Effects of increased CO2 concentration on nutrient limited coastal summer plankton depend on temperature

Increasing seawater temperature and CO2 concentrations both are expected to increase coastal phytoplankton biomass and carbon to nutrient ratios in nutrient limited seasonally stratified summer conditions. This is because temperature enhances phytoplankton growth while grazing is suggested to be reduced during such bottom-up controlled situations. In addition, enhanced CO2 concentrations potentially favor phytoplankton species, that otherwise depend on costly carbon concentrating mechanisms (CCM). The trophic consequences for consumers under such conditions, however, remain little understood. We set out to experimentally explore the combined effects of increasing temperature and CO2 concentration for phytoplankton biomass and stoichiometry and the consequences for trophic transfer (here for copepods) on a natural nutrient limited Baltic Sea summer plankton community. The results show, that warming effects were translated to the next trophic level by switching the system from a bottom-up controlled to a mainly top-down controlled one. This was reflected in significantly down-grazed phytoplankton and increased zooplankton abundance in the warm temperature treatment (22.5°C). Additionally, at low temperature (16.5°C) rising CO2 concentrations significantly increased phytoplankton biomass. The latter effect however, was due to direct negative impact of CO2 on copepod nauplii which released phytoplankton from grazing in the cold but not in the warm treatments. Our results suggest that future seawater warming has the potential to switch trophic relations between phytoplankton and their grazers under nutrient limited conditions with the consequence of potentially disguising CO2 effects on coastal phytoplankton biomass.

(Table 2) Concentrations of persistant organic pollutants in the yolk of glaucous gull eggs, Bjørnøya, Svalbard archipelago

It is largely unknown if and how persistent organic pollutants (POPs) affect the transfer of maternal hormones to eggs. This occurs despite an increasing number of studies relating environmental conditions experienced by female birds at the time of egg formation to maternal hormonal effects. Here we report the concentrations of maternal testosterone, 17beta-estradiol and major classes of POPs (organochlorines, brominated flame retardants and metabolically-derived products) in the yolk of unincubated, third-laid eggs of the glaucous gull (Larus hyperboreus), a top-predator in the Arctic marine environment. Controlled for seasonal and local variation, positive correlations were found between the concentrations of certain POPs and testosterone. Contaminant-related changes in the relative concentrations of testosterone and 17beta-estradiol were also observed. In addition, yolk steroid concentrations were associated with contaminant profiles describing the proportions of different POPs present in the yolk. Eggs from nests in which two sibling eggs hatched or failed to hatch differed in POP profiles and in the relative concentrations of testosterone and 17beta-estradiol. Although the results of this correlative study need to be interpreted with caution, they suggest that contaminant-related changes in yolk steroids may occur, possibly affecting offspring performance over and above toxic effects brought about by POPs in eggs.

