17 results found
Rodgers KB, Schlunegger S, Slater RD, et al., 2020, Re‐emergence of anthropogenic carbon into the ocean’s mixed layer strongly amplifies transient climate sensitivity, Geophysical Research Letters, ISSN: 0094-8276
Stichel T, Kretschmer S, Geibert W, et al., 2020, Particle-seawater interaction of neodymium in the North Atlantic, ACS Earth and Space Chemistry, ISSN: 2472-3452
Dissolved neodymium (Nd) isotopes (expressed as εNd) have been widely used as a water mass tracer in paleoceanography. However, one aspect of the modern biogeochemical cycle of Nd that has been sparsely investigated is the interplay between dissolved and particulate phases in seawater. We here present the first regional data set on particulate Nd isotope compositions (εNdp) and concentrations ([Nd]p) from five stations in the western North Atlantic Ocean along the GEOTRACES GA02 transect, in conjunction with previously published dissolved Nd isotope compositions (εNdd) and concentrations ([Nd]d)1. Key observations and interpretations from our new particulate data set include the following: (1) A low fractional contributions of [Nd]p to the total Nd inventory per volume unit of seawater (~5%), with significant increases of up to 45% in benthic boundary layers. (2) Increasing Nd concentrations in suspended particulate matter ([Nd]SPM) and fractions of lithogenic material with water depth, suggesting the removal of Nd poor phases. (3) Different provenances of particulates in the subpolar and subtropical gyres as evidenced by their Nd isotope fingerprints reaching from εNdp ≈ -20 near the Labrador Basin (old continental crust), over εNdp ≈ -4 between Iceland and Greenland (young mafic provenance), to values of εNdp ≈-13 in the subtropics (similar to African dust signal). (4) Vertical heterogeneity of εNdp, as well as large deviations from ambient seawater values in the subpolar gyre, indicate advection of lithogenic particles in this area. (5) Vertically homogenous εNdp values in the subtropical gyre, indistinguishable from εNdd values, are indicative of predominance of vertical particulate supply. The process of reversible scavenging only seems to influence particulate signatures below 3 km. Overall, we do not find evidence on enhanced particle dissolution, often invoked to explai
Skinner LC, Sadekov A, Brandon M, et al., 2019, Rare Earth Elements in early-diagenetic foraminifer 'coatings': Pore-water controls and potential palaeoceanographic applications, Geochimica et Cosmochimica Acta, Vol: 245, Pages: 118-132, ISSN: 0016-7037
Rare Earth Element (REE) distributions in the ocean bear the fingerprints of several key environmental processes, including vertical particle/organic carbon fluxes, water column/pore-water oxygenation and ocean transports. The use of ‘fossil’ REE analyses in the service of palaeoceanography as redox, water transport or nutrient cycling ‘proxies’ has long been a tantalizing possibility. Here we demonstrate the application of a novel laser-ablation microanalysis approach for the rapid and accurate measurement of the REE composition of early diagenetic ‘coatings’ on fossil foraminifera. By applying this new method to a range of core-top and multi-core samples, we show that ‘authigenic’ REE enrichments on planktonic foraminifer surfaces (REEfs) reflect a primary seawater signature that becomes overprinted during sediment burial due to early diagenetic processes that control the flux of REEs to pore-fluids. Thus ‘light’ REEs (LREEs), and eventually ‘middle’ REEs (MREEs) are generally enriched in foraminifer 'coatings' relative to seawater, while Ce-anomalies (Ce/Ce*) recorded in surface sediments are typically more positive than local seawater values and are further ‘eroded’ during burial with the onset of anoxic conditions in the sediment. Similar patterns have previously been observed in pore-fluid measurements. Indeed, we show that Mn and Fe concentrations measured in foraminifer ‘coatings’ track the availability of these elements in pore-water, indicating that they are not associated with a secondary oxide phase. We propose that these elements, along with REEs are instead adsorbed directly from pore-fluids. In contrast, U in authigenic coatings tracks the removal of this element from solution under sub-oxic conditions, supporting the use of U/Ca in foraminifer coatings as a redox proxy. Although our results confirm a significant early diagenetic influence on REEfs, we also
