Biogeography of benthic foraminifera in contourite drift systems

2021 ◽  
Author(s):  
Anna Saupe ◽  
Johanna Schmidt ◽  
Jassin Petersen ◽  
André Bahr ◽  
Patrick Grunert
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Benthic Foraminifera ◽  
Distribution Patterns ◽  
Bottom Current ◽  
Data Sets ◽  
Data Set ◽  
Suspension Feeders ◽  
Gulf Of Cádiz ◽  
Iberian Margin

<div> <p><span>Benthic foraminifera colonize a wide range of marine environments, including contourite drift systems (CDS). CDS are characterized by sustained bottom currents and cover large areas on the seafloor, e.g., in the North Atlantic. Due to their high sedimentation rates, they represent fundamental archives for paleoclimatology and paleoceanography. Some studies already highlight the influence of high current velocities on assemblages of epibenthic foraminifera and suggest their applicability as a reliable proxy for bottom current reconstructions (Schönfeld, 2002; Jorissen et al., 2007 and references therein). Certain epibenthic foraminiferal species live as highly adapted opportunistic suspension feeders using elevated substrates as a unique ecological niche. Through their elevated microhabitat, they optimize the uptake of suspended food particles gaining an advantage over other epibenthic organisms. However, their application as a bottom current proxy has so far been limited to the Iberian Margin and has been barely tested outside the Gulf of Cadiz (e.g., Diz et al., 2004).</span></p> </div><div> <p><span>The present study aims to document biogeographic distribution patterns of benthic foraminifera in extended CDS from different latitudes. Two data sets from the high-latitude North Atlantic (50-62°N) are presented here. The surface samples of the first data set originate from the Björn and Gardar drifts between the Reykjanes Ridge and the Rockall Plateau south of Iceland. Deposition is primarily controlled by the Iceland Scotland Overflow Water. The second data set is located further west within the Eirik Drift on the southern slope of the Greenland margin. The main controlling water mass is the Deep Western Boundary Current.</span></p> </div><div> <p><span>Initial results show that epibenthic species dominate over infaunal taxa. The data set is mainly determined by the tubular agglutinated species <em>Rhabdammina abyssorum</em>, <em>Saccorhiza ramosa</em>, and <em>Rhizammina algaeformis</em>, as well as hyaline forms such as <em>Hoeglundina elegans</em>, <em>Cibicidoides wuellerstorfi</em>, and <em>Cibicides refulgens</em>. </span><span>Thus, several different suspension-feeding taxa dominate the data set. Three assemblages of benthic foraminifera are distinguished: agglutinated suspension feeders dominating in more clayey environments, hyaline suspension feeders dominating in sandier environments with increased current velocities, and infaunal detritus feeders dominating below 2000 m water depth.</span></p> </div><div> <p><span>The presented data sets are currently complemented by samples from the Campos drift on the Brazilian margin (10°-22°S). Together, the low, mid and high latitude data sets will improve our understanding of biogeographic distribution patterns of benthic foraminifera in CDS. The expected results will be fundamental to ensure the applicability of foraminifera-based proxy methods for bottom current reconstruction.</span></p> </div><div> <p><strong><span>References</span></strong></p> </div><div> <p><span>Diz, P., Guillermo, F., Costas, S., Souto, C., Alejo, I., 2004. Distribution of benthic foraminifera in coarse sediments, Ria de Vigo, NW Iberian Margin. </span>J. Foraminifer. Res. 34, 258–275. https://doi.org/10.2113/34.4.258</p> </div><div> <p>Jorissen, F.J., Fontanier, C., Thomas, E., 2007. <span>Paleoceanographical proxies based on deep-sea benthic foraminiferal assemblage characteristics, in: Hillaire-Marcel, C., de Vernal, A. (Eds.), Proxies in Late Cenozoic Paleoceanography: Pt. 2: Biological Tracers and Biomarkers. pp. 263–325. https://doi.org/10.1016/S1572-5480(07)01012-3</span></p> </div><div><span>Schönfeld, J., 2002. Recent benthic foraminiferal assemblages in deep high-energy environments from the Gulf of Cadiz (Spain). </span></div><p>Mar. Micropaleontol. 44, 141–162. https://doi.org/10.1016/S0377-8398(01)00039-1</p>

scholarly journals How deep does sand deposits in the Alentejo basin (Gulf of Cadiz) reach? Evaluating slope stability from bottom-current activities through time

