SiPCA-expedition: on ice, fish and sunlight

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SiPCA-expedition: on ice, fish and sunlight

Published on
August 4, 2017

Researchers from Wageningen Marine Research returned home from a successful sampling expedition on board of the German icebreaker RV Polarstern. Together with their partners from the Alfred Wegener Institute (Germany) they collected a lot of samples to study the sea-ice ecosystem of the Arctic Ocean. Their research is part of the Iceflux project.

Fishing under the ice

During the SiPCA expedition a lot of fishing took place. With the indispensable help of Polarstern’s crew, 20 SUIT (Surface and Under Ice Trawl) hauls were conducted to sample organisms from underneath the sea-ice, plus 15 RMT (Rectangular Midwater Trawl) hauls to sample deeper water layers. The nets contained animals such as krill, amphipods, gastropods (or sea snails) and copepods. All material was preserved for later analyses back home. Unexpectedly, in the northern part of our research area the catches from both nets contained only low numbers of animals. The bird and mammal observers also reported that there seemed to be little life in this region, which was a lot different from the southern part of our research area. Only few Polar cod were caught with the SUIT, but colleagues fishing with a bottom trawl were more successful in catching fish and were happy to share these with less fortunate but interested researchers.

The SUIT (Surface and Under-Ice Trawl) team watches the net as it shears to the side of the ship, ready to dive underneath the ice (Photo Susanne Kühn)
The SUIT (Surface and Under-Ice Trawl) team watches the net as it shears to the side of the ship, ready to dive underneath the ice (Photo Susanne Kühn)

More than just a net

The SUIT not only catches animals, but is also used to investigate properties of the sea ice environment. “The SUIT has an advanced sensor array measuring e.g. water temperature, sea-ice thickness and chlorophyll-a, which can be used to link physical habitat properties with under-ice organisms”, explains Iceflux physicist Benjamin Lange from the Alfred Wegener Institute (AWI). Chlorophyll-a is a pigment used by algae to extract energy from sunlight. The quantity of this pigment is used by researchers as an indicator for algal abundance. Light transmission and sea-ice thickness measurements done by the SUIT sensors will be used to estimate the amount of chlorophyll-a, and thus the amount of ice algae, in the sea-ice. This information can help to study the importance of sea-ice algae as a food source. To be able to estimate the chlorophyll-a from the SUIT sensors, measurements were also done on the sea-ice itself by, firstly, measuring light transmission using a sensor that is attached to an ‘L-arm’ which is put through a hole in the ice, and, secondly, by taking ice cores and measure the amount of chlorophyll-a inside after they have melted.

Team Iceflux performing light transmission measurements using an L-arm. For comparison a light sensor is held up to the sky to measure the amount of light that is available (Photo Fokje Schaafsma).
Team Iceflux performing light transmission measurements using an L-arm. For comparison a light sensor is held up to the sky to measure the amount of light that is available (Photo Fokje Schaafsma).

A mini-SUIT

Measurements on the properties of sea-ice similar to those made by SUIT were done with a Remotely Operated Vehicle (ROV) which can be deployed though a hole in the ice. “If we compare the SUIT and ROV measurements with ice-thickness measurements using a helicopter-borne electromagnetic instrument (known as the EM-bird) we can quantify sea-ice properties on different scales”, says Lange. “This information can then be combined to classify and model regional, and perhaps even the overall Arctic sea-ice habitats”. AWI biologists and physicists also developed a fishing net that can be attached to the ROV. This ‘mini-SUIT’ was successfully used to sample for instance copepods and amphipods from directly underneath the ice.

Deployment of the RMT, the Rectangular Midwater Trawl (Photo Elisa Bravo Rebolledo)
Deployment of the RMT, the Rectangular Midwater Trawl (Photo Elisa Bravo Rebolledo)
The bottom trawl is being deployed (Photo Ulrich Küster)
The bottom trawl is being deployed (Photo Ulrich Küster)
Route of Polarstern during SiPCA (by AWI)
Route of Polarstern during SiPCA (by AWI)
An example of a SUIT profile showing several parameters measured during each haul: sea ice draft, salinity, water temperature and water chlorophyll a biomass. (Graphics: Giulia Castellani)
An example of a SUIT profile showing several parameters measured during each haul: sea ice draft, salinity, water temperature and water chlorophyll a biomass. (Graphics: Giulia Castellani)
A Polar bear watches Polarstern passing by (Photo: Susanne Kühn)
A Polar bear watches Polarstern passing by (Photo: Susanne Kühn)
A Brünnich’s guillemot landed unexpectedly in Bram’s observation post. A fine occasion for a selfie! (Photo: Bram Fey)
A Brünnich’s guillemot landed unexpectedly in Bram’s observation post. A fine occasion for a selfie! (Photo: Bram Fey)
The EM-bird is flown over the sea ice by a helicopter (Photo: Susanne Kühn)
The EM-bird is flown over the sea ice by a helicopter (Photo: Susanne Kühn)