Chronology for climate change: Developing age models for the biogeochemical ocean flux study cores

We construct age models for a suite of cores from the northeast Atlantic Ocean by means of accelerator mass spectrometer dating of a key core, BOFS 5K, and correlation with the rest of the suite. The effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation. The degree of bioturbation is estimated by comparing modeled profiles with dispersal of the Vedde Ash layer in core 5K, and we find a mixing depth of roughly 8 cm for sand-sized material. Using this value, we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years, with lesser effect on fine carbonate (<10 mu m) ages. The bioturbation model illustrates problems associated with the dating of ''instantaneous'' events such as ash layers and the ''Heinrich'' peaks of ice-rafted detritus. Correlations between core 5K and the other cores from the BOFS suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes, magnetic susceptibility, water and carbonate content, and via marker horizons in X radiographs and ash beds

Ethik, Ökonomie und faire Preise – Eine explorative Analyse der Wirkungszusammenhänge im Schweizer Baugewerbe

This thesis examines the extent to which ethics in the form of an Ethics Management System (EMS) can support construction economics in fair pricing. A critical review of the literature on ethics, economics, and pricing management in the Swiss construction industry reveals that the economic market mechanism is unable to ensure fair pricing due to legal circumstances. Addressing this failure, this thesis focuses on how an EMS could secure price fairness between builders, construction service providers, and planners. This focus is achieved by addressing the current knowledge gap regarding causal links of an EMS on fair pricing from the perspective of public infrastructure construction projects carried out according to strict legal requirements. The research takes the form of an exploratory analysis, focusing on stakeholders of the aforementioned industry, using a qualitative methodology that involves face-to-face, semi-structured interviews with 26 construction industry experts in the German-speaking part of Switzerland and southern Germany between November 2019 and March 2020. However, to obtain a holistic view of the current situation, this exploratory analysis includes four other stakeholder groups such as the legal sector, education, building associations, and the media, in addition to the main players such as builders, construction service providers, and planners. This research project investigates what problems and difficulties these stakeholders perceive, how they define a fair price, and whether they comprehend the pricing process as fair. Furthermore, how ethics are sensed and how ethics are experienced and lived in everyday life. The evaluation revealed a uniform definition of price fairness among all experts. However, builders postulate the insufficient quality and costly claim management. Contractors and planners, on the other hand, complain about the low-price level and deadline pressure. Other stakeholder groups criticise the lack of empathy and the one-sided technical-process-oriented training of the construction service providers. The thesis presents a new understanding of how an EMS could unite the interests of these stakeholder groups and bring about price fairness beyond the market mechanism, to achieve the greatest possible profit for all parties involved

Icebergs in the North Atlantic: Modelling circulation changes and glacio-marine deposition

In order to investigate meltwater events in the North Atlantic, a simple iceberg generation, drift, and melting routine was implemented in a high-resolution OGCM. Starting from the modelled last glacial state, every 25th day cylindrical model icebergs 300 meters high were released at 32 specific points along the coasts. Icebergs launched at the Barents Shelf margin spread a light meltwater lid over the Norwegian and Greenland Seas, shutting down the deep convection and the anti-clockwise circulation in this area. Due to the constraining ocean circulation, the icebergs produce a tongue of relatively cold and fresh water extending eastward from Hudson Strait that must develop at this location, regardless of iceberg origin. From the total amount of freshwater inferred by the icebergs, the thickness of the deposited IRD could be calculated in dependance of iceberg sediment concentration. In this way, typical extent and thickness of Heinrich layers could be reproduced, running the model for 250 years of steady state with constant iceberg meltwater inflow