2020 ◽  
Author(s):  
Davide Mencaroni ◽  
Roger Urgeles ◽  
Jonathan Ford ◽  
Jaume Llopart ◽  
Cristina Sànchez Serra ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Sediment Supply ◽  
Excess Pore Pressure ◽  
Bottom Current ◽  
Gulf Of Cadiz ◽  
Strait Of Gibraltar ◽  
Gulf Of Cádiz ◽  
The Stability ◽  
Iberian Margin ◽  
Excess Pore

<p>Contourite deposits are generated by the interplay between deepwater bottom-currents, sediment supply and seafloor topography. The Gulf of Cadiz, in the Southwest Iberian margin, is a famous example of extensive contourite deposition driven by the Mediterranean Outflow Water (MOW), which exits the Strait of Gibraltar, flows northward following the coastline and distributes the sediments coming from the Guadalquivir and Guadiana rivers. The MOW and related contourite deposits affect the stability of the SW Iberian margin in several ways: on one hand it increases the sedimentation rate, favoring the development of excess pore pressure, while on the other hand, by depositing sand it allows pore water pressure to dissipate, potentially increasing the stability of the slope.</p><p>In the Gulf of Cadiz, grain size distribution of contourite deposits is influenced by the seafloor morphology, which splits the MOW in different branches, and by the alternation of glacial and interglacial periods that affected the MOW hydrodynamic regimes. Fine clay packages alternates with clean sand formations according to the capacity of transport of the bottom-current in a specific area. Generally speaking, coarser deposits are found in the areas of higher MOW flow energy, such as in the shallower part of the slope or in the area closer to the Strait of Gibraltar, while at higher water depths the sedimentation shifts to progressively finer grain sizes as the MOW gets weaker. Previous works show that at present-day the MOW flows at a maximum depth of 1400 m, while during glacial periods the bottom-current could have reached higher depths.</p><p>In this study we derived the different maximum depths at which the MOW flowed by analyzing the distribution of sands at different depths along the Alentejo basin slope, in the Northern sector of the Gulf of Cadiz.</p><p>Here we show how changes in sand distribution along slope, within the stratigraphic units deposited between the Neogene and the present day, are driven by glacial – interglacial period alternation that influenced the hydrodynamic regime of the MOW.</p><p>By deriving the depositional history of sand in the Alentejo basin, we are able to correlate directly the influence that climatic cycles had on the MOW activity. Furthermore, by interpreting new multi-channel seismic profiles we have been able to derive a detailed facies characterization of the uppermost part of the Gulf of Cadiz.</p><p>An accurate definition of sand distribution along slope plays an important role in evaluating the stability of the slope itself, e.g. to understand if the sediments may be subjected to excess pore pressure generation. As sand distribution is a direct function of the bottom-current transport capacity, the ultimate goal of this study is to understand how climate variations can affect the stability of submarine slope by depositing contourite-related sand.</p>

Comparison of Foraminiferal, Coccolithophorid, and Radiolarian Paleotemperature Equations: Assemblage Coherency and Estimate Concordancy

1982 ◽  
Vol 17 (3) ◽  
pp. 279-313 ◽  
Author(s):  
Barbara Molfino ◽  
Nilva G. Kipp ◽  
Joseph J. Morley
Keyword(s):  
Regression Analysis ◽  
High Latitude ◽  
Correlation Coefficients ◽  
Distribution Patterns ◽  
Sea Surface ◽  
Ice Age ◽  
Data Sets ◽  
Critical Temperatures ◽  
Low Latitude ◽  
Sea Bed

AbstractThe Imbrie-Kipp method of paleotemperature estimation is rigorously tested by comparing Atlantic temperature equations independently derived from the microfossils of three biotic groups: the Foraminifera, Coccolithophorida, and Radiolaria. This method consists of two steps: factor analysis of the modern sea-bed data of the individual groups which resolves discrete biogeographic assemblages and regression analysis of the modern assemblage data with observed sea-surface temperature data to obtain paleotemperature equations. Assemblage biogeography shows a simple subdivision into warm (low latitude) and cold (high latitude) for all biotic groups. Between biotic groups there is greater similarity among high-latitude assemblages than low-latitude ones. Correlating the assemblage data with observed sea-surface temperatures to produce temperature distribution patterns shows differences of less than 2°C in their optimum and critical temperatures. Regression analysis produced accurate temperature equations for each biotic group, all with standard errors of estimate of less than or equal to 2°C. Multiple correlation coefficients were all greater than 0.970. Applying these equations to two multiple biotic data sets (the modern and ice-age sea-bed data) and comparing their temperature estimates using the standard error pooled, shows over 87% concordancy for both data sets. Unlike the modern data, the discordancy among temperature estimates of the ice-age data shows a distinct geographic distribution; its cause is believed to be oceanographic, a difference in the water-mass structure between the modern and ice-age ocean.

