Physical oceanography from the Drake Passage and Bransfield Strait during Meteor cruise M56

This data publication is the electronic version of hydrographical and fluorometric data which were taken during the Antarctic cruise ANT I No. 56 of 'Meteor' from November 13th to December 18th 1980. The data were measured by means of the Optik Sonde (OS) of the SFB95. The data set contains the temperature and salinity profiles, the profiles of attenuation (extinction) coefficient at 670 nm wavelength and the fluorescence of chlorophyll expressed as chlorophyll a concentration values.

Landfast sea-ice and platelet-layer thickness and conductivity of Atka Bay, Antarctica, December 2012

Ice shelves strongly impact coastal Antarctic sea-ice and the associated ecosystem through the formation of a sub-sea-ice platelet layer. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In this study, we applied a laterally-constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the landfast sea ice of Atka Bay, eastern Weddell Sea, in 2012. In addition to consistent fast-ice thickness and -conductivities along > 100 km transects; we present the first comprehensive, high resolution platelet-layer thickness and -conductivity dataset recorded on Antarctic sea ice. The reliability of the algorithm was confirmed by using synthetic data, and the inverted platelet-layer thicknesses agreed within the data uncertainty to drill-hole measurements. Ice-volume fractions were calculated from platelet-layer conductivities, revealing that an older and thicker platelet layer is denser and more compacted than a loosely attached, young platelet layer. The overall platelet-layer volume below Atka Bay fast ice suggests that the contribution of ocean/ice-shelf interaction to sea-ice volume in this region is even higher than previously thought. This study also implies that multi-frequency EM induction sounding is an effective approach in determining platelet layer volume on a larger scale than previously feasible. When applied to airborne multi-frequency EM, this method could provide a step towards an Antarctic-wide quantification of ocean/ice-shelf interaction.

Benthic oxygen and nitrogen fluxes at different time series sites in the southern North Sea, 2012 to 2014

Benthic oxygen and nitrogen fluxes were quantified within the years 2012 to 2014 at different time series sites in the southern North Sea with the benthic lander NuSObs (Nutrient and Suspension Observatory). In situ incubations of sediments, in situ bromide tracer studies, sampling of macrofauna and pore water investigations revealed considerable seasonal and spatial variations of oxygen and nitrogen fluxes. Seasonal and spatial variations of oxygen fluxes were observed between two different time series sites, covering different sediment types and/or different benthic macrofaunal communities. On a sediment type with a high content of fine grained particles (<63 µm) oxygen fluxes of -15.5 to -25.1 mmol/m**2/d (June 2012), -2.0 to -8.2 mmol/m**2/d (March 2013), -16.8 to -21.5 mmol/m**2/d (November 2013) and -6.1 mmol/m**2/d (March 2014) were measured. At the same site a highly diverse community of small species of benthic macrofauna was observed. On a sediment type with a low content of fine grained particles (<63 µm) high oxygen fluxes (-33.2 mmol/m**2/d August 2012; -47.2 to -55.1 mmol/m**2/d November 2013; -16.6 mmol/m**2/d March 2014) were observed. On this sediment type a less diverse benthic macrofaunal community, which was dominated by the large bodied suspension feeder Ensis directus, was observed. Average annual rain rates of organic carbon and organic nitrogen to the seafloor of 7.44 mol C/m**2/y and 1.34 mol N/m**2/y were estimated. On average 79% of the organic bound carbon and 95% of the organic bound nitrogen reaching the seafloor are recycled at the sediment-water interface.

Water chemistry of lakes in Zackenbergdalen between 1997-2003, East Greenland

The ecology of arctic lakes is strongly influenced by climate-generated variations in snow coverage and by the duration of the ice-free period, which, in turn, affect the physical and chemical conditions of the lakes (Wrona et al., 2005, http://www.acia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch08_Final.pdf). Most arctic lakes are characterised by a long period (8-10 months) of ice-cover, cold water and low algal biomass. The water temperature and nutrient concentrations, and most probably the nutrient input from the catchments, are closely related to the duration of snow- and ice-cover in the lakes. In years when the ice-out is late, - that is, in late July, - phytoplankton photosynthesis is limited by the lack of light and nutrients. Less food is then available to the next link in the food chain, such as copepods and daphnids, with implication on their growth rates.

