Full steam ahead with the sampling on the RRS James Clark Ross: ORCHESTRA Part 3…by Carol Arrowsmith

Carol sampling at the CTD on the
RRS James Clark Ross currently
 out in the Weddell Sea

Carol is half way through a research cruise across the Weddell Sea as part of ORCHESTRA, see her previous blogs Investigating the Southern Ocean: Part 1 and From Chile to the Falklands and beyond: ORCHESTRA Part 2… 

We are now cruising along the 60^oS latitude, having crossed the Drake Passage, passing Elephant Island (off the tip of the Antarctic Peninsula), between Coronation and Laurie Island and are now out in the Weddell Sea at approximately 23^oW. This leg of the ORCHESTRA hydrographic/tracer section covers the northern rim of the Weddell Gyre and is called ANDREXII (Antarctic Deep Water Rates of Export). This leg was previously sampled 10 years ago so we are interested to see the difference global warming has made to the ocean.

We are roughly half way into our sampling of sea water for temperature, salinity, dissolved oxygen, dissolved inorganic carbon, total alkalinity, inorganic nutrients as well as taking meteorological and surface ocean observations. The sample collections and data measurements are being undertaken by various teams of scientists from NOC, BAS and PML, as well as me from the BGS. My samples, for the determination of oxygen and carbon isotope ratios (to tell us about heat and carbon source), will be analysed when they arrive back at the stable isotope laboratory of the BGS head office in Nottingham later this year. We are collecting samples from various depths from 100 “stations” (stopping points on the cruise), we have collected 67 stations and collected 1200 samples so far (and its quite hard work!)…

Some of the women on board the JCR with me celebrating
International Women’s Day 2019 in the snow and hail!

The sea water samples collected from various depths in the ocean are taken using an instrument called a CTD. A CTD is a device used to measure the Conductivity (used to determine salinity), Temperature, and pressure of seawater (the D stands for "depth," which is closely related to pressure) of the ocean but also collects discrete water samples. The water samples are taken using 24 “niskin” bottles arranged around in a circular rosette. The CTD is lowered into the water with the niskin bottles opened at both ends until it reaches the maximum bottom depth. Using a weighted trigger that is sent down a cable the bottles can be closed remotely. The 24 niskins are closed at different depths as the CTD is brought back to the surface. So niskin 1 contains the deepest water sample and 24 the surface sample. Getting water samples from different depths in the ocean is important to understand how the water chemistry and physical properties changes with depth. We expect to see more anthropogenic impact in the upper few hundreds of meters of the ocean.

See my previous blogs 1 and 2:
Investigating the Southern Ocean: Part 1
From Chile to the Falklands and beyond: ORCHESTRA Part 2

ORCHESTRA is in the second year of a five year collection programme around the World’s oceans. I will be collecting samples from the RRS James Clark Ross. I will be tweeting @CarolArrowsmith and @ORCHESTRAPROJ and Facebooking (Orchestra project) along the way, as well as updating the BGS Geoblogy. Carol Arrowsmith is a chief technician in the stable isotope facility at the BGS.