Helicopter-borne sea ice thickness measurements during cruises ARK-XX/2 and ARK-XXII/2 (SPACE) in the Arctic Ocean

Helicopter-borne electromagnetic sea ice thickness measurements were performed over the Transpolar Drift in late summers of 2001, 2004, and 2007, continuing ground-based measurements since 1991. These show an ongoing reduction of modal and mean ice thicknesses in the region of the North Pole of up to 53 and 44%, respectively, since 2001. A buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi- and second-year ice in earlier years to first-year ice in 2007, which had modal and mean summer thicknesses of 0.9 and 1.27 m. Measurements of second-year ice which still persisted at the North Pole in April 2007 indicate a reduction of late-summer second-year modal and mean ice thicknesses since 2001 of 20 and 25% to 1.65 and 1.81 m, respectively. The regime shift to younger and thinner ice could soon result in an ice free North Pole during summer.

Physical oceanography during Maria S. Merian cruise MSM21/2

Flemish Pass, located at the western subpolar margin, is a passage (sill depth 1200 m) that is constrained by the Grand Banks and the underwater plateau Flemish Cap. In addition to the Deep Western Boundary Current (DWBC) pathway offshore of Flemish Cap, Flemish Pass represents another southward transport pathway for two modes of Labrador Sea Water (LSW), the lightest component of North Atlantic Deep Water carried with the DWBC. This pathway avoids potential stirring regions east of Flemish Cap and deflection into the interior North Atlantic. Ship-based velocity measurements between 2009 and 2013 at 47°N in Flemish Pass and in the DWBC east of Flemish Cap revealed a considerable southward transport of Upper LSW through Flemish Pass (15-27%, -1.0 to -1.5 Sv). About 98% of the denser Deep LSW were carried around Flemish Cap as Flemish Pass is too shallow for considerable transport of Deep LSW. Hydrographic time series from ship-based measurements show a significant warming of 0.3°C/decade and a salinification of 0.03/decade of the Upper LSW in Flemish Pass between 1993 and 2013. Almost identical trends were found for the evolution in the Labrador Sea and in the DWBC east of Flemish Cap. This indicates that the long-term hydrographic variability of Upper LSW in Flemish Pass as well as in the DWBC at 47°N is dominated by changes in the Labrador Sea, which are advected southward. Fifty years of numerical ocean model simulations in Flemish Pass suggest that these trends are part of a multidecadal cycle.

Benthic oxygen flixes on the Washington shelf and slope

Benthic oxygen fluxes calculated from in situ microelectrode profiles arc compared with benthic flux chamber O2 uptake measurements on a transect of eight stations across the continental shelf and three stations on the slope of Washington State. Station depths ranged from 40 to 630 m and bottom-water oxygen concentrations were 127-38 µM. The fluxes measured by the two methods were similar on the slope, but on the shelf, the chamber flux exceeded the microelectrode flux by as much as a factor of 3-4. We attribute this difference to pore-water irrigation, a process which apparently accounts for the oxidation of a significant amount of organic C in the continental shelf sediments. Combining our diffusive flux data with other data demonstrates clearly that the bottomwater oxygen concentration must play some significant role in determining the sedimentary oxygen consumption rate. Numerical simulation of the microelectrode 0, profiles suggests that roughly half the diffusive 0, flux must be consumed within - 1 mm of the sediment surface. If this conclusion is correct, then the magnitude of the diffusive flux depends both on the bottom-water oxygen concentration and on the supply rate of labile C to the sediment surf'ace.

Wet and dry resistivities along three orthogonal directions of ODP Holes 185-801C and 185-1149B

The results of shore-based three-axis resistivity and X-ray computed tomography (CT) measurements on cube-shaped samples recovered during Leg 185 are presented along with moisture and density, P-wave velocity, resistivity, and X-ray CT measurements on whole-round samples of representative lithologies from Site 1149. These measurements augment the standard suite of physical properties obtained during Leg 185 from the cube samples and samples obtained adjacent to the cut cubes. Both shipboard and shore-based measurements of physical properties provide information that assists in characterizing lithologic units, correlating cored material with downhole logging data, understanding the nature of consolidation, and interpreting seismic reflection profiles.

Ocean temperature and salinity measured by CTD SRDLs deployed on southern elephant seals from King George Island with links to datasets

West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry toward ice shelves are needed to constrain future changes in melt rates. Six years of seal-acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship-based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending toward the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat toward the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet.

The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent and its impact on the near-coastal salinity, oxygen and nutrient distributions

The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent (PCUC) in January and February 2013 is investigated using a multi-platform four-dimensional observational approach. Research vessel, multiple glider and mooring-based measurements were conducted in the Peruvian upwelling regime near 12°30'S. The dataset consists of more than 10000 glider profiles and repeated vessel-based hydrography and velocity transects. It allows a detailed description of the eddy formation and its impact on the near-coastal salinity, oxygen and nutrient distributions. In early January, a strong PCUC with maximum poleward velocities of ca. 0.25 m/s at 100 to 200 m depth was observed. Starting on January 20 a subsurface anticyclonic eddy developed in the PCUC downstream of a topographic bend, suggesting flow separation as the eddy formation mechanism. The eddy core waters exhibited oxygen concentrations less than 1mol/kg, an elevated nitrogen-deficit of ca. 17µmol/l and potential vorticity close to zero, which seemed to originate from the bottom boundary layer of the continental slope. The eddy-induced across-shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean. Small scale salinity and oxygen structures were formed by along-isopycnal stirring and indications of eddy-driven oxygen ventilation of the upper oxygen minimum zone were observed. It is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open-ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off Peru.

Air photography Samoylov Island

For the qualitative description of surface properties like vegetation cover or land-water-ratio of Samoylov Island as well as for the evaluation of fetch homogeneity considerations of the eddy covariance measurements and for the up-scaling of chamber flux measurements, a detailed surface classification of the island at the sub-polygonal scale is necessary. However, up to know only grey-scale Corona satellite images from the 1960s with a resolution of 2 x 2 m and recent multi-spectral LandSat images with a resolution of 30 x 30 m were available for this region. Both are not useable for the desired classification because of missing spectral information and inadequate resolution, respectively. During the Lena 2003 expedition, a survey of the island by air photography was carried out in order to obtain images for surface classification. The photographs were taken from a helicopter on 10.07.2002, using a Canon EOS100 reflex camera, a Soligor 19-23 mm lens and colour slide film. The height from which the photographs were taken was approximately 600 meters. Due to limited flight time, not all the area of the island could be photographed and some regions could only be photographed with a slanted view. As a result, the images are of a varying quality and resolution. In Potsdam, after processing the films were scanned using a Nikon LS-2000 scanner at maximal resolution setting. This resulted in a ground resolution of the scanned images of approximately 0.3x0.3 m. The images were subsequently geo-referenced using the ENVI software and a referenced Corona image dating from 18.07.1964 (Spott, 2003). Geo-referencing was only possible for the Holocene river terrace areas; the floodplain regions in the western part of the island could not be referenced due to the lack of ground reference points. In Figure 3.7-1, the aerial view of Samoylov Island composed of the geo-referenced images is shown. Further work is necessary for the classification and interpretation of the images. If possible, air photography surveys will be carried out during future expeditions in order to determine changes in surface pattern and composition.