140 research outputs found
Plio-Pleistocene variability of the East Pacific Thermocline and the Intertropical Convergence Zone
The transition from the Pliocene to the Pleistocene was accompanied by major tectonic reorganizations of key oceanic gateways. In particular, the gradual closure of the Panama Gateway and the constriction of the Indonesian Gateway significantly affected the structure of the Pacific thermocline. In the East Pacific, the thermocline shoaled from an early Pliocene El Niñoâlike depth to its modern state, which had significant implications for global climate. Here we use Mg/Ca temperature estimates from subsurface and thermocline dwelling foraminifera to reconstruct the meridional PlioâPleistocene evolution of the Southeast Pacific thermocline, in relation to atmospheric circulation changes. In combination with similar reconstructions from the northâequatorial Pacific, our data indicate a change in the thermocline, responding to the northward displacement of the Intertropical Convergence Zone/South Pacific High system between ~3.8 and 3.5 Ma. After 3.5 Ma, we record a second major phase of thermocline shoaling, which points to the Intertropical Convergence Zone/South Pacific Highâsystem movement toward its modern position along with the gradual cooling of the Northern Hemisphere and its associated glaciation. These findings highlight that a warming globe may affect equatorial regions more intensively due to the potential temperatureâdriven movement of the Intertropical Convergence Zone/South Pacific High and their associated oceanic systems
Radiocarbon Evidence for the Contribution of the Southern Indian Ocean to the Evolution of Atmospheric CO 2 Over the Last 32,000 Years
It is widely assumed that the ventilation of the Southern Ocean played a crucial role in driving glacialâinterglacial atmospheric CO2 levels. So far, however, ventilation records from the Indian sector of the Southern Ocean are widely missing. Here we present reconstructions of water residence times (depicted as ÎÎ14C and ÎÎŽ13C) for the last 32,000 years on sediment records from the Kerguelen Plateau and the Conrad Rise (~570â to 2,500âm water depth), along with simulated changes in ocean stratification from a transient climate model experiment. Our data indicate that Circumpolar Deep Waters in the Indian Ocean were part of the glacial carbon pool. At our sites, close to or bathed by upwelling deep waters, we find two pulses of decreasing ÎÎ14C and ÎŽ13C values (~21â17 ka; ~15â12 ka). Both transient pulses precede a similar pattern in downstream intermediate waters in the tropical Indian Ocean as well as rising atmospheric CO2 values. These findings suggest that 14Câdepleted, CO2ârich Circumpolar Deep Water from the Indian Ocean contributed to the rise in atmospheric CO2 during Heinrich Stadial 1 and also the Younger Dryas and that the southern Indian Ocean acted as a gateway for sequestered carbon to the atmosphere and tropical intermediate waters
Deglacial patterns of South Pacific overturning inferred from 231Pa and 230Th
The millennialâscale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond. Despite its importance for the climate system, the evolution of the South Pacific overturning circulation (SPOC) is by far less well understood. A recently published study highlights the potential applicability of the 231Pa/230Thâproxy in the Pacific. Here, we present five sedimentary downâcore profiles of 231Pa/230Thâratios measured on a depth transect from the Pacific sector of the Southern Ocean to test this hypothesis using downcore records. Our data are consistent with an increase in SPOC as early as 20 ka that peaked during Heinrich Stadial 1. The timing indicates that the SPOC did not simply react to AMOC changes via the bipolar seesaw but were triggered via Southern Hemisphere processes
Absolute efficiency estimation of photon-number-resolving detectors using twin beams
A nonclassical light source is used to demonstrate experimentally the
absolute efficiency calibration of a photon-number-resolving detector. The
photon-pair detector calibration method developed by Klyshko for single-photon
detectors is generalized to take advantage of the higher dynamic range and
additional information provided by photon-number-resolving detectors. This
enables the use of brighter twin-beam sources including amplified pulse pumped
sources, which increases the relevant signal and provides measurement
redundancy, making the calibration more robust
Reduced admixture of North Atlantic Deep Water to the deep central South Pacific during the last two glacial periods
Key Points: âą Little deep water circulation changes in the past 240,000 years in the central South Pacific âą Reduced North Atlantic Deep Water admixture during glacials to the Southern Ocean âą South Pacific lithogenic material mainly sourced from SE Australia and South New Zealand
