attempt to estimate the barotropic components;
(iv) to examine the temperature and salinity structure of the water flowing through Drake Passage, and thus identify the significant water masses;
(v) to calculate the total flux of water through Drake Passage by combining all available measurements.

Thirty one full depth stations were performed during JR195: two test stations, and 29 of the 30 nominal stations for the SR1b Drake Passage section. Two 500 m stations were added as part of POL's cruise JR198. The CTD was an underwater SBE 9 plus unit equipped with the following sensors: dual temperature and conductivity sensors, a SBE-43 oxygen probe, an Aquatracka MKIII fluorometer, a transmissometer, an upward-looking downwelling PAR sensor, and an altimeter. A downward-looking LADCP (RDI Workhorse Monitor 300 kHz) was deployed on the CTD frame at all stations, except for the two JR198 500 m stations when it was replaced by a 600 kHz LADCP from Bangor University (see separate CSR).

Various underway measurements were obtained, including navigation, VM-ADCP, sea surface temperature and salinity, water depth and various meteorological parameters.

Chief scientist

Margaret J Yelland (National Oceanography Centre, Southampton)

Project

ACCLAIM (Antarctic Circumpolar Current Levels by Altimetry and Islands Measurements)

Coordinating body

Natural Environment Research Council (NERC)

Cruise report

(30 MB)

Ocean/sea areas

General

Southern Ocean

Specific

Drake Passage

Track charts

(0.52 MB)

Measurements

Physical oceanography

Surface measurements underway (T,S)

Quantity: activity duration in days = 12
Description: JCR surface hydrography sensors suite including a fluorometer, a SBE45 thermosalinograph measuring conductivity and water temperature for salinity measurements, a hull mounted PRT100 sea surface temperature sensor (located close to the non-toxic supply intake on the hull at a depth on 6m).

Surface measurements underway (T,S)

Quantity: number of samples = 35
Description: Bottle salinity samples collected from non-toxic water supply and analysed by bench salinometer

Water bottle stations

Quantity: number of samples = 228
Description: Bottle salinity samples collected with rosette sampler analysed by bench salinometer

CTD stations

Quantity: number of stations = 31
Description: SBE911 plus CTD and rosette sampler equipped with dual temperature and conductivity sensors, SBE-43 oxygen probe, Aquatracka MKIII fluorometer, transmissometer, upward-looking downwelling PAR sensor, and altimeter.

Transparency (eg transmissometer)

Optics (eg underwater light levels)

Current profiler (eg ADCP)

Quantity: activity duration in days = 12
Description: 75 kHz RD Instruments Ocean Surveyor (OS75) Vessel Mounted ADCP

Current profiler (eg ADCP)

Quantity: number of stations = 31
Description: Downward-looking RDI Workhorse Monitor 300 kHz LADCP mounted on the CTD frame.

Other physical oceanographic measurements

Quantity: number of profiles = 20
Description: Vertical microstructure profiling was carried out on 25/11/2009 from 9:43Z to 11:36Z in an area adjacent to the Drake South shallow BPR. The VMP cast were to ~900 m and recorded standard T, C and P plus high resolution T,C, P, current shear and fluorescence.

Chemical oceanography

Oxygen

Biology and fisheries

Phytoplankton pigs (eg chlorophyll, fluorescence)

Meteorology

Incident radiation

Quantity: activity duration in days = 12
Description: short wave radiation (TIR), photosynthetically active radiation (PAR)

Other meteorological measurements

Quantity: activity duration in days = 12
Description: JCR meteorological sensors suite to measure: air temperature and humidity, atmospheric pressure, short wave radiation (TIR), photosynthetically active radiation (PAR) and wind speed and direction.

Geology and geophysics

Single-beam echosounding

Quantity: activity duration in days = 12
Description: Bathymetry by a Kongsberg EA600 single beam echo sounder

Moorings, landers, buoys

Physical oceanography