Authors: 
T. Ernsdorf*, G. Heinemann*, and C. Drüe*

*Environmental Meteorology, University of Trier, Germany

Conference Where Poster was Originally Presented:
11th European Meteorological Society (EMS) Annual Meeting & 10th European Conference on Application of Meteorology (ECAM), Berlin, Germany, September 12-16, 2011

Abstract/Summary:
The aircraft based experiment IKAPOS (Investigation of Katabatic winds and POlynyas during Summer) was performed in June 2010 over northwestern Greenland. The main goals were studies of the summertime katabatic wind system and of the atmospheric boundary layer (ABL) over the North Water Polynya (NOW). IKAPOS is mainly based on measurements using research aircraft POLAR 5 of Alfred-Wegner-Institute (AWI, Bremerhaven). In order to study the turbulence structure and 3D spatial structures of mean quantities, POLAR 5 was instrumented with a turbulence measurement system collecting data on a nose boom sampling at a rate of 100 Hz, additional basic meteorological equipment, radiation and surface temperature sensors, laser altimeter, and photo and video cameras.

Katabatic winds play a key role in exchange processes of energy and momentum between the atmosphere and the underlying surface over the ice sheet of Greenland. During summer, cooling of the boundary layer and hence the katabatic forcing is much less than during winter, but strong winds can occur under appropriate synoptic forcing. On the other hand, the NOW represents one of the largest polynyas of the Arctic, and the air-sea interaction over the NOW has important consequences for ocean processes, ice formation, gas exchange and biology.

For different synoptic situations four flights over the NOW and one flight each over the Humboldt and the Steenstrup Glaciers were performed. Over the glaciers, katabatic winds with up to 14 m/s wind speed were found. Over the NOW, a stable, but fully turbulent ABL was present during conditions of strong and relatively warm synoptically induced northerly winds. Strong surface inversions were found in the lowest 100 m – 200 m agl. As a consequence of channeling effects at Smith Sound a well-pronounced low-level jet with wind speed maxima of more than 20 m/s was detected. Thus wind-induced sea-ice export from the Nares Strait is considerably increased.

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Authors:
Ines Tavernier*, Elie Verleyen*, Dominic A. Hodgson**, Katrien Heirman***, Satoshi Imura****, Sakae Kudoh****, Koen Sabbe*, Marc De Batist**, Ann-Eline Debeer*, and Wim Vyverman* 

* Protistolgy and Aquatic Ecology – Ghent University, Ghent, Belgium
** British Antarctic Survey – Cambridge, UK
*** Renard Centre of Marine Geology –Ghent University, Ghent, Belgium
**** National Institue of Polar Research – Tokyo, Japan

Originally presented at:
VLIZ young scientists' day 2011, Bruges, Belgium (25 February 2011)

Abstract/Summary:
The past two millennia are of particular interest to the understanding of the Earth’s Climate System, because the boundary conditions of the climate did not change dramatically. The Northern Hemisphere (NH) climate is in that timeframe characterized by three main periods of climate change, namely the Medieval Warm Period (MWP; 1100-700 yr BP), the Little Ice Age (LIA; 500-100 yr BP) and the recent temperature increase. For the Southern Hemisphere (SH), the occurrence and timing of these climate anomalies are however less consistent (Verleyen et al. in press), probably due to relative paucity of proxy data (Mann et al. 2008). We aim to reconstruct climate variability during the past two millennia in the Lützow Holm Bay region, East Antarctica by means of a multi-proxy analysis on lake sediments. The distinct zones in the cores, based on diatom, pigment and lithostratigraphic analyses, correspond to a shift from marine to lacustrine conditions with a clear transition zone in between. These different environmental conditions provide information on coastal oceanographic conditions between 1975 and 1280 cal. yr BP, and on limnological conditions between 1155 cal. yr BP and present. The marine part of the sediment cores likely reflects ecological changes such as a declining water depth causing changes in light climate and sea ice dynamics as a result of lake isolation rather than climate variability. Between 640 and 560 cal. yr BP, the relatively higher chlorophyll and carotenoid concentrations and higher diatom productivity, are linked to a higher primary productivity and hence point to the presence of a slightly warmer period. This warm period shows a delayed response by c. 150 years compared to the NH MWP, which confirms the simulations by Goosse et al. (2004). There is no evidence for a LIA-like event in this region, similar to previous findings in East Antarctica (Verleyen et al. in press). The data from the upper centimeters of the core point to only very small direct and/or indirect changes in snowfall during the recent decades and are in agreement with a relatively modest warming in East Antarctica, probably related to a buffering effect of the ozone hole (Marshall et al. 2009). We conclude that there still is a strong need for additional well-dated high-resolution records to test the apparent interhemispherical differences in paleoclimate variability.

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Authors:
Anja Bock*, Julian Kinzel**, Synnøve M. Kolstø***, Ditte Mogensen****, Torgeir O. Røthe*** 

* University of Marburg, Germany
** University of Kiel, Germany
*** University of Bergen, Norway
**** University of Helsinki, Finland

Originally presented at:
IPY Field School 2011, UNIS, Svalbard, Norway

Abstract/Summary:
Billefjorden (BF) is the innermost branch of Isfjorden (IF), located at the west coast of Spitsbergen. Due to a shallow sill at its entrance, BF acts as an archive of the previous year's winter conditions in IF, as it accumulates locally produced brine water during sea ice production (winter water mass transformation). Thus, polynya activity is mirrored in bottom water properties of BF. CTD cross- and along sections in both fjord systems are obtained in order to identify respective water masses and quantify the eastward penetration of relatively warm waters originating from the West Spitsbergen Current (WSC). This study aims to estimate the effect of sea ice production on the water masses in BF during winter 2010/11. Experimental results are verified by means of a 1D, atmospherically forced polynya model. Our findings indicate that, compared to former winters, winter water mass transformation during the winter season 2010/11 was more effective, indicated by one of the densest bottom water masses in BF since 2000. Respective polynya model outputs confirm this conclusion, suggesting rather large sea ice production due to a great spatial polynya extent.

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Authors:
Alexander Haumann*, Jan van Angelen*, Jan Lenaerts*, and Michiel van den Broeke*

* Institute for Marine and Atmospheric research Utrecht, University of Utrecht, The Netherlands

Originally presented at:
ResClim Summer School: Role of sea ice in the climate system

Abstract/Summary:
We gain insights into many characteristics of the temporal and spatial variability of the sea ice cover by studying wind driven sea ice transport in the Southern Ocean. From a satellite record (1989-2006) of sea ice concentration and sea ice motion, key parameters were deduced which reveal the evolution and distribution of sea ice. We use output from a regional climate model to analyze the surface wind field over Antarctica and the sea ice covered ocean. The regions of the largest sea ice extent, the Ross and Weddell Sea, are also those areas where most of the sea ice transport takes place and where its variability is the largest. Visualizations of directional constancy of the wind and sea ice transport show that spatial patterns of persistent southerly or south-easterly winds along the Antarctic coast coincide with those of ice transport. Adjacent to the large Ross ice shelve constant outflow of cold air takes place almost year-round. Here, sea ice is constantly exported from the coastal region, and large polynyas form. As the cold winds not only lead to sea ice transport but also support refreezing of the open water, it is not surprising that in these areas large sea ice production rates have been found. An index has been deduced that captures the outflow of cold continental air from the Ross Ice Shelf. We show that the long-term variations in outflow correlate well with changes in the sea ice extent in the Ross Sea sector. The results suggest, that the positive trend in sea ice extent of this region might be associated with an increasing cold air outflow.

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