scholarly journals Radiocarbon Age Profiles and Size Dependency of Mixing in Northeast Atlantic Sediments

Radiocarbon ◽  
2001 ◽  
Vol 43 (2B) ◽  
pp. 929-937 ◽  
Author(s):  
Louise Brown ◽  
Gordon T Cook ◽  
Angus B MacKenzie ◽  
John Thomson
Keyword(s):  
Planktonic Foraminifera ◽  
Sediment Accumulation ◽  
Deep Ocean ◽  
Coarse Fraction ◽  
Surface Mixed Layer ◽  
Radiocarbon Age ◽  
Sediment Size ◽  
Common Technique ◽  
Sediment Component ◽  
Selection Of

In recent years, the most common technique for radiocarbon dating of deep-ocean sediments has been accelerator mass spectrometry (AMS) analysis of hand-picked planktonic foraminifera (forams). Some studies have exposed age offsets between different sediment size fractions from the same depth within a core and this has important implications when establishing a chronological framework for palaeoceanographic records associated with a particular sediment component. The mechanisms generating the age offsets are not fully understood, a problem compounded by the fact that the fraction defined as “large” varies between different studies. To explore this problem, we dated samples of hand-picked forams from two Biogeochemical Ocean Flux Study (BOFS) cores, for which the presence of an offset between the bulk carbonate and >150 μm foraminiferal calcite had already been demonstrated. The presence of a constant age offset between bulk carbonate and coarse fraction material at the two BOFS sites has been confirmed, but the magnitude of the offset is dependent on whether a simple size-separation technique or hand-picking of well-preserved forams is applied. This may be explained if the selection of well preserved forams biases the sample towards those specimens that have spent least time in the surface mixed layer (SML) or have undergone less size selective mixing. Modeling of the 14C profiles demonstrates that SML depth and sediment accumulation rates are the same for both the bulk and coarse sediment fractions, which is consistent with the hypothesis that size-selective mixing is responsible for the age offset.

scholarly journals Radiocarbon Age Offsets in Different-Sized Carbonate Components of Deep-Sea Sediments

Radiocarbon ◽  
1995 ◽  
Vol 37 (2) ◽  
pp. 91-101 ◽  
Author(s):  
John Thomson ◽  
G. T. Cook ◽  
Robert Anderson ◽  
A. B. MacKenzie ◽  
D. D. Harkness ◽  
...  
Keyword(s):  
Sediment Accumulation ◽  
Sediment Surface ◽  
Surface Mixed Layer ◽  
Bulk Sediment ◽  
Radiocarbon Age ◽  
Oxygen Isotope Record ◽  
Isotope Record ◽  
Large Foraminifera ◽  
Sediment Age ◽  
Northeastern Atlantic

We compared accelerator mass spectrometry (AMS) 14C ages of large (>150 μm) pelagic foraminifera with radiometric bulk carbonate 14C ages in two northeastern Atlantic cores. The foraminiferal ages are consistently older than those of the bulk sediment (by + 0.76 ka in Core 11881 and by + 1.1 ka in Core 11886), whereas corresponding fine (<5 μm) fraction ages are similar to those of the bulk sediment carbonate. We calculated near-identical sediment accumulation rates from both the foraminiferal and bulk sediment age/depth relations (3.0 cm ka−1 in Core 11881 and 5.9 cm ka−1 in Core 11886). Consideration of various factors that might produce such offsets leads us to believe that they are not artifacts, but were most probably caused by differential bioturbation of the different size-fractions in the sediment surface mixed layer. The importance of this finding is that many paleoceanographic records, such as the oxygen isotope record, also derive from analyses of large foraminifera, so that these records must be offset in time from the bulk of the sediments that they characterize.

scholarly journals Radiocarbon Age Offsets Between Two Surface Dwelling Planktonic Foraminifera Species During Abrupt Climate Events in the SW Iberian Margin

2019 ◽  
Vol 34 (1) ◽  
pp. 63-78 ◽  
Author(s):  
Blanca Ausín ◽  
Negar Haghipour ◽  
Lukas Wacker ◽  
Antje H. L. Voelker ◽  
David Hodell ◽  
...  
Keyword(s):  
Planktonic Foraminifera ◽  
Radiocarbon Age ◽  
Surface Dwelling ◽  
Climate Events ◽  
Iberian Margin

Early to mid-Holocene Atlantic water influx and deglacial meltwater events, Beaufort Sea Slope, Arctic Ocean

2004 ◽  
Vol 61 (1) ◽  
pp. 14-21 ◽  
Author(s):  
John T. Andrews ◽  
Gita Dunhill
Keyword(s):  
Arctic Ocean ◽  
Planktonic Foraminifera ◽  
Sediment Accumulation ◽  
Beaufort Sea ◽  
Atlantic Water ◽  
The Arctic ◽  
Silty Clay ◽  
Cold Event ◽  
Radiocarbon Dates ◽  
Average Grain Size

