Marine geoscience

Marine Geoscience 94. Anti-phase seasonality and paleothermometry of G. ruber and G. trilobus upstream of the Agulhas Current U. Fallet MSc, Royal NIOZ, The Netherlands; U. Fallet, Royal NIOZ; G.-J.A. Brummer, Royal NIOZ; J. Zinke, Royal NIOZ, Vrije Universiteit Amsterdam; S. Vogels, Royal NIOZ, Vrije Universiteit Amsterdam; H. Ridderinkhof, Royal To infer past ocean temperatures we examined the first time-series fluxes of planktonic foraminifera retrieved upstream of the modern Agulhas Current. Using deep-moored sediment traps we find a distinct anti-phase response to the seasonal migration of the Intertropical Convergence Zone (ITCZ) in the shell fluxes of common surface-dwelling G. ruber and G. trilobus. Maximum fluxes of G. ruber occur in late austral summer (February – March) when sea surface temperature (SST) averages 30°C. By contrast G. trilobus maxima appear in early winter (June – July) at a lower average SST of around 25°C when chlorophyll a increases. Cross-correlation of the 2.5 year time-series data showed that the G. ruber/G. trilobus ratio (R/T ratio) closely followed the seasonal cycle in SST, as did their paired δ18O and Mg/Ca. From these results we derived five independent temperature equations for improved paleothermometry in the southwestern Indian Ocean that specify summer, winter and flux-weighted annual mean SST. We conclude that the R/T ratio, together with their δ18O and Mg/Ca, not only allow for seasonal paleothermometry but also minimize a large error introduced by differential seasonal productivity. 79. Sedimentary organic matter diagenesis along an oxygen gradient Dr. ir. K.G.J. Nierop, Utrecht University, Netherlands; G.J. Reichart, Utrecht University; N.R. Schoenmaker, Utrecht University; J.S. Sinninghe Damsté, Utrecht University/Royal NIOZ Organic matter consists of a complex mixture of different biochemicals exhibiting numerous morphologies and stages of biological oxidation. The degradation process often occurs with oxygen being the oxidant, however, under oxygen-depleted conditions, other electron donors such as nitrate, sulfate, iron and manganese are used to oxidize organic matter. A transect of multicores through the intense oxygen minimum zone (OMZ) in the Arabian Sea shows enhanced preservation of organic carbon within the low bottom water oxygen environment. Based on amino acid analysis, Vandewiele et al. (2009) concluded that the organic matter inside and below the OMZ was ‘extensively degraded’, implying significant microbial reworking of the organic matter even in the Here we investigate the early stages (upper 20 cm) of organic matter diagenesis and preservation in three sediment cores that differ in low bottom water oxygenation by analytical pyrolysis techniques. An enhanced accumulation of nitrogen-rich organic matter occurred with decreasing oxygen concentrations. This may suggest that this, most likely protein-derived material may account for part of the enhanced organic carbon burial fluxes in the ocean’s low oxygen zones. 160. Redox sensitive trace elements in black shales from the late Archean Transvaal Supergroup: evidence for atmospheric oxygen? J.A. Roholl BSc, Utrecht Universtiy, The Netherlands; P. Mason, Utrecht University, Utrecht, Netherlands; H. Tsikos, Rhodes University, Grahamstown, South Africa Redox sensitive trace elements such as Mo, Re and U have the potential to record changes in the degree of oxygenation in the Earth’s atmosphere and hydrosphere during the Archean and Proterozoic. Molybdenum can be released by oxic weathering of the crust. It is mobile in solution as the molybdate ion in the presence of oxygen, and precipitates in the oceans under euxinic (anoxic, sulfidic) conditions following reaction with sulphide to form thiomolybdate (MoO4-xSx2–). Enrichments in Mo have recently been discovered in the Mount McRae shale, Hammersley Basin, Australia as well as the Transvaal Supergroup, South Africa. Elevated Mo has been linked, along with Re enrichments, to the first ‘whiff’of atmospheric oxygen, approximately 2.5 billion years ago. Here we apply a similar methodology to investigate traces of late Archean atmospheric oxygenation, in black shales and (banded) cherts from the Campbellrand-Kuruman formations in the Transvaal supergroup (2.5-2.6 Ga), South Africa. Samples were obtained from drill cores from mines in Griqualand west. Shales contain abundant pyrite globules and have high concentrations of organic carbon. Preliminary trace element data, determined by ICP-AES and ICP-MS, will be presented for crushed bulk-rock samples. 