Transport of planktic foraminifera by ocean currents in the Uruguayan margin

2020 ◽  
Author(s):  
Anne Kruijt ◽  
Andrew Mair ◽  
Peter Nooteboom ◽  
Anna S. von der Heydt ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Biological Activity ◽  
General Circulation ◽  
Ocean Currents ◽  
Western Boundary ◽  
Planktic Foraminifera ◽  
The Core ◽  
Temperature Distributions ◽  
Species Analysis ◽  
Core Site ◽  
Ocean Conditions

<p><span>Fossils of planktic foraminifera are found in marine sediments and are widely used as a proxy for past ocean conditions. The habitat of these unicellular marine zooplankton ranges from tropical to polar regions and is mostly located in the upper mixed layer of the ocean. The foraminifera form a calcium carbonate ’shell’ around their cell during their lifespan. When they die, foraminifera lose their ability to control their buoyancy and their shells sink to the ocean floor. It is often assumed that the proxies which are derived from the shells in sediment cores represent ocean conditions above the location of deposition. However, foraminifera are transported by ocean currents, both during and after their lifespan. Hence, the paleoclimatic conditions recorded from their shells may originate far from the core site, generating large footprints in foraminifera-based paleoclimatic proxies.</span><span> </span></p><p><span>In this project, we quantify the influence of the transport by ocean currents on the proxy signal of foraminifera found at core sites in the Uruguayan margin of the Punta del Este basin. This is a region where two western boundary currents meet: The southward flowing Brazil current and the northward flowing Malvinas current. We use a high resolution (0.1° horizontally) ocean general circulation model to track virtual sinking particles and the local oceanic conditions along their pathways. These model results are compared to proxy- and species analysis from the core sites. We found that offsets in modelled proxy signals due to transport in the Uruguayan margin are strongly linked to the relative position of the core site to the Brazil-Malvinas confluence. These offsets are most pronounced in the tails of the temperature distributions where they can reach up to +/- 7°C at sites located in the confluence zone. Species analysis from core tops taken slightly north of this region show more cold water species than reflected by the modelled temperature distributions, suggesting biological activity and nutrient availability not taken into account in the model play an important additional role in the relative abundances of species. <br></span><span>Our model simulations have provided both a first order insight into the potential proxy-signal offsets in highly dynamic ocean regions and show that understanding of the interplay between transportation effects and the biological activity of foraminifera is crucial for the interpretation of these proxies.</span></p><p> </p>

scholarly journals Estimating the Continental Response to Global Warming Using Pattern-Scaled Sea Surface Temperatures and Sea Ice

2016 ◽  
Vol 29 (24) ◽  
pp. 9125-9139 ◽  
Author(s):  
Adeline Bichet ◽  
Paul J. Kushner ◽  
Lawrence Mudryk
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
Sea Surface ◽  
Climate Projections ◽  
Western Boundary ◽  
Sea Ice Concentration ◽  
Continental Climate

Abstract Better constraining the continental climate response to anthropogenic forcing is essential to improve climate projections. In this study, pattern scaling is used to extract, from observations, the patterned response of sea surface temperature (SST) and sea ice concentration (SICE) to anthropogenically dominated long-term global warming. The SST response pattern includes a warming of the tropical Indian Ocean, the high northern latitudes, and the western boundary currents. The SICE pattern shows seasonal variations of the main locations of sea ice loss. These SST–SICE response patterns are used to drive an ensemble of an atmospheric general circulation model, the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5), over the period 1980–2010 along with a standard AMIP ensemble using observed SST—SICE. The simulations enable attribution of a variety of observed trends of continental climate to global warming. On the one hand, the warming trends observed in all seasons across the entire Northern Hemisphere extratropics result from global warming, as does the snow loss observed over the northern midlatitudes and northwestern Eurasia. On the other hand, 1980–2010 precipitation trends observed in winter over North America and in summer over Africa result from the recent decreasing phase of the Pacific decadal oscillation and the recent increasing phase of the Atlantic multidecadal oscillation, respectively, which are not part of the global warming signal. The method holds promise for near-term decadal climate prediction but as currently framed cannot distinguish regional signals associated with oceanic internal variability from aerosol forcing and other sources of short-term forcing.

