This study is based on the investigations of the deep marine sediment core HH13 – 089GC which was collected on a scientific cruise to Jan Mayen and East Greenland with the University’s research vessel R/V Helmer Hansen. The cruise took place between June 23rd to July 7th of 2013, and core HH13 – 089GC was collected on June 30th 2013. Table 1 provides further information about the coring location, coring depth and core length for core HH13 – 089GC.
Table 1. Coring location and other information about core HH13-089GC.
Station Date Time
HH13-089GC 30.06.13 17:47 East Greenland Scoresbysund 4
70.04.955’ N 017.44.911 W
1616 497
3.1 Compressed High-Intensity Radiated Pulse (CHIRP)
Chirp sub-bottom profilers provide vertical resolution of the upper 30 m of unconsolidated sediments.
The profilers are high-frequency-modulated marine sources in which the vertical resolution of the system is dependent on the bandwidth of the source, and the horizontal resolution is dependent on the characteristics of the source (Quinn et al., 1998).
The R/V Helmer Hanssen is equipped with a hull-mounted sub-bottom profiler (EdgeTech 3300) which was used for collecting a chirp profile. Chirp data was obtained to find suitable core sites in undisturbed sediments.
Table 2. Study Chirp profile parameters (Ship speed, ping rate, frequency and pulse length)
Ship speed (knots) Ping rate (Hz) Frequency (kHz) Pulse length (ms-1)
3.2 Swath Bathymetry
Swath bathymetry was collected on board R/V Helmer Hanssen using a multibeam eco-sounder system. The system consists of a large set of echo-sounders set in a line, opposite to the direction of travel. The eco-sounders are pointing sideways and each is inclined at a different angle to the vertical (Denbigh, 1989). The multiple beams are sent out by the echo-sounders in a fan shape, reflected at the seafloor and recorded by the ship. The frequencies used are dependant of water depth, and the data collected provide the basis for creating a bathymetric map illustrating the seafloor morphology (https://woodshole.er.usgs.gov/operations/sfmapping/swath.htm) Collected February 2nd 2017.
The multibeam eco-sound system used on board R/V Helmer Hanssen is the Kongsberg EM 300 which can map the seafloor bathymetry down to 5000 m, using a frequency of 30 kHz and a swath width of 150 degrees.
3.3 Conductivity – temperature – depth profile (CTD)
A CTD device is an important oceanographic research tool used for continuous measurement of conductivity and temperature changes with depth. The electronic instruments of the CTD device can provide a profile of the chemical and physical properties through the entire water column above the sampling site. The conductivity can be calculated to salinity, which together with temperature provides information about water density. The measurement was done prior to coring on board the R/V Helmer Hanssen using the Seabird 911 plus CTD instrument. It is important to remember that the CTD measurements represents the water masses at this specific study area in present time.
3.4 Sediment coring
The coring was done on board the R/V Helmer Hanssen using a gravity corer. The corer consists of a core- cutter and catcher at the end of a six-meter-long steel pipe, with a weight on top. Inside of the steel pipe is a plastic liner which will eventually hold the sediment sample. The weight at the top allows the core cutter and steel pipe to penetrate the sea floor sediments, and the core catcher prevents the material from falling out during retrieval. Once retrieved and back on deck, the sediment sample lies protected inside the plastic liner which is then removed from the steel pipe, closed off, cleaned and cut into meter-sections. The sections are closed off at both ends with plastic caps and labelled with the core- name, depth, upward direction and section number. In the case of core HH13 – 089 GC, the corer managed to retrieve 4.97 m of sediments. The core was cut into five sections, four of which measured 1 m and one which measured 97 cm. The sections were kept in the University’s cooler room at approximately + 4 ᴼC until their opening in April 2016.
3.5 Multi sensor core logger (MSCL)
The multi sensor core logging was done at the laboratory at the Department of Geosciences, University of Tromsø (UiT), Norway, and the MSCL used was the GEOTEK Multi Sensor Core Logger (MSCL-S). This system can provide high resolution data concerning physical, elemental and mineralogical properties from sediment and rock cores (GEOTEK, 2014). The MSCL system can measure magnetic susceptibility, wet bulk density, p-wave velocity and p-wave amplitude, and temperature
(https://uit.no/om/enhet/artikkel?p_document_id=390245&p_dimension_id=88137&men=28927 Collected February 1st 2017).
Magnetic susceptibility
Magnetic susceptibility (MS) is a measurement of the degree of magnetization of the sediments when exposed to a magnetic field. Positive magnetic susceptibility reflects a strengthen magnetic field due to the presence of paramagnetic, ferromagnetic, ferrimagnetic or antiferromagnetic material. Negative magnetic susceptibility on the other hand reflects a weakened magnetic field due to the presence of diamagnetic material (GEOTEK, 2014). The measurement of magnetic susceptibility of core HH13-089GC was done using the MSCL loop sensor.
3.6 Laboratory work
Most of the laboratory work was carried out by the author in the laboratory of the Department of Geosciences, UiT. The work started in the beginning of April 2016 and carried out until February 2017. The dating of samples was carried out by the 14CHRONO Centre at Queen’s University in Belfast, United Kingdom, and the stable isotope analysis was carried out by the Department of Earth Science and Bjerknes Centre for Climate Research at the University of Bergen, Norway. A description of all the laboratory work will now follow.
Figure 4: 3D model of the Geotek MSCL-XCT (Figure from http://www.geotek.co.uk/products/mscl-xct).