Holocene high-resolution cores from the margin of the Arctic Ocean are rare. Core P189AR-P45 collected in 405-m water depth on the Beaufort Sea slope, west of the Mackenzie River delta (70°33.03′N and 141°52.08′W), is in close vertical proximity to the present-day upper limit of modified Atlantic water. The 5.11-m core spans the interval between ∼6800 and 10,400 14C yr B.P. (with an 800-yr ocean reservoir correction). The sediment is primarily silty clay with an average grain-size of 9 φ. The chronology is constrained by seven radiocarbon dates. The rate of sediment accumulation averaged 1.35 mm/yr. Stable isotopic data (δ18O and δ13C) were obtained on the polar planktonic foraminifera Neogloboquadrina pachyderma (s) and the benthic infaunal species Cassidulina neoteretis. A distinct low-δ18O event is captured in both the benthic and planktonic data at ∼10,000 14C yr B.P.—probably recording the glacial Lake Agassiz outburst flood associated with the North Atlantic preboreal cold event. The benthic foraminifera are dominated in the earliest Holocene by C. neoteretis, a species associated with modified Atlantic water masses. This species decreases toward the core top with a marked environmental reversal occurring ∼7800 14C yr B.P. possibly coincident with the northern hemisphere 8200 cal yr B.P. cold event.

scholarly journals Common species link global ecosystems to climate change: dynamical evidence in the planktonic fossil record

2017 ◽  
Vol 284 (1858) ◽  
pp. 20170722 ◽  
Author(s):  
Bjarte Hannisdal ◽  
Kristian Agasøster Haaga ◽  
Trond Reitan ◽  
David Diego ◽  
Lee Hsiang Liow
Keyword(s):  
Large Scale ◽  
Planktonic Foraminifera ◽  
Deep Ocean ◽  
Common Species ◽  
Ecosystem Structure ◽  
Environmental Forcing ◽  
Widespread Species ◽  
Quantitative Evidence ◽  
And Function

Common species shape the world around us, and changes in their commonness signify large-scale shifts in ecosystem structure and function. However, our understanding of long-term ecosystem response to environmental forcing in the deep past is centred on species richness, neglecting the disproportional impact of common species. Here, we use common and widespread species of planktonic foraminifera in deep-sea sediments to track changes in observed global occupancy (proportion of sampled sites at which a species is present and observed) through the turbulent climatic history of the last 65 Myr. Our approach is sensitive to relative changes in global abundance of the species set and robust to factors that bias richness estimators. Using three independent methods for detecting causality, we show that the observed global occupancy of planktonic foraminifera has been dynamically coupled to past oceanographic changes captured in deep-ocean temperature reconstructions. The causal inference does not imply a direct mechanism, but is consistent with an indirect, time-delayed causal linkage. Given the strong quantitative evidence that a dynamical coupling exists, we hypothesize that mixotrophy (symbiont hosting) may be an ecological factor linking the global abundance of planktonic foraminifera to long-term climate changes via the relative extent of oligotrophic oceans.

scholarly journals Common species link global ecosystems to climate change

2016 ◽  
Author(s):  
Bjarte Hannisdal ◽  
Kristian A. Haaga ◽  
Trond Reitan ◽  
David Diego ◽  
Lee Hsiang Liow
Keyword(s):  
Large Scale ◽  
Environmental Changes ◽  
Planktonic Foraminifera ◽  
Species Abundance ◽  
Direct Interaction ◽  
Deep Ocean ◽  
Common Species ◽  
Global Changes ◽  
Ecosystem Structure ◽  
Widespread Species

Common species shape the world around us, and changes in their commonness signify large-scale shifts in ecosystem structure and function. Dominant taxa drive productivity and biogeochemical cycling, in direct interaction with abiotic components of the Earth system. However, our understanding of the dynamic response of ecosystems to global environmental changes in the past is limited by our ability to robustly estimate fossil taxonomic richness, and by our neglect of the importance of common species. To rectify this, we use observations of the most common and widespread species to track global changes in their distribution in the deep geological past. Our simple approach is robust to factors that bias richness estimators, including widely used sampling-standardization methods, which we show are highly sensitive to variability in the species-abundance distribution. Causal analyses of common species frequency in the deep-sea sedimentary record detect a lagged response in the ecological prominence of planktonic foraminifera to oceanographic changes captured by deep-ocean temperature records over the last 65 million years, encompassing one of Earth's major climate transitions. Our results demonstrate that common species can act as tracers of a past global ecosystem and its response to physical changes in Earth's dynamic history.

