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 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.

A revised seawater sulfate oxygen isotope record for the last 4 Myr

2016 ◽  
Vol 175 ◽  
pp. 239-251 ◽  
Author(s):  
Stefan Markovic ◽  
Adina Paytan ◽  
Hong Li ◽  
Ulrich G. Wortmann
Keyword(s):  
Oxygen Isotope ◽  
Seawater Sulfate ◽  
Oxygen Isotope Record ◽  
Isotope Record

Pigment Preservation in Lake Sediments: A Comparison of Sedimentary Environments in Trout Lake, Wisconsin

1991 ◽  
Vol 48 (3) ◽  
pp. 472-486 ◽  
Author(s):  
James P. Hurley ◽  
David E. Armstrong
Keyword(s):  
Accumulation Rate ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Surface ◽  
Water Interface ◽  
Sedimentary Pigments ◽  
Sedimentary Environments ◽  
Trout Lake ◽  
Secondary Carotenoids ◽  
Β Carotene

Fluxes and concentrations of a phorbins and major algal carotenoids were quantified in sediment trap material and sediment cores from two basins of Trout Lake, Wisconsin (TrDH and TrAB). The basins were chosen to contrast the influence of oxygen content at the sediment–water interface (TrDH, oxic and TrAB, reducing), sediment accumulation rate, and focusing. Pigment diagenesis occurred in both basins, but transformations and destruction were more extensive in TrDH. Although untransformed chlorophyll a was the major phorbin deposited at the sediment surface of both basins (51–64 mol%), pigment destruction, coupled with transition to pheophytin, accounted for substantial losses, especially in oxic TrDH sediments. Fucoxanthin, peridinin, and diadinoxanthin, despite representing > 70% of the deposited carotenoid flux, were substantially degraded or transformed in both basins. However, preservation was relatively high for secondary carotenoids, such as diatoxanthin and β-carotene, and for a major cryptomonad pigment, alloxanthin. Residual profiles in sediments show that pigment sedimentation from the epilimnion and accumulation in the permanent sediments are not directly related and that diagenesis must be considered in interpreting sedimentary pigments.

Temperature sensitivity of planktic foraminifera and its influence on the oxygen isotope record

1998 ◽  
Vol 33 (3-4) ◽  
pp. 223-240 ◽  
Author(s):  
Stefan Mulitza ◽  
Tobias Wolff ◽  
Jürgen Pätzold ◽  
Walter Hale ◽  
Gerold Wefer
Keyword(s):  
Oxygen Isotope ◽  
Temperature Sensitivity ◽  
Planktic Foraminifera ◽  
Oxygen Isotope Record ◽  
Isotope Record

A 5000-year lacustrine sediment oxygen isotope record of late Holocene climate change in Newfoundland, Canada

2022 ◽  
Vol 278 ◽  
pp. 107376
Author(s):  
Matthew S. Finkenbinder ◽  
Byron A. Steinman ◽  
Broxton W. Bird ◽  
Ellen C. Heilman ◽  
Alexandria R. Aspey ◽  
...  
Keyword(s):  
Climate Change ◽  
Oxygen Isotope ◽  
Late Holocene ◽  
Lacustrine Sediment ◽  
Holocene Climate ◽  
Holocene Climate Change ◽  
Oxygen Isotope Record ◽  
Isotope Record

Speleothems, Travertines, and Paleoclimates

1983 ◽  
Vol 20 (1) ◽  
pp. 1-29 ◽  
Author(s):  
G. J. Hennig ◽  
R. Grün ◽  
K. Brunnacker
Keyword(s):  
Oxygen Isotope ◽  
Deep Sea ◽  
Clear Relationship ◽  
Sufficient Data ◽  
Geographic Position ◽  
Oxygen Isotope Record ◽  
Isotope Record ◽  
Age Range ◽  
Stimulation Of ◽  
Frequency Curves

AbstractAge data for about 660 speleothems and about 140 spring-deposited travertines were collected, including many unpublished results. These data were plotted as histograms and also as error-weighted frequency curves on a 350,000-yr scale. These plots clearly show periods of increased speleothem/travertine growth as well as times of cessation. The periods of most frequent speleothem growth were between approximately 130,000 and 90,000 yr ago and since about 15,000 yr ago. Such periods before 150,000 yr ago, however, cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range. A comparison with the oxygen-isotope record of deep-sea core V28–:238 shows a clear relationship, indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations. The evident climatic stimulation of Quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem/travertine growth as a function of geographic position.

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