72. Modeling ocean biogeochemistry in the Cretaceous: what triggers ocean anoxia? I. Ruvalcaba-Baroni MSc, Utrecht University, Netherlands; C Slomp, University Utrecht; H Brinkhuis, Accumulating evidence from sediment core records and model studies of global biogeochemical cycling suggest that changes in the marine phosphorus (P) and nitrogen (N) cycles may have been of specific importance for the initiation of oceanic anoxia in the Cretaceous. Thus, a moderate increase in nutrient delivery to an ocean with a sluggish circulation can result in a cascade effect causing complete oxygen depletion in the deep sea. The source of the nutrients that possibly acted as the trigger for anoxia remains unclear, however, and proposed mechanisms include increased riverine nutrient delivery and changes in upwelling regimes. The relative roles of N and P availability in controlling primary productivity are also not fully understood. Recent work on N cycling in the modern ocean suggests that anammox is a major pathway for N removal. Here, we expand an existing model of the coupled cycles of P, carbon and oxygen in the ocean with the marine N cycle. With the updated version of the model, we specifically assess the role of changes in ocean redox conditions for N-removal and we test the hypothesis that enhanced availability of P can fuel N-fixation and organic C burial and trigger oceanic anoxia. 31. Gateway restriction and climatic conditions of the Mediterranean Sea during the Messinian Salinity Crisis; A box model including Sr-isotope ratios R.P.M. Topper MSc, Utrecht University, Netherlands; P.Th. Meijer, Department of Earth Sciences, Utrecht University, Budapestlaan 4 3584CD Utrecht, The Netherlands; R. Flecker, BRIDGE, School of Geographical Sciences, Bristol University, University Road, Bristol BS8 ISS, United Kingdom; M.J.R. Wortel, Department of Earth Sciences, Utrecht University, Budapestlaan 4 3584CD Utrecht, The Netherlands Combining Sr-isotope ratios measured in Mediterranean Late Miocene successions with data on past salinity, Flecker et al. (2002) and Flecker and Ellam (2006) were able to derive quantitative information on the Mediterranean hydrological budget at times before and during the Messinian Salinity Crisis. The authors obtained this hydrological budget by inverting the salinity and strontium data with steady-state solutions to the conservation equations of salt, strontium and water. In this study, we incorporate Sr ratios and a Late Miocene water budget from Gladstone et al. (2007) in the box model from Meijer (2006) which quantifies the Mediterranean water and salt budget under specified conditions of connectivity with the Atlantic Ocean, representing tectonic restrictions of the Rifian and Betic gateways, and atmospheric fluxes, induced by climatic changes. This model will give insight in the coeval behaviour and temporal evolution of salt and Sr-ratios under changing contributions of ocean and fresh water. Model evaluation is performed using the Sr-ratio data set compiled by Flecker and Ellam (2006). Results from our model have implications for the timing and extent of Late Miocene Atlantic gateway restrictions and climatic changes and hence for scenarios for pre-MSC and MSC intervals. 2. An application to correct for cracks in core photographs C.J.R. Zeeden MSc, Utrecht University, The Netherlands; F. Hilgen, Stratigraphy and Paleontology, Utrecht University, The Netherlands,; L. Lourens, Stratigraphy and Paleontology, Utrecht University, The Netherlands,; U. Röhl, Colour data from deep-sea cores has become an important tool in past climate reconstructions and stratigraphy to characterise changes in lithology. This is because image scanning is a fast, inexpensive and non-destructive method to retrieve high-resolution records. Cracks in the sediment, however, may significantly alter the colour data. Here we present new algorithms to correct the colour data for cracks. As an example, we will discuss the application of this method using a core from the Ocean Drilling Program. We analyse images in a way that we calculate mean values, median values and standard deviations of Red, Green, Blue (RGB) and grayscale data. To correct for dark/cracked areas within images, we exclude all data darker than a user-defined threshold value from analysis. The research within the GTSnext project leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement

Source: http://www.gtsnext.eu/publications/abstracts/20100422_Zeeden_NAC.pdf