Sea ice thickness from airborne electromagnetic (EM) induction sounding acquired from fixed-wing aircraft POLAR 5 surveys from several airports in Spitsbergen, Greenland, Canada and Alaska

While summer Arctic sea-ice extent has decreased over the past three decades, it is subject to large interannual and regional variations. Methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice-thickness distribution to recent change, limiting the ability to forecast sea-ice change over the next decade. We present results from a 2400 km long pan-Arctic airborne electromagnetic (EM) ice thickness survey in April 2009, the first-ever large-scale EM thickness dataset obtained by fixed-wing aircraft over key regions of old ice in the Arctic Ocean between Svalbard and Alaska. The data provide detailed insight into ice thickness distributions characteristic for the different regions. Comparison with previous EM surveys shows that modal thicknesses of old ice had changed little since 2007, and remained within the expected range of natural variability.

(Table 2) Organochlorine concentrations in polar bears (Ursus maritimus) from East Greenland 1999-2001

Persistent organochlorine (OC) contaminants (PCBs, DDTs, chlordanes (CHLs), dieldrin, hexachlorocyclohexanes (HCHs), chlorobenzenes (CBzs)) were determined in adipose tissue of 92 polar bears (Ursus maritimus) sampled between 1999 and 2001 in central East Greenland (69°00'N to 74°00'N). OC data were presented from subadults (S: females: <5 years and males: <6 years), adult females (F: >=5 years) and adult males (M: >=6 years). Summed chlorobiphenyl (SumCBs) concentrations (41 congeners including co-eluters), SumCHLs and SumDDTs were the dominant classes of OCs. SumCBs concentrations were found to be 6470, 8240 and 9100 ng/g lipid weight (lw) i subadults, adult females and adult males, respectively. The corresponding figures were: 2010 (S), 2220 (F) and 1710 (M) ng/ g lw for SumCHLs and 462 (S), 462 (F) and 559 (M) ng/g lw for SumDDTs. The dominant CB congeners were CB153 (32.3%), CB180 (21.4%), CB170 (12.2%) and CB138 (11.0%). The metabolite p,p'-DDE (88.2%) dominated the SumDDTs, while oxychlordane was the dominant (57.1%) CHL-related compound. Concentrations of SumCBs, SumCBzs, SumDDTs, mirex and dieldrin were highest in adult males, whereas concentrations of SumHCHs were lower than in adult females but not than those in subadults. Adult females had the lowest concentrations of SumCBzs, mirex and dieldrin. Concentrations of SumCHLs were lowest in adult males, intermediate in subadults and highest in adult females. SumCB, SumHCH and SumCHL concentrations showed high seasonal variability in adult females but remained relatively constant in adult males and subadults. In general, the OC levels in females appeared to be highest in March and lowest in January or September. Concentrations of SumCBzs and dieldrin showed seasonal variability in all three groups, with a maximum in March in adult females. SumCBz concentrations in adult males and subadults of both sexes peaked in April-July, and dieldrin concentrations peaked in April-July in subadults, but not until August in adult males. SumDDT concentrations increased from January to a maximum in April-July for subadults and in August for adults. Temporal trends within the last decade were examined by comparing the present data to the concentrations reported in samples from 1990 from the same region. SumCB, p,p'-DDE and SumHCH concentrations in 1999-2001 were 22.1%, 66.3% and 39.3% lower than the 1990 concentrations, respectively. in contrast, SumCHL and dieldrin concentrations showed differences amongst sex and age groups in the temporal trends, where present concentrations are between 24.4% to 69.3% and 27.0% to 69.0% lower, respectively, relative to the 1990 levels. However, power analysis suggested that firm conclusions could not be drawn regarding the general time trend based on these two sampling periods. The range of half-lives of the various OC classes were estimated to lie between 4.5 and 20.6 years depending on the age and sex groups considered.

Lake level reconstructions at Laguna Potrok Aike (southern Patagonia, Argentina) for the last 49 ka

Four seismic surveys and a stratigraphic record from southernmost Patagonia (Argentina) based on 51 AMS-14C dates obtained in the framework of ICDP expedition 5022 "Potrok Aike Maar Lake Sediment Archive Drilling Project" (PASADO) provide a database to compare the 106 m composite profile from the lake centre with piston cores from the littoral and outcrops in the catchment area. Based on event correlation using distinct volcanic ash layers with unique geochemical composition and optically stimulated luminescence (OSL) dates on feldspars, sediment records are firmly linked. This approach allows to match the sediment record with water levels during the past ca. 49 ka providing evidence for lake level variations. Reconstructed lake levels were 20 m higher than today during the last Glacial until the early Holocene. With the migration of the Southern Hemispheric Westerlies over this site the lake level dropped ca. 55 m for a period of two millennia. Thereupon the water balance was more positive again causing a stepwise rise of the lake level until the maximum was reached during the Little Ice Age with a subsequent lowering since the 20th century. We suggest that the mid- to late-Holocene lake level variation is caused by intensity changes of the Southern Hemispheric Westerlies.

Borehole temperature, submarine permafrost methane concentrations and pore water chemistry measured on borehole BK2, central Laptev Sea shelf

Submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the East Siberian shelf. Sediment drilled 52 m down from the sea ice in Buor Khaya Bay, central Laptev Sea revealed unfrozen sediment overlying ice-bonded permafrost. Methane concentrations in the overlying unfrozen sediment were low (mean 20 µM) but higher in the underlying ice-bonded submarine permafrost (mean 380 µM). In contrast, sulfate concentrations were substantially higher in the unfrozen sediment (mean 2.5 mM) than in the underlying submarine permafrost (mean 0.1 mM). Using deduced permafrost degradation rates, we calculate potential mean methane efflux from degrading permafrost of 120 mg/m**2 per year at this site. However, a drop of methane concentrations from 190 µM to 19 µM and a concomitant increase of methane d13C from -63 per mil to -35 per mil directly above the ice-bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column. High rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice-bonded permafrost as their source.