Iceland-Faroe Ridge overflow dynamics, 55-6 ka BP

2020 ◽  
Author(s):  
Maryam Mirzaloo ◽  
Dirk Nürnberg ◽  
Markus Kienast ◽  
Jeroen van der Lubbe
Keyword(s):  
Grain Size ◽  
Ocean Circulation ◽  
Academic Career ◽  
Meridional Overturning Circulation ◽  
Bottom Current ◽  
Oceanic Circulation ◽  
Climate Conditions ◽  
Bottom Currents ◽  
The Past ◽  
Bulk Chemistry

<p>The understanding of the past changes in this critical area of oceanic circulation will be beneficial to predict future climate conditions and their related socio-economic impacts. Sediment cores recovered from the western flank of the Iceland-Faroe Ridge (IFR; P457-905 and -909) provide unique archives to reconstruct changes in the Iceland-Scotland overflow water (ISOW), an important component of the Atlantic Meridional Overturning Circulation (AMOC) over the last 55-6 ka BP. We provide high-resolution records of lithogenic grain-size and XRF bulk chemistry on millennial timescales. The age models of both cores have been constrained by radiocarbon datings of planktonic foraminifera and distinct tephra layers, which include the well-known Faroe-Marine-Ash-Zones (FMAZ) II and III. Both grain-size and XRF bulk chemistry (Zr/Rb and Ti/K) reveal prominent Dansgaard-Oeschger sedimentary cycles, which reflect considerable changes in near-bottom current strength and sediment transport/deposition. The transition between cold Greenland Stadials (GSs) and warm Greenland Interstadials (GIs) occur in typical, recurring sedimentation patterns. The GIs are characterized by relatively strong bottom currents and the transport/deposition of basaltic (Ti-rich) silts from local volcanic sources resembling the modern ocean circulation pattern. In contrast, fine grained felsic (K-rich) sediments were deposited during GSs, when the ISOW was weak. In particular, the Heinrich (like) Stadials HS1 and HS2 stand out as intervals of very fine felsic sediment deposition and hence, slackened bottom currents. The bottom currents appear to progressively strengthen throughout the GIs, and sharply decline towards the GSs. This pattern contrasts with records from north of the IFR, which might be explained by a diminishing contribution of the flow cascading over the IFR. Together, these new records show strong changes in bottom current dynamics related to the Iceland-Scotland overflow, which has a strong influence on the past and modern climate of the North Atlantic Region. However, climate change is an interdisciplinary field of research. HOSST-TOSST transatlantic interdisciplinary research program provides the unique opportunity for constructive communication and collaboration among scientists with different skills filling knowledge gaps and bridging the earth sciences with social and economic disciplines. Such interdisciplinary programs at early stages in an academic career is necessary to move and encourage the new generation of the scientific community toward a tradition of broad‐scale interactions.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p>

scholarly journals Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation

2010 ◽  
Vol 6 (5) ◽  
pp. 1811-1852 ◽  
Author(s):  
A. Bozbiyik ◽  
M. Steinacher ◽  
F. Joos ◽  
T. F. Stocker
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Carbon Stocks ◽  
Meridional Overturning Circulation ◽  
Climate Conditions ◽  
Tropical Regions ◽  
The North ◽  
Northern Latitudes

Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes that are well documented in the literature but there is a clear distinction between northern and southern perturbations. Changes in the physical variables affect, in return, the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large re-organizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results.

scholarly journals Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation

2011 ◽  
Vol 7 (1) ◽  
pp. 319-338 ◽  
Author(s):  
A. Bozbiyik ◽  
M. Steinacher ◽  
F. Joos ◽  
T. F. Stocker ◽  
L. Menviel
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Carbon Stocks ◽  
Meridional Overturning Circulation ◽  
Climate Conditions ◽  
Tropical Regions ◽  
Proxy Records ◽  
The North

Abstract. CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes qualitatively in agreement with results documented in the literature, but there is a clear distinction between northern and southern perturbations. Changes in the physical variables, in turn, affect the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 concentration by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large reorganizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results. The proxy records, in general, show good agreement with the model's response to a North Atlantic freshwater perturbation.

scholarly journals Utilizing sponge spicules in taxonomic, ecological and environmental reconstructions: a review

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e10601
Author(s):  
Magdalena Łukowiak
Keyword(s):  
Ocean Circulation ◽  
Environmental Data ◽  
Silicon Isotope ◽  
Structural Elements ◽  
Climate Conditions ◽  
The Past ◽  
Sponge Spicules ◽  
Silica Cycle ◽  
Taxonomic Assignments ◽  
Water Depths