scholarly journals Twelve thousand years of dust: the Holocene global dust cycle constrained by natural archives

2015 ◽  
Vol 11 (6) ◽  
pp. 869-903 ◽  
Author(s):  
S. Albani ◽  
N. M. Mahowald ◽  
G. Winckler ◽  
R. F. Anderson ◽  
L. I. Bradtmiller ◽  
...  
Keyword(s):  
North Atlantic ◽  
Data Sets ◽  
Dust Deposition ◽  
Data Set ◽  
The Holocene ◽  
The North ◽  
Dust Mass ◽  
The North Atlantic ◽  
Mass Accumulation ◽  
Natural Archives

Abstract. Mineral dust plays an important role in the climate system by interacting with radiation, clouds, and biogeochemical cycles. In addition, natural archives show that the dust cycle experienced variability in the past in response to global and local climate change. The compilation of the DIRTMAP (Dust Indicators and Records from Terrestrial and MArine Palaeoenvironments) paleodust data sets in the last 2 decades provided a benchmark for paleoclimate models that include the dust cycle, following a time slice approach. We propose an innovative framework to organize a paleodust data set that builds on the positive experience of DIRTMAP and takes into account new scientific challenges by providing a concise and accessible data set of temporally resolved records of dust mass accumulation rates and particle grain size distributions. We consider data from ice cores, marine sediments, loess–paleosol sequences, lake sediments, and peat bogs for this compilation, with a temporal focus on the Holocene period. This global compilation allows the investigation of the potential, uncertainties, and confidence level of dust mass accumulation rate reconstructions and highlights the importance of dust particle size information for accurate and quantitative reconstructions of the dust cycle. After applying criteria that help to establish that the data considered represent changes in dust deposition, 45 paleodust records have been identified, with the highest density of dust deposition data occurring in the North Atlantic region. Although the temporal evolution of dust in the North Atlantic appears consistent across several cores and suggests that minimum dust fluxes are likely observed during the early to mid-Holocene period (6000–8000 years ago), the magnitude of dust fluxes in these observations is not fully consistent, suggesting that more work needs to be done to synthesize data sets for the Holocene. Based on the data compilation, we used the Community Earth System Model to estimate the mass balance of and variability in the global dust cycle during the Holocene, with dust loads ranging from 17.2 to 20.8 Tg between 2000 and 10 000 years ago and with a minimum in the early to mid-Holocene (6000–8000 years ago).

Decoupling of surface ocean hydrology and Greenland ice core records in the eastern North Atlantic during the last glacial inception 

2021 ◽  
Author(s):  
Svetlana Radionovskaya ◽  
Luke Skinner ◽  
Mervyn Greaves
Keyword(s):  
Climate Variability ◽  
North Atlantic ◽  
Benthic Foraminifera ◽  
Ice Cores ◽  
Last Glacial ◽  
Surface Ocean ◽  
The North ◽  
The North Atlantic ◽  
Iberian Margin ◽  
The Last Glacial

<p>MIS 4, a key paleoclimatic interval for the last glacial inception, is characterized by a rapid CO<sub>2</sub> drop of approx. ~28ppm and a large drop in temperature (as seen in Antarctic ice cores). SSTs in the North Atlantic are thought to be coupled to AMOC strength, whereby various proxies suggest a weaker and shoaled AMOC during the transition from MIS5a to MIS4. Furthermore, several millennial events also occurred during MIS 4, including Heinrich Stadial 6 and DO events 16-19. MIS 4 is thus an ideal interval to study and eventually to disentangle, glacial-interglacial and millennial variability.</p><p>Here, we present high resolution planktonic and benthic foraminifera geochemical data from several marine sediment cores from the Iberian Margin (including stable isotope and trace element data). The Iberian Margin is a prime location to study millennial-scale climate variability as isotope records of planktonic and benthic foraminifera simultaneously recorded rapid climate change expressed in Greenland and Antarctic ice cores, respectively, during the last glacial period. However, our results so far, suggest that surface ocean response at this site does not track Greenland temperature, as would be expected for this region of the North Atlantic. Perhaps the most striking, our planktic Mg/Ca record shows a late onset of rapid MIS 4 cooling at the start of Heinrich 6, and no clear millennial variability signal. This is in agreement with SST reconstructed using alkenones (Pailler and Bard, 2002) and planktonic foraminifera faunal assemblages (Salgueiro et al., 2010) from nearby core sites. Local d18O seawater reconstructions imply major hydrological changes in the region, which is supported by the “dry event” seen in speleothems from North Eastern Iberia (Perez-Mehias et al., 2019) and Italy (Columbu et al., 2020), just before Heinrich 6. We propose that the observed changes may reflect changes in regional ocean and atmospheric circulation patterns such as the interaction of the strength and position of the Azores Current, Iberian Poleward Current and the Subtropical Gyre, which in turn could depend on the larger scale AMOC and wind driven surface ocean changes due to glacial-interglacial and millennial variability. Further links to moisture transport, ice sheet growth and carbon cycle are yet to be investigated.</p><p> </p><p><strong>References</strong></p><p>Columbu, A., Chiarini, V., Spötl, C., Benazzi, S., Hellstrom, J., Cheng, H. and De Waele, J., 2020. Speleothem record attests to stable environmental conditions during Neanderthal–modern human turnover in southern Italy. Nature Ecology & Evolution, 4(9), pp.1188-1195.</p><p>Pailler, D. and Bard, E., 2002. High frequency palaeoceanographic changes during the past 140 000 yr recorded by the organic matter in sediments of the Iberian Margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 181(4), pp.431-452.</p><p>Pérez-Mejías, C., Moreno, A., Sancho, C., Martín-García, R., Spötl, C., Cacho, I., Cheng, H. and Edwards, R., 2019. Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia. Quaternary Science Reviews, 224, p.105946.</p><p>Salgueiro, E., Voelker, A., de Abreu, L., Abrantes, F., Meggers, H. and Wefer, G., 2010. Temperature and productivity changes off the western Iberian margin during the last 150 ky. Quaternary Science Reviews, 29(5-6), pp.680-695.</p>