Constraints on the amplitude of Mid-Pliocene (3.6–2.4 Ma) eustatic sea-level fluctuations from the New Zealand shallow-marine sediment record

2008 ◽  
Vol 367 (1886) ◽  
pp. 169-187 ◽  
Author(s):  
Tim R Naish ◽  
Gary S Wilson
Keyword(s):  
New Zealand ◽  
Sea Level ◽  
Sediment Accumulation ◽  
Ice Sheet ◽  
Deep Ocean ◽  
Antarctic Ice Sheet ◽  
Shallow Marine ◽  
Sea Level Fluctuations ◽  
Late Neogene ◽  
Sea Level Oscillations

Ice-volume calibrations of the deep-ocean foraminiferal δ 18 O record imply orbitally influenced sea-level fluctuations of up to 30 m amplitude during the Mid-Pliocene, and up to 30 per cent loss of the present-day mass of the East Antarctic Ice Sheet (EAIS) assuming complete deglaciation of the West Antarctic Ice Sheet (WAIS) and Greenland. These sea-level oscillations have driven recurrent transgressions and regressions across the world's continental shelves. Wanganui Basin, New Zealand, contains the most complete shallow-marine Late Neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100 ka sea-level cycle since ca 3.6 Ma. This paper presents a synthesis of faunally derived palaeobathymetric data for shallow-marine sedimentary cycles corresponding to marine isotope stages M2–100 ( ca 3.4–2.4 Ma). Our approach estimates the eustatic sea-level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation. The sea-level estimates are consistent with those from δ 18 O curves and numerical ice sheet models, and imply a significant sensitivity of the WAIS and the coastal margins of the EAIS to orbital oscillations in insolation during the Mid-Pliocene period of relative global warmth. Sea-level oscillations of 10–30 m were paced by obliquity.

How well is the deep Tore seamount basin ventilated?

2020 ◽  
Author(s):  
Laura Antón ◽  
Susana Lebreiro ◽  
Silvia Nave ◽  
Luke Skinner ◽  
Elizabeth Michel ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Water Depth ◽  
Deep Water ◽  
Planktonic Foraminifera ◽  
Deep Ocean ◽  
South Atlantic ◽  
Age Difference ◽  
The South ◽  
Deep Basin ◽  
Iberian Margin

&lt;p&gt;The Last Glacial Maximum (LGM) was characterized by increased carbon storage in the deep ocean, as well as extremely poorly ventilated southern-sourced deep water (AABW) compared to northern-sourced deep water (NADW).&lt;/p&gt;&lt;p&gt;Here we analyse benthic (Cibicidoides wellerstorfi) d&lt;sup&gt;13&lt;/sup&gt;C, and compare 3 sites sitting on the deep floor at 5 km water depth: MD13-3473 in the Tore inside basin; MD03-2698 in the Iberian margin; and TN057-21 in the South Atlantic. The Tore Seamount is a geological structure 300 km off the West Iberian margin at 40&amp;#176;N latitude. It has a crater-like morphology with a 5500 m deep basin in its middle, where calypso core MD13-3473 was collected, confined from the open ocean by a summit rim at 2200 m water depth (wd). The only connection between the deepest Tore Seamount basin and the Atlantic circulation is a NE gateway down to 4300 mwd.&lt;/p&gt;&lt;p&gt;The results for the LGM show similar values around -1.0 &amp;#8240; for the South Atlantic and the Iberian margin, in other words these sites were both bathed by AABW. However, the Tore basin record exhibits values around 0 &amp;#8240;, similarly to open sites in the Iberian margin at 3.5 km depth. This seems to indicate a remarkable isolation of the Tore inside basin from the Atlantic deep bottom waters influence.&lt;/p&gt;&lt;p&gt;Among other things, we plan to examine the residence time of the Tore basin bottom water by measuring the radiocarbon age difference between benthic and planktonic foraminifera.&amp;#160;&lt;/p&gt;&lt;p&gt;Our results confer to this enclosed environment the status of an in-situ deep ocean laboratory where to test hypotheses of past ocean circulation changes like the role of deep waters in sequestering glacial CO&lt;sub&gt;2&lt;/sub&gt;. Core MD13-3473 covers 430 thousands of years, therefore 5 deglacial cycles (Spanish project &amp;#8220;TORE5deglaciations&amp;#8221;, CTM2017-84113-R, 2018-2020).&lt;/p&gt;

scholarly journals Submesoscale Baroclinic Instability in the Bottom Boundary Layer

2018 ◽  
Vol 48 (11) ◽  
pp. 2571-2592 ◽  
Author(s):  
Jacob O. Wenegrat ◽  
Jörn Callies ◽  
Leif N. Thomas
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Baroclinic Instability ◽  
Slope Angle ◽  
Deep Ocean ◽  
Bottom Boundary Layer ◽  
Surface Mixed Layer ◽  
Nonlinear Simulation ◽  
Bottom Boundary ◽  
Topographic Slope

AbstractWeakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode, a bottom boundary layer counterpart to surface mixed layer instabilities. The instability results from the release of available potential energy, which can be generated because of the observed bottom intensification of turbulent mixing in the deep ocean, or the Ekman adjustment of a current on a slope. Linear stability analysis suggests that the growth rates of bottom boundary layer baroclinic instabilities can be comparable to those of the surface mixed layer mode and are relatively insensitive to topographic slope angle, implying the instability is robust and potentially active in many areas of the global oceans. The solutions of two separate one-dimensional theories of the bottom boundary layer are both demonstrated to be linearly unstable to baroclinic instability, and results from an example nonlinear simulation are shown. Implications of these findings for understanding bottom boundary layer dynamics and processes are discussed.

Evolutionary ecology of Early Paleocene planktonic foraminifera: size, depth habitat and symbiosis

Paleobiology ◽  
2012 ◽  
Vol 38 (3) ◽  
pp. 374-390 ◽  
Author(s):  
Heather S. Birch ◽  
Helen K. Coxall ◽  
Paul N. Pearson
Keyword(s):  
Evolutionary Ecology ◽  
Dissolved Inorganic Carbon ◽  
Planktonic Foraminifera ◽  
Deep Ocean ◽  
Test Size ◽  
Early Paleocene ◽  
Ocean Carbon ◽  
Reconstructed Surface ◽  
Mass Extinction Event ◽  
The Impact

The carbon stable isotope (δ13C) composition of the calcitic tests of planktonic foraminifera has an important role as a geochemical tracer of ocean carbon system changes associated with the Cretaceous/Paleogene (K/Pg) mass extinction event and its aftermath. Questions remain, however, about the extent of δ13C isotopic disequilibrium effects and the impact of depth habitat evolution on test calcite δ13C among rapidly evolving Paleocene species, and the influence this has on reconstructed surface-to-deep ocean dissolved inorganic carbon (DIC) gradients. A synthesis of new and existing multispecies data, on the relationship between δ13C and δ18O and test size, sheds light on these issues. Results suggest that early Paleocene species quickly radiated into a range of depths habitats in a thermally stratified water column. Negative δ18O gradients with increasing test size in some species ofPraemuricasuggest either ontogenetic or ecotypic dependence on calcification temperature that may reflect depth/light controlled variability in symbiont photosynthetic activity. The pattern of positive δ13C test-size correlations allows us to (1) identify metabolic disequilibrium δ13C effects in small foraminifera tests, as occur in the immediate aftermath of the K/Pg event, (2) constrain the timing of evolution of foraminiferal photosymbiosis to 63.5 Ma, ∼0.9 Myr earlier than previously suggested, and (3) identify the apparent loss of symbiosis in a late-ranging morphotype ofPraemurica. These findings have implications for interpreting δ13C DIC gradients at a resolution appropriate for incoming highly resolved K/Pg core records.

SCAN SAMPLING AND WATERFOWL ACTIVITY BUDGET STUDIES: DESIGN AND ANALYSIS CONSIDERATIONS

Behaviour ◽  
2001 ◽  
Vol 138 (11-12) ◽  
pp. 1391-1405 ◽  
Author(s):  
Graham Hepworth ◽  
Andrew Hamilton
Keyword(s):  
Sampling Technique ◽  
Time Of Day ◽  
Sampling Variance ◽  
Sampling Studies ◽  
Large Numbers ◽  
Common Technique ◽  
The Mean ◽  
Statistical Issues ◽  
Different Levels ◽  
Selection Of

AbstractScan sampling is a common technique used to quantify the activities of animals, including waterfowl. When large numbers are present, it is often impractical to record the activities of each individual, and sub-sampling is employed. We present a method for the design and analysis of scan sampling studies involving sub-sampling, based on an actual study of waterfowl activity on a waste stabilisation pond. The design we propose avoids subjectivity in the selection of individuals, is truly random rather than haphazard, and is adaptable to other situations. It allows for the population on each sampling occasion to be divided into separate strata with samples taken from each. The method of analysis addresses the statistical issues arising from such designs. In estimating the proportion of individuals engaged in an activity, it uses the information from observations in which some of the individuals are counted but their activities not recorded, and estimates the sampling variance introduced by sub-sampling. In comparing the mean proportions for different levels of a factor, such as time of day, the method uses restricted maximum likelihood (REML), an algorithm which can account for the sampling variance as well as for missing data. It is anticipated that the methods described in this paper will assist researchers using the scan sampling technique, or workers in any discipline where sampling characteristics are similar.

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