1,139 research outputs found
Dynamic constraints on CO2 uptake by an iron-fertilized Antarctic
The topics covered include the following: tracer distribution and dynamics in the Antarctic Ocean; a model of Antarctic and Non-Antarctic Oceans; effects on an anthropogenically affected atmosphere; effects of seasonal iron fertilization; and implications of the South Atlantic Ventilation Experiment C-14 results
Cenozoic paleoceanography 1986: An introduction
New developments in Cenozoic paleoceanography include the application of climate models and atmospheric general circulation models to questions of climate reconstruction, the refinement of conceptual models for interpretation of the carbon isotope record in terms of carbon mass balance, paleocirculation, paleoproductivity, and the regional mapping of paleoceanographic events by acoustic stratigraphy. Sea level change emerges as a master variable to which changes in the ocean environment must be traced in many cases, and tests of the onlap-offlap paradigm therefore are of crucial importance
Tracing Noble Gas Radionuclides in the Environment
Trace analysis of radionuclides is an essential and versatile tool in modern
science and technology. Due to their ideal geophysical and geochemical
properties, long-lived noble gas radionuclides, in particular, 39Ar (t1/2 = 269
yr), 81Kr (t1/2 = 2.3x10^5 yr) and 85Kr (t1/2 = 10.8 yr), have long been
recognized to have a wide range of important applications in Earth sciences. In
recent years, significant progress has been made in the development of
practical analytical methods, and has led to applications of these isotopes in
the hydrosphere (tracing the flow of groundwater and ocean water). In this
article, we introduce the applications of these isotopes and review three
leading analytical methods: Low-Level Counting (LLC), Accelerator Mass
Spectrometry (AMS) and Atom Trap Trace Analysis (ATTA)
Cooling and ventilating the abyssal ocean
The abyssal ocean is filled with cold, dense waters that sink along the Antarctic continental slope and overflow sills that lie south of the Nordic Seas. Recent integrations of chlorofluorocarbon‐11 (CFC) measurements are similar in Antarctic Bottom Water (AABW) and in lower North Atlantic Deep Water (NADW), but Antarctic inputs are ≈ 2°C colder than their northern counterparts. This indicates comparable ventilation rates from both polar regions, and accounts for the Southern Ocean dominance over abyssal cooling. The decadal CFC‐based estimates of recent ventilation are consistent with other hydrographic observations and with longer‐term radiocarbon data, but not with hypotheses of a 20th‐century slowdown in the rate of AABW formation. Significant variability is not precluded by the available ocean measurements, however, and interannual to decadal changes are increasingly evident at high latitudes
The Deglacial Evolution of North Atlantic Deep Convection
Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon (14C)–depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation
Multivalent display of minimal Clostridium difficile glycan epitopes mimics antigenic properties of larger glycans
Synthetic cell-surface glycans are promising vaccine candidates against
Clostridium difficile. The complexity of large, highly antigenic and
immunogenic glycans is a synthetic challenge. Less complex antigens providing
similar immune responses are desirable for vaccine development. Based on
molecular-level glycan–antibody interaction analyses, we here demonstrate that
the C. difficile surface polysaccharide-I (PS-I) can be resembled by
multivalent display of minimal disaccharide epitopes on a synthetic scaffold
that does not participate in binding. We show that antibody avidity as a
measure of antigenicity increases by about five orders of magnitude when
disaccharides are compared with constructs containing five disaccharides. The
synthetic, pentavalent vaccine candidate containing a peptide T-cell epitope
elicits weak but highly specific antibody responses to larger PS-I glycans in
mice. This study highlights the potential of multivalently displaying small
oligosaccharides to achieve antigenicity characteristic of larger glycans. The
approach may result in more cost-efficient carbohydrate vaccines with reduced
synthetic effort
Arctic ocean chronology confirmed by accelerator 14C dating
The role of the Arctic Ocean in Earth's climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable Arctic chronology. The first Arctic Ocean chronology based on U-Th and 14C data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates. New accelerator 14C data support the earlier U-Th-magnetostratigraphic dates and confirm the reliability of the established Arctic Ocean chronology