Lique C, Johnson HL, Plancherel Y, 2018, Emergence of deep convection in the Arctic Ocean under a warming climate, Climate Dynamics, Vol: 50, Pages: 3833-3847, ISSN: 0930-7575
The appearance of winter deep mixed layers in the Arctic Ocean under a warming climate is investigated with the HiGEM coupled global climate model. In response to a four times increase of atmospheric CO2 levels with respect to present day conditions, the Arctic Basin becomes seasonally ice-free. Its surface becomes consequently warmer and, on average, slightly fresher. Locally, changes in surface salinity can be far larger (up to 4 psu) than the basin-scale average, and of a different sign. The Canadian Basin undergoes a strong freshening, while the Eurasian Basin undergoes strong salinification. These changes are driven by the spin up of the surface circulation, likely resulting from the increased transfer of momentum to the ocean as sea ice cover is reduced. Changes in the surface salinity field also result in a change in stratification, which is strongly enhanced in the Canadian Basin and reduced in the Eurasian Basin. Reduction, or even suppression, of the stratification in the Eurasian Basin produces an environment that is favourable for, and promotes the appearance of, deep convection near the sea ice edge, leading to a significant deepening of winter mixed layers in this region (down to 1000 m). As the Arctic Ocean is transitioning toward a summer ice-free regime, new dynamical ocean processes will appear in the region, with potentially important consequences for the Arctic Ocean itself and for climate, both locally and on larger scales.
Lique C, Johnson HL, Plancherel Y, 2018, Correction to: Emergence of deep convection in the Arctic Ocean under a warming climate, Climate Dynamics, Vol: 50, Pages: 3849-3851, ISSN: 0930-7575
Tachikawa K, Arsouze T, Bayon G, et al., 2017, The large-scale evolution of neodymium isotopic composition in the global modern and Holocene ocean revealed from seawater and archive data, Chemical Geology, Vol: 457, Pages: 131-148, ISSN: 0009-2541
Neodymium isotopic compositions (143Nd/144Nd or εNd) have been used as a tracer of water masses and lithogenic inputs to the ocean. To further evaluate the faithfulness of this tracer, we have updated a global seawater εNd database and combined it with hydrography parameters (temperature, salinity, nutrients and oxygen concentrations), carbon isotopic ratio and radiocarbon of dissolved inorganic carbon. Archive εNd data are also compiled for leachates, foraminiferal tests, deep-sea corals and fish teeth/debris from the Holocene period (< 10,000 years).At water depths ≥ 1500 m, property-property plots show clear correlations between seawater εNd and the other variables, suggesting that large-scale water mass mixing is a primary control of deepwater εNd distribution. At ≥ 200 m, basin-scale seawater T-S-εNd diagrams demonstrate the isotopic evolution of different water masses. Seawater and archive εNd values are compared using property-property plots and T-S-εNd diagrams. Archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the Pacific. Both positive and negative offsets exist in the northern North Atlantic. Applying multiple regression analysis to deep (≥ 1500 m) seawater data, we established empirical equations that predict the main, large-scale, deepwater εNd trends from hydrography parameters. Large offsets from the predicted values are interpreted as a sign of significant local/regional influence. Dominant continental influence on seawater and archive εNd is observed mainly within 1000 km from the continents. Generally, seawater and archive εNd values form gradual latitudinal trend in the Atlantic and Pacific at depths ≥ 600 m, consistent with the idea that Nd isotopes help distinguish between northern/southern sourced water contributions at intermediate and deep water depths.