scholarly journals Methanesulphonic acid movement in solid ice cores

2004 ◽  
Vol 39 ◽  
pp. 540-544 ◽  
Author(s):  
Barbara T. Smith ◽  
Tas D. Van Ommen ◽  
Mark A. J. Curran
Keyword(s):  
Diffusion Coefficient ◽  
Biological Activity ◽  
Sea Ice ◽  
Diffusion Mechanism ◽  
Ice Core ◽  
Ice Cores ◽  
East Antarctica ◽  
The Core ◽  
Central Value

AbstractMethanesulphonic acid (MSA) is an important trace-ion constituent in ice cores, with connections to biological activity and sea-ice distribution. Post-depositional movement of MSA has been documented in firn, and this study investigates movement in solid ice by measuring variations in MSA distribution across several horizontal sections from an ice core after 14.5 years storage. The core used is from below the bubble close-off depth at Dome Summit South, Law Dome, East Antarctica. MSA concentration was studied at 3 and 0.5 cm resolution across the core widths. Its distribution was uniform through the core centres, but the outer 3 cm showed gradients in concentrations down to less than half of the central value at the core edge. This effect is consistent with diffusion to the surrounding air during its 14.5 year storage. The diffusion coefficient is calculated to be 2 ×10–13 m2 s–1, and the implications for the diffusion mechanism are discussed.

scholarly journals A novel hybrid of Hypericum undulatum (Wavy-leaved St. John’s-wort, Hypericaceae) and its subsequent dispersal

2020 ◽  
Vol 2 (3) ◽  
Author(s):  
Andrew Jones ◽  
Fred Rumsey
Keyword(s):  
De Novo ◽  
Parental Species ◽  
Species Range ◽  
The Novel ◽  
The Core ◽  
St John’S Wort ◽  
St John's Wort ◽  
Core Site

The novel hybrid Hypericum undulatum Schousb. ex. Willd. x H. perforatum L. is described from Cardiganshire (v.c.46) and given the name H. x cereticae R.A. Jones, F.J. Rumsey & N. Robson.  Despite reduced fertility it shows indications of ongoing introgression and signs of recent dispersal up to 5 km from the core site. The hybrid has arisen recently at the northern extremes of the rarer (H. undulatum) parental species’ range, although at neither site are the parents currently sympatric and in the outlying population both are absent, supporting the belief that here it has not arisen de novo but has colonised through unknown agencies.

scholarly journals The Deep Western Boundary Current at Cape Farewell: Results from a Moored Current Meter Array

2010 ◽  
Vol 40 (4) ◽  
pp. 815-829 ◽  
Author(s):  
Sheldon Bacon ◽  
Peter M. Saunders
Keyword(s):  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Marked Contrast ◽  
The Core ◽  
Deep Western Boundary Current ◽  
The Difference ◽  
Long Term Trend ◽  
Made In