Most sponges produce skeletons formed by spicules, structural elements that develop in a wide variety of sizes and tridimensional shapes. The morphologies of spicules are often unique to clade- or even species-level taxa which makes them particularly useful in taxonomic assignments. When dead sponge bodies disintegrate, spicules become incorporated into sediments and sometimes accumulate into enormous agglomerations called spicule mats or beds, or fossilize to form special type of rocks called the spiculites. The record of fossil and subfossil sponge spicules is extraordinarily rich and often serves as a basis for far-reaching reconstructions of sponge communities, though spicules are also bearers of significant ecological and environmental information. Specific requirements and preferences of sponges can be used to interpret the environment in which they lived, and reconstruct oscillations in water depths, pH, temperatures, and other parameters, providing snapshots of past climate conditions. In turn, the silicon isotope compositions in spicules (δ30Si) are being increasingly often used to estimate the level of silicic acid in the marine settings throughout the geological history, which enables to reconstruct the past silica cycle and ocean circulation. This contribution provides a review of the use of sponge spicules in reconstructions of sponge communities, their ecology, and environments, and aims to detect the pertinent gaps in their utilization. Even though spicules are well known for their significance as bearers of taxonomic, ecological, and environmental data, their potential remains to be fully exploited.

scholarly journals Hybrid turbidite-drift channel complexes: An integrated multiscale model

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 562-568 ◽  
Author(s):  
A. Fuhrmann ◽  
I.A. Kane ◽  
M.A. Clare ◽  
R.A. Ferguson ◽  
E. Schomacker ◽  
...  
Keyword(s):  
Sediment Transport ◽  
High Resolution ◽  
Large Scale ◽  
Sediment Accumulation ◽  
Multiscale Model ◽  
Transport Processes ◽  
Bottom Current ◽  
Oceanic Circulation ◽  
Bottom Currents ◽  
Gravity Flows

Abstract The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems.

scholarly journals 100 Years of the Ocean General Circulation

2018 ◽  
Vol 59 ◽  
pp. 7.1-7.32 ◽  
Author(s):  
Carl Wunsch ◽  
Raffaele Ferrari
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Large Scale ◽  
Time Dependent ◽  
Steady Flows ◽  
Oceanic Circulation ◽  
Boundary Current ◽  
Geophysical Fluid Dynamics ◽  
The Past ◽  
The Tropics

Abstract The central change in understanding of the ocean circulation during the past 100 years has been its emergence as an intensely time-dependent, effectively turbulent and wave-dominated, flow. Early technologies for making the difficult observations were adequate only to depict large-scale, quasi-steady flows. With the electronic revolution of the past 50+ years, the emergence of geophysical fluid dynamics, the strongly inhomogeneous time-dependent nature of oceanic circulation physics finally emerged. Mesoscale (balanced), submesoscale oceanic eddies at 100-km horizontal scales and shorter, and internal waves are now known to be central to much of the behavior of the system. Ocean circulation is now recognized to involve both eddies and larger-scale flows with dominant elements and their interactions varying among the classical gyres, the boundary current regions, the Southern Ocean, and the tropics.

scholarly journals Orbital- and millennial-scale Antarctic Circumpolar Current variability in Drake Passage over the past 140,000 years

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shuzhuang Wu ◽  
Lester Lembke-Jene ◽  
Frank Lamy ◽  
Helge W. Arz ◽  
Norbert Nowaczyk ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Sediment Grain Size ◽  
The Past ◽  
Circumpolar Current ◽  
Millennial Scale

AbstractThe Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

scholarly journals A modeling sensitivity study of the influence of the Atlantic meridional overturning circulation on neodymium isotopic composition at the Last Glacial Maximum

2008 ◽  
Vol 4 (3) ◽  
pp. 191-203 ◽  
Author(s):  
T. Arsouze ◽  
J.-C. Dutay ◽  
M. Kageyama ◽  
F. Lacan ◽  
R. Alkama ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Oceanic Circulation ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial ◽  
Modern Control

Abstract. Using a simple parameterisation that resolves the first order global Nd isotopic composition (hereafter expressed as εNd in an Ocean Global Circulation Model, we have tested the impact of different circulation scenarios on the εNd in the Atlantic for the Last Glacial Maximum (LGM), relative to a modern control run. Three different LGM freshwater forcing experiments are performed to test for variability in the εNd oceanic distribution as a function of ocean circulation. Highly distinct representations of the ocean circulation are generated in the three simulations, which drive significant differences in εNd, particularly in deep waters of the western part of the basin. However, at the LGM, the Atlantic is more radiogenic than in the modern control run, particularly in the Labrador basin and in the Southern Ocean. A fourth experiment shows that changes in Nd sources and bathymetry drive a shift in the εNd signature of the basin that is sufficient to explain the changes in the εNd signature of the northern end-member (NADW or GNAIW glacial equivalent) in our LGM simulations. All three of our LGM circulation scenarios show good agreement with the existing intermediate depth εNd paleo-data. This study cannot indicate the likelihood of a given LGM oceanic circulation scenario, even if simulations with a prominent water mass of southern origin provide the most conclusive results. Instead, our modeling results highlight the need for more data from deep and bottom waters from western Atlantic, where the εNd change in the three LGM scenarios is the most important (up to 3 εNd. This would also aid more precise conclusions concerning the evolution of the northern end-member εNd signature, and thus the potential use of εNd as a tracer of past oceanic circulation.

