Radionuclides in sediments of the Aare and Rhine river system: Fallouts, discharges, depth-age relations, mass accumulation rates and transport along the river

Abstract. The role of nutrients, such as phosphorus (P), and their impact on primary productivity and the fluctuations in atmospheric CO2 over glacial-interglacial periods are intensely debated. Suggestions as to the importance of P evolved from an earlier proposal that P actively participated in changing productivity rates and therefore climate change, to most recent ones that changes in the glacial ocean inventory of phosphorus were important but not influential if compared to other macronutrients, such as nitrate. Using new data coming from a selection of ODP sites, we analyzed the distribution of oceanic P sedimentary phases and calculate reactive P burial fluxes, and we show how P burial fluxes changed over the last glacial-interglacial period at these sites. Concentrations of reactive P are generally lower during glacial times, while mass accumulation rates (MAR) of reactive P show higher variability. If we extrapolate for the analyzed sites, we may assume that in general glacial burial fluxes of reactive P are lower than those during interglacial periods by about 8%, because the lack of burial of reactive P on the glacial shelf reduced in size, was apparently not compensated by burial in other regions of the ocean. Using the calculated changes in P burial, we evaluate their possible impact on the phosphate inventory in the world oceans. Using a simple mathematical approach, we find that these changes alone could have increased the phosphate inventory of glacial ocean waters by 17–40% compared to interglacial stages. Variations in the distribution of sedimentary P phases at the investigated sites seem to indicate that at the onset of interglacial stages, shallower sites experienced an increase in reactive P concentrations, which seems to point to P-richer waters at glacial terminations. All these findings would support the Shelf-Nutrient Hypothesis, which assumes that during glacial low stands nutrients are transferred from shallow sites to deep sea with possible feedback on the carbon cycle.

Download Full-text

A new method for measuring the bulk volume of small rock samples for determinations of porosity and mass accumulation rates

Journal of Sedimentary Research ◽

10.1306/d4268496-2b26-11d7-8648000102c1865d ◽

1996 ◽

Vol 66 (5) ◽

pp. 1036-1039 ◽

Cited By ~ 1

Author(s):

M. S. Yeager ◽

N. C. Slowey

Keyword(s):

New Method ◽

Accumulation Rates ◽

Rock Samples ◽

Bulk Volume ◽

Mass Accumulation Rates ◽

Mass Accumulation

Download Full-text

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

Climate of the Past Discussions ◽

10.5194/cpd-10-4277-2014 ◽

2014 ◽

Vol 10 (6) ◽

pp. 4277-4363 ◽

Cited By ~ 4

Author(s):

S. Albani ◽

N. M. Mahowald ◽

G. Winckler ◽

R. F. Anderson ◽

L. I. Bradtmiller ◽

...

Keyword(s):

North Atlantic ◽

Accumulation Rates ◽

Dust Deposition ◽

The Holocene ◽

The North ◽

Dust Mass ◽

The North Atlantic ◽

Mass Accumulation Rates ◽

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 paleodust datasets in the last two decades provided a target for paleoclimate models that include the dust cycle, following a time slice approach. We propose an innovative framework to organize a paleodust dataset that moves on from the positive experience of DIRTMAP and takes into account new scientific challenges, by providing a concise and accessible dataset 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 investigation of the potential, uncertainties and confidence level of dust mass accumulation rates 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, 43 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 suggest 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 datasets for the Holocene. Based on the data compilation, we used the Community Earth System Model to estimate the mass balance and variability of the global dust cycle during the Holocene, with dust load ranging from 17.1 to 20.5 Tg between 2000 and 10 000 years ago, and a minimum in the Early to Mid-Holocene (6000–8000 years ago).

Download Full-text

Data Report: Mass accumulation rates and composition of Neogene ice-rafted debris, Site 919, Irminger Basin

10.2973/odp.proc.sr.163.118.1999 ◽

1999 ◽

Author(s):

L.A. Krissek

Keyword(s):

Accumulation Rates ◽

Mass Accumulation Rates ◽

Mass Accumulation

Download Full-text

Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

Quaternary Research ◽

10.1016/s0033-5894(03)00040-1 ◽

2003 ◽

Vol 59 (3) ◽

pp. 411-419 ◽

Cited By ~ 94

Author(s):

Helen M. Roberts ◽

Daniel R. Muhs ◽

Ann G. Wintle ◽

Geoff A. T. Duller ◽

E. Arthur Bettis

Keyword(s):

North America ◽

Radiative Forcing ◽

Luminescence Dating ◽

Accumulation Rates ◽

Last Glacial ◽

Global Circulation ◽

Global Circulation Models ◽

Mass Accumulation Rates ◽

Mass Accumulation ◽

Dust Accumulation

AbstractA high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.