(Table T1) Radiolaria abundance of ODP Hole 175-1082A

A primary objective of Leg 175 was to investigate the upwelling history of the Benguela Current. Upwelling along the coast is found over the shelf in several well-established cells, as well as along the shelf-slope break, and extends over the 1000-m isobath. Streaming filaments along the coast also carry upwelled water off shore (Shannon, 1985). The upwelled nutrient-rich waters are sourced from the South Atlantic central water mass, which is a mixture of subtropical and subantarctic water masses. Below the central water mass lies Antarctic intermediate water (Shannon and Hunter, 1988, doi:10.2989/025776188784480735; Stramma and Peterson, 1989, doi:10.1175/1520-0485(1989)019<1440:GTITBC>2.0.CO;2). The upwelling system supports a robust marine community (Shannon and Pillar, 1986) where radiolarians are abundant (Bishop et al., 1978, doi:10.1016/0146-6291(78)90010-3). The endemic nature of radiolarians makes them useful in reconstructing the paleocirculation patterns. The biogeographic distribution of many species is limited by water-mass distribution. In a given geographic region, species may also have discrete depth habitats. However, their depth of occurrence can change worldwide because the depths of water masses vary with latitude (Boltovskoy, 1999). Consequently, species found at shallow depths at high latitudes (cold-water fauna) are observed deeper in the water column at lower latitudes. The low-latitude submergence of cold-water species broadens their distribution, resulting in species distributions that can cover multiple geographic regions (Kling, 1976, doi:10.1016/0011-7471(76)90880-9; Casey, doi:10.1016/0031-0182(89)90017-5; 1971; Boltovskoy, 1987, doi:10.1016/0377-8398(87)90014-4). Since radiolarian distribution is closely related to water-mass distribution and controlled by climatic conditions rather than geographic regions, similar assemblages characterize the equatorial, subtropical, transition, subpolar, and polar regions of ocean basins (Petrushevskaya, 1971a; Casey, 1989, doi:10.1016/0031-0182(89)90017-5; Boltovskoy, 1999). Numerous radiolarian species found in water masses in the Angola and Benguela Current systems have also been observed in plankton net samples, sediment traps, and surface-sediment studies in the Atlantic sector of the Southern Ocean, where they exhibited particular water-mass affinities (Abelmann, 1992a, doi:10.1007/BF00243107; Abelmann 1992b, doi:10.1007/BF00243108; Abelmann and Gowing, 1997, doi:10.1016/S0377-8398(96)00021-7). This report presents data on the radiolarian fauna recovered from Site 1082 sediments in the form of a survey of species reflecting the latitudinal migration of the Angola-Benguela Front and upwelling. The data constitute a time series of relative radiolarian abundances at very high resolution (every 20 cm) of the upper 12 m of Hole 1082A.

High-resolution marine record of sediment core MD99-2343 in the Balearic Sea

The IMAGES core MD99-2343, recovered from a sediment drift north of the island of Minorca, in the north-western Mediterranean Sea, holds a high-resolution sequence that is perfectly suited to study the oscillations of the overturning system of the Western Mediterranean Deep Water (WMDW). Detailed analysis of grain-size and bulk geochemical composition reveals the sensitivity of this region to climate changes at both orbital and centennial-millennial temporal scales during the last 50 kyr. The dominant orbital pattern in the K/Al record indicates that sediment supply to the basin was controlled by the insolation evolution at 40°N, which forced changes in the fluvial regime, with more efficient sediment transport during insolation maxima. This orbital control also modulated the long-term pattern of the WMDW intensity as illustrated by the silt/clay ratio. However, deep convection was particularly sensitive to climatic changes at shorter time-scales, i.e. to centennial-millennial glacial and Holocene oscillations that are well documented by all the paleocurrent intensity proxies (Si/Al, Ti/Al and silt/clay ratios). Benthic isotopic records (d13C and d18O) show a Dansgaard-Oeschger (D-O) pattern of variability of WMDW properties, which can be associated with changing intensities of the deep currents system. The most prominent reduction on the WMDW overturning was caused by the post-glacial sea level rise. Three main scenarios of WMDW overturning are revealed: a strong mode during D-O Stadials, a weak mode during D-O Interstadials and an intermediate mode during cooling transitions. In addition, D-O Stadials associated with Heinrich events (HEs) have a very distinct signature as the strong mode of circulation, typical for the other D-O Stadials, was never reached during HE due to the surface freshening induced by the inflowing polar waters. Consequently, the WMDW overturning system oscillated around the intermediate mode of circulation during HE. Though surface conditions were more stable during the Holocene, the WMDW overturning cell still reacted synchronously to short-lived events, as shown by increments in the planktonic d18O record, triggering quick reinforcements of the deep water circulation. Overall, these results highlight the sensitivity of the WMDW to rapid climate change which in the recent past were likely induced by oceanographic and atmospheric reorganizations in the North Atlantic region.

