SIRGAS reference frame realization SIR11P01

To estimate the kinematics of the SIRGAS reference frame, the Deutsches Geodätisches Forschungsinstitut (DGFI) as the IGS Regional Network Associate Analysis Centre for SIRGAS (IGS RNNAC SIR), yearly computes a cumulative (multi-year) solution containing all available weekly solutions delivered by the SIRGAS analysis centres. These cumulative solutions include those models, standards, and strategies widely applied at the time in which they were computed and cover different time spans depending on the availability of the weekly solutions. This data set corresponds to the multi-year solution SIR11P01. It is based on the combination of the weekly normal equations covering the time span from 2000-01-02 (GPS week 1043) to 2011-04-16 (GPS week 1631), when the IGS08 reference frame was introduced. It refers to ITRF2008, epoch 2005.0 and contains 230 stations with 269 occupations. Its precision was estimated to be ±1.0 mm (horizontal) and ±2.4 mm (vertical) for the station positions, and ±0.7 mm/a (horizontal) and ±1.1 mm/a (vertical) for the constant velocities. Computation strategy and results are in detail described in Sánchez and Seitz (2011). The IGS RNAAC SIR computation of the SIRGAS reference frame is possible thanks to the active participation of many Latin American and Caribbean colleagues, who not only make the measurements of the stations available, but also operate SIRGAS analysis centres processing the observational data on a routine basis (more details in http://www.sirgas.org). The achievements of SIRGAS are a consequence of a successful international geodetic cooperation not only following and meeting concrete objectives, but also becoming a permanent and self-sustaining geodetic community to guarantee quality, reliability, and long-term stability of the SIRGAS reference frame. The SIRGAS activities are strongly supported by the International Association of Geodesy (IAG) and the Pan-American Institute for Geography and History (PAIGH). The IGS RNAAC SIR highly appreciates all this support.

Geochemistry of the oldest Atlantic oceanic crust

Controversy has surrounded the issue of whether mantle plume activity was responsible for Pangaean continental rifting and massive flood volcanism (resulting in the Central Atlantic Magmatic Province or CAMP, emplaced around 200 Ma) preceding the opening of the central Atlantic Ocean in the Early Mesozoic. Our new Sr-Nd-Pb isotopic and trace element data for the oldest basalts sampled from central Atlantic oceanic crust by deep-sea drilling show that oceanic crust generated from about 160 to 120 Ma displays clear isotopic and chemical signals of plume contamination (e.g., 87Sr/86Sr(i) = 0.7032-0.7036, epsilonNd(t) =+6.2 to +8.2, incompatible element patterns with positive Nb anomalies), but these signals are muted or absent in crust generated between 120 and 80 Ma, which resembles young Atlantic normal mid-ocean ridge basalt. The plume-affected pre-120 Ma Atlantic crustal basalts are isotopically similar to lavas from the Ontong Java Plateau, and may represent one isotopic end-member for CAMP basalts. The strongest plume signature is displayed near the center of CAMP magmatism but the hotspots presently located nearest this location in the mantle reference frame do not appear to be older than latest Cretaceous and are isotopically distinct from the oldest Atlantic crust. The evidence for widespread plume contamination of the nascent Atlantic upper mantle, combined with a lack of evidence for a long-lived volcanic chain associated with this plume, leads us to propose that the enriched signature of early Atlantic crust and possibly the eruption of the CAMP were caused by a relatively short-lived, but large volume plume feature that was not rooted at a mantle boundary layer. Such a phenomenon has been predicted by recent numerical models of mantle circulation.