scholarly journals Improving the dynamics of Northern Hemisphere high-latitude vegetation in the ORCHIDEE ecosystem model

2015 ◽  
Vol 8 (7) ◽  
pp. 2263-2283 ◽  
Author(s):  
D. Zhu ◽  
S. S. Peng ◽  
P. Ciais ◽  
N. Viovy ◽  
A. Druel ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
High Latitude ◽  
Ecosystem Model ◽  
Evaluation Framework ◽  
Soil Freezing ◽  
Data Sets ◽  
Organic Carbon Content ◽  
Data Set ◽  
Functional Types ◽  
The Impact

Abstract. Processes that describe the distribution of vegetation and ecosystem succession after disturbance are an important component of dynamic global vegetation models (DGVMs). The vegetation dynamics module (ORC-VD) within the process-based ecosystem model ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems) has not been updated and evaluated since many years and is known to produce unrealistic results. This study presents a new parameterization of ORC-VD for mid- to high-latitude regions in the Northern Hemisphere, including processes that influence the existence, mortality and competition between tree functional types. A new set of metrics is also proposed to quantify the performance of ORC-VD, using up to five different data sets of satellite land cover, forest biomass from remote sensing and inventories, a data-driven estimate of gross primary productivity (GPP) and two gridded data sets of soil organic carbon content. The scoring of ORC-VD derived from these metrics integrates uncertainties in the observational data sets. This multi-data set evaluation framework is a generic method that could be applied to the evaluation of other DGVM models. The results of the original ORC-VD published in 2005 for mid- to high-latitudes and of the new parameterization are evaluated against the above-described data sets. Significant improvements were found in the modeling of the distribution of tree functional types north of 40° N. Three additional sensitivity runs were carried out to separate the impact of different processes or drivers on simulated vegetation distribution, including soil freezing which limits net primary production through soil moisture availability in the root zone, elevated CO2 concentration since 1850, and the effects of frequency and severity of extreme cold events during the spin-up phase of the model.

Prediction of sample size effects on the measured temporal and geographic distribution patterns of species

Paleobiology ◽  
1987 ◽  
Vol 13 (1) ◽  
pp. 100-107 ◽  
Author(s):  
Carl F. Koch
Keyword(s):  
Species Richness ◽  
Sample Size ◽  
Size Effects ◽  
Large Data ◽  
Distribution Patterns ◽  
Data Sets ◽  
Data Set ◽  
Large Computer ◽  
Two Samples ◽  
Unique Species

Few paleontological studies of species distribution in time and space have adequately considered the effects of sample size. Most species occur very infrequently, and therefore sample size effects may be large relative to the faunal patterns reported. Examination of 10 carefully compiled large data sets (each more than 1,000 occurrences) reveals that the species-occurrence frequency distribution of each fits the log series distribution well and therefore sample size effects can be predicted. Results show that, if the materials used in assembling a large data set are resampled, as many as 25% of the species will not be found a second time even if both samples are of the same size. If the two samples are of unequal size, then the larger sample may have as many as 70% unique species and the smaller sample no unique species. The implications of these values are important to studies of species richness, origination, and extinction patterns, and biogeographic phenomena such as endemism or province boundaries. I provide graphs showing the predicted sample size effects for a range of data set size, species richness, and relative data size. For data sets that do not fit the log series distribution well, I provide example calculations and equations which are usable without a large computer. If these graphs or equations are not used, then I suggest that species which occur infrequently be eliminated from consideration. Studies in which sample size effects are not considered should include sample size information in sufficient detail that other workers might make their own evaluation of observed faunal patterns.