Download Full-text

The linkage of dust cycle dynamics and loess during the Last Glacial Maximum in Europe

10.5194/egusphere-egu2020-13946 ◽

2020 ◽

Author(s):

Patrick Ludwig ◽

Erik J. Schaffernicht ◽

Yaping Shao ◽

Joaquim G. Pinto

Keyword(s):

Central Europe ◽

Last Glacial Maximum ◽

Emission Rates ◽

Accumulation Rates ◽

Deposition Rates ◽

Loess Deposits ◽

The Last Glacial Maximum ◽

Mass Accumulation Rates ◽

Mass Accumulation ◽

The Last Glacial

<p>In this work, we present different aspects of the mineral dust cycle dynamics and the linkage to loess deposits during the Last Glacial Maximum (LGM) in Europe. To this aim, we simulate the LGM dust cycle at high resolution using a regional climate-dust model. The simulated dust deposition rates are found to be comparable with the mass accumulation rates of the loess deposits determined from Loess sites across Europe. In contrast to the present-day prevailing westerlies, easterly wind directions (36&#8201;%) and cyclonic regimes (22&#8201;%) were dominant circulation patterns over central Europe during the LGM. This supports the hypothesis that recurring east sector winds, dynamically linked with a high-pressure system over the Eurasian ice sheet (EIS), are an important component for the dust transport from the EIS margins towards the central Europe loess belt. Our simulations reveal the occurrence of highest dust emission rates in Europe during summer and autumn, with the highest emission rates located near the southernmost EIS margins corresponding to the present-day German-Polish border region. Coherent with the persistent easterlies, westwards running dust plumes resulted in high deposition rates in western Poland, northern Czechia, the Netherlands, the southern North Sea region and on the North German Plain including adjacent regions in central Germany. Further, a detailed analysis of the characteristics of LGM cyclones shows that they were associated with higher wind speeds and less precipitation than their present-day counterparts. These findings highlight the importance of rapid and cyclic depositions by cyclones for the LGM dust cycle. The agreement between the simulated deposition rates and the mass accumulation rates of the loess deposits corroborates the proposed LGM dust cycle hypothesis for Europe.</p>

Download Full-text

Productivity patterns and N-fixation associated with Pliocene-Holocene sapropels: paleoceanographic and paleoecological significance

Biogeosciences ◽

10.5194/bg-8-415-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 415-431 ◽

Cited By ~ 12

Author(s):

D. Gallego-Torres ◽

F. Martinez-Ruiz ◽

P. A. Meyers ◽

A. Paytan ◽

F. J. Jimenez-Espejo ◽

...

Keyword(s):

Organic Matter ◽

Primary Production ◽

Late Quaternary ◽

Eastern Mediterranean ◽

N Fixation ◽

Accumulation Rates ◽

Ecological Changes ◽

Bottom Waters ◽

Mass Accumulation Rates ◽

Mass Accumulation

Abstract. We have studied a suite of 35 sapropel sequences from a transect of four ODP sites across the Eastern Mediterranean to explore for paleoproductivity patterns and provide new insights on ecological changes during their deposition. Paleoproductivity variations were identified using TOC and Babio mass accumulation rates and δ15Ntotal and δ13Corg values. Elevated Ba/Al and TOC mass accumulation rates record periods of basin-wide amplified productivity. Our data further support that sapropels were formed by cyclic increases in primary production of marine organic matter largely sustained by N-fixing bacteria. This productivity increase was triggered by climate factors leading to increased fluvial discharge and amplified nutrient input that also favored the establishment of N-fixing bacteria. Enhanced productivity led to depletion of deepwater dissolved oxygen and consequently improved organic matter preservation. Primary production was more intense during the middle to Late Pleistocene compared to Pliocene equivalents, coinciding with increasing total sedimentation rates. δ15N values are dramatically lower in the sapropels than in TOC-poor background sediments, indicating a major contribution from nitrogen-fixing bacteria to the higher productivity during sapropel deposition. Additionally, different degrees of denitrification occurred as a consequence of water column oxygenation which in turns evolved from stagnant anoxic bottom waters during Pliocene sapropels to oxygen depleted and sluggish circulation in late Quaternary layers. These differences between sapropel layers provide new evidences for the general evolution of the Eastern Mediterranean basin during the last 3 Mys in terms of paleoceanographic conditions and the intensity of climate variability leading to sapropel deposition.

Download Full-text

Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay

Quaternary Research ◽

10.1006/qres.2001.2285 ◽

2002 ◽

Vol 57 (1) ◽

pp. 58-70 ◽

Cited By ~ 67

Author(s):

Steven M. Colman ◽

Pattie C. Baucom ◽

John F. Bratton ◽

Thomas M. Cronin ◽

John P. McGeehin ◽

...

Keyword(s):

Chesapeake Bay ◽

Deep Water ◽

Sediment Cores ◽

Sediment Accumulation ◽

Complex Mixture ◽

Estuarine Sediments ◽

Accumulation Rates ◽

Pollen Stratigraphy ◽

Mass Accumulation Rates ◽

Mass Accumulation

AbstractRapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites.Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.

Download Full-text