Stable isotope ratios and chemistry on corals from the Caribbean Sea

Instrumental climate data are limited in length and only available with low spatial coverage before the middle of the 20th century. This is too short to reliably determine and interpret decadal and longer scale climate variability and to understand the underlying mechanisms with sufficient accuracy. A proper knowledge of past variability of the climate system is needed to assess the anthropogenic impact on climate and ecosystems, and also important with regard to long-range climate forecasting. Highly-resolved records of past climate variations that extend beyond pre-industrial times can significantly help to understand long-term climate changes and trends. Indirect information on past environmental and climatic conditions can be deduced from climate-sensitive proxies. Large colonies of massive growing tropical reef corals have been proven to sensitively monitor changes in ambient seawater. Rapid skeletal growth, typically ranging between several millimeters to centimeters per year, allows the development of proxy records at sub-seasonal resolution. Stable oxygen isotopic composition and trace elemental ratios incorporated in the aragonitic coral skeleton can reveal a detailed history of past environmental conditions, e.g., sea surface temperature (SST). In general, coral-based reconstructions from the tropical Atlantic region have lagged behind the extensive work published using coral records from the Indian and Pacific Oceans. Difficulties in the analysis of previously utilized coral archives from the Atlantic, typically corals of the genera Montastrea and Siderastrea, have so far exacerbated the production of long-term high-resolution proxy records. The objective of this study is the evaluation of massive fast-growing corals of the species Diploria strigosa as a new marine archive for climate reconstructions from the tropical Atlantic region. For this purpose, coral records from two study sites in the eastern Caribbean Sea (Guadeloupe, Lesser Antilles; and Archipelago Los Roques, Venezuela) were examined. At Guadeloupe, a century-long monthly resolved multi-proxy coral record was generated. Results present the first d18O (Sr/Ca)-SST calibration equations for the Atlantic braincoral Diploria strigosa, that are robust and consistent with previously published values using other coral species from different regions. Both proxies reflect local variability of SST on a sub-seasonal scale, which is a precondition for studying seasonally phase-locked climate variations, as well as track variability on a larger spatial scale (i.e., in the Caribbean and tropical North Atlantic). Coral Sr/Ca reliably records local annual to interannual temperature variations and is higher correlated to in-situ air temperature than to grid-SST. The warming calculated from coral Sr/Ca is concurrent with the strong surface temperature increase at the study site during the past decades. Proxy data show a close relationship to major climate signals from the tropical Pacific and North Atlantic (the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)) affecting the seasonal cycle of SST in the North Tropical Atlantic (NTA). Coral oxygen isotopes are also influenced by seawater d18O (d18Osw) which is linked to the hydrological cycle, and capture large-scale climate variability in the NTA region better than Sr/Ca. Results from a quantitative comparison between extreme events in the two most prominent modes of external forcing, namely the ENSO and NAO, and respective events recorded in seasonal coral d18O imply that SST variability at the study site is highly linked to Pacific and North Atlantic variability, by this means supporting the assumptions of observational- and model-based studies which suggest a strong impact of ENSO and NAO forcings onto the NTA region through a modulation of trade wind strength in winter. Results from different spectral analysis tools suggest that interannual climate variability recorded by the coral proxies is II largely dictated by Pacific ENSO forcing, whereas at decadal and longer timescales the influence of the NAO is dominan. tThe Archipelago Los Roques is situated in the southeastern Caribbean Sea, north of the Venezuelan coast. Year-to-year variations in monthly resolved coral d18O of a nearcentury- long Diploria strigosa record are significantly correlated with SST and show pronounced multidecadal variations. About half of the variance in coral d18O can be explained by variations in seawater d18O, which can be estimated by calculating the d18Oresidual via subtracting the SST component from measured coral d18O. The d18Oresidual and a regional precipitation index are highly correlated at low frequencies, suggesting that d18Osw variations are primarily atmospheric-driven. Warmer SSTs at Los Roques broadly coincide with higher precipitation in the southeastern Caribbean at multidecadal time scales, effectively strengthening the climate signal in the coral d18O record. The Los Roques coral d18O record displays a strong and statistically significant relationship to different indices of hurricane activity during the peak of the Atlantic hurricane season in boreal summer and is a particularly good indicator of decadal-multidecadal swings in the latter indices. In general, the detection of long-term changes and trends in Atlantic hurricane activity is hampered due to the limited length of the reliable instrumental record and the known inhomogeneity in the observational databases which result from changes in observing practice and technology over the years. The results suggest that coral-derived proxy data from Los Roques can be used to infer changes in past hurricane activity on timescales that extend well beyond the reliable record. In addition, the coral record exhibits a clear negative trend superimposed on the decadal to multidecadal cycles, indicating a significant warming and freshening of surface waters in the genesis region of tropical cyclones during the past decades. The presented coral d18O time series provides the first and, so far, longest continuous coral-based record of hurricane activity. It appears that the combination of both signals (SST and d18Osw) in coral d18O leads to an amplification of large-scale climate signals in the record, and makes coral d18O even a better proxy for hurricane activity than SST alone. Atlantic hurricane activity naturally exhibits strong multidecadal variations that are associated with the Atlantic Multidecadal Oscillation (AMO), the major mode of lowfrequency variability in the North Atlantic Ocean. However, the mechanisms underlying this multidecadal variability remain controversial, primarily because of the limited instrumental record. The Los Roques coral d18O displays strong multidecadal variability with a period of approximately 60 years that is closely related to the AMO, making the Archipelago Los Roques a very sensitive location for studying low-frequency climate variability in the Atlantic Ocean. In summary, the coral records presented in this thesis capture different key climate variables in the north tropical Atlantic region very well, indicating that fast-growing Diploria strigosa corals represent a promising marine archive for further proxy-based reconstructions of past climate variability on a range of time scales.

