Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events? (Site U610, DSDP Leg. 94)

2021 ◽  
Author(s):  
Dakota Holmes ◽  
David De Vleeschouwer ◽  
Audrey Morley
Keyword(s):  
Meridional Overturning Circulation ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
North Atlantic Current ◽  
Planktic Foraminifera ◽  
Climate Change Research ◽  
The North ◽  
Depth Scale ◽  
Climate Events ◽  
Glacial Climate

<p>Abrupt climate events are important features of glacial climate scales on centennial and millennial timescales. These events' mechanistic trigger is often ascribed to either ice sheet-related feedback mechanisms or large freshwater pulses. In both cases, amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Using sediment core DSDP U610B (53°13.297N, 18°53.213W) located in the Rockall Trough, we present a high-resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19.3 to 19.1 to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, U610 is influenced by Wyville Thomson Overflow Water flowing southwards. We utilise a multiproxy approach including paired grain size analysis, planktic foraminifera assemblage counts, and ice-rafted debris counts within the same samples allowing us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. We also present for the first time a new splice and composite depth scale for Site U610. Based on preliminary results, rapid shifts in both deep overflow and surface climate characterise this period.</p>

Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events?

2020 ◽  
Author(s):  
Dakota Holmes ◽  
Audrey Morley
Keyword(s):  
Ocean Circulation ◽  
Geographical Location ◽  
Greenland Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
North Atlantic Current ◽  
Climate Change Research ◽  
The North ◽  
Climate Events

<p>Abrupt climate events are generally believed to be characteristic of glacial (intermediate-to-large cryosphere) climate states, requiring either sizeable ice-sheets or large freshwater pulses to act as triggers for abrupt climate changes to occur. Amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Here we present a high resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19c to 19a to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Sediment core DSDP 610B (53°13.297N, 18°53.213W), located approximately 700-km west of Ireland, was specifically chosen due to its high sedimentation rate during interglacial periods, excellent core recovery over the Quaternary and its unique geographical location. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, 610B is influenced by Wyville Thomson Overflow Water flowing southwards. A multiproxy approach including paired grain size analysis, planktic foraminifer assemblage counts, and ice-rafted debris counts within the same samples allows us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. This study is societally relevant as future freshwater inputs from a melting Greenland ice sheet may impact ocean circulation, potentially causing shifts in climate for many European countries.</p>

scholarly journals Change in the North Atlantic circulation associated with the mid-Pleistocene transition

2018 ◽  
Vol 14 (11) ◽  
pp. 1639-1651 ◽  
Author(s):  
Gloria M. Martin-Garcia ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
Fátima Abrantes
Keyword(s):  
North Atlantic ◽  
Major Change ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
North Atlantic Current ◽  
The North ◽  
Oceanic Fronts ◽  
Surface Circulation ◽  
The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37∘34.285′ N, 10∘7.562′ W; 2585 m b.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55∘ N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100 ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100 ky cycles.

Does ocean resolution affect the rate of AMOC weakening?

2020 ◽  
Author(s):  
Helene Hewitt ◽  
Laura Jackson ◽  
Malcolm Roberts ◽  
Dorotea Iovino ◽  
Torben Koenigk ◽  
...  
Keyword(s):  
Deep Water ◽  
Horizontal Resolution ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Deep Water Formation ◽  
North Atlantic Current ◽  
The North ◽  
Water Formation ◽  
The Mean ◽  
Mean State

<p>We examine the weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to increasing CO<sub>2</sub> at different horizontal resolutions in HadGEM3-GC3.1 and in a small ensemble of models with differing resolutions. There is a strong influence of the ocean mean state on the AMOC weakening: models with a more saline western subpolar gyre have a greater formation of deep water there. This makes the AMOC more susceptible to weakening from an increase in CO<sub>2</sub> since weakening ocean heat transports weaken the contrast between ocean and atmospheric temperatures and hence weaken the buoyancy loss. In models with a greater proportion of deep water formation further north (in the Greenland-Iceland-Norwegian basin), deep-water formation can be maintained by shifting further north to where there is a greater ocean-atmosphere temperature contrast.</p><p>We show that ocean horizontal resolution can have an impact on the mean state, and hence AMOC weakening. In the models examined, those with higher resolutions tend to have a more westerly path of the North Atlantic Current and hence greater impact of the warm, saline subtropical Atlantic waters on the western subpolar gyre. This results in greater dense water formation in the western subpolar gyre. Although there is some improvement of the higher resolution models over the lower resolution models in terms of the mean state, both still have biases and it is not clear which biases are the most important for influencing the AMOC strength and response to increasing CO<sub>2</sub>.</p><p> </p>

scholarly journals The Internal Generation of the Atlantic Ocean Interdecadal Variability