The social wasp Vespula germanica (Fabricius) (Hymenoptera: Vespidae) population dynamics in England over 39 years.

2018 ◽  
Vol 154 (2) ◽  
pp. 149-155
Author(s):  
Michael Archer
Keyword(s):  
Population Dynamics ◽  
Population Dynamic ◽  
Ecological Factors ◽  
Social Wasp ◽  
Data Sets ◽  
Data Set ◽  
Vespula Germanica ◽  
The Social ◽  
Minimum Number ◽  
Suction Traps

1. Yearly records of worker Vespula germanica (Fabricius) taken in suction traps at Silwood Park (28 years) and at Rothamsted Research (39 years) are examined. 2. Using the autocorrelation function (ACF), a significant negative 1-year lag followed by a lesser non-significant positive 2-year lag was found in all, or parts of, each data set, indicating an underlying population dynamic of a 2-year cycle with a damped waveform. 3. The minimum number of years before the 2-year cycle with damped waveform was shown varied between 17 and 26, or was not found in some data sets. 4. Ecological factors delaying or preventing the occurrence of the 2-year cycle are considered.

Predictive and Descriptive CoMFA Models: The Effect of Variable Selection

2018 ◽  
Vol 21 (2) ◽  
pp. 117-124 ◽  
Author(s):  
Bakhtyar Sepehri ◽  
Nematollah Omidikia ◽  
Mohsen Kompany-Zareh ◽  
Raouf Ghavami
Keyword(s):  
Variable Selection ◽  
Predictive Power ◽  
Selection Method ◽  
Data Sets ◽  
Data Set ◽  
Comfa Model ◽  
Variable Selection Method

Aims & Scope: In this research, 8 variable selection approaches were used to investigate the effect of variable selection on the predictive power and stability of CoMFA models. Materials & Methods: Three data sets including 36 EPAC antagonists, 79 CD38 inhibitors and 57 ATAD2 bromodomain inhibitors were modelled by CoMFA. First of all, for all three data sets, CoMFA models with all CoMFA descriptors were created then by applying each variable selection method a new CoMFA model was developed so for each data set, 9 CoMFA models were built. Obtained results show noisy and uninformative variables affect CoMFA results. Based on created models, applying 5 variable selection approaches including FFD, SRD-FFD, IVE-PLS, SRD-UVEPLS and SPA-jackknife increases the predictive power and stability of CoMFA models significantly. Result & Conclusion: Among them, SPA-jackknife removes most of the variables while FFD retains most of them. FFD and IVE-PLS are time consuming process while SRD-FFD and SRD-UVE-PLS run need to few seconds. Also applying FFD, SRD-FFD, IVE-PLS, SRD-UVE-PLS protect CoMFA countor maps information for both fields.

Human Activity Recognition using Fourier Transform Inspired Deep Learning Combination Model

2019 ◽  
Vol 9 (1) ◽  
pp. 16-31
Author(s):  
Kyungkoo Jun
Keyword(s):  
Fourier Transform ◽  
Deep Learning ◽  
Short Term Memory ◽  
Window Size ◽  
Sensor Data ◽  
Data Sets ◽  
Data Set ◽  
Proposed Model ◽  
Testing Data ◽  
Labeling Scheme

Background & Objective: This paper proposes a Fourier transform inspired method to classify human activities from time series sensor data. Methods: Our method begins by decomposing 1D input signal into 2D patterns, which is motivated by the Fourier conversion. The decomposition is helped by Long Short-Term Memory (LSTM) which captures the temporal dependency from the signal and then produces encoded sequences. The sequences, once arranged into the 2D array, can represent the fingerprints of the signals. The benefit of such transformation is that we can exploit the recent advances of the deep learning models for the image classification such as Convolutional Neural Network (CNN). Results: The proposed model, as a result, is the combination of LSTM and CNN. We evaluate the model over two data sets. For the first data set, which is more standardized than the other, our model outperforms previous works or at least equal. In the case of the second data set, we devise the schemes to generate training and testing data by changing the parameters of the window size, the sliding size, and the labeling scheme. Conclusion: The evaluation results show that the accuracy is over 95% for some cases. We also analyze the effect of the parameters on the performance.

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