(Table 1) Horizontal and vertical ice flow velocities for seven markers around Vostok Station

Combined geodetic, geophysical and glaciological in situ measurements are interpreted regarding surface height changes over subglacial Lake Vostok and the local mass balance of the ice sheet at Vostok station. Repeated GPS observations spanning 5 years and long-term surface accumulation data show that the height of the lake surface has not changed over the observation period. The application of the mass conservation equation to purely observational data yields an ice mass balance for Vostok station close to equilibrium.

(Table 1) Paleomagnetic of reoriented core pieces of IODP Hole 304-U1309D

Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. The common occurrence of these structures in slow and ultra-slow spread oceanic crust suggests that they accommodate a significant component of plate divergence. However, the subsurface geometry of detachment faults in oceanic core complexes remains unclear. Competing models involve either: (a) displacement on planar, low-angle faults with little tectonic rotation; or (b) progressive shallowing by rotation of initially steeply dipping faults as a result of flexural unloading (the "rolling-hinge" model). We address this debate using palaeomagnetic remanences as markers for tectonic rotation within a unique 1.4 km long footwall section of gabbroic rocks recovered by Integrated Ocean Drilling Program (IODP) sampling at Atlantis Massif oceanic core complex on the Mid-Atlantic Ridge (MAR). These rocks contain a complex record of multipolarity magnetizations that are unrelated to alteration and igneous stratigraphy in the sampled section and are inferred to result from progressive cooling of the footwall section over geomagnetic polarity chrons C1r.2r, C1r.1n (Jaramillo) and C1r.1r. For the first time we have independently reoriented drill-core samples of lower crustal gabbros, that were initially azimuthally unconstrained, to a true geographic reference frame by correlating structures in individual core pieces with those identified from oriented imagery of the borehole wall. This allows reorientation of the palaeomagnetic data, placing far more rigorous constraints on the tectonic history than those possible using only palaeomagnetic inclination data. Analysis of the reoriented high temperature reversed component of magnetization indicates a 46° ± 6° anticlockwise rotation of the footwall around a MAR-parallel horizontal axis trending 011° ± 6°. Reoriented lower temperature components of normal and reversed polarity suggest that much of this rotation occurred after the end of the Jaramillo chron (0.99 Ma). The data provide unequivocal confirmation of the key prediction of flexural, rolling-hinge models for oceanic core complexes, whereby oceanic detachment faults initiate at higher dips and rotate to their present day low-angle geometries as displacement increases.

Geochemical analyses and Delta47 values in shallow water corals

Geochemical variations in shallow water corals provide a valuable archive of paleoclimatic information. However, biological effects can complicate the interpretation of these proxies, forcing their application to rely on empirical calibrations. Carbonate clumped isotope thermometry (Delta47) is a novel paleotemperature proxy based on the temperature dependent "clumping" of 13C-18O bonds. Similar ?47-temperature relationships in inorganically precipitated calcite and a suite of biogenic carbonates provide evidence that carbonate clumped isotope variability may record absolute temperature without a biological influence. However, large departures from expected values in the winter growth of a hermatypic coral provided early evidence for possible Delta47 vital effects. Here, we present the first systematic survey of Delta47 in shallow water corals. Sub-annual Red Sea Delta47 in two Porites corals shows a temperature dependence similar to inorganic precipitation experiments, but with a systematic offset toward higher Delta47 values that consistently underestimate temperature by ~8 °C. Additional analyses of Porites, Siderastrea, Astrangia and Caryophyllia corals argue against a number of potential mechanisms as the leading cause for this apparent Delta47 vital effect including: salinity, organic matter contamination, alteration during sampling, the presence or absence of symbionts, and interlaboratory differences in analytical protocols. However, intra- and inter-coral comparisons suggest that the deviation from expected Delta47 increases with calcification rate. Theoretical calculations suggest this apparent link with calcification rate is inconsistent with pH-dependent changes in dissolved inorganic carbon speciation and with kinetic effects associated with CO2 diffusion into the calcifying space. However, the link with calcification rate may be related to fractionation during the hydration/hydroxylation of CO2 within the calcifying space. Although the vital effects we describe will complicate the interpretation of Delta47 as a paleothermometer in shallow water corals, it may still be a valuable paleoclimate proxy, particularly when applied as part of a multi-proxy approach.