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The added value of convection-permitting ensemble forecasts of sea breeze compared to a Bayesian forecast driven by the global ensemble
Dynamical downscaling of ensemble forecasts to convectionpermitting resolutions aims to improve forecast skill by explicitly
resolving mesoscale dynamical features. The success of this approach is dependent on the ability of the model to spin up smaller
features embedded in the larger scale flow and provide more local information than could be inferred from knowledge of the
climatological response to the large scale flow alone. Here we
test whether such additional information is obtained from the
Met Office Global and Regional Ensemble Prediction Systems
(MOGREPS) for the sea-breeze phenomena which is resolved
properly only at convection-permitting resolutions but is driven
by large-sale conditions that are well represented in the global
driving model. The sea breeze is detected using a new automatic
tracking algorithm suitable for use in convective-scale forecast
data. The skill of probabilistic forecasts of sea-breeze occurrence from the high resolution ensemble is compared to that of a
Bayesian forecast trained on paired high/low resolution ensemble
members. This creates a statistical forecast of the high-resolution
ensemble member given knowledge of the global forecast ensemble alone. The aim of this paper is twofold: -firstly to assess
whether the information about sea breeze occurrence is encoded
in a few large-scale parameters and can be forecast by a statistical
method ; secondly to estimate what information is gained by running the high resolution forecast beyond that which is contained
in these large-scale flow parameters. Comparison of the two
forecasting methods using a variety of verification methods all
lead to the same conclusion: although both the Bayesian forecast
and convection-permitting ensemble provide information about
sea-breeze occurrence, the convection-permitting ensemble is
significantly more able to discriminate between sea-breeze events
and non-events for all lead times
Temperature and carbonate ion effects on Mg/Ca and Sr/Ca ratios in benthic foraminifera : aragonitic species Hoeglundina elegans
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 21 (2006): PA1007, doi:10.1029/2005PA001158.Core top samples from Atlantic (Little Bahama Banks (LBB)) and Pacific (Hawaii and Indonesia) depth transects have been analyzed in order to assess the influence of bottom water temperature (BWT) and aragonite saturation levels on Mg/Ca and Sr/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans. Both the Mg/Ca and Sr/Ca ratios in H. elegans tests show a general decrease with increasing water depth. Although at each site the decreasing trends are consistent with the in situ temperature profile, Mg/Ca and Sr/Ca ratios in LBB are substantially higher than in Indonesia and Hawaii at comparable water depths with a greater difference observed with increasing water depth. Because we find no significant difference between results obtained on “live” and “dead” specimens, we propose that these differences are due to primary effects on the metal uptake during test formation. Evaluation of the water column properties at each site suggests that in situ CO3 ion concentrations play an important role in determining the H. elegans Mg/Ca and Sr/Ca ratios. The CO3 ion effect is limited, however, only to aragonite saturation levels ([ΔCO3]aragonite) below 15 μmol kg−1. Above this level, temperature exerts a dominant effect. Accordingly, we propose that Mg/Ca and Sr/Ca in H. elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships: Mg/Ca = (0.034 ± 0.002)BWT + (0.96 ± 0.03) and Sr/Ca = (0.060 ± 0.002)BWT + (1.53 ± 0.03) (for [ΔCO3]aragonite > 15 μmol kg−1). The standard error associated with these equations is about ±1.1°C. Reconstruction of deeper water temperatures is complicated because in undersaturated waters, changes in Mg/Ca and Sr/Ca ratios reflect a combination of changes in [CO3] and BWT. Overall, we find that Sr/Ca, rather than Mg/Ca, in H. elegans may be a more accurate proxy for reconstructing paleotemperatures.Yair Rosenthal acknowledges the support of Amtzia
Genin and the Hebrew University, Forchheimer Fellowship, during his
sabbatical in the Inter-University Institute in Eilat, Israel. This project
has been funded by NSF Awards OCE 0220922 to Y.R. and OCE
0220776 to D.W.O. and B.K.L
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