Surface velocity fields, digital elevation models and ice front positions derived from multi-mission SAR remote sensing data at Sjögren Inlet glaciers, Antarctic Peninsula

Substantial retreat or disintegration of numerous ice shelves have been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel retreated gradually since the late 1980's and broke-up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice discharge, consequently contributing to sea level rise. We present a detailed long-term study (1993-2014) on the dynamic response of Sjögren Inlet glaciers to the disintegration of Prince Gustav Ice Shelf. We analyzed various remote sensing datasets to observe the reactions of the glaciers to the loss of the buttressing ice shelf. A strong increase in ice surface velocities was observed with maximum flow speeds reaching 2.82±0.48 m/d in 2007 and 1.50±0.32 m/d in 2004 at Sjögren and Boydell glaciers respectively. Subsequently, the flow velocities decelerated, however in late 2014, we still measured about two times the values of our first measurements in 1996. The tributary glaciers retreated 61.7±3.1 km² behind the former grounding line of the ice shelf. In regions below 1000 m a.s.l., a mean surface lowering of -68±10 m (-3.1 m/a) was observed in the period 1993-2014. The lowering rate decreased to -2.2 m/a in recent years. Based on the surface lowering rates, geodetic mass balances of the glaciers were derived for different time steps. High mass loss rate of -1.21±0.36 Gt/a was found in the earliest period (1993-2001). Due to the dynamic adjustments of the glaciers to the new boundary conditions the ice mass loss reduced to -0.59±0.11 Gt/a in the period 2012-2014, resulting in an average mass loss rate of -0.89±0.16 Gt/a (1993-2014). Including the retreat of the ice front and grounding line, a total mass change of -38.5±7.7 Gt and a contribution to sea level rise of 0.061±0.013 mm were computed. Analysis of the ice flux revealed that available bedrock elevation estimates at Sjögren Inlet are too shallow and are the major uncertainty in ice flux computations. This temporally dense time series analysis of Sjögren Inlet glaciers shows that the adjustments of tributary glaciers to ice shelf disintegration are still going on and provides detailed information of the changes in glacier dynamics.

Tab. 1: Zircon isotopic data and rock ages from the Antarctic Peninsula

Morphological and U-Pb isotope studies on sedimentary zircons reflect the orogenic evolution of their former host rocks. The orogenic history of detrital zircons from the Trinity Peninsula Formation (TPF) defines the former geological surrounding of the sedimentation basin of the TPF. Same few weil rounded, polycyclic zircons of Precambrian age and Cambrian overprint give hints for an old cratonic source rock. Because of their very low frequency compared with euhedral types, the contribution of an cratonic shield area to the bulk of the sedimentary debris is neglectable low. Euhedral zircons of granitoid origin and Carboniferous age indicate a derivation from an area of widespread Carboniferous intrusions. Except for southern South America and unsurveyed regions in the Antarctic Peninsula itself, no region could deliver zircons with a Carboniferous age record. The only acceptable explanation for the origin of these zircons is a position of the Antarctic Peninsula during the sedimentation of the TPF approximately southwest of southern South America.

Geological map of Potter Peninsula (King George Island, South Shetland Islands, Antarctic Peninsula)

We present here a new geological map of Potter Peninsula (King George Island, South Shetland Islands). Like on adjacent Barton Peninsula, the morphology on Potter Peninsula is predominantly characterized by a glacial landscape with abrasion platforms offshore, in parts steep cliffs along the coast, and a rather smooth, hilly countryside in the interior. Potter Peninsula forms part of the downthrown Warszawa Block. The volcanic sequence cropping out here belongs to the King George Island Supergroup, with an observed local minimum thickness of approx. 90 m (Kraus 2005). The most prominent morphological feature is Three Brothers Hill (196 m), a well known andesitic plug showing conspicuous columnar jointing. It marks the final stage of activity of a Paleogene volcano, whose eruption products (lava flows and pyroclastic rocks), together with hypabyssal intrusions related to the volcanism, make up most of the lithology observed on Potter Peninsula (Kraus 2005). The Three Brothers Hill volcanic complex is eroded down to its deepest levels. Thus, the stratigraphically deepest units from the initial phase of volcanic activity are cropping out in some parts (Kraus & del Valle, in Wienke et al. 2008). The lithology on Potter Peninsula comprises lava flows (~50%), pyroclastic rocks (ash-fallout, pyroclastic flow deposits, volcanic breccia and agglomerates, ~30%) and hypabyssal intrusions (dykes, sills and small subvolcanic intrusive bodies, ~20%). 40Ar/39Ar datings carried out on magmatic dykes from Potter Peninsula indicate a short, but intense intrusive event during the Lutetian (Kraus et al. 2007).

Pollen, DNA and Vegetation records from surface sediments of lacustrine lakes along a forest tundra - tundra transect at the Taymyr peninsula, northern Siberia

Reliable information of past vegetation changes are important to project future changes, especially for areas undergoing rapid transitioning such as the boreal treeline. The application of detailed sedDNA records has the potential to enhance our understanding of vegetation changes gained mainly from pollen studies of lake sediments. This study investigates sedDNA and pollen records from 31 lakes along a gradient of increasing larch forest cover in northern Siberia (Taymyr Peninsula) and compares them with vegetation field surveys within the lake's catchment. With respect to vegetation richness, sedDNA recorded 114 taxa, about half of them to species level, while pollen analyses identified 43 pollen taxa. Both approaches exceed the 31 taxa revealed by vegetation field surveys of 400 m**2 plots. From north to south, Larix percentages increase, as is consistently recorded by all three methods. Furthermore, tundra sites are separated from forested sites in the plots of the principal component analyses. Comparison of ordination results by Procrustes and Protest analyses yields a significant fit among all compared pairs of records. Despite the overall comparability of sedDNA and pollen analyses certain idiosyncrasies in the compositional signal are observed, such as high percentages of Alnus and Betula in all pollen spectra and high percentages of Salix in all sedDNA spectra. In conclusion, our results from the treeline show that sedDNA analyses perform better than pollen in recording site-specific richness (i.e. presence/absence of certain vegetation taxa in the direct vicinity of the lake) and perform as good as pollen in tracing regional vegetation composition.

Mineral, chemical and isotope compositions of clay subfractions from formations of the Srednii Peninsula, Murmansk coast of the Barents Sea

Fine-grained clay subfractions (SFs) with particle size of <0.1, 0.1-0.2, 0.2-0.3, 0.3-0.6, 0.6-2.0, and 2-5 µm separated from claystone of Upper Precambrian Pumanskaya and Poropelonskaya formations on the Srednii Peninsula were studied by transmission electron microscopy, X-ray diffraction, and Rb-Sr methods. All subfractions consist of low-temperature illite and chlorite, and contribution of chlorite decreases with diminishing particle size. The crystallinity index and I002/I001 ratio increase from coarse- to fine-grained SFs. Leaching by ammonium acetate solution and Rb-Sr systematics in combination with mineralogical and morphological data indicate that illite in Upper Proterozoic claystone from the Srednii Peninsula formed during three time intervals: 810-830, 610-620, and about 570 Ma ago. The first generation of this mineral with low Rb/Sr ratio dominates in coarse-grained SFs while the second and third generations with a high Rb/Sr ratio prevail in fine-grained SFs. All of three generations are known in Poropelon claystone, whereas Puman claystone contains only illite of the first and second generations. Geological processes responsible for multistage illite evolution in claystones are discussed.