24 research outputs found
Holocene fluctuations of neodymium isotope ratios in eastern Fram Strait sediments - An indication for deepwater variability?
EGU2012-11739
The Fram Strait as the only deep water connection of the worldâs oceans to the Arctic plays a substantial role for the heat influx to the Arctic Ocean and controls freshening of the Nordic Seas through Arctic sea ice export. Large amounts of warm and saline Atlantic Water derived from the North Atlantic Drift transport most of the heat through eastern Fram Strait to the Arctic basin, resulting in year-round ice-free conditions. Arctic sea ice and cold and fresh waters exit the western part of the strait southward along the Greenland shelf. However, little is still known about the water mass transport at intermediate and bottom water depths in the Fram Strait. High-resolution Holocene sediment sequences from the Western Svalbard margin have been investigated for its neodymium isotope ratios stored in ferromanganese oxyhydroxide coatings of the sediment to derive information on the source of bottom seawater passing the site. The radiogenic isotope data are compared to a multitude of proxy indicators for the climatic and oceanographic variability in the eastern Fram Strait during the past 8,500 years. In order to obtain a calibration of the Nd isotope compositions extracted from sediments to modern bottom water mass signatures in the area, a set of core top and water samples from different water depths in the Fram Strait was additionally investigated for its present-day Nd isotope signatures. A significantly higher inflow of deepwater produced in the Nordic Seas to the core site is inferred for the earlier periods of the Holocene. Cooler surface water conditions and increased sea ice abundances during the late Holocene coincide with more radiogenic Nd isotope ratios likely resembling the neoglacial trend of the northern North Atlantic
Cold-water corals in the Bay of Biscay - occurrences and distribution in space and time (TransBiscay) - Cruise No. M84/5, May 31 - June 21, 2011, Vigo (Spain) - Brest (France)
The scientific objectives of METEOR cruise M84/5 focused on the measurement
and analysis of the environmental controls of modern and fossil cold-water coral growth
along a transect in the Bay of Biscay. In four working areas we successfully deployed lander
systems and CTD/Roâs to document the physical and hydrochemical characteristics of bottom
water masses and the water column in general. These are used to shed light on potential
linkages to modern cold-water coral growth and distribution. These investigations were
flanked by plankton tows in surface waters. The base for all investigations was a thorough
hydroacoustic survey to characterize potential cold-water coral bearing areas with living
colonies. Based on these maps we deployed all video-guided gear such as the OFOS-video
sled, the TV grab, and the lander systems. Benthic assemblages and sedimentary structures
have been documented and sampled with the OFOS and a box corer. Simultaneously, genetic
samples of the living coral material were taken for additional studies. Furthermore, we have
taken gravity cores to investigate the paleoceanographic conditions as well as the timing of
cold-water coral colonization in the Bay of Biscay. Along with the coring efforts, a detailed
sampling and study of porewater properties was performed. An additional aim of this cruise
was to investigate the influence of boundary exchange processes on the Neodymium isotopy
in bottom waters along the pathway of the Mediterranean Outflow water (MOW) by taking
multiple samples with the CTD/Ro.
The new data and samples of this METEOR cruise will provide the framework to
investigate the timing of cold-water coral colonization in the Bay of Biscay, as well as its
interplay with the ambient hydrography and geochemistry. This successful cruise has
provided the basis to investigate the scientific aims of this expedition in great detail
Trace Metals and Their Isotopes in the Tropical Atlantic Ocean - Cruise No. M81/1, February 04 â March 08, 2010, Las Palmas (Canary Islands, Spain) â Port of Spain (Trinidad & Tobago)
Summary
Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and
particulate trace metals and their isotopic compositions (TEIs) in the full water column of the
tropical Atlantic Ocean and their driving factors including main external inputs and internal
cycling and ocean circulation. The research program is embedded in the international
GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of
and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the
trace metal clean and contamination-free sampling of waters and particulates for subsequent
analyses of the TEIs in the home laboratories of the national and international participants.
Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was
realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated
GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully
made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate
samples were also collected under trace metal clean conditions using established in-situ pump
systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then
continued northwestward along the northern margin of South America until it reached Port of
Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange
with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon
outflow. In terms of internal cycling the equatorial high biological productivity band, as well as
increased productivity associated with the Amazon Plume were covered. All major water masses
contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow
equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep
stations were sampled for the different dissolved TEIs, which were in most cases accompanied
by particulate sampling. In addition, surface waters were continuously sampled under trace metal
clean conditions using a towed fish
Online preconcentration ICP-MS analysis of rare earth elements in seawater
The rare earth elements (REEs) with their systematically varying properties are powerful tracers of continental inputs, particle scavenging intensity and the oxidation state of seawater. However, their generally low (âŒpmol/kg) concentrations in seawater and fractionation potential during chemical treatment makes them difficult to measure. Here we report a technique using an automated preconcentration system, which efficiently separates seawater matrix elements and elutes the preconcentrated sample directly into the spray chamber of an ICP-MS instrument. The commercially available âseaFASTâ system (Elemental Scientific Inc.) makes use of a resin with ethylenediaminetriacetic acid and iminodiacetic acid functional groups to preconcentrate REEs and other metals while anions and alkali and alkaline earth cations are washed out. Repeated measurements of seawater from 2000 m water depth in the Southern Ocean allows the external precision (2Ï) of the technique to be estimated at <23% for all REEs and <15% for most. Comparison of Nd concentrations with isotope dilution measurements for 69 samples demonstrates that the two techniques generally agree within 15%. Accuracy was found to be good for all REEs by using a five point standard addition analysis of one sample and comparing measurements of mine water reference materials diluted with a NaCl matrix with recommended values in the literature. This makes the online preconcentration ICP-MS technique advantageous for the minimal sample preparation required and the relatively small sample volume consumed (7 mL) thus enabling large data sets for the REEs in seawater to be rapidly acquired
The GEOTRACES Intermediate Data Product 2014
The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-? data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes
Water mass mixing versus local weathering inputs along the Bay of Biscay: Evidence from dissolved hafnium and neodymium isotopes
Highlights
âą Nd isotope data reflect advection and dilution of Mediterranean Outflow Water on its way north in the Bay of Biscay.
âą Combined Hf and Nd isotopes are a sensitive indicator of inputs from land as well as long distance advection and mixing.
âą Nd isotope results of this and earlier studies demonstrate the temporally variable flow path of Mediterranean Sea Water.
We present dissolved neodymium and hafnium concentrations and isotope compositions of surface and deep-water masses from the Bay of Biscay. Neodymium isotope signatures in surface waters of the Bay of Biscay are mostly dominated by local weathering inputs from the surrounding continental margin. Subsurface Eastern North Atlantic Central Water (ENACW) shows a distinct Nd isotope signature (ΔNd â
â12) at the southwestern-most station and is significantly diluted by mixing with more radiogenic waters or shifted by inputs of relatively radiogenic particulate Nd on its way north along the European margin. Furthermore, the Nd isotope data clearly show a declining fraction of Mediterranean Sea Water (MSW) at intermediate depths on its way north indicating that only 40% to 60% of MSW still present in the mixture at the Galician margin arrive at the stations further north in the Bay of Biscay. An interannual variability of the flow path of MSW is identified when comparing the results of the Nd isotope compositions and salinity data of this study with those of earlier studies from the area.
In agreement with Nd isotope and concentration analyses the Hf isotope composition of MSW is set by large-scale inputs of terrigenous material into the Mediterranean as can be deduced from elevated Hf concentrations still observable at the Galician margin. Hf isotope signatures of all water masses of the Bay of Biscay, moreover, are overprinted by local weathering inputs and do not reflect water mass mixing. However, combined dissolved Nd and Hf isotopes serve as indicators of local weathering influences on signatures expected from long distance water mass mixing