Sub-Antarctic Islands

During the past decades the regional climate of the Antarctic Peninsula has seen an unprecedented increase in atmospheric temperatures, leading among other things to the recession of glaciers. One of the key questions is whether this recent warming is a one off situation or whether it is part of a natural cycle. Aim of the marine geology in the region is to reconstruct past climate between 2000-4000 years ago in order to make comparisons with modern climatic observations.

For that reason, this leg of the expedition is of utmost interest for Juliane Müller (AWI). With her Helmholtz early-career research group “PALICE” which will begin from April 2016 at AWI and the University of Bremen, her research focuses on understanding sea-ice changes in, and associated climate oscillations around, Antarctica. Sea-ice has a strong albedo effect (reflection of solar radiation) and effectively caps exchanges between the ocean and atmosphere. It therefore plays a critical role in the heat transfer and budget of the polar regions. Moreover sea-ice influences algal growth, which considerably contributes to sequestering CO₂ from the atmosphere. The degree to which the current Antarctic sea-ice cover is part of a natural cycle of variability, or not, is still being debated. Looking into past sea-ice changes will provide further insight into answering this question.

The marine sediment cores obtained from this expedition provide archives of past environmental change through use of “proxies”. In order to know where and for how long sea-ice persisted, Juliane Müller’s research group will be undertaking organic-geochemical analysis of the cores obtained. In particular their work will deal with identifying organic molecules produced by diatoms living in the sea-ice. As sea-ice retreats, these algal molecules descend to the ocean floor where they are then preserved in the sediment column. Algal molecules are targeted, as opposed to algal shells, due to the better preservation potential. These molecules are also referred to as geochemical fossils or biomarkers. The PALICE group will assess whether differences in regional fossil algal occurrence exists and if ocean surface water temperatures  and intensity of sea-ice cover can be quantified through use of biomarkers. This data is important to inform climate models. If the empirical data does not match that of models, the latter likely needs refining.

To present proxy-reconstruction of the palaeo-sea ice cover surrounding Antarctica have been based on microfossil investigations. However, regional absence or poor preservation of the latter exists, hence alternative methods are required. The cores we obtained from the Bransfield Strait contain well preserved diatoms hence are ideally suited for developing biomarker analysis for palaeo-climatic reconstructions. We revisited some locations that had been previously cored with Polarstern in the 1980’s, as fresh material is required for biomarker analysis. The already existent analysis of the previous sites (such as diatom counts) will complement the biomarker data developed from the fresh cores.

Obtaining the sediment cores in the Bransfield Strait (open ocean between the Antarctic Peninsula and South-Shetland Islands) took most of the week. Synchronously the Geodesy group (Lutz Eberlein & Peter Busch, Univ. Dresden) undertook a number of helicopter flights. Aim of the geodetic work is to take repeat high precision measurements at predefined (in some cases re-visited) bedrock exposures, using the global positioning system (GPS), to obtain information of the horizontal and vertical land movement in millimetre per year. The measured horizontal displacement is predominantly associated with the movement of the Antarctic continental plate with respect to other micro-plates within the Bransfield Strait (~ movement of 1mm/year). By setting up geodetic points west and east of the Bransfield Strait the relative plate movements can be quantified. The vertical component illustrates the degree of crustal deformation associated with historical and recent ice mass loss in the region (glacier melt & recession). The viscoelastic response of the solid earth to ice unloading is also in the range of a few millimetres per year.

One of the geodetic points is located close to the Chilean Antarctic station “Arturo Prat”. The station was built by the Chilean Army in 1947 on Greenwich Island (southern most south Shetland Island) and is presently used to support scientific endeavours. We were very well received by the station commander Francisco Mayorga Morales and ample support for the geodetic work was given. During our visit we were able to get a first impression of living conditions at Arturo Prat. Similar to the AWI Neumayer Station, a small group of people man the station during winter. During the short summer season up to forty persons stay at the station.

The land geology group were also able to exploit short good weather windows to fly to several South Shetland Islands. Alessa Geiger (Uni Glasgow) and Max Zundel (U Bremen) obtained erratic and/or bedrock samples from Half Moon, Nelson, Gibbs and Elefant Island. The steep coastal terrain concomitant with snow and ice cover of some sites provided for challenging sampling. In order to land with the helicopters, near-horizontal coastal regions and high-lying ice free plateaus were selected as sampling sites. Through use of hand lens, hammer, chisel and a battery driven hand-saw we obtained several samples for thermochronology and cosmogenic nuclide exposure dating. Moreover observations of the local geology, glaciology and glacial geomorphology were made, critical for interpreting rock sample results. As analysis of the samples commences, the land geologists hope to shed more light onto the long-term tectonic and glacial histories of the Islands.

During the past two days we were mainly located around the famous Elefant Islands. This wild and predominantly glaciated Island became famous as it provided Ernest Shackleton’s crew shelter after the HMS Endurance was enclosed and demolished by pack ice in 1916 (see blog post No. 8). During deteriorating weather conditions and a heavy storm on the 10th of March, we also took shelter at Elefant Island. Luckily the weather improved and helicopter flights to Gibbs Island were possible on the 11th of March. We continue the marine geology work on the continental slopes of the Drake Passage and also reached the second biological station north of Elefant Island. All participants are well, even with 5 meter high waves – it seems one gets used to everything at some point!

Frank Lamy

Chief Scientist PS97

Position: 60°35´S; 55°42´W

(35 nautical miles north of Elefant Island.)