Age determination and grain size distribution of sediment core GeoB3375-1

The palaeoclimatic conditions during the Last Glacial Maximum (LGM) of southern South America and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially. Longer palaeoclimatic records covering the Late Quaternary are rare. A particularly sensitive area to Late Quaternary climatic changes is the Norte Chico, northern Chile, because of its extreme climatic gradients. Small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments. To unveil the history of shifting climatic zones in northern Chile, we present a sedimentological study of a marine sediment core (GeoB 3375-1) from the continental slope off the Norte Chico (27.5°S). Sedimentological investigations include bulk- and silt grain-size determinations by sieving, Atterberg separation, and detailed SediGraph analyses. Additionally, clay mineralogical parameters were obtained by X-ray diffraction methods. The 14C-dated core, covering the time span from approximately 10,000 to 120,000 cal. yr B.P., consists of hemipelagic sediments. Terrigenous sedimentological parameters reveal a strong cyclicity, which is interpreted in terms of variations of sediment provenance, modifications of the terrestrial weathering regimes, and modes of sediment input to the ocean. These interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern Chile (27.5°S) through the Late Quaternary. The cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles. For the palaeoclimatic signal, this means that more humid conditions coincide with maxima of the precession index, as e.g. during the LGM. Higher seasonal precipitation for this part of Chile is most likely derived from frontal winter rain of the Southern Westerlies. Thus, the data presented here favour not only an equatorward shift of this atmospheric circulation system during the LGM, but also precession-controlled latitudinal movements throughout the Late Quaternary. Precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the Northern Hemisphere monsoonal system in the Atlantic Ocean region.

Radiocarbon ages, diatom abundance and laminae description of sediment core MD03-2597

Laminated sediments are unique archives of palaeoenvironmental and palaeoceanographic conditions, recording changes on seasonal and interannual timescales. Diatom-rich laminated marine sediments are examined from Dumont d'Urville Trough, East Antarctic Margin, to determine changes in environmental conditions on the continental shelf from 1136 to 3122 cal. yr BP. Scanning electron microscope backscattered electron imagery (BSEI) and secondary electron imagery are used to analyse diatom assemblages from laminations and to determine interlamina relationships. Diatom observations are quantified with conventional assemblage counts. Laminae are primarily classified according to visually dominant species identified in BSEI and, secondarily, by terrigenous content. Nine lamina types are identified and are characterized by: Hyalochaete Chaetoceros spp. resting spores (CRS); CRS and Fragilariopsis spp.; Fragilariopsis spp.; Corethron pennatum and Rhizosolenia spp.; C. pennatum; Rhizosolenia spp.; mixed diatom assemblage; Stellarima microtrias resting spores (RS), Porosira glacialis RS and Coscinodiscus bouvet; and P. glacialis RS. Formation of each lamina type is controlled by seasonal changes in sea ice cover, nutrient levels and water column stability. Quantitative diatom assemblage analysis revealed that each lamina type is dominated by CRS and Fragilariopsis sea ice taxa, indicating that sea ice cover was extensive and persistent in the late Holocene. However the lamina types indicate that the sea ice regime was not consistent throughout this period, notably that a relatively warmer period, ~3100 to 2500 cal. yr BP, was followed by cooling which resulted in an increase in year round sea ice by ~1100 cal. yr BP.

Radioisotope stratigraphy, sedimentology and geochemistry of Late Quaternary sediments from the Eastern Arctic Ocean