Topsoil properties and abundance of Acari and Collembola species in northern Victoria Land, Antarctica

Soil fauna in the extreme conditions of Antarctica consists of a few microinvertebrate species patchily distributed at different spatial scales. Populations of the prostigmatic mite Stereotydeus belli and the collembolan Gressittacantha terranova from northern Victoria Land (Antarctica) were used as models to study the effect of soil properties on microarthropod distributions. In agreement with the general assumption that the development and distribution of life in these ecosystems is mainly controlled by abiotic factors, we found that the probability of occurrence of S. belli depends on soil moisture and texture and on the sampling period (which affects the general availability of water); surprisingly, none of the analysed variables were significantly related to the G. terranova distribution. Based on our results and literature data, we propose a theoretical model that introduces biotic interactions among the major factors driving the local distribution of collembolans in Antarctic terrestrial ecosystems.

Geochemistry on water profiles from the Kara Sea

As a part of the Russian-German project "Siberian River-Runoff (SIRRO)" the major element composition of the dissolved load and the major and trace element composition of particulate load and bottom sediment of the Yenisei River and Estuary were analyzed and examined in context of the basin lithology and climate. In addition, the processes controlling the transformation of the river load in the estuarine mixing zone were investigated. The chemical composition of the dissolved and particulate load of the Yenisei fluvial endmember is generally comparable to that of other major world rivers. The dissolved load is chiefly controlled by carbonate weathering and the chemical composition of the river suspended particulate matter (SPM) is similar to that of the North American Shale Composite (NASC), which represents the weathering product of the upper continental crust. The Chemical Index of Alteration (CIA) of the Yenisei SPM amounts to 71, which indicates moderate chemical weathering. With regard to the SPM geochemistry, the Yenisei occupies an intermediate position between the adjacent rivers Khatanga and the Lena. Drastic changes in the composition of the river load are seen in the mixing zone between fresh and salt water. While dissolved Na, Ca, Mg, K, CI, S04, F, Br, Sr and HC03 behave conservatively, dissolved Fe is completely removed from solution at very low salinities. Particulate Mn exhibits a pronounced mid-salinity minimum concomitant with a maximum of dissolved Mn, which is probably related to suboxic conditions in the area of the so-called "marginal filter", where highest turbidities are found. The Mn-minimum in SPM is paralleled by depletions of the elements Ba, Zn, Cd, Ni, Cu and V, which can be associated with manganese particles. The estuarine bottom sediments are composed of mud and sand and the sedimentological parameters of the bottom sediments have to be considered for the interpretation of the bulk geochemical data. The chemical composition of the mud is comparable to the SPM, whereas the sand is relatively enriched in Si/Al, Ba/Al, Zr/Al and Sr/Al ratios and depleted in transition metals.

Physical and chemical analysis of firn cores from Ronne Ice Shelf, Antarctica

This data on the distribution of the accumulation rate and 18O content of near-surface layers in the eastern part of the Ronne Ice Shelf, Antarctica, were derived from an analysis of 16 firn cores. The firn cores were drilled along the traverse route of the Filchner-V-Campaign in 1995. The traverse followed an ice flowline of the Foundation Ice Stream and reached the margin of the inland ice, an area which has not yet been investigated. On the ice shelf the accumulation rates decrease with distance from the coast. Ascending to the inland ice the accumulation rates again reach almost coastal values. This regional distribution is in agreement with the temperature gradient along the traverse. The 18O content of the near-surface layers is closely related to the 10 m firn temperature. They strongly decrease from the grounding line towards the inland ice. At the southernmost site at 1100 m a.s.l., the mean d18O value of the firn decreases to -40?. Ice with that isotopic signature was found in cores from the central part of the Ronne Ice Shelf just above the marine ice layer, indicating that it originates from this area. All ice deposited as snow further south was melted beneath the ice shelf after passing the grounding-line area. The time series of accumulation rate and 18O content reveal no climatic trend during the last 30-50 years.

Eruption of the Håkon Mosby mud volcano recorded by the long-term observatory on mud-volcano eruptions (LOOME) between 2009 and 2010

Submarine mud volcanoes are considered an important source of methane to the water column. However, the temporal variability of their fluid transport including mud and methane emissions is largely unknown. Assuming that this transport was continuous and at steady state, methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we have investigated non-steady state situations of vigorous mud movements and their reflection in fluid flow, seabed temperature and bathymetry. Time series of pressure, temperature, pH and seafloor photography were collected by a benthic observatory (LOOME) for 431 days at the active Håkon Mosby mud volcano. These new data document eruptions, which were accompanied by pulses of hot subsurface fluids and triggered rapid sediment uplift and lateral movement, as well as emissions of free gas.