scholarly journals Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

2020 ◽  
Author(s):  
Shuzhuang Wu ◽  
Lester Lembke-Jene ◽  
Frank Lamy ◽  
Helge Arz ◽  
Norbert Nowaczyk ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Cold Water ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
The Past ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Millennial Scale

Abstract The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

scholarly journals Effect of changing ocean circulation on deep ocean temperature in the last millennium

2020 ◽  
Vol 11 (4) ◽  
pp. 925-951
Author(s):  
Jeemijn Scheen ◽  
Thomas F. Stocker
Keyword(s):  
Surface Temperature ◽  
Ocean Circulation ◽  
Little Ice Age ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Ocean Temperature ◽  
Temperature Anomalies ◽  
The Past ◽  
The Impact

Abstract. Paleoreconstructions and modern observations provide us with anomalies of surface temperature over the past millennium. The history of deep ocean temperatures is much less well-known and was simulated in a recent study for the past 2000 years under forced surface temperature anomalies and fixed ocean circulation. In this study, we simulate the past 800 years with an illustrative forcing scenario in the Bern3D ocean model, which enables us to assess the impact of changes in ocean circulation on deep ocean temperature. We quantify the effect of changing ocean circulation by comparing transient simulations (where the ocean dynamically adjusts to anomalies in surface temperature – hence density) to simulations with fixed ocean circulation. We decompose temperature, ocean heat content and meridional heat transport into the contributions from changing ocean circulation and changing sea surface temperature (SST). In the deep ocean, the contribution from changing ocean circulation is found to be as important as the changing SST signal itself. Firstly, the small changes in ocean circulation amplify the Little Ice Age signal at around 3 km depth by at least a factor of 2, depending on the basin. Secondly, they fasten the arrival of this atmospheric signal in the Pacific and Southern Ocean at all depths, whereas they delay the arrival in the Atlantic between about 2.5 and 3.5 km by two centuries. This delay is explained by an initial competition between the Little Ice Age cooling and a warming due to an increase in relatively warmer North Atlantic Deep Water at the cost of Antarctic Bottom Water. Under the consecutive Atlantic meridional overturning circulation (AMOC) slowdown, this shift in water masses is inverted and ageing of the water causes a late additional cooling. Our results suggest that small changes in ocean circulation can have a large impact on the amplitude and timing of ocean temperature anomalies below 2 km depth.

Can satellites replace mooring arrays? Satellite altimetry transport estimates of the Atlantic overturning meridional circulation along the RAPID 26°N mooring array

2020 ◽  
Author(s):  
Alejandra Sanchez-Franks ◽  
Eleanor Frajka-Williams ◽  
Ben Moat
Keyword(s):  
Surface Layer ◽  
Ocean Circulation ◽  
Satellite Altimetry ◽  
Large Scale ◽  
Function Analysis ◽  
Spatial Scales ◽  
Meridional Overturning Circulation ◽  
Return Flow ◽  
Western Boundary ◽  
Oceanic Circulation

<p>The Atlantic meridional overturning circulation (AMOC) is a large-scale oceanic circulation comprising a 2-layer flow: the net northward flow in the upper 1000 m of the Atlantic and net southward flow below. Variations in the AMOC have significant repercussions for the climate system hence there is a need for proxies that can measure changes in the AMOC on larger spatial scales. Here we show a direct calculation of ocean circulation at 26°N from satellites compares well with transport estimates from the RAPID mooring array. In the surface layer (1000 m), transport is estimated from satellite altimetry and has a correlation of r=0.79 (significant at 95% level) with the MOC transport estimates from RAPID. We find that the relationship between sea level anomaly and dynamic height from the western boundary RAPID moorings is robust in the surface layer, with poor agreement occurring largely below 1000 m. Below 1000 m, the return flow of the AMOC is estimated using ocean bottom pressure from satellite gravimetry. This has a correlation of r=0.75 (significant at the 95% level) when compared to the deeper (1000-5000 m) RAPID transports. Combining the results from satellite altimetry and gravimetry, estimates of full-depth 2-layer circulation at 26°N are demonstrated. Finally, empirical orthogonal function analysis reveals that the barotropic and baroclinic streamfunctions are linked to wind stress curl and buoyancy forcing, respectively.</p>

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