To reconstruct Recent and past sedimentary environments, marine sediments of Upper Pleistocene and Holocene ages from the eastern Arctic Ocean and especially from the Nansen-Gakkel Ridge (NGR) were investigated by means of radioisotopic, geochemical and sedimentological methods. In combination with mass physical property data and lithological analysis these investigations allow clearly to characterize the depositional environments. Age dating by using the radioisotope 230Th gives evidence that the investigated sediments from the NGR are younger than 250,000 years. Identical lithological sediment sequences within and between sediment cores from the NGR can be related to sedimentary processes which are clearly controlled by palaeoclimate. The sediments consist predominantly of siliciclastic, terrigenous ice-rafted detritus (IRD) deriving from assorted and redeposited sediments from the Siberian shelfs. By their geochemical composition the sediments are similar to mudstone, graywacke and arcose. Sea-ice as well as icebergs play a major roll in marine arctic sedimentation. In the NGR area rapid change in sedimentary conditions can be detected 128,000 years ago. This was due to drastic change in the kind of ice cover, resulting from rapid climatic change within only hundreds of years. So icebergs, deriving mostly from Siberian shelfs, vanished and sea-ice became dominant in the eastern Arctic Ocean. At least three short-period retreats of the shelf ice between 186,000 and 128,000 years are responsible for the change of coarse to fine-grained sediments in the NGR area. These warmer stages lasted between 1,000 and 3,000 years. By monitoring and comparing the distribution patterns of sedimentologic, mass physical and geochemical properties with 230Th ex activity distribution patterns in the sediment cores from the NGR, there is clear evidence that sediment dilution is responsible for high 230Th ex activity variations. Thus sedimentation rate is the controlling factor of 230Th ex activity variations. The 230Th flux density in sediments from the NGR seems to be highly dependent On topographic Position. The distribution patterns of chemical elements in sediment cores are in general governed by lithology. The derivation of a method for dry bulk density determination gave the opportunity to establish a high resolution stratigraphy on sediment cores from the eastern Arctic Ocean, based on 230Thex activity analyses. For the first time sedimentation and accumulation rates were determined for recent sediments in the eastern Arctic Ocean by 230Th ex analyses. Bulk accumulation rates are highly variable in space and time, ranging between 0.2 and 30 g/cm**2/ka. In the sediments from the NGR highly variable accumulation rates are related to the kind of ice cover. There is evidence for hydrothermal input into the sediments of the NGR. Hydrothermal activity probably also influences surficial sediments in the Sofia Basin. High contents of As are typical for surficial sediments from the NGR. In particular SL 370-20 from the bottom of the rift valley has As contents exceeding in parts 300 ppm. Hydrothermal activity can be traced back to at least 130,000 years. Recent to subrecent tectonic activity is documented by the rock debris in KAL 370 from the NGR. In four other sediment cores from the NGR rift valley area tectonically induced movements can be dated to about 130,000 years ago, related most probably to the rapid climate change. Processes of early diagenesis in sediments from the NGR caused the aobilization and redeposition of Fe, Mn and Mo. These diagenetic processes probably took place during the last 130,000 years. In sediment cores from the NGR high amounts of kaolinite are related to coarse grained siliciclastic material, probably indicating reworking and redeposition of siberian sandstones with kaolinitic binding material. In contrast to kaolinite, illite is correlated to total clay and 232Th contents. Aragonite, associated with serpentinites in the rift valley area of the NGR, was precipitated under cold bottom-water conditions. Preliminary data result in a time of formation about 60 - 80 ka ago. Manganese precipitates with high Ni contents, which can be related to the ultrabasic rocks, are of similar age.

In-situ stress conditions at ODP Site 131-808

Shipboard laboratory index property data, shore-based consolidation tests, and in-situ stress and pore-pressure measurements are used in this study to constrain the stress conditions at ODP Site 808, Nankai Trough. Results of these tests are presented along with additional interpretations of porosity rebound and permeability. The sediment at Site 808 is highly affected by excess fluid pressures throughout the sediment column. Excess fluid pressure is severe below the major fault boundary, the décollement. The in-situ measurement of lateral stresses, which are shallow in the sediment section, confirms that the principal stress direction is rotated from a "normal" basin-type condition where the principal stress direction is vertical.

Pliocene-Pleistocene alkenone, nitrogen and opal record of ODP Site 175-1082

In this study we present combined high-resolution records of sea surface temperature (SST), phytoplankton productivity, and nutrient cycling in the Benguela Upwelling System (BUS) for the past 3.5 Ma. The SST record provided evidence that upwelling activity off Namibia mainly intensified ca. 2.4-2.0 Ma ago in response to the cooling of the Southern Ocean and the resultant strengthening of trade winds. As revealed by productivity-related proxies, BUS intensification led to a major transition in regional biological productivity when considering the termination of the Matuyama Diatom Maximum (a diatom high-production event). Major oceanic reorganization in the Benguela was accompanied by nutrient source changes, as indicated by a new nitrogen isotopic (delta15N) record that revealed a stepwise increase at ca. 2.4 and ca. 1.5 Ma ago. The change in source region likely resulted from significant changes in intermediate water formation tied to the reorganization of oceanic conditions in the Southern Ocean, which may have in turn mainly controlled the global ocean N cycle, and therefore the N isotopic composition of nutrients since 3.5 Ma ago.