Abstract An analysis is made of data from 30 Aanderaa recording current meters (RCMs) set on nine moorings located east of Cape Farewell, the southern tip of Greenland. The purpose of the measurements was to allow for the estimation of transport in the deep western boundary current (DWBC) below a depth of about 1500 m. The records commenced in September 2005 and lasted from 9.5 to 11.5 months. After calibration of the raw data, 12-h averages of temperature and current were derived and the latter employed to estimate the flow across and along the array direction. The 9.5-month average transport of water colder than 3°C was found to be 7.8 Sv (1 Sv ≡ 1 × 106 m3 s−1) with a standard error of 0.8 Sv. For water denser than σθ = 27.85 kg m−3, the transport is calculated as 4.5 Sv. Whether either of these values is significantly different from comparable measurements made 500 km upstream cannot be determined. In marked contrast, for σθ > 27.8 kg m−3, the transport is estimated as only 9.0 Sv, smaller than the widely accepted value of 13 Sv for nearby measurements made in 1978. A reevaluation of the calculations and assumptions made then allows one to determine the uncertainty of the earlier estimate and thereby conclude that the difference between the previous and present measurements is significant, that is, that the transport has decreased between 1978 and 2005–06. A weakening of the transport during the 9.5-month period is also observed, along with a warming and an increase in salinity in the core of the DWBC. These latter changes are shown to be consistent with interannual variability rather than a long-term trend.

Event detection and visualization of ocean eddies simulated by ocean general circulation model

2019 ◽  
Vol 10 (03) ◽  
pp. 1950018
Author(s):  
Daisuke Matsuoka ◽  
Fumiaki Araki ◽  
Hideharu Sasaki
Keyword(s):  
High Resolution ◽  
General Circulation ◽  
Numerical Study ◽  
Circulation Model ◽  
General Circulation Models ◽  
Ocean Currents ◽  
Time Step ◽  
Data Set ◽  
Ocean Eddies ◽  
Ocean General Circulation

Numerical study of ocean eddies has been carried out by using high-resolution ocean general circulation models. In order to understand ocean eddies from the large volume data produced by simulations, visualizing only eddy distribution at each time step is insufficient; time-variations in eddy events and phenomena must also be considered. However, existing methods cannot precisely find and track eddy events such as amalgamation and bifurcation. In this study, we propose an original approach for eddy detection, tracking, and event visualization based on an eddy classification system. The proposed method detects streams and currents as well as eddies, and it classifies discovered eddies into several categories using the additional stream and current information. By tracking how the classified eddies vary over time, detecting events such as eddy amalgamation and bifurcation as well as the interaction between eddies and ocean currents becomes achievable. We adopt the proposed method for two ocean areas in which strong ocean currents exist as case studies. We visualize the detected eddies and events in a time series of images, allowing us to acquire an intuitive understanding of a region of interest concealed in a high-resolution data set. Furthermore, our proposed method succeeded in clarifying the occurrence place and seasonality of each type of eddy event.

scholarly journals Regulation of the T-cell receptor delta enhancer by functional cooperation between c-Myb and core-binding factors.

1994 ◽  
Vol 14 (1) ◽  
pp. 473-483 ◽  
Author(s):  
C Hernandez-Munain ◽  
M S Krangel
Keyword(s):  
T Cell ◽  
T Cell Receptor ◽  
Transcriptional Activation ◽  
Cell Receptor ◽  
Enhancer Activity ◽  
Control Of Gene Expression ◽  
Enhancer Element ◽  
The Core ◽  
Core Site ◽  
Factor C

A T-cell-specific transcriptional enhancer lies within the J delta 3-C delta intron of the human T-cell receptor (TCR) delta gene. The 30-bp minimal enhancer element denoted delta E3 carries a core sequence (TGTGGTTT) that binds a T-cell-specific factor, and that is necessary but not sufficient for transcriptional activation. Here we demonstrate that the transcription factor c-Myb regulates TCR delta enhancer activity through a binding site in delta E3 that is adjacent to the core site. Both v-Myb and c-Myb bind specifically to delta E3. The Myb site is necessary for enhancer activity, because a mutation that eliminates Myb binding abolishes transcriptional activation by the delta E3 element and by the 370-bp TCR delta enhancer. Transfection of cells with a c-Myb expression construct upregulates delta E3 enhancer activity, whereas treatment of cells with an antisense c-myb oligonucleotide inhibits delta E3 enhancer activity. Since intact Myb and core sites are both required for delta E3 function, our data argue that c-Myb and core binding factors must cooperate to mediate transcriptional activation through delta E3. Efficient cooperation depends on the relative positioning of the Myb and core sites, since only one of two overlapping Myb sites within delta E3 is functional and alterations of the distance between this site and the core site disrupt enhancer activity. Cooperative regulation by c-Myb and core-binding factors is likely to play an important role in the control of gene expression during T-cell development.

scholarly journals Origin and Pathway of Equatorial 13°C Water in the Pacific Identified by a Simulated Passive Tracer and Its Adjoint*

2009 ◽  
Vol 39 (8) ◽  
pp. 1836-1853 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao ◽  
Ichiro Fukumori ◽  
Rana A. Fine ◽  
Eric J. Lindstrom
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
South Pacific ◽  
Equatorial Region ◽  
Equatorial Pacific ◽  
Western Boundary ◽  
Passive Tracer ◽  
The South ◽  
Mode Water ◽  
Eastern Equatorial Pacific

Abstract The origin and pathway of the thermostad water in the eastern equatorial Pacific Ocean, often referred to as the equatorial 13°C Water, are investigated using a simulated passive tracer and its adjoint, based on circulation estimates of a global general circulation model. Results demonstrate that the source region of the 13°C Water lies well outside the tropics. In the South Pacific, some 13°C Water is formed northeast of New Zealand, confirming an earlier hypothesis on the water’s origin. The South Pacific origin of the 13°C Water is also related to the formation of the Eastern Subtropical Mode Water (ESTMW) and the Sub-Antarctic Mode Water (SAMW). The portion of the ESTMW and SAMW that eventually enters the density range of the 13°C Water (25.8 < σθ < 26.6 kg m−3) does so largely by mixing. Water formed in the subtropics enters the equatorial region predominantly through the western boundary, while its interior transport is relatively small. The fresher North Pacific ESTMW and Central Mode Water (CMW) are also important sources of the 13°C Water. The ratio of the southern versus the northern origins of the water mass is about 2 to 1 and tends to increase with time elapsed from its origin. Of the total volume of initially tracer-tagged water in the eastern equatorial Pacific, approximately 47.5% originates from depths above σθ = 25.8 kg m−3 and 34.6% from depths below σθ = 26.6 kg m−3, indicative of a dramatic impact of mixing on the route of subtropical water to becoming the 13°C Water. Still only a small portion of the water formed in the subtropics reaches the equatorial region, because most of the water is trapped and recirculates in the subtropical gyre.

Gliders Measure Western Boundary Current Transport from the South Pacific to the Equator*

2012 ◽  
Vol 42 (11) ◽  
pp. 2001-2013 ◽  
Author(s):  
Russ E. Davis ◽  
William S. Kessler ◽  
Jeffrey T. Sherman
Keyword(s):  
El Niño ◽  
El Nino ◽  
Layer Structure ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
The Core ◽  
A Value ◽  
Coral Sea ◽  
Near Shore

Abstract “Spray” gliders, most launched from small boats near shore, have established a sustainable time series of equatorward transport through the Solomon Sea. The first 3.5 years (mid-2007 through 2010) are analyzed. Coast-to-coast equatorward transport through the Solomon Sea fluctuates around a value of 15 Sv (1 Sv ≡ 106 m3 s−1) with variations approaching ±15 Sv. Transport variability is well correlated with El Niño indices like Niño-3.4, with strong equatorward flow during one El Niño and weak flow during two La Niñas. Mean transport is centered in an undercurrent focused in the western boundary current; variability has a two-layer structure with layers separated near 250 m (near the core of the undercurrent) that fluctuate independently. The largest variations are in midbasin, confined to the upper layer, and are well correlated with ENSO. Analysis of velocity and salinity on isopycnals shows that the western boundary current within the Solomon Sea consists of a deep core coming from the Coral Sea and a shallow core that enters the Solomon Sea in mid basin. Analysis of the structure of transport and its fluctuations is presented.

scholarly journals Water Mass Export from Drake Passage to the Atlantic, Indian, and Pacific Oceans: A Lagrangian Model Analysis

2005 ◽  
Vol 35 (7) ◽  
pp. 1206-1222 ◽  
Author(s):  
Yann Friocourt ◽  
Sybren Drijfhout ◽  
Bruno Blanke ◽  
Sabrina Speich
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Drake Passage ◽  
General Circulation Models ◽  
Lagrangian Model ◽  
Global Ocean ◽  
Western Boundary ◽  
Intermediate Water ◽  
Boundary Current ◽  
The Indian Ocean

Abstract The northward export of intermediate water from Drake Passage is investigated in two global ocean general circulation models (GCMs) by means of quantitative particle tracing diagnostics. This study shows that a total of about 23 Sv (Sv ≡ 106 m3 s−1) is exported from Drake Passage to the equator. The Atlantic and Pacific Oceans are the main catchment basins with 7 and 15 Sv, respectively. Only 1–2 Sv of the water exported to the Atlantic equator follow the direct cold route from Drake Passage without entering the Indian Ocean. The remainder loops first into the Indian Ocean subtropical gyre and flows eventually into the Atlantic Ocean by Agulhas leakage. The authors assess the robustness of a theory that relates the export from Drake Passage to the equator to the wind stress over the Southern Ocean. Our GCM results are in reasonable agreement with the theory that predicts the total export. However, the theory cannot be applied to individual basins because of interocean exchanges through the “supergyre” mechanism and other nonlinear processes such as the Agulhas rings. The export of water from Drake Passage starts mainly as an Ekman flow just northward of the latitude band of the Antarctic Circumpolar Current south of South America. Waters quickly subduct and are transferred to the ocean interior as they travel equatorward. They flow along the eastern boundaries in the Sverdrup interior and cross the southern basins northwestward to reach the equator within the western boundary current systems.

scholarly journals Effect of a Variable Eddy Transfer Coefficient in an Eddy-Permitting Model of the Subpolar North Atlantic Ocean

2005 ◽  
Vol 35 (3) ◽  
pp. 289-307 ◽  
Author(s):  
Daniel Deacu ◽  
Paul G. Myers
Keyword(s):  
Atlantic Ocean ◽  
Transfer Coefficient ◽  
North Atlantic ◽  
General Circulation ◽  
North Atlantic Ocean ◽  
Negative Impact ◽  
Labrador Sea ◽  
Western Boundary ◽  
Near Surface ◽  
Eastern North Atlantic

Abstract The effect of using a variable eddy transfer coefficient for the Gent–McWilliams (GM) parameterization in a (1/3)°-resolution ocean model of the subpolar North Atlantic Ocean is investigated. Results from four experiments with different implementations of this coefficient are compared among themselves as well as with two control experiments. A series of improvements have been obtained in all of the experiments that use a low level of explicit horizontal tracer diffusion. These include a better representation of the overflow waters originating from the Nordic seas, leading to a more realistic deep western boundary current and to increased eddy activity in the deep ocean in the eastern North Atlantic. In the same experiments, the GM velocities “help” the Labrador Sea Water to spread from the deep convection region to the currents that surround it without incurring significant spurious diapycnal mixing. Thus, two classical pathways for the spreading of this water are established. Moreover, the simulated Labrador Current and the near-surface circulation in the eastern North Atlantic are in better agreement with flow patterns inferred from observations. The increased release of available potential energy obtained in the experiments with variable eddy transfer coefficients is responsible for the simulation of a flow that varies less in time. An overly strong countercurrent still occurs in the Labrador Sea in these experiments, and it has a negative impact on the pathway of the North Atlantic Current in the “Northwest Corner” and on the hydrography of the Labrador Sea. Nonetheless and overall, the use of the variable eddy transfer coefficient has led to better representations of the general circulation and hydrography in the subpolar North Atlantic.

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