2018 ◽  
Vol 31 (16) ◽  
pp. 6411-6432 ◽  
Author(s):  
Olivier Arzel ◽  
Thierry Huck ◽  
Alain Colin de Verdière
Keyword(s):  
Spatial Structure ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Interdecadal Variability ◽  
North Atlantic Current ◽  
Temperature Anomalies ◽  
The North ◽  
The North Atlantic ◽  
Atlantic Current

Abstract Numerical simulations of a realistic ocean general circulation model forced by prescribed surface fluxes are used to study the origin and structure of intrinsic interdecadal variability of the ocean circulation. When eddy-induced turbulent diffusivities are low enough, spontaneous oscillations of the Atlantic meridional overturning circulation (AMOC) with periods O(20) yr and amplitude O(1) Sv (1 Sv ≡ 106 m3 s−1) emerge. The transition from the steady to the oscillatory regime is shown to be consistent with a supercritical Hopf bifurcation of the horizontal Peclet number. Adding atmospheric thermal damping is shown to have a very limited influence on the domain of existence of intrinsic variability. The spatial structure of the mode consists of a dipole of sea surface temperature (SST)/sea surface height (SSH) anomalies centered at about 50°N with stronger variance in the western part of the subpolar gyre, in agreement with the observed Atlantic multidecadal oscillation (AMO) signature in this region. Specific features include a westward propagation of temperature anomalies from the source region located on the western flank of the North Atlantic Current (NAC) and a one-quarter phase lag between surface and subsurface (800 m) temperature anomalies. Local linear stability calculations including viscous and diffusive effects confirm that the North Atlantic Current is baroclinically unstable on scales of O(1000) km with growth rates of O(1) yr−1. Both the spatial structure of the mode and the period agree in magnitude with in situ measurements in the North Atlantic, suggesting that this intrinsic ocean mode participates in the observed Atlantic bidecadal climate variability.

scholarly journals A simple conceptual model of abrupt glacial climate events

2007 ◽  
Vol 14 (6) ◽  
pp. 709-721 ◽  
Author(s):  
H. Braun ◽  
A. Ganopolski ◽  
M. Christl ◽  
D. R. Chialvo
Keyword(s):  
Conceptual Model ◽  
Stochastic Resonance ◽  
Statistical Significance ◽  
Nonlinear Resonance ◽  
Characteristic Time Scale ◽  
The North ◽  
The Stability ◽  
Climate Events ◽  
Threshold Process ◽  
Glacial Climate

Abstract. Here we use a very simple conceptual model in an attempt to reduce essential parts of the complex nonlinearity of abrupt glacial climate changes (the so-called Dansgaard-Oeschger events) to a few simple principles, namely (i) the existence of two different climate states, (ii) a threshold process and (iii) an overshooting in the stability of the system at the start and the end of the events, which is followed by a millennial-scale relaxation. By comparison with a so-called Earth system model of intermediate complexity (CLIMBER-2), in which the events represent oscillations between two climate states corresponding to two fundamentally different modes of deep-water formation in the North Atlantic, we demonstrate that the conceptual model captures fundamental aspects of the nonlinearity of the events in that model. We use the conceptual model in order to reproduce and reanalyse nonlinear resonance mechanisms that were already suggested in order to explain the characteristic time scale of Dansgaard-Oeschger events. In doing so we identify a new form of stochastic resonance (i.e. an overshooting stochastic resonance) and provide the first explicitly reported manifestation of ghost resonance in a geosystem, i.e. of a mechanism which could be relevant for other systems with thresholds and with multiple states of operation. Our work enables us to explicitly simulate realistic probability measures of Dansgaard-Oeschger events (e.g. waiting time distributions, which are a prerequisite for statistical analyses on the regularity of the events by means of Monte-Carlo simulations). We thus think that our study is an important advance in order to develop more adequate methods to test the statistical significance and the origin of the proposed glacial 1470-year climate cycle.

scholarly journals Role of the North Atlantic circulation in the mid-Pleistocene transition

2018 ◽  
Author(s):  
Gloria M. Martin-Garcia ◽  
Francisco J. Sierro ◽  
José A. Flores ◽  
Fátima Abrantes
Keyword(s):  
North Atlantic ◽  
Major Change ◽  
Water Masses ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
North Atlantic Current ◽  
The North ◽  
Oceanic Fronts ◽  
Surface Circulation ◽  
The North Atlantic