Evidence from the Florida Straits for Younger Dryas ocean circulation changes

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA1205, doi:10.1029/2010PA002032.The waters passing through the Florida Straits today reflect both the western portion of the wind-driven subtropical gyre and the northward flow of the upper waters which cross the equator, compensating North Atlantic Deep Water export as part of the large-scale Atlantic meridional overturning circulation. It has been postulated from various lines of evidence that the overturning circulation was weaker during the Younger Dryas cold event of the last deglaciation. We show here that the contrast in the oxygen isotopic composition of benthic foraminiferal tests across the Florida Current is reduced during the Younger Dryas. This most likely reflects a decrease in the density gradient across the channel and a decrease in the vertical shear of the Florida Current. This reduced shear is consistent with the postulated reduction in the Atlantic meridional overturning circulation. We find that the onset of this change in density structure and flow at the start of the Younger Dryas is very abrupt, occurring in less than 70 years.We thank the National Science Foundation (grants OCE‐0648258 and OCE‐0096472) and the Comer Science and Education Foundation for supporting this research. MWS was supported by a NOAA Global Change Postdoctoral Fellowship

Earthquake nucleation in the lower crust by local stress amplification

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep

Geochemical response of the mid-depth Northeast Atlantic Ocean to freshwater input during Heinrich events 1 to 4

PublishedArticleHeinrich events are intervals of rapid iceberg-sourced freshwater release to the high latitude North Atlantic Ocean that punctuate late Pleistocene glacials. Delivery of fresh water to the main North Atlantic sites of deep water formation during Heinrich events may result in major disruption to the Atlantic Meridional Overturning Circulation (AMOC), however, the simple concept of an AMOC shutdown in response to each freshwater input has recently been shown to be overly simplistic. Here we present a new multi-proxy dataset spanning the last 41,000 years that resolves four Heinrich events at a classic mid-depth North Atlantic drill site, employing four independent geochemical tracers of water mass properties: boron/calcium, carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates. We also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast North Atlantic. Our data reveal distinct geochemical signatures for each Heinrich event, suggesting that the sites of fresh water delivery and/or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released. At no time during the last 41 kyr was the mid-depth northeast North Atlantic dominantly ventilated by southern-sourced water. Instead, we document persistent ventilation by Glacial North Atlantic Intermediate Water (GNAIW), albeit with variable properties signifying changes in supply from multiple contributing northern sources.This research used samples provided by the Integrated Ocean Drilling (Discovery) Program IODP, which is sponsored by the US National Science Foundation and participating countries under management of Joint Oceanographic Institutions, Inc. We thank Walter Hale and Alex Wülbers for help with sampling, Kirsty Crocket for providing additional samples and Matt Cooper, Andy Milton, Mike Bolshaw and Dave Spanner for analytical support. Heiko Pälike, David Thornalley and Rachel Mills are thanked for productive discussions and comments on earlier versions of this work. We also thank three anonymous reviewers for their constructive feedback, which greatly improved the manuscript. Funding for this project was provided by NERC studentships to A.J.C. (grant NE/D005728/2) and T.B.C. (NE/I528626/1), with additional funding support from a Royal Society Wolfson Research Merit Award and NERC grants NE/F00141X/1 and NE/I006168/1 to P.A.W. and NE/D00876X/2 to G.L.F

Southwest Pacific modulation of abrupt climate change during the Antarctic Cold Reversal - Younger Dryas

The giant piston core, MD97-2121 (2314-m water depth), collected north of the Subtropical Front, New Zealand, provides a well-dated, stable isotopic record of subtropical and sub-Antarctic influences on the surface and deep ocean over the last deglaciation, especially during the Antarctic Cold Reversal (ACR; ~ 14.1-12.4 ka) and Younger Dryas (YD; 13.0-11.5 ka). After the Last Glacial Maximum, benthic foraminiferal

An occurrence of Tuhua Tephra in deep-sea sediments from offshore eastern North Island, New Zealand

We identify c. 7000 cal yr BP Tuhua Tephra in a marine sediment core from offshore eastern North Island, New Zealand. Its mineral assemblage includes aegirine, which is diagnostic for the Tuhua (Mayor Island) Volcanic Centre, and electron microprobe analyses of glass shards yield compositions close to published analyses of the tephra onshore, closer to the source. Associated radiocarbon ages on planktonic foraminifera from the core show that its age lies within the range previously determined for the caldera-forming event that generated Tuhua Tephra. This occurrence, >380 km southeast of the source, indicates that the dispersal of the ash was bi-directional, and that earlier estimates of this tephra's volume may be conservative