Pedogeomorphology, geochronology and paleobotany of soil profiles obtained in the Nagqu area, central Tibet

Vast areas on the Tibetan Plateau are covered by alpine sedge mats consisting of different species of the genus Kobresia. These mats have topsoil horizons rich in rhizogenic organic matter which creates turfs. As the turfs have recently been affected by a complex destruction process, knowledge concerning their soil properties, age and pedogenesis are needed. In the core area of Kobresia pygmaea mats around Nagqu (central Tibetan Plateau, ca. 4500 m a.s.l.), four profiles were subjected to pedological, paleobotanical and geochronological analyses concentrating on soil properties, phytogenic composition and dating of the turf. The turf of both dry K. pygmaea sites and wet Kobresia schoenoides sites is characterised by an enrichment of living (dominant portion) and dead root biomass. In terms of humus forms, K. pygmaea turfs can be classified as Rhizomulls mainly developed from Cambisols. Wet-site K. schoenoides turfs, however, can be classified as Rhizo-Hydromors developed from Histic Gleysols. At the dry sites studied, the turnover of soil organic matter is controlled by a non-permafrost cold thermal regime. Below-ground remains from sedges are the most frequent macroremains in the turf. Only a few pollen types of vascular plants occur, predominantly originating from sedges and grasses. Large amounts of microscopic charcoal (indeterminate) are present. Macroremains and pollen extracted from the turfs predominantly have negative AMS 14C ages, giving evidence of a modern turf genesis. Bulk-soil datings from the lowermost part of the turfs have a Late Holocene age comprising the last ca. 2000 years. The development of K. pygmaea turfs was most probably caused by an anthropo(zoo)-genetically initiated growth of sedge mats replacing former grass-dominated vegetation ('steppe'). Thus the turfs result from the transformation of pre-existing topsoils comprising a secondary penetration and accumulation of roots. K. schoenoides turfs, however, are characterised by a combined process of peat formation and penetration/accumulation of roots probably representing a (quasi) natural wetland vegetation.

Characteristics of soils from the Quartermain Mountain area, Antarctica

Soil-forming processes and soil development rates are compared and contrasted on glacial deposits in two adjacent and coeval valleys of the Quartermain Mountains, which are important because they display Miocene glacial stratigraphy and some of the oldest landforms in the McMurdo Dry Valleys. More than 100 soil profiles were examined on seven drift sheets ranging from 115 000 to greater than 11.3 million years in age in Beacon Valley and Arena Valley. Although the two valleys contain drifts of similar age, they differ markedly in ice content of the substrate. Whereas Arena Valley generally has 'dry-frozen' permafrost in the upper 1 m and minimal patterned ground, Beacon Valley contains massive ice buried by glacial drift and ice-cored rock glaciers and has ice-cemented permafrost in the upper 1 m and considerable associated patterned ground. Arena Valley soils have twice the rate of profile salt accumulation than Beacon Valley soils, because of lower available soil water and minimal cryoturbation. The following soil properties increase with age in both valleys: weathering stage, morphogenetic salt stage, thickness of the salt pan, the quantity of profile salts, electrical conductivity of the horizon of maximum salt enrichment, and depth of staining. Whereas soils less than 200 000 years and older soils derived from sandstone-rich ground moraine are Typic Anhyorthels and Anhyturbels, soils of early Quaternary and older age, particularly on dolerite-rich drifts, are Petronitric Anhyorthels. Arena Valley has the highest pedodiversity recorded in the McMurdo Dry Valleys. The soils of the Quartermain Mountains are the only soils in the McMurdo Dry Valleys known to contain abundant nitrates.

Pore water chemistry of sediment core GeoB15101-7 and water chemistry of CTD casts GeoB15101-1 and GeoB15101-6

Submarine brine lakes feature sharp and persistent concentration gradients between seawater and brine, though these should be smoothed out by free diffusion in open ocean settings. The anoxic Urania basin of the Eastern Mediterranean contains an ultra sulfidic, hypersaline brine of Messinian origin above a thick layer of suspended sediments. With a dual modeling approach we reconstruct its contemporary stratification by geochemical solute transport fundamentals, and show that thermal convection is required to maintain mixing in the brine and mud layer. The origin of the Urania basin stratification was dated to 1650 years before present, which may be linked to a major earthquake in the region. The persistence of the chemoclines may be key to the development of diverse and specialized microbial communities. Ongoing thermal convection in the fluid mud layer may have important, yet unresolved consequences for sedimentological and geochemical processes, also in similar environments.