Multi-proxy analyses of sediment cores from the Pakistan continental margin

Late Holocene laminated sediments from a core transect centred in the oxygen minimum zone (OMZ) impinging at the continental slope off Pakistan indicate stable oxygen minimum conditions for the past 7000 calendar years. High SW-monsoon-controlled biological productivity and enhanced organic matter preservation during this period is reflected in high contents of total organic carbon (TOC) and redox-sensitive elements (Ni, V), as well as by a low-diversity, high-abundance benthic foraminiferal Buliminacea association and high abundance of the planktonic species Globigerina bulloides indicative of upwelling conditions. Surface-water productivity was strongest during SW monsoon maxima. Stable OMZ conditions (reflected by laminated sediments) were found also during warm interstadial events (Preboreal, Bølling-Allerød, and Dansgaard-Oeschger events), as well as during peak glacial times (17-22.5 ka, all ages in calendar years). Sediment mass accumulation rates were at a maximum during the Preboreal and Younger Dryas periods due to strong riverine input and mobilisation of fine-grained sediment coinciding with rapid deglacial sea-level rise, whereas eolian input generally decreased from glacial to interglacial times. In contrast, the occurrence of bioturbated intervals from 7 to 10.5 ka (early Holocene), in the Younger Dryas (11.7-13 ka), from 15 to 17 ka (Heinrich event 1) and from 22.5 to 25 ka (Heinrich event 2) suggests completely different conditions of oxygen-rich bottom waters, extremely low mass and organic carbon accumulation rates, a high-diversity benthic fauna, all indicating lowered surface-water productivity. During these intervals the OMZ was very poorly developed or absent and a sharp fall of the aragonite compensation depth favoured the preservation of pteropods. The abundance of lithogenic proxies suggests aridity and wind transport by northwesterly or northeasterly winds during these periods coinciding with the North Atlantic Heinrich events and dust peaks in the Tibetan Loess records. The correlation of the monsoon-driven OMZ variability in the Arabian Sea with the rapid climatic fluctuations in the high northern latitudes suggests a close coupling between the climates of the high and low latitudes at a global scale.

Temperature reconstruction of sediment cores from the northeastern Arabian Sea

In order to reconstruct the monsoonal variability during the late Holocene we investigated a complete, annually laminated sediment record from the oxygen minimum zone (OMZ) off Pakistan for oxygen isotopes of planktic foraminifera and alkenone-derived sea surface temperatures (SST). Significant SST changes of up to 3°C which cannot be explained by changes in the alkenone-producing coccolithophorid species (inferred from the Gephyrocapsa oceanica / Emiliania huxleyi ratio) suggest that SST changes are driven by changes in the monsoon strength. Our high-(decadal)-resolution data indicate that the late Holocene in the northeastern Arabian Sea was not characterized by a stable uniform climate, as inferred from the Greenland ice cores, but by variations in the dominance of the SW monsoon conditions with significant effects on temperatures. Highest SST fluctuations of up to 3.0°C and 2.5°C were observed for the time interval from 4600 to 3300 years B.P. and during the past 500 years. The significant, short-term SST changes during the past 500 years might be related to climatic instabilities known from the northern latitudes ("Little Ice Age") and confirm global effects. Surface salinity values, reconstructed from delta18O records after correction for temperature-related oxygen isotope fractionation, suggest that in general, the past 5000 years were characterized by higher-than-recent evaporation and more intense SW monsoon conditions. However, between 4600 and 3700 years B.P., evaporation dropped, SW monsoon weakened, and NE monsoon conditions were comparatively enhanced. For the past 1500 years we infer strongly fluctuating monsoon conditions. Comparisons of reconstructed salinity records with ice accumulation data from published Tibetan ice core and Tibetan tree ring width data reveal that during the past 2000 years, enhanced evaporation in the northeastern Arabian Sea correlates with periods of increased ice accumulation in Tibet, and vice versa. This suggests a strong climatic relationship between both monsoon-controlled areas.

