ALBERT

Beschreibung: Es wird die These, daß Zinn-führende Granite eine besondere geochemische Spezialisierung aufweisen, an den Beispielen des Sarrabus- (1), San-Vito- (2), Quirra- (3), Arburese- (4) und Monte-Linas-Granites (5) in S-Sardinien geprüft. Sie repräsentieren herzynische Plutongranite mit relativ hohem Intrusionsstockwerk und scharf ausgebildeten Intrusivkontakten zu schwach metamorphen altpaläozoischen Rahmengesteinen der Grünschieferfazies. Zinnlagerstätten treten nur im Umfeld der Massive (4) und (5), Mo-W-Vererzungen im Bereich der Massive (3) und (5) auf. Petrologisch bestehen die Massive hauptsächlich aus Leukogranit, untergeordnet und lokal treten auch Monzogranit, Granodiorit und Tonalit auf. Typisch für die Massive (3), (4) und (5) sind Zweiglimmergranite und Greisenbildungen mit unbedeutenden Anreicherungen der Elemente Sr, Mo, W, Zn und Cu. Petrochemisch sind die Granitoide als raum-zeitliche Differentationsreihen kalkalkalischer Magmen aufzufassen, an deren Ende Zweiglimmergranite als höchst spezialisierte Differentiate stehen. Ihre Sr^87/Sr^96 - Zusammensetzung deutet auf eine krustale Herkunft der Ausgangsschmelzen hin. Die Konzentration signifikanter Elemente der Frühkristallisation (Ti, Zr, Mg, Fe, P, Ca, Ba und Sr) nimmt zu den sauren Differentiaten hin ab, die der Spätkristallisation (F, B, Sn, Rb, Li) diametral zu. Danach erreichte der Quirra-Granit ein höchstes Differentationsniveau. Die Entwicklung der Massive im Einzelnen wird von folgenden Mechanismen kontrolliert: 1. Durch in-situ-Differentation bei der Entwicklung aller Massive, 2. durch emanative Differentation bei der Entwicklung des Quirra- (3), Monte-Linas- (5) und, mit Einschränkung, auch des Arburese-Granites (4), 3. durch nachträgliche metasomatische Stoffverschiebungen hauptsächlich bei der Entwicklung des Quirra- (3), Arburese- (4) und Monte-Linas-Granites (5). Bei Letzteren treten auch anomale Zinngehalte in Flußsedimenten, im granitischen Festgestein und seiner Biotite sowie in den Kontaktgesteinen auf. Die Häufigkeit anomaler Werte von 17 Indikatorgrößen, ihre Mittelwerte und Streuungen sowie die Intensität der geochemischen Spezialisierung in Bezug auf Sn, Rb, Li und F grenzen die Massive (3), (4) und (5) einhellig als für weitere Prospektionsarbeiten interessante Gebiete ab. Die absolute Intensität der Spezialisierung erreicht aber nicht das Ausmaß bekannter Zinnprovinzen. So sind für diese Granite z. B. relativ niedrige Bor- und z. T. auch Fluorwerte charakteristisch. Allgemein sind die Indikatorgrößen deutlich vom Intrusionsniveau eines Granites abhängig. Der Vergleich mit Literaturdaten führt zu einer Klassifizierung in geochemisch spezialisierte Granite 1. und 2. Ordnung im Rb-Ba-Sr- und K/Rb-Rb/Sr-Diagramm. Zinn-führende Granite heben sich also innerhalb gewisser geochemischer Variationsbreiten deutlich von sterilen Graniten ab.

