Code and readme of a MATLAB-based graphical user interface program for computing functionals of the geopotential

We present a novel graphical user interface program GrafLab (GRAvity Field LABoratory) for spherical harmonic synthesis (SHS) created in MATLAB®. This program allows to comfortably compute 38 various functionals of the geopotential up to ultra-high degrees and orders of spherical harmonic expansion. For the most difficult part of the SHS, namely the evaluation of the fully normalized associated Legendre functions (fnALFs), we used three different approaches according to required maximum degree: (i) the standard forward column method (up to maximum degree 1800, in some cases up to degree 2190); (ii) the modified forward column method combined with Horner's scheme (up to maximum degree 2700); (iii) the extended-range arithmetic (up to an arbitrary maximum degree). For the maximum degree 2190, the SHS with fnALFs evaluated using the extended-range arithmetic approach takes only approximately 2-3 times longer than its standard arithmetic counterpart, i.e. the standard forward column method. In the GrafLab, the functionals of the geopotential can be evaluated on a regular grid or point-wise, while the input coordinates can either be read from a data file or entered manually. For the computation on a regular grid we decided to apply the lumped coefficients approach due to significant time-efficiency of this method. Furthermore, if a full variance-covariance matrix of spherical harmonic coefficients is available, it is possible to compute the commission errors of the functionals. When computing on a regular grid, the output functionals or their commission errors may be depicted on a map using automatically selected cartographic projection.

Geochemistry measured on sediment core GeoB12309-5

Laminated sediment records from the oxygen minimum zone in the Arabian Sea offer unique ultrahigh-resolution archives for deciphering climate variability in the Arabian Sea region. Although numerous analytical techniques are available it has become increasingly popular during the past decade to analyze relative variations of sediment cores' chemical signature by non-destructive X-ray fluorescence (XRF) core scanning. We carefully selected an approximately 5 m long sediment core from the northern Arabian Sea (GeoB12309-5: 24°52.3' N; 62°59.9' E, 956 m water depth) for a detailed, comparative study of high-resolution techniques, namely non-destructive XRF core scanning (0.8 mm resolution) and ICP-MS/OES analysis on carefully selected, discrete samples (1 mm resolution). The aim of our study was to more precisely define suitable chemical elements that can be accurately analyzed and to determine which elemental ratios can be interpretated down to sub-millimeter-scale resolutions. Applying the Student's t-test our results show significantly correlating (1% significance level) elemental patterns for all S, Ca, Fe, Zr, Rb, and Sr, as well as the K/Ca, Fe/Ti and Ti/Al ratios that are all related to distinct lithological changes. After careful consideration of all errors for the ICP analysis we further provide respective factors of XRF Core Scanner software error's underestimation by applying Chi-square-tests, which is especially relevant for elements with high count rates. As demonstrated by these new, ultra-high resolution data core scanning has major advantages (high-speed, low costs, few sample preparation steps) and represents an increasingly required alternative over the time consuming, expensive, elaborative, and destructive wet chemical analyses (e.g., by ICP-MS/OES after acid digestions), and meanwhile also provides high-quality data in unprecedented resolution.

Chlorofluorocarbons and noble gas measured on water bottle samples during three POLARSTERN cruises

We use a 27 year long time series of repeated transient tracer observations to investigate the evolution of the ventilation time scales and the related content of anthropogenic carbon (Cant) in deep and bottom water in the Weddell Sea. This time series consists of chlorofluorocarbon (CFC) observations from 1984 to 2008 together with first combined CFC and sulphur hexafluoride (SF6) measurements from 2010/2011 along the Prime Meridian in the Antarctic Ocean and across the Weddell Sea. Applying the Transit Time Distribution (TTD) method we find that all deep water masses in the Weddell Sea have been continually growing older and getting less ventilated during the last 27 years. The decline of the ventilation rate of Weddell Sea Bottom Water (WSBW) and Weddell Sea Deep Water (WSDW) along the Prime Meridian is in the order of 15-21%; the Warm Deep Water (WDW) ventilation rate declined much faster by 33%. About 88-94% of the age increase in WSBW near its source regions (1.8-2.4 years per year) is explained by the age increase of WDW (4.5 years per year). As a consequence of the aging, the Cant increase in the deep and bottom water formed in the Weddell Sea slowed down by 14-21% over the period of observations.

Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Eregli (2011)

We investigated gas bubble emissions at the Don-Kuban paleo-fan in the northeastern Black Sea regarding their geological setting, quantities as well as spatial and temporal variabilities during three ship expeditions between 2007 and 2011. About 600 bubble-induced hydroacoustic anomalies in the water column (flares) originating from the seafloor above the gas hydrate stability zone (GHSZ) at ~700 m water depth were found. At about 890 m water depth a hydrocarbon seep area named "Kerch seep area" was newly discovered within the GHSZ. We propose locally domed sediments ('mounds') discovered during ultra-high resolution bathymetric mapping with an autonomous underwater vehicle (AUV) to result from gas hydrate accumulation at shallow depths. In situ measurements indicated spatially limited temperature elevations in the shallow sediment likely induced by upward fluid flow which may confine the local GHSZ to a few meters below the seafloor. As a result, gas bubbles are suspected to migrate into near-surface sediments and to escape the seafloor through small-scale faults. Hydroacoustic surveys revealed that several flares originated from a seafloor area of about 1 km**2 in size. The highest flare disappeared in about 350 m water depth, suggesting that the released methane remains in the water column. A methane flux estimate, combining data from visual quantifications during dives with a remotely operated vehicle (ROV) with results from ship-based hydroacoustic surveys and gas analysis revealed that between 2 and 87 x 10**6 mol CH4 yr-1 escaped into the water column above the Kerch seep area. Our results show that the finding of the Kerch seep area represents a so far underestimated type of hydrocarbon seep, which has to be considered in methane budget calculations.