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents, and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530 ka (MIS20-MIS14) is reconstructed, based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37°34.285' N, 10°7.562' W; 2585 m bsl). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55° N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100-ky cyclicity associated to the Mid-Pleistocene Transition. In surface, this change consisted in the re-distribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF) and the increase in the North Atlantic Deep Water (NADW) formation. During glacials prior to MIS 16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south-north, and east-west, thermal gradients and blockading the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the important increase in the meridional overturning circulation, in combination with the north-westward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheets growth, which worked as a positive feedback to prolong the glacials towards 100-ky cycles.

scholarly journals Recent high-energy marine events in the sediments of Lagoa de Óbidos and Martinhal (Portugal): recognition, age and likely causes

2012 ◽  
Vol 12 (5) ◽  
pp. 1367-1380 ◽  
Author(s):  
P. J. M. Costa ◽  
S. A. G. Leroy ◽  
J. L. Dinis ◽  
A. G. Dawson ◽  
S. Kortekaas
Keyword(s):  
North Atlantic ◽  
High Energy ◽  
Coastal Hazards ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
The North ◽  
A Value ◽  
Wide Range ◽  
Visual Description ◽  
The North Atlantic Oscillation

Abstract. A key issue in coastal hazards research is the need to distinguish sediments deposited by past extreme storms from those of past tsunamis. This study contributes to this aim by investigating patterns of sedimentation associated with extreme coastal flood events, in particular, within the Lagoa de Óbidos (Portugal). The recent stratigraphy of this coastal lagoon was studied using a wide range of techniques including visual description, grain-size analysis, digital and x-ray photography, magnetic susceptibility and geochemical analysis. The sequence was dated by 14C, 210Pb and Optically Stimulated Luminescence. Results disclose a distinctive coarser sedimentary unit, within the top of the sequence studied, and shown in quartz sand by the enrichment of elements with marine affinity (e.g., Ca and Na) and carbonates. The unit fines upwards and inland, thins inland and presents a sharp erosive basal contact. A noticeable post-event change in the sedimentary pattern was observed. The likely agent of sedimentation is discussed here and the conceivable association with the Great Lisbon tsunami of AD 1755 is debated, while a comparison is attempted with a possibly synchronous deposit from a tsunami in Martinhal (Algarve, Portugal). The possibility of a storm origin is also discussed in the context of the storminess of the western Portuguese coast and the North Atlantic Oscillation. This study highlights certain characteristics of the sedimentology of the deposits that may have a value in the recognition of extreme marine inundation signatures elsewhere in the world.

scholarly journals JENIS DAN SEBARAN SEDIMEN DI PERAIRAN PAPELA DAN SEKITARNYA, ROTE-NDAO, NUSA TENGGARA TIMUR

2016 ◽  
Vol 13 (3) ◽  
pp. 153
Author(s):  
Deny Setiady ◽  
Udaya Kamiludin ◽  
Nienu Yayu Gerhaneu
Keyword(s):  
Grain Size ◽  
Water Area ◽  
Silty Sand ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Sediment Grain Size ◽  
Sediment Distribution ◽  
The North ◽  
Sandy Silt ◽  
Seafloor Sediments