Beschreibung: Summary Summary The thesis that tin bearing granites exhibit a significant geochemical character is tested by investigations of the Sarrabus (1), San Vito (2), Quirra (3), Arburese (4), and Monte Linas (5) Granite, all situated in south Sardinia. These massifs represent Hercynian granitic intrusives of high intrusion level and knife-like contacts to the adjacent rocks of Lower Palaeozoic age of greenshist facies. Endogenous tin deposits exist only spatially to the massifs (4) and (5), Mo-W-mineralizations in connection to the massifs (3) and (5). Petrologically all massifs consist principally of leucogranite. Monzogranite, granodiorite, and tonalite are rare and occure only locally. A peculiarity within the massifs (3), (4), and (5) are muscovite biotite granites and greisen with unimportant concentrations of the elements Sn, Mo, W, Zn, and Cu. Petrochemically the granitoids represent a spatial and temporal suite of a calc-alkaline magma with the muscovite biotite granites as highest specialized members. The crustal origin of the primary magmas is proven by Sr^87/Sr^96 datas. Generally the concentration of significant elements characterizing the early cristallization of a magma (Ti, Zr, Mg, Fe, P, Ca, Ba, and Sr) increase in direction of the later differentiates. The granitophile elements (F, B, Sn, Rb, Li) against that are enriched. The magmatic evolution of the massifs is governed by the following processes: 1. By in situ differentiation in the formation of all massifs, 2. by emanative differentiation in the formation of the massifs (3) and (5), with reservation also massif (4), 3. by later metasomatic chemical changes that occurred during greisenization especially in the formation of the massifs (3), (4), and (5). Anomalous tin contents are observed in alluvial sediments, leucogranites, and their biotites and country rocks distinctly of massif (5). The abundance of anomalous values of 17 proximity indicators, their mean and dispersion values and the degree of total geochemical specialization of Sn, Rb, Li, and F in the leucogranites determine uniformely the massifs (3), (4), and (5) as most interesting prospects for further detail exploration activities. The intensity of metallogenetic specialization is not as high as in other provinces. So the intrusives have extreme low concentrations of B and relative low contents of F. Generally the proximity indicators are dependent on the intrusion level of the granites. Together with reference datas from other areas one can establish geochemically specialized intrusives of first and second order. Tin bearing granites are distinguished within certain levels of clustering distinctly from barren granites.

Beschreibung: thesis

Beschreibung: DFG, SUB Göttingen

Beschreibung: Zur Ermittlung von geochemischen "proximity indicators" für den erzhöffigen (oberen) Abschnitt des Alpinen Muschelkalks wurden 11 Probennahmeprofile aus den Nördlichen Kalkalpen sowie als Vergleich 2 Probennahmeprofile aus den Südlichen Kalkalpen bearbeitet. Die Probennahme erfolgte in annähernd homogenen Gesteinsserien systematisch, in inhomogenen oberen und mittleren Partien des Alpinen Muschelkalks auch (fazies-) differenziert. Aus insgesamt ca. 1750 Schichtmetern wurden 652 Proben zur geochemischen Analyse aufbereitet. Die Bestimmung des Mg- und der Spurenelementgehalte von Sr, Zn, Pb, Fe, Mn, Cu und Cr erfolgten mit einem Atom-Absorptionsspektrophotometer (AAS). Die Fluoranalyse geschah mit ionenselektiven Elektroden (potentiometrische Fluoridbestimmung). Der Anteil der unlöslichen Rückstände wurde gravimetrisch ermittelt und fallweise mit Hilfe eines Roentgendiffraktometers näher untersucht. Die Auswertung der ca. 10 600 Analysendaten erfolgte über EDV. Mit Hilfe von Rechenprogrammen wurden Ca-Gehalte, Korrelationskoeffizienten, geometrische Mittelwerte und Streuungen ermittelt. Ober die konventionelle Statistik der geochemischen Analysendaten mit Ermittlung r e g i o n a l e r Background- und Threshold-Daten hinaus wurden zusätzlich l o k a l e Background- und Threshold-Werte festgestel1t, um die l o k a l e n Anomalien der als regional repräsentativ angenommenen Profile herauszuarbeiten und vergleichbar zu machen. Die Obergrenze des Alpinen Muschelkalks mußte nach konventionellen lithologischen Gesichtspunkten angenommen werden. Eine genauere stratigraphische Korrelierung der Probennahmeprofile war jedoch durch Tuff-Lagen (Pietra verde) möglich, soweit diese aufgeschlossen waren. Korrelationsrechnungen gaben Hinweise auf die Bindung der einzelnen Elemente sowie ihre primäre und sekundäre Anreicherung im Sediment. Die Hauptelemente Ca und Mg stammen vorherrschend aus dem Calcit- und Dolomitanteil. Säureunlösliche Rück stände setzen sich neben Quarz hauptsächlich aus Tonmineralen der Illit-Gruppe (mixed layers) zusammen. Sr-Gehalte sind eindeutig an den Kalkanteil, Fe und Cr überwiegend an Tonminerale gebunden. Zn, Mn und Cu liegen gleichwertig in Bindung an Tonminerale wie an das Karbonatgitter vor. Pb scheint überwiegend an den Kar bonatanteil gebunden zu sein. Extrem hohe Spurenelementkonzentrationen ("Ausreißer") von Pb, Zn, Fe, Cu und Mn werden auf einzelne, zufällig erfaßte Sulfid-, Oxyd- und Karbonatminerale dieser Elemente zurückgeführt. Die Analyse der Pb-Daten erwies sich nicht in allen Belangen als befriedigend. Die Gehalte von Pb in Karbonatgesteinen bewegen sich für den Entwicklungsstand des hier benutzten Analysegeräts zu nahe an der Nachweisgrenze. Die Auswertung erbrachte: - Stratiforme Anomalien, die über mehrere Probennahmeprofile verfolgbar und an bestimmte stratigraphische Niveaus gebunden sind. - Diskordante Anomalien, die in der Umgebung von bekannten Erzkörpern durch primäre oder sekundäre Migration hervorgerufen wurden. Die oberen Partien des Alpinen Muschelkalks sind meist hornsteinführend, insbesondere in der räumlichen und zeitlichen Nachbarschaft der Vulkanite. Dabei ist besonders auffällig, daß der Si02-Anteil im Liegenden und Hangenden von Tuff-Lagen (Pietra verde, 4 Zyklen) ungewöhnlich ansteigt. Dort entnommene Karbonatgesteinsproben zeigen stratiform anomal erhöhte Spurenelementkonzentrationen von Pb und Zn, fallweise begleitet von anomal er höhten F-, Fe-, Mn- und Cr-Werten. Stratiforme Anomalien von Zn-Pb-F, lokal auch von Fe-Cu-Mn-Cr, konnten regional über die Flexenpaß-Profile, Profil Zugspitze N und Martinswand verfolgt werden. In gleichem stratigraphischem Niveau wurden an anderer Stelle (Profile Davos-Silberberg, Krabachjoch u. St.Veith) diskordante Pb-Zn, F-, Fe-Mn- oder Cu-Anomalien be obachtet. Durch die wesentlich höheren Spurenelementkonzentrationen in diskordanten Anomalien wird die hier zu erwartende stratiforme Anomalie verdeckt. Im unteren und mittleren Teil des Alpinen Muschelkalks lokal auftretende, anomal erhöhte Spurenelementkonzentrationen waren dagegen regional nicht stratigraphisch korrelierbar. Geochemische Untersuchungen an Karbonatgesteinen aus den Südlichen Kalkalpen (Profile Valle Ambata/Auronzo und Topla/Mezica) lieferten keine Hinweise auf die Möglichkeit der Korrelation mit den Stratiformen Anomalien der Nördlichen Kalkalpen. Gegenüber den Karbonatgesteinen, Mergeln und Tonsteinen zeigt die Pietra verde signifkant erhöhte Gehalte von Zn und F. Diese deuten einen genetischen Zusammenhang zwischen einer zeitgleichen Zufuhr mit den Pyroklastika und einer Konzentration von Zn und F in den zwischengeschalteten Karbonatgesteinen an. Die Elemente Zn und F zeigten untereinander eine deutliche Korrelation. Bei der Suche nach schichtgebundenen Pb/Zn-Vorkommen in Karbonatgesteinen kann daher die Analyse der F-Gehalte als geochemische Prospektionshilfe (proximity indicator) herangezogen werden.

Beschreibung: ABSTRACT In order to determinate geochemical proximity indicators of the ore-bearing (upper) parts of the 'Alpiner Muschelkalk' (Anisian s. str.) rock samples have been taken from 11 standard profiles in the 'Nördliche Kalk alpen', and for comparison 2 standard profiles in the 'Südliche Kalkalpen'. Sampling was done systematically in aproximative homogeneous carbonate sequences and (facies-) differentiated in inhomogeneous sequences in the middle and upper parts of the 'Alpiner Muschelkalk'. 652 samples collected over 1.750 meters in total have been upgraded for geochemical analysis. Contents of Mg and trace elements like Sr, Zn, Pb, Fe, Mn, Cu and Cr have been determined by atomic absorption spectrophotometry. The F-analysis was done by a fluoride ion activity electrode (potentiometric fluorid analysis). Insoluble residues have been determined gravimetrically and occasionally examined by x-ray-diffraction. The analysis of about 10.600 data obtained has been processed by computer programme. Ca-data, correlation coefficients, geometric means and scattering have been computed by mathematical systems. Besides conventional statistics of geochemical analysis data like determination of regional backgrounds and thresholds, local backgrounds and thresholds have been computed, too, for showing and making comparable local anomalies of regional representative standard profiles. The border to the hanging wall had to be determined by conventional lithological conception. A more exact stratigraphical correlation of standard profiles was made possible by tuffs as far as they outcropped. Correlation coefficients showed the mineralogical bounding of elements as well as the primary and secondary concentrations in the sedimentary sequences. The major elements Ca and Mg originate predominantly from calcite and dolomite. Insoluble residues consist essentially of clay minerals of Illite-group (mixed layers) and quartz. Sr is clearly bound to calcite, Fe and Cr are linked to clay minerals as well as to calcite. Extremely high trace element concentrations of Pb, Zn, Fe, Mn and Cu are considered to originate from accidently caught sulfides, oxides or carbonates of these elements. Analysis of Pb data was not satisfactory in each matter, as the contents of Pb in carbonate rocks are to close to the noise of used AAS. The evaluation showed: — Stratiform anomalies, which can be correlated in several standard profiles and which are bound to distinct stratigraphic levels. -Discordantanomalies, which are caused by primary or secondary migration from ore bodies nearby. In the upper parts of the 'Alpiner Muschelkalk occur cherty limestones, especially in regional and stra tigraphical neighbourhood of volcanics. It is conspicuous, that carbonates belonging to the foot wall and hanging wall of tuffs (Pietra verde) are unusual rich of silica. Carbonate samples of this matter show stra tiform anomalous high trace element concentrations of Pb and Zn, occasionally accompanied by anomalous high concentrations of F, Fe, Mn and Cr. Stratiform anomalies of Zn-Pb-F, in some profiles also of Fe-Mn-Cu-Cr, can be correlated regionally in the Flexenpass-profiles and the profiles Zugspitze and Martinswand. At the same stratigraphical level there have been observed anomalies of Pb-, Zn-, F-, Fe-, Mn- or Cu at other places (profiles Davos-Silberberg, Kra bachjoch and St. Veith). Here the expected stratiform anomalies are masked by the higher trace element con centrations of discordant anomalies. The trace element concentrations of the lower and middle part of the 'Alpiner Muschelkalk' however, are not stratigraphically correlated. Geochemical data of the two profiles from the 'Südliche Kalkalpen' (profiles Valle Ambata/Auronzo and Topla/Me2ica) do not indicate a correlation with stratiform anomalies of the 'Nördliche Kalkalpen'. In opposition to the carbonates, marls and clays, the 'Pietra verde' shows significant higher contents of Zn and F. This indicates a genetic connection between the pyroclastics and the concentration of Zn and F in the intercalated carbonates. The elements Zn and F exhibit an evident correlation. The analysis of F may find application as a proximity indicator for exploration of stratabound lead-zinc occurrences in carbonate rocks.

Beschreibung: thesis

Beschreibung: DFG, SUB Göttingen

Beschreibung: Methane (CH4) production in the ocean surface mixed layer is a widespread but still largely unexplained phenomenon. In this context marine algae have recently been described as a possible source of CH4 in surface waters. In the present study we investigated the effects of temperature and light intensity (including daylength) on CH4 formation from three widespread marine algal species Emiliania huxleyi, Phaeocystis globosa, and Chrysochromulina sp. Rates of E. huxleyi increased by 210% when temperature increased in a range from 10°C to 21.5°C, while a further increase in temperature (up to 23.8°C) showed reduction of CH4 production rates. Our results clearly showed that CH4 formation of E. huxleyi is controlled by light: When light intensity increased from 30 to 2,670 μmol m−2 s−1, CH4 emission rates increased continuously by almost 1 order of magnitude and was more than 1 order of magnitude higher when the daylength (light period) was extended from 6/18 hr light-dark cycle to continuous light. Furthermore, light intensity is also an important factor controlling CH4 emissions of Chrysochromulina sp. and P. globosa and could therefore be a species-independent regulator of phytoplankton CH4 production. Based on our results, we might conclude that extensive blooms of E. huxleyi could act as a main regional source of CH4 in surface water, since blooming of E. huxleyi is related to the seasonal increase in both light and temperature, which also stimulate CH4 production. Under typical global change scenarios, E. huxleyi will increase its CH4 production in the future.

Beschreibung: The isotopic composition of Si in biogenic silica (BSi), such as opal buried in the oceans' sediments, has changed over time. Paleorecords suggest that the isotopic composition, described in terms of δ30Si, was generally much lower during glacial times than today. There is consensus that this variability is attributable to differing environmental conditions at the respective time of BSi production and sedimentation. The detailed links between environmental conditions and the isotopic composition of BSi in the sediments remain, however, poorly constrained. In this study, we explore the effects of a suite of offset boundary conditions during the Last Glacial Maximum (LGM) on the isotopic composition of BSi archived in sediments in an Earth System Model of intermediate complexity (EMIC). Our model results suggest that a change in the isotopic composition of Si supply to the glacial ocean is sufficient to explain the observed overall low(er) glacial δ30Si in BSi. All other processes explored trigger model responses of either wrong sign or magnitude or are inconsistent with a recent estimate of bottom water oxygenation in the Atlantic Sector of the Southern Ocean. Caveats, mainly associated with generic uncertainties in today's pelagic biogeochemical modules, remain.

Beschreibung: A geoarchaeological soil phosphorus (P) prospection is used to identify a gate within the prehistoric rampart of the Milseburg hillfort (Hesse, Germany). This study compares the application of a P fractionation scheme and P extraction with ammonium-oxalate. We hypothesized that oxalate-extractable P (P-ox) and the related degree of P saturation (DPS) could replace the more expensive and time-consuming fractionation schemes for geoarchaeological investigations. Comparing the results, the P fractionation helped to verify the existence of another section of the prehistoric ramparts and to identify the location of a gate within it. It also helped to discover the archaeologically relevant soil depths in the investigated area. This information could not be retrieved from the P-ox data alone. Soil P-ox contents and DPS values are relatively unspecific with regard to prehistoric land use. However, DPS at least indicates settled versus unsettled areas. Still, the results of the P fractionation more clearly delineate Iron Age land use areas including settlement, non-settlement, rampart, and rampart gap (probable gate). Thus, in geoarchaeological contexts, this method seems to be preferable to a singular P-ox extraction. However, for better results, P-ox determination could be integrated into a P fractionation scheme.

Beschreibung: Riparian zones are important buffer zones for streams as they are hotspots of nitrate transformation and removal in agricultural catchments. However, mixing of water from different sources and various transformation processes can complicate the quantification of nitrate turnover in riparian zones. In this study, we analyzed nitrate concentration and isotope data in riparian groundwater along a 2-km stream section in central Germany. We developed a mathematical model combining end-member mixing and isotope modeling to account for mixing of river water and groundwater and quantify nitrate transformation in riparian groundwater. This enabled us to explicitly determine the extent of denitrification (as process leading to permanent nitrate removal from riparian groundwater) and transient nitrate removal by additional processes associated with negligible isotope fractionation (e.g., plant uptake and microbial assimilation) and to perform an extensive uncertainty analysis. Based on the nitrogen isotope data of nitrate, the simulations suggest a mean removal of up to 27% by additional processes and only about 12% by denitrification. Nitrate removal from riparian groundwater by additional processes exceeded denitrification particularly in winter and at larger distance from the river, underlining the role of the river as organic carbon source. This highlights that nitrate consumption by additional processes predominates at the field site, implying that a substantial fraction of agricultural nitrogen input is not permanently removed but rather retained in the riparian zone. Overall, our model represents a useful tool to better compare nitrogen retention to permanent nitrogen removal in riparian zones at various temporal and spatial scales.

Beschreibung: Emissions of the potent greenhouse gas methane (CH4) from streams and rivers are a significant component of global freshwater methane emissions. The distribution of CH4 production and oxidation within stream sections and in vertical sediment profiles is not well understood, and the environmental controls on CH4 production and emission in such systems create a significant challenge for assessing larger-scale dynamics. Here we investigate factors driving the spatial variability of sediment potential methane production (PMP) and potential methane oxidation (PMO) in a temperate stream network in Germany. PMP was highly variable, ranging from 5 × 10−4 to 28.58 μg CH4 gDW−1 d−1 and PMO ranged from 0.43 μg CH4 gDW−1 d−1 to 14.41 μg CH4 gDW−1 d−1. Important drivers of spatial variability of PMP and PMO in the sediments of the stream main-stem were related to fine sediment fraction and organic carbon content. At smaller spatial scale, that is, in a sub-catchment stream section, the drivers were more complex and included sediment nitrogen and organic carbon content, as well as porewater dissolved organic carbon, dissolved organic matter quality, and metal concentrations. As with reservoirs and impounded rivers, fine sediment deposition and organic carbon content were found to be key controls on the spatial variability of CH4 production and oxidation. These findings enhance our understanding of CH4 dynamics, improve the potential for identifying CH4 production hotspots in small streams, and provide a potential means for upscaling emission rates in larger-scale assessments.

Beschreibung: Separate evaluation of methane (CH4) emission dynamics (e.g., oxidation, production, and transportation) at the soil-plant-atmosphere and soil-water-atmosphere interfaces has been limited in tropical rice paddies, but it is crucial for comprehending the entire CH4 cycles. We investigated CH4 oxidation, production, and transportation through plant and water pathways during the reproductive stage in a tropical Thailand rice paddy field using natural abundance carbon stable isotope ratios (δ13CH4 and δ13CO2). Mass balance equations using δ13CH4 and δ13CO2 in soil gases indicated that CH4 oxidation in the planted soil exceeded those in the interrow soil due to oxygen supply through rice roots. In addition, at 1–11 cm depth acetate fermentation was the dominant process in the planted soil, whereas in the interrow soil the dominant process was H2/CO2 reduction. The water pathway showed a significant negative correlation between CH4 flux and released δ13CH4 over 24 hr, driven by a diel change in episodic ebullition, steady ebullition, and diffusion, all due to diel changes in soil temperature and atmospheric pressure. In contrast, the plant pathway showed a significant positive relationship between CH4 flux and emitted δ13CH4 throughout one day. A comparison of the diel change in emitted δ13CH4 between the water and plant pathways showed that the rice plants transported CH4 in soil bubbles without any large isotopic fractionation. The diel change in the plant-mediated CH4 transportation was mainly controlled by diel changes in soil bubble expansion and CH4 diffusion through plants, which were probably regulated by diel changes in soil temperature and atmospheric pressure.

Beschreibung: During seawater circulation in permeable intertidal sands, organic matter degradation alters the composition of percolating fluids and remineralization products discharge into surficial waters. Concurrently, coastal seawater nutrient and organic matter composition change seasonally due to variations in pelagic productivity. To assess seasonal changes in organic matter degradation in the intertidal zone of a high energy beach (Spiekeroog Island, southern North Sea, Germany), we analyzed shallow pore waters for major redox constituents (oxygen [O2], manganese [Mn], and iron [Fe]) and inorganic nitrogen species (nitrite [NO2−], nitrate [NO3−], and ammonium [NH4+]) in March, August, and October. Surface water samples from a local time series station were used to monitor seasonal changes in pelagic productivity. O2 and NO3− were the dominating pore water constituents in March and October. Dissolved Mn, Fe, and NH4+ were more widely distributed in August. Seasonal changes in seawater temperature as well as organic matter and nitrate supply by seawater were assumed to affect microbial rates and degradation pathways. Pore water and seawater variability led to seasonally changing constituent effluxes to surface waters. Mn, Fe, and NH4+ effluxes are minimal in March and reached their maximum in August. Furthermore, the intertidal sands switched from a net dissolved inorganic nitrogen sink in March to a net source in August. In conclusion, seasonal effects on intertidal pore water biogeochemistry affect constituent fluxes across the sediment-water interface. The seasonality of the beach bioreactor must be considered when fluxes are extrapolated to annual timescales.

Beschreibung: Neodymium (Nd) isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance. To better constrain the controls of water mass provenance and nonconservative effects on the archived Nd isotope signal, we present a new depth transect of Nd isotope reconstructions from the Blake Bahama Outer Ridge along the North American continental margin covering the past 30 ka. We investigated five sediment cores that lie directly within the main flow path of the Deep Western Boundary Current, a major advection route of North Atlantic Deep Water. We found offsets between core tops and seawater Nd isotopic compositions that are observed elsewhere in the Northwest Atlantic. A possible explanation for this is the earlier suggested redistribution of sediment by nepheloid layers at intermediate as well as abyssal depths, transporting material downslope and along the continental margin. These processes potentially contributed to Nd isotope excursions recorded in Northwest Atlantic sediment cores during the Bølling-Allerød and early Holocene. An Atlantic-wide comparison of Nd isotope records shows that the early Holocene excursions had an additional contribution from conservative advection of unradiogenic dissolved Nd. Nevertheless, the trends of the Nd isotope records are in general agreement with previous reconstructions of water mass provenance from the entire Atlantic and also reveal millennial-scale changes during the last deglaciation in temporal high resolution, which have rarely been reported before. Further, the new records confirm that during cold periods the Northwest Atlantic was bathed by an increased contribution of southern sourced water.