Osborne AH, Hathorne EC, Schijf J, et al., 2017, The potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past, Geochemistry, Geophysics, Geosystems, Vol: 18, Pages: 1550-1568, ISSN: 1525-2027
Dissolved rare earth element (REE) concentration data from intermediate and deep seawater form an array characterized by higher middle‐REE enrichments (MREE/MREE*) in the North Atlantic and a progressive increase in heavy‐to‐light REE ratios (HREE/LREE) as water masses age. The REEs in foraminifera are fractionated toward higher MREE/MREE* and lower HREE/LREE relative to seawater. Calculations based on a scavenging model show that the REE patterns in uncleaned core‐top foraminifera resemble those adsorbed onto calcite, particulate organic material, and hydrous ferric oxides but the full extent of the REE fractionation measured in foraminifera was not reproduced by the model. However, differences in the HREE/LREE and MREE/MREE* ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater REE distribution. Under oxic conditions, the HREE/LREE and MREE/MREE* compositions of uncleaned foraminifera at the sediment/seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth. In suboxic sedimentary environments, all uncleaned foraminiferal REE concentrations are elevated relative to core‐top values indicating addition of REEs from pore waters. The HREE/LREE ratio is highest when sedimentation rates were greatest and when high Fe/Ca ratios in the uncleaned foraminifera indicate that Fe was mobile. In sediments that have not experienced suboxic conditions during burial, uncleaned foraminifera preserve the seawater signal taken up at the sediment/seawater interface and are therefore suggested to be a suitable archive of changes in the REE signal of past bottom waters.
Iudicone D, Rodgers KB, Plancherel Y, et al., 2016, The formation of the ocean's anthropogenic carbon reservoir, SCIENTIFIC REPORTS, Vol: 6, ISSN: 2045-2322
The shallow overturning circulation of the oceans transports heat from the tropics to the mid-latitudes. This overturning also influences the uptake and storage of anthropogenic carbon (Cant). We demonstrate this by quantifying the relative importance of ocean thermodynamics, circulation and biogeochemistry in a global biochemistry and circulation model. Almost 2/3 of the Cant ocean uptake enters via gas exchange in waters that are lighter than the base of the ventilated thermocline. However, almost 2/3 of the excess Cant is stored below the thermocline. Our analysis shows that subtropical waters are a dominant component in the formation of subpolar waters and that these water masses essentially form a common Cant reservoir. This new method developed and presented here is intrinsically Lagrangian, as it by construction only considers the velocity or transport of waters across isopycnals. More generally, our approach provides an integral framework for linking ocean thermodynamics with biogeochemistry.
Zheng X-Y, Plancherel Y, Saito MA, et al., 2016, Rare earth elements (REEs) in the tropical South Atlantic and quantitative deconvolution of their non-conservative behavior, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 177, Pages: 217-237, ISSN: 0016-7037
Osborne AH, Haley BA, Hathorne EC, et al., 2015, Rare earth element distribution in Caribbean seawater: Continental inputs versus lateral transport of distinct REE compositions in subsurface water masses, MARINE CHEMISTRY, Vol: 177, Pages: 172-183, ISSN: 0304-4203
Lique C, Johnson HL, Plancherel Y, et al., 2015, Ocean change around Greenland under a warming climate, CLIMATE DYNAMICS, Vol: 45, Pages: 1235-1252, ISSN: 0930-7575
Plancherel Y, 2015, Hydrographic biases in global coupled climate models and their relation to the meridional overturning circulation, CLIMATE DYNAMICS, Vol: 44, Pages: 1-44, ISSN: 0930-7575
Plancherel Y, 2014, On the relationships between features of the depth-latitude meridional overturning streamfunctions across global coupled climate models, CLIMATE DYNAMICS, Vol: 42, Pages: 2983-3004, ISSN: 0930-7575
Rodgers KB, Aumont O, Fletcher SEM, et al., 2014, Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring, BIOGEOSCIENCES, Vol: 11, Pages: 4077-4098, ISSN: 1726-4170
Plancherel Y, Rodgers KB, Key RM, et al., 2013, Role of regression model selection and station distribution on the estimation of oceanic anthropogenic carbon change by eMLR, BIOGEOSCIENCES, Vol: 10, Pages: 4801-4831, ISSN: 1726-4170
Lam P, Jensen MM, Kock A, et al., 2011, Origin and fate of the secondary nitrite maximum in the Arabian Sea, BIOGEOSCIENCES, Vol: 8, Pages: 1565-1577, ISSN: 1726-4170
Plancherel Y, Cowen JP, 2007, Towards measuring particle-associated fecal indicator bacteria in tropical streams, WATER RESEARCH, Vol: 41, Pages: 1501-1515, ISSN: 0043-1354
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