Daerah Penelitian terletak di perairan Papela dan sekitarnya yang merupakan bagian dari Selat Rote yang secara administratif merupakan wilayah dari Kabupaten Rote-Ndao, Provinsi Nusa Tenggara Timur. Di daerah penelitian pada 40 lokasi telah dilakukan pengambilan sedimen dasar laut dengan pemercontoh comot, deskripsi megaskopis dan analisis besar butir. Penelitian bertujuan untuk mengetahui jenis sedimen, sebaran sedimen dan lingkungan pengendapannya. Berdasarkan hasil analisis besar butir nomenklatur sedimen di daerah penelitian dijumpai 4 jenis sedimen yaitu: kerikil, pasir, pasir lanauan, lanau pasiran dan lanau. Sebaran kerikil terdapat di dua tempat, yaitu di utara dan selatan tepian daerah penelitian.Sebaran pasir mencapai kurang lebih 30 % dari luas perairan penelitian, pasir lanauan menutupi kurang 5 % dari luas perairan penelitian, lanau pasiran mempunyai sebaran kurang lebih 30 % dari luas perairan daerah penelitian dan sebaran lanau terdapat di muka muara sungai bagian dalam Teluk Papela dengan tutupan kurang lebih 5 % dari luas perairan penelitian.Kata kunci Sedimen permukaan dasar laut, analisis besar butir, sebaran sedimen, perairan Papela The study area is located in Papela waters area and that is part of the Rote Strait, administratively is a region of Rote-Ndao regency, East Nusa Tenggara Province. The method of research conducted is sampling seafloor sediments, megaskopis description and analysis of the grain size. The study area is located in Papela waters area and that is part of the Rote Strait, administratively is a region of Rote-Ndao regency, East Nusa Tenggara Province. The method of research conducted is sampling seafloor sediments, megaskopis description and analysis of the grain size. The purpose of research is the grain size analysis of seabed surface sediment to determine the type of sediment, sediment distribution and depositional environment. Based on nomenklature sediment grain size analysis result in the study area was found four types of sediments , there are: gravelly, sand, silty sand, sandy silt and silt Distribution of gravel found in two places, namely on the north and south banks of the study area. Distribution of sand reaches approximately 30% of the water area of research, silty sand covering approximately 5% of the water area of research, sandy silt has spread approximately 30% of the total water area of research and distribution of silt contained in the inner face of the Gulf estuaries Papela with cover approximately 5% of the water area of research. Keywords: Surficial sediment, grain size analysis, sediment distribution, Papela Waters

scholarly journals Radionuclide wiggle-matching reveals a non-synchronous Early Holocene climate oscillation in Greenland and Western Europe around a grand solar minimum

2019 ◽  
Author(s):  
Florian Mekhaldi ◽  
Markus Czymzik ◽  
Florian Adolphi ◽  
Jesper Sjolte ◽  
Svante Björck ◽  
...  
Keyword(s):  
North Atlantic ◽  
Solar Minimum ◽  
Ice Cores ◽  
Meridional Overturning Circulation ◽  
Early Holocene ◽  
Solar Forcing ◽  
Concentration Data ◽  
The North ◽  
The North Atlantic ◽  
Climate Events

Abstract. Several climate events have been reported from the Early Holocene superepoch, the best known of these being the Preboreal oscillation (PBO). It is still unclear how the PBO and the number of climate events observed in Greenland ice cores and European terrestrial records are related to one another. This is mainly due to uncertainties in the chronologies of the records. Here, we present new high resolution 10Be concentration data from the varved Meerfelder Maar sediment record in Germany, spanning the period 11310–11000 years BP. These new data allow us to synchronize this well-studied record as well as Greenland ice-core records to the IntCal13 time-scale via radionuclide wiggle-matching. In doing so, we show that the climate oscillations identified in Greenland and Europe between 11450 and 11000 years BP were not synchronous but terminated and began, respectively, with the onset of a grand solar minimum. A similar spatial anomaly pattern is found in a number of modeling studies on solar forcing of climate in the North Atlantic region. We further postulate that freshwater delivery to the North Atlantic would have had the potential to amplify solar forcing through a slowdown of the Atlantic meridional overturning circulation (AMOC) reinforcing surface air temperature anomalies in the region.

Grain Size and Provenance of Bahia la Choya Sediments

1987 ◽  
Vol 2 ◽  
pp. 44-51 ◽  
Author(s):  
Lawrence T. Sumpter
Keyword(s):  
Grain Size ◽  
Tidal Flat ◽  
Volcanic Rocks ◽  
Heavy Minerals ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Rock Fragments ◽  
The North ◽  
Average Grain Size ◽  
Carbonate Shell

A grain size analysis (including the carbonate fraction) was performed on sediment samples from each of the following environments of Bahia la Choya: tidal flat, spit, beach, and estero. The sediments of the tidal flat have an average grain size of 2.88 phi, range from very well sorted to moderately well sorted, and have a carbonate shell fraction ranging from 1 to 30%. The spit sediments have an average grain size of 0.96 phi, are moderately to poorly sorted, and have a carbonate shell fraction of approximately 50%. The beach sediments have an average grain size of 1.22 phi, range from poorly sorted to moderately well sorted, and have a carbonate shell fraction of approximately 48%. The sediments of the estero average 39% sand, 40% silt, and 20% clay. The carbonate fraction in the estero is approximately 25%. The noncarbonate fraction in all the environments is made up of feldspar, quartz, biotite, heavy minerals, and igneous rock fragments.The major source for the sediment is the Pelican Point granite on the south side of the bay. Pleistocene rock in and around the bay provides a second source of sediment and volcanic rocks to the north may also contribute to the sediment.

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