The South Pacific is a sensitive location for the variability of the global oceanic thermohaline circulation given that deep waters from the Atlantic Ocean, the Southern Ocean, and the Pacific basin are exchanged. Here we reconstruct the deep-water circulation of the central South Pacific for the last two glacial cycles (from 240,000âyears ago to the Holocene) based on radiogenic neodymium (Nd) and lead (Pb) isotope records complemented by benthic stable carbon data obtained from two sediment cores located on the flanks of the East Pacific Rise. The records show small but consistent glacial/interglacial changes in all three isotopic systems with interglacial average values of -5.8 and 18.757 for ΔNd and 206Pb/204Pb, respectively, whereas glacial averages are -5.3 and 18.744. Comparison of this variability of Circumpolar Deep Water (CDW) to previously published records along the pathway of the global thermohaline circulation is consistent with reduced admixture of North Atlantic Deep Water (NADW) to CDW during cold stages. The absolute values and amplitudes of the benthic ÎŽ13C variations are essentially indistinguishable from other records of the Southern Hemisphere and confirm that the low central South Pacific sedimentation rates did not result in a significant reduction of the amplitude of any of the measured proxies. In addition, the combined detrital Nd and strontium (87Sr/86Sr) isotope signatures imply that Australian and New Zealand dust has remained the principal contributor of lithogenic material to the central South Pacific
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
Independent tuning of size and coverage of supported Pt nanoparticles using atomic layer deposition
Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl) platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance
Reduced admixture of North Atlantic Deep Water to the deep central South Pacific during the last two glacial periods
First deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf: experiences from the MARUM-MeBo70 on Polarstern-Expedition PS104
The MARUM-MeBo (abbreviation for Meeresboden-BohrgerÀt, the German expression for seafloor drill rig) is
a robotic drilling system that is developed since 2004 at the MARUM Center for Marine Environmental
Sciences at the University of Bremen in close cooperation with Bauer Maschinen GmbH and other industry
partners. The MARUM-MeBo drill rigs can be deployed from multipurpose research vessel like, RV MARIA
S. MERIAN, RV METEOR, RV SONNE and RV POLARSTERN and are used for getting long cores both in
soft sediments as well as hard rocks in the deep sea.
The first generation drill rig, the MARUM-MeBo70 is dedicated for drilling depths of more than 70 m
(Freudenthal and Wefer, 2013). Between 2005 and 2017 it was deployed on 18 research expeditions and
drilled more than. 3 km into different types of lithologies including carbonate and crystalline rocks, gas
hydrates, sands and gravel, glacial till and hemipelagic mud with an average recovery rate of 67 %.
In February and March 2017 the MeBo70 was used on the West Antarctic continental shelf in the Amundsen
Sea Embayment for the first time. The goal of the deployment on RV Polarstern expedition PS104 was to
recover a series of sediment cores from different ages that will provide material for investigating the
glaciation history of this area known as the most dynamic drainage area of the West Antarctic Ice Sheet. In
this presentation we will focus on the operational experiences of this first deployment of a multi-barrel sea
floor drill rig on the Antarctic continental shelf.
References: Freudenthal, T and Wefer, G (2013) Drilling cores on the sea floor with the remote-controlled
sea floor drilling rig MeBo. Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337.
doi:10.5194/gi-2-329-201
First results of sedimentological investigations of MeBo drill cores recovered from the West Antarctic continental shelf in the Amundsen Sea
During expedition PS104 with RV Polarstern in February and March 2017 the MARUM MeBo 70 seabed drilling system was deployed at nine sites on the continental shelf of the Amundsen Sea Embayment, West Antarctica. A total of 57 meters of sediment core were recovered from 11 boreholes located in Pine Island Bay, Pine Island Trough, Bear Ridge and Cosgrove-Abbot Trough with recovery rates ranging from 7 to 76%. The main scientific objective of the drilling was to reconstruct the Late Mesozoic to Quaternary environmental history in this part of the Antarctic continental margin, with a special focus on the past dynamics of the marine based West Antarctic Ice Sheet (WAIS) from its inception to the last glacial cycle. Another main goal of the expedition was to test the suitability of the MeBo drill system for operating on the Antarctic continental shelf and recovering pre-glacial and glacially influenced sedimentary sequences.
Here we will present the first results of sedimentological investigations carried out on the drill cores. These comprise (i) visual lithological descriptions, (ii) CT-scanning records of core stratigraphy, sedimentary structures, and possible artefacts induced by the drilling process, (iii) measurements of physical properties performed with a multi-sensor core logger, and (iv) characterisation of the geochemical composition of the drilled sedimentary strata using X-ray fluorescence (XRF) scanner data. Preliminary biostratigraphic investigations conducted on board ship indicated that the recovered sedimentary strata were deposited during various time slices spanning from the Late CretaceousâPalaeocene to the Late Quaternary. We will provide an update of these initial chronological findings.
Keywords: Drill cores, shelf sediments, West Antarctic Ice Sheet
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