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Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
The Polarstern recently ended a two-month expedition in the Central Arctic in Longyearbyen, Svalbard. The international and interdisciplinary research team, led by the Alfred Wegener Institute, focused on the summer melting of Arctic sea ice in three different regimes. The comprehensive inventory revealed major differences between the various sea ice regimes and a low sea ice concentration in the study area. In addition, bacteria and zooplankton dominated the biological communities, while the expected ice algae could hardly be found.
The CONTRASTS expedition was the first to focus on the parallel comparison of different Arctic sea ice regimes during the main melt season. The research team on board, led by Dr Marcel Nicolaus, sea ice physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), successfully detected three different sea ice regimes and set up measuring stations to investigate them further. Marcel Nicolaus explains: "We were able to visit one ice floe in each of the three ice regimes four times over the past two months. Between our station work, autonomous measuring stations and cameras continuously collected data. The observations thus covered six weeks of the most intensive summer melting period."
Surprisingly, hardly any ice algae were found in or under the ice floes during the entire expedition, even in Regime 3, where little ice melt had taken place. A similar absence was observed two years earlier during the expedition ArcWatch 1, while previous expeditions consistently reported a dominance of ice algae. Whether this reflects a drastic decline of ice algae or their early melting before the CONTRASTS expedition is still unclear. However, analysis of the collected sediment samples from 4000 m depth could provide answers. With the help of microscopy and the new planktoscope system, Alexandra Kraberg (AWI) was only able to detect a few isolated ice algae cells among millions of phytoplankton. Instead, the observed high biomass was dominated by the microbial recycling of organic matter and abundant zooplankton, which transported carbon into the deep sea via fecal balls. During the study, the ecosystem dynamics depended little on light but were strongly characterized by microbial processes and trophic associations that allowed copepods and other zooplankton to feed on bacteria. Ongoing analyses are now investigating how the ice regime, atmosphere and marine conditions interact and influence ecology and the carbon cycle.
"This year, the ice concentration in the study region was unusually low in July and August, presumably due to the prevailing winds in spring, which dispersed the ice," reports Dr Marcel Nicolaus from the Arctic. "As a result, the Polarstern was often able to travel through the ice at up to 5 knots - significantly faster than the expected 2.5-3 knots. Despite its advanced age, the measured ice was relatively thin, averaging 1.5 meters, and only showed a few ridges." The sea ice extent, which will reach its annual minimum in the Arctic in September, is currently around the same level as last year and is therefore expected to be above the all-time minimum in 2012. By definition, an area is considered to be covered by sea ice if it has an ice concentration of at least 15 per cent. When calculating the extent of sea ice, it is irrelevant whether 100 % is ice-covered or up to 85 % of the water is open.
Parallel sea ice measurements, coordinated with the Polarstern expedition, were carried out as part of the IceBird campaign with the AWI research aircraft Polar 6, lead by Gerit Birnbaum (AWI). In addition to the ice thickness and distribution of melt ponds, their depth was also recorded from the air for the first time using a special laser. The distribution and depth of melt ponds have a decisive influence on the energy balance of the Arctic ice: the dark areas of water on light-colored ice reduce the albedo, i.e., the reflection of solar energy. This is why the development of melt ponds was also the focus of the work on the ice floes, with surprising results: even minimal temperature decreases of less than 0.5 °C could trigger short-term freezing processes on the surface. Dr Marcel Nicolaus describes what the research team was able to observe in July and August: "Initially, the surface melting was dominated by warm air temperatures. Then the ice increasingly melted on the underside due to oceanic heat. Rain additionally accelerated the melting and changed the surface properties, such as albedo, roughness, thermal conductivity, water content and, above all, the way the ice appears in satellite images, in a very short time. It was particularly impressive to see how melt ponds disappeared within a short period of time because they suddenly drained. This led to an increase in albedo, just like snowfall."
On board, a total of 57 scientific participants from 13 different countries worked together along with 43 crew members. They will now continue to analyze the recorded data and collected samples at their home institutes. The Polarstern is now undertaking another Arctic expedition to the sea area north-east of Greenland under the leadership of physical oceanographer Prof. Dr Torsten Kanzow from the AWI. The ship is expected to return to its home port of Bremerhaven at the end of October.
Background: the investigated sea ice regimes
A sea ice regime is defined by its age, origin, drift and the conditions in the ocean and atmosphere. The Polarstern travelled to three distinct ice regimes one after the other. Initial analyses on board the Polarstern confirmed that the team had correctly selected the ice floes representing each regime. For example, the drift routes and thus the origins of the ice could be calculated. The following regimes were investigated:
- Regime 1: one-year-old ice in the marginal ice zone (MIZ), thin and very flat. This regime is expected to dominate the Arctic in the future. This year it has drifted surprisingly strongly to the east.
- Regime 2: predominantly second and multi-year ice formed in the Russian Arctic, often with sediment inclusions. While it used to dominate the picture of the central Arctic, it is now melting increasingly before it reaches the Fram Strait.
- Regime 3: multi-year ice from the regions north of Greenland and Canada. The oldest and most deformed ice, as it was exposed to high pressures over a long period of time. This ice has receded considerably and was widespread in the past.
Dr. Marcel Nicolaus (zur Zeit noch an Bord Polarstern)
mnicolaus@awi-polarstern.de
https://we.tl/t-XYBHO89HHA Aktuelles Videomaterial
https://multimedia.awi.de/pincollection.jspx?collectionName=%7B91035899-a0fa-455... Fotos zur CONTRASTS Expedition
https://www.awi.de/ueber-uns/service/presse.html Onlineversion dieser Pressemitteilung
ROV in use
Quelle: Evgenii Salganik
Copyright: Alfred-Wegener-Institut / Evgenii Salganik
Merkmale dieser Pressemitteilung:
Journalisten, Studierende, Wissenschaftler, jedermann
Meer / Klima
überregional
Buntes aus der Wissenschaft, Forschungsprojekte
Englisch
ROV in use
Quelle: Evgenii Salganik
Copyright: Alfred-Wegener-Institut / Evgenii Salganik
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