Stable carbon and oxygen isotope ratios of foraminifera in surface sediments of the South China Sea

The relationship between planktonic and benthic foraminiferal stable-isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and Last Glacial Maximum (LGM) samples from the South China Sea (SCS). The harmonic variation of benthic delta18O in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic delta18O variations. Planktonic delta18O fluctuates with sea surface temperature (SST) and salinity (SSS). The N-S temperature gradient results in planktonic delta18O decreasing from the northeast to the south. Cool, saline waters driven by the winter monsoon are interpreted to have been responsible for the high delta18O values in the northeast SCS. The East Asian monsoons not only bring nutrients into the South China Sea and maintain high nutrient concentration levels at the southwestern and northeastern ends, which cause depleted delta13C both in planktonic (surface) and benthic (bottom) samples but also reduce planktonic/benthic delta18O differences. The distribution of delta18O and delta13C in the surface and LGM samples are strikingly similar, indicating that the impact of SST and SSS has been maintained, and nutrient inputs, mainly from the northeastern and southwestern ends, have been controlled by monsoons since the LGM. Comparisons of the modern and LGM delta18O indicate a difference of about 3.6 °C in bottom-water temperature and a large surface-to-bottom temperature gradient during the LGM as compared to today.

Mineralogy of sediment cores from the continental slope of Chile

Marine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial records. Glacial climates (28,000-18,000 cal yr B.P.) were generally cold-humid with a cold-semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000-4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000-0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

Nd and Mn concentration in planktonic foraminifera

Neodymium isotopes are becoming widely used as a palaeoceanographic tool for reconstructing the source and flow direction of water masses. A new method using planktonic foraminifera which have not been chemically cleaned has proven to be a promising means of avoiding contamination of the deep ocean palaeoceanographic signal by detrital material. However, the exact mechanism by which the Nd isotope signal from bottom waters becomes associated with planktonic foraminifera, the spatial distribution of rare earth element (REE) concentrations within the shell, and the possible mobility of REE ions during changing redox conditions, have not been fully investigated. Here we present REE concentration and Nd isotope data from mixed species of planktonic foraminifera taken from plankton tows, sediment traps and a sediment core from the NW Atlantic. We used multiple geochemical techniques to evaluate how, where and when REEs become associated with planktonic foraminifera as they settle through the water column, reside at the surface and are buried in the sediment. Analyses of foraminifera shells from plankton tows and sediment traps between 200 and 2938 m water depth indicate that only ~20% of their associated Nd is biogenically incorporated into the calcite structure. The remaining 80% is associated with authigenic metal oxides and organic matter, which form in the water column, and remain extraneous to the carbonate structure. Remineralisation of these organic and authigenic phases releases ions back into solution and creates new binding sites, allowing the Nd isotope ratio to undergo partial equilibration with the ambient seawater, as the foraminifera fall through the water column. Analyses of fossil foraminifera shells from sediment cores show that their REE concentrations increase by up to 10-fold at the sediment-water interface, and acquire an isotopic signature of bottom water. Adsorption and complexation of REE3+ ions between the inner layers of calcite contributes significantly to elevated REE concentrations in foraminifera. The most likely source of REE ions at this stage of enrichment is from bottom waters and from the remineralisation of oxide phases which are in chemical equilibrium with the bottom waters. As planktonic foraminifera are buried below the sediment-water interface redox-sensitive ion concentrations are adjusted within the shells depending on the pore-water oxygen concentration. The concentration of ions which are passively redox sensitive, such as REE3+ ions, is also controlled to some extent by this process. We infer that (a) the Nd isotope signature of bottom water is preserved in planktonic foraminifera and (b) that it relies on the limited mobility of particle reactive REE3+ ions, aided in some environments by micron-scale precipitation of MnCO3. This study indicates that there may be sedimentary environments under which the bottom water Nd isotope signature is not preserved by planktonic foraminifera. Tests to validate other core sites must be carried out before downcore records can be used to interpret palaeoceanographic changes.