Interstitial water iodine enrichments in sediments from the eastern Pacific

The vertical distribution of iodine has been examined in interstitial waters of sediment cores from the Peru Basin, Bauer Basin, Guatemala Basin and the East Pacific Rise and the sediments have been analyzed for iodine and organic carbon. Interstitial water profiles show a strong enrichment of iodine at the sediment surface relative to overlying sea water. This enrichment is much greater than would have been expected had all the iodine originated solely from the breakdown of newly sedimented plankton. This implies recycling of iodine in the region of the water-sediment interface with most of the upward diffusing iodine being rescavenged and a small fraction escaping to the deep sea. A flux equivalent to 1–5% of the diffusive flux from interstitial waters can account for an excess iodine anomaly previously described for deep Pacific waters

A stratigraphic framework for the Miocene from the lower Tagus Basin (Lisbon, Setúbal Península, Portugal) Depositional sequences, biostratigraphy and isotopic ages

Rev. Soc. Geol. España, 12(1), ano 1999Lithostratigraphy, main biostratigraphic events (first and last ocurrence), 87Sr/86Sr as well as KlAr isotopic ages, are presented for the Lower Tagus basin (LTB) Miocene (Lisboa and Peninsula de Setubal regions). Eight depositional sequences (DS) delimited by regional disconformities related with transgressive surfaces are defined. The main features of the Depositional Sequences are as follows: Depositional sequence (DS) A (Aquitanian). Biostratigraphy (Biost.): Small mammals from Km 10: MN2 (MN3?); ostracoda: Aquitanian fauna. Isotopic age (IA): glauconites (KlAr) values between 19 and 24 Ma. 87Sr/86Sr ages from the glauconite levels: 22.3 (+0.4-0.7) Ma. Lower and upper boundaries not well established. DS BO (Lower Burdigalian). Biost.: foraminifera - Fa Globigerinoides altiaperturus (NS); mammals - Fa Brachyodus intermedius (MN3); ostracoda - La Hemicyprideis helvetica and Pokomyella lusitanica at the LTB. IA (87Sr/86Sr): Foz da Fonte -19.S (±0.2) Ma, Penedo Sui (base) - 20.0(±0.4)Ma; Almada (top) - 18.3 (+0.-0.2) Ma. Mammal sites: Av. do Uruguai - 21.S( +O.S- 0.3) Ma; Univ. Cat6lica - 20.S (+0.3-0.2) Ma. DS Bl (Middle Burdigalian). Biost.: foraminifera - Catapsydrax unicavus and Globigerinoides altiaperturus (N6); mammals - Fa Gomphotherium, La of Brachyodus (MN4); ostracoda -La Ruggieria (R.) micheliniana, Cnestocythere truncata, Pokomiella minor and Triebelina raripila. fA (87Sr/86Sr) Foz da Fonte - 19.7 (+0.3-0.2) to 18.S (+0.2-0.S) Ma. DS B2 (Upper Burdigalian). Biost.: mammals -Fa Bunolistriodon and Megacricetodon primitivus (MN4); ostracoda - La Miocyprideisfortisensis. IA (87Sr/86Sr): Penedo Norte 17.7 (+0.7-0.S) Ma; 17.8 (+0.7- O.S) Ma. DS Ll (Upper Burdigalian and Langhian). Biost.: foraminifera - Fa Praeorbulina (N8); mammals - Fa (upper part) Hispanotherium and Megacricetodon collongensis, La M. primitivus (MNS); ostracoda - Fa Pterigocythereis (P.) siveteri and Loxoconcha (L.) ducasseae. IA (87Sr/86Sr): Penedo Norte 17.3 (+0.6-0.5) Ma. DS SI (Upper Langhian and Serravallian). Biost.: foraminiferaFa Orbulina suturalis, O. universa and Globorotalia cf. menardii; ostracoda -Fa Aurila (u.) oblonga, Ruggieria (R.) nuda, R. tetraptera tetraptera, Nomurocythereis seminulum, Pterygocythereis (P.) jonesi y Olinfalunia costata. IA (87Sr/86Sr): Chelas 14.7 (+ 1.S-0.S) Ma, Almada (Brielas ) (lower part) - 14.0 (±0.4 ) Ma, Penedo (upper part) 12.S (+ 1.0-2.0) Ma. DS S2? (Upper Serravallian) is poorly characterized due to strong condensation (Foz da Fonte-Rib. Lage) and poor outcrops (Lisbon region). Biost.: foraminifera - La Globigerinoides subquadratus (top). DS Tl (Tortonian). Biost.: foraminifera - La Globorotalia mayeri (lower part), Fa Neogloboquadrina acostaensis (upper part); ostracoda - Fa Aurila (U.) zbyszewskii, Celtia quadridentada and Cyheretta (C.) simplex. IA: Penedo Norte: KlAr- 1O.9S±0.2S Ma; 87Sr/86Sr - 11.3 (+ 1.7-2.8) Ma; Almada (Foz de Rego) - 8.3 (+ 1.9-3.3) Ma; Fonte da Telha S.2 (+3.1-1.2) Ma

The Neogene of Algarve (Portugal)

A synthesis about the Neogene and Quaternary of Algarve (Southern Portugal) is presented. New isotopic 87Sr/86Sr ages as well as biostratigraphic data about the Miocene deposits allow to present a new stratigraphic frame for the previously characterized units. The Lagos-Portimão Formation corresponds to deposits of temperate carbonate platform sedimentological type, developed during a long time span (Lower Burdigalian to Upper Serravallian). A major change in sedimentation conditions (carbonate to siliciclastic environments) occurred in the Lower Tortonian with the deposition of yellowish sands. Spongoliths rich in microfossils are represented in Algarve inland. Their age is not well established; calcareous nannofossils indicate the CN5a zone (Upper Serravallian) while foraminifera point out at least Nl6 zone (Lower Tortonian). In the Upper Tortonian, the sedimentation is widespread in Eastern Algarve, related with the Guadalquivir Basin infill. The deposits begin with detrital limestones, locally very rich in Heterostegina, passing to fossiliferous conglomerates and siltstones (Cacela Formation). Coarse-grained conglomerates at Galvana (Faro) pose some age problems. K/Ar age on glauconite indicates 6.72±0.17 Ma. However, glauconites may be reworked from older deposits (Cacela Formation). The Galvana Conglomerate could be related to Pliocene deposits are not well characterized. Olhos de Água sands, with a thin marine intercalation rich in marine vertebrates (fishes, a crocodile, cetaceans, sirenians), may be Upper Pliocene; however, the vertebrates point out to a Serravallian to Tortonian age. 87Sr/86Sr ages on oysters from above the level with vertebrates point out to 3.0(+2.5-1.0) Ma. Similar sand deposits occur at Morgadinho (Luz de Tavira). These sands are overlain by marls, lignite clays, lacustrine limestones and a silty calcareous crust. A small mammals association indicate an age span between Upