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Book ; Online: Glacial ENSO and Atlantic Meridional Overturning Circulation - Link to model results, supplementary data to: Merkel, Ute; Prange, Matthias; Schulz, Michael (2010): ENSO variability and teleconnections during glacial climates. Quaternary Science Reviews, 29, 86-100

Merkel, Ute / Prange, Matthias / Schulz, Michael

2012

Abstract: ... for preindustrial climate (PI) has been performed. Details of the experiments are described in Merkel et al. (2010 ...

Abstract	Numerical experiments using the general circulation model CCSM3 have been performed for glacial climates: Last Glacial Maximum (LGM), Heinrich Stadial 1 (HS1), Marine Isotope Stage 3 Stadial (MIS3-ST) and Marine Isotope Stage 3 Interstadial (MIS3-IST). As a reference, a control simulation for preindustrial climate (PI) has been performed. Details of the experiments are described in Merkel et al. (2010). The datasets contain timeseries from the last 100 years of each model simulation. For each experiment, we present: - annual mean timeseries of the maximum of the Atlantic Meridional Overturning Circulation between 30°N and 80°N and below 500 m. - monthly mean timeseries of sea surface temperature area-averaged over the Nino3-region (5°S-5°N, 150°W-90°W).
Language	English
Dates of publication	2012-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1016/j.quascirev.2009.11.006
DOI	10.1594/PANGAEA.786514
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Solar sensitivity experiments for the pre-industrial time period using the comprehensive global climate model CCSM3 (Community Climate System Model 3), supplementary data to: Varma, Vidya; Prange, Matthias; Lamy, Frank; Merkel, Ute; Schulz, Michael (2011): Solar-forced shifts of the Southern Hemisphere Westerlies during the Holocene. Climate of the Past, 7, 339-347

Varma, Vidya / Lamy, Frank / Merkel, Ute / Prange, Matthias / Schulz, Michael

2011

Abstract: ... SWW.

REFERENCE:
Varma, Vidya; Prange, Matthias; Lamy, Frank; Merkel, Ute; Schulz, Michael ...

Abstract	The Southern Hemisphere Westerly Winds (SWW) constitute an important zonal circulation that influences large-scale precipitation patterns and ocean circulation. Variations in their intensity and latitudinal position have been suggested to exert a strong influence on the CO2 budget in the Southern Ocean, thus making them a potential factor affecting the global climate. The possible influence of solar forcing on SWW variability during the Holocene is addressed. Solar sensitivity experiments with a comprehensive global climate model (CCSM3) are carried out to study the response of SWW to solar variability. In addition, It is shown that a high-resolution iron record from the Chilean continental slope (41° S), which is interpreted to reflect changes in the position of the SWW, is significantly correlated with reconstructed solar activity during the past 3000 years. Taken together, the proxy and model results suggest that centennial-scale periods of lower (higher) solar activity caused equatorward (southward) shifts of the annual mean SWW. REFERENCE: Varma, Vidya; Prange, Matthias; Lamy, Frank; Merkel, Ute; Schulz, Michael (2011): Corrigendum to "Solar-forced shifts of the Southern Hemisphere Westerlies during the Holocene". Climate of the Past, 7, 339-347
Language	English
Dates of publication	2011-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is cited by doi:10.5194/cp-7-985-2011 ; This dataset is supplement to doi:10.5194/cp-7-339-2011
DOI	10.1594/PANGAEA.775485
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Transient Holocene experiments under orbital forcing using the comprehensive global climate model CCSM3 (Community Climate System Model 3), supplementary data to: Varma, Vidya; Prange, Matthias; Merkel, Ute; Kleinen, Thomas; Lohmann, Gerrit; Pfeiffer, Madlene; Renssen, Hans; Wagner, Axel; Wagner, Sebastian; Schulz, Michael (2012): Holocene evolution of the Southern Hemisphere westerly winds in transient simulations with global climate models. Climate of the Past, 8(2), 391-402

Varma, Vidya / Kleinen, Thomas / Lohmann, Gerrit / Merkel, Ute / Pfeiffer, Madlene / Prange, Matthias / Renssen, Hans / Schulz, Michael / Wagner, Axel / Wagner, Sebastian

2011

Abstract: The Southern Hemisphere Westerly Winds (SWW) have been suggested to exert a critical influence on global climate through wind-driven upwelling of deep water in the Southern Ocean and the potentially resulting atmospheric CO2 variations. The investigation ...

Abstract	The Southern Hemisphere Westerly Winds (SWW) have been suggested to exert a critical influence on global climate through wind-driven upwelling of deep water in the Southern Ocean and the potentially resulting atmospheric CO2 variations. The investigation of the temporal and spatial evolution of the SWW along with forcings and feedbacks remains a significant challenge in climate research. In this study, the evolution of the SWW under orbital forcing from the early Holocene (9 kyr BP) to pre-industrial modern times is examined with transient experiments using the comprehensive coupled global climate model CCSM3. Analyses of the model results suggest that the annual and seasonal mean SWW were subject to an overall strengthening and poleward shifting trend during the course of the early-to-late Holocene under the influence of orbital forcing, except for the austral spring season, where the SWW exhibited an opposite trend of shifting towards the equator.
Language	English
Dates of publication	2011-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.5194/cp-8-391-2012
DOI	10.1594/PANGAEA.776063
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Monthly Tahiti coral Sr/Ca and oxygen isotope data from IODP Hole 310-M0024A, supplementary data to: Felis, Thomas; Merkel, Ute; Asami, Ryuji; Deschamps, Pierre; Hathorne, Ed C; Kölling, Martin; Bard, Edouard; Cabioch, Guy; Durand, Nicolas; Prange, Matthias; Schulz, Michael; Cahyarini, Sri Yudawati; Pfeiffer, Miriam (2012): Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1. Nature Communications, 3, 965

Felis, Thomas / Asami, Ryuji / Bard, Edouard / Cabioch, Guy / Deschamps, Pierre / Durand, Nicolas / Hathorne, Ed C / Kölling, Martin / Merkel, Ute / al., et

2012

Abstract: The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate ... ...

Abstract	The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.
Language	English
Dates of publication	2012-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1038/ncomms1973
DOI	10.1594/PANGAEA.786743
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Article ; Online: Deforming polar active matter in a scalar field gradient

Muhamet Ibrahimi / Matthias Merkel

New Journal of Physics, Vol 25, Iss 1, p

2023 Volume 013022

Abstract: Active matter with local polar or nematic order is subject to the well-known Simha-Ramaswamy instability. It is so far unclear how, despite this instability, biological tissues can undergo robust active anisotropic deformation during animal morphogenesis. ...

Abstract	Active matter with local polar or nematic order is subject to the well-known Simha-Ramaswamy instability. It is so far unclear how, despite this instability, biological tissues can undergo robust active anisotropic deformation during animal morphogenesis. Here we ask under which conditions protein concentration gradients (e.g. morphogen gradients), which are known to control large-scale coordination among cells, can stabilize such deformations. To this end, we study a hydrodynamic model of an active polar material. To account for the effect of the protein gradient, the polar field is coupled to the boundary-provided gradient of a scalar field that also advects with material flows. Focusing on the large system size limit, we show in particular: (a) the system can be stable for an effectively extensile coupling between scalar field gradient and active stresses, i.e. gradient-extensile coupling, while it is always unstable for a gradient-contractile coupling. Intriguingly, there are many systems in the biological literature that are gradient-extensile, while we could not find any that are clearly gradient-contractile. (b) Stability is strongly affected by the way polarity magnitude is controlled. Taken together, our findings, if experimentally confirmed, suggest new developmental principles that are directly rooted in active matter physics.
Keywords	active matter ; morphogenesis ; instability ; tissue deformation ; Science ; Q ; Physics ; QC1-999
Subject code	510
Language	English
Publishing date	2023-01-01T00:00:00Z
Publisher	IOP Publishing
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Stiffening of under-constrained spring networks under isotropic strain.

Lee, Cheng-Tai / Merkel, Matthias

Soft matter

2022 Volume 18, Issue 29, Page(s) 5410–5425

Abstract: Disordered spring networks are a useful paradigm to examine macroscopic mechanical properties of amorphous materials. Here, we study the elastic behavior of under-constrained spring networks, ...

Abstract	Disordered spring networks are a useful paradigm to examine macroscopic mechanical properties of amorphous materials. Here, we study the elastic behavior of under-constrained spring networks,
Language	English
Publishing date	2022-07-27
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d2sm00075j
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Phase separation dynamics in deformable droplets.

Gsell, Simon / Merkel, Matthias

Soft matter

2022 Volume 18, Issue 13, Page(s) 2672–2683

Abstract: Phase separation can drive spatial organization of multicomponent mixtures. For instance in developing animal embryos, effective phase separation descriptions have been used to account for the spatial organization of different tissue types. Similarly, ... ...

Abstract	Phase separation can drive spatial organization of multicomponent mixtures. For instance in developing animal embryos, effective phase separation descriptions have been used to account for the spatial organization of different tissue types. Similarly, separation of different tissue types is also observed in stem cell aggregates, where the emergence of a polar organization can mimic early embryonic axis formation. Here, we describe such aggregates as deformable two-phase fluid droplets, which are suspended in a fluid environment (third phase). Using hybrid finite-volume Lattice-Boltzmann simulations, we numerically explore the out-of-equilibrium routes that can lead to the polar equilibrium state of such a droplet. We focus on the interplay between spinodal decomposition and advection with hydrodynamic flows driven by interface tensions, which we characterize by a Peclet number Pe. Consistent with previous work, for large Pe the coarsening process is generally accelerated. However, for intermediate Pe we observe long-lived, strongly elongated droplets, where both phases form an alternating stripe pattern. We show that these "croissant" states are close to mechanical equilibrium and coarsen only slowly through diffusive fluxes in an Ostwald-ripening-like process. Finally, we show that a surface tension asymmetry between both droplet phases leads to transient, rotationally symmetric states whose resolution leads to flows reminiscent of Marangoni flows. Our work highlights the importance of advection for the phase separation process in finite, deformable systems.
Language	English
Publishing date	2022-03-30
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d1sm01647d
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article ; Online: Structure and Rheology in Vertex Models under Cell-Shape-Dependent Active Stresses.

Lin, Shao-Zhen / Merkel, Matthias / Rupprecht, Jean-François

Physical review letters

2023 Volume 130, Issue 5, Page(s) 58202

Abstract: Biological cells can actively tune their intracellular architecture according to their overall shape. Here we explore the rheological implication of such coupling in a minimal model of a dense cellular material where each cell exerts an active mechanical ...

Abstract	Biological cells can actively tune their intracellular architecture according to their overall shape. Here we explore the rheological implication of such coupling in a minimal model of a dense cellular material where each cell exerts an active mechanical stress along its axis of elongation. Increasing the active stress amplitude leads to several transitions. An initially hexagonal crystal motif is first destabilized into a solid with anisotropic cells whose shear modulus eventually vanishes at a first critical activity. Increasing activity beyond this first critical value, we find a re-entrant transition to a regime with finite hexatic order and finite shear modulus, in which cells arrange according to a rhombile pattern with periodically arranged rosette structures. The shear modulus vanishes again at a third threshold beyond which spontaneous tissue flows and topological defects of the nematic cell shape field arise. Flow and stress fields around the defects agree with active nematic theory, with either contractile or extensile signs, as also observed in several epithelial tissue experiments.
MeSH term(s)	Cell Shape ; Stress, Mechanical ; Rheology
Language	English
Publishing date	2023-02-17
Publishing country	United States
Document type	Journal Article
ZDB-ID	208853-8
ISSN	1079-7114 ; 0031-9007
ISSN (online)	1079-7114
ISSN	0031-9007
DOI	10.1103/PhysRevLett.130.058202
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Book ; Online: Generic elasticity of thermal, under-constrained systems

Lee, Cheng-Tai / Merkel, Matthias

2023

Abstract: Athermal (i.e. zero-temperature) under-constrained systems are typically floppy, but they can be rigidified by the application of external strain, which is theoretically well understood. Here and in the companion paper, we extend this theory to finite ... ...

Abstract	Athermal (i.e. zero-temperature) under-constrained systems are typically floppy, but they can be rigidified by the application of external strain, which is theoretically well understood. Here and in the companion paper, we extend this theory to finite temperatures for a very broad class of under-constrained systems. In the vicinity of the athermal transition point, we derive from first principles expressions for elastic properties such as isotropic tension $t$ and shear modulus $G$ on temperature $T$, isotropic strain $\varepsilon$, and shear strain $\gamma$, which we confirm numerically. These expressions contain only three parameters, which depend on the microscopic structure of the system. These respectively describe entropic rigidity, energetic rigidity, and an interaction between isotropic and shear strain. Our results imply that in under-constrained systems, entropic and energetic rigidity interact like two springs in series. This also allows for a simple explanation of the previously observed scaling relation $t\sim G\sim T^{1/2}$ at $\varepsilon=\gamma=0$. Our work unifies the physics of systems as diverse as polymer fibers & networks, membranes, and vertex models for biological tissues. Comment: 6 pages, 4 figures
Keywords	Condensed Matter - Soft Condensed Matter ; Condensed Matter - Statistical Mechanics ; Physics - Biological Physics
Subject code	612
Publishing date	2023-04-14
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Book ; Online: Partition sum of thermal, under-constrained systems

Lee, Cheng-Tai / Merkel, Matthias

2023

Abstract: Athermal (i.e. zero-temperature) under-constrained systems are typically floppy, but they can be rigidified by the application of external strain. Following our recently-developed analytical theory for the athermal limit, here and in the companion paper, ...

Abstract	Athermal (i.e. zero-temperature) under-constrained systems are typically floppy, but they can be rigidified by the application of external strain. Following our recently-developed analytical theory for the athermal limit, here and in the companion paper, we extend this theory to under-constrained systems at finite temperatures close to the athermal transition point. We derive from first principles the partition sum for a broad class of under-constrained systems, from which we obtain analytic expressions for elastic material properties such as isotropic tension $t$ and shear modulus $G$ in terms of isotropic strain $\varepsilon$, shear strain $\gamma$, and temperature $T$. Our work unifies the physics of systems as diverse as polymer fibers & networks, membranes, and vertex models for biological tissues. Comment: 14 pages, no figures
Keywords	Condensed Matter - Soft Condensed Matter ; Condensed Matter - Statistical Mechanics ; Physics - Biological Physics
Subject code	612
Publishing date	2023-04-14
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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