A refined Pliocene to early Pleistocene chronostratigraphic frame at ODP Hole 653A (West Mediterranean)

Two planktonic foraminiferal oxygen isotope records of ODP Hole 653A (Tyrrhenian Sea) are presented for the time period extending from approximately 0.8 to 3.0 Ma. Six, generally accepted, synchronous bioevents were used to precise the oxygen isotope chronology and to identify the oxygen isotope stages 22 down to 114. Subsequently, this oxygen isotope chronology was used to determine the synchronism or diachronism of various other biostratigraphic events with those recorded in the Singa and Ficarazzi land sections (Italy) and those in other DSDP/ODP sites. New results concern the diachronity of the FOD of the planktonic foraminiferal species N. atlantica, G.truncatulinoides truncatulinoides and G. inflata between ODP Hole 653A and the Italian landsections. Because many species entered the Mediterranean in short term fluxes, strongly related to the southward migration of cool North Atlantic surface waters, their time distribution through the Pliocene-Pleistocene generally corresponds to alternated intervals of presence and absence. This should explain most of the apparently diachronous appearances and disappearances. Alternating presence-absence patterns are of less importance for the various nannofossil events. The LOD of D. surculus occurs during the transition of stage 100 to 101 in both ODP Hole 653A and the Singa section, which is in perfect agreement with the disappearance of this species from the open ocean. The LOD of D. pentaradiatus in the Mediterranean occurs in stages 100-99, which seems to be consistent with the extinction of this species in the southern Hemisphere. G. oceanica, which corresponds to the 4 µm < Gephyrocapsa spp <5.5 µm is recorded in stages 65 to 64 at ODP Hole 653A. The Gephyrocapsa spp. >5.5 µm first occurred in stage 51 at Hole 653A, which fits within the uncertainty interval for this event stretching from stage 51 to 47 in the open ocean and seems therefore a useful tool for conventional biostratigraphy in the Mediterranean.

High-resolution in situ oxygen microprofiles, porewater and solid phase geochemistry from the Crimean shelf (Black Sea) from Maria S. Merian cruise MSM15/1

The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 µmol O2/L) and hypoxic (< 63 µmol O2/L) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 µmol/L even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol/m**2/d on average in the oxic zone, to 7 mmol/m**2/d on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol/m**2/d), but declined to 1.3 mmol/m**2/d in bottom waters with oxygen concentrations below 20 µmol/L. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic-hypoxic zone, to 10 % in the hypoxic-anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.

Amino acid geochronology of foraminifera test from north Queensland margin

In this study, we demonstrate the utility of amino acid geochronology based on single-foraminiferal tests in Quaternary sediment cores from the Queensland margin, Australia. The large planktonic foraminifer Pulleniatina obliquiloculata is ubiquitous in shelf, slope, and basin sediments of north Queensland as well as pantropical oceans. Fossil tests are resistant to dissolution, and retain substantial concentrations of amino acids (2-4 nmol/mg of shell) over hundreds of thousands of years. Amino acid D and L isomers of aspartic acid (Asp) and glutamic acid (Glu) were separated using reverse phase chromatography, which is sensitive enough to analyze individual foraminifera tests. In all, 462 Pulleniatina tests from 80 horizons in 11 cores exhibit a systematic increase in D/L ratios down core. D/L ratios were determined in 32 samples whose ages are known from AMS 14C analyses. In all cases, the Asp and Glu D/L ratios are concordant with 14C age. D/L ratios of equal-age samples are slightly lower for cores taken from deeper water sites, reflecting the sensitivity of the rate of racemization to bottom water temperature. Beyond the range of 14C dating, previously identified marine oxygen-isotope stage boundaries provide approximate ages of the sediments up to about 500,000 years. For this longer time frame, D/L ratios also vary systematically with isotope-correlated ages. The rate of racemization for Glu and Asp was modeled using power functions. These equations can be used to estimate ages of samples from the Queensland margin extending back at least 500,000 years. This analytical approach provides new opportunities for geochronological control necessary to understand fundamental sedimentary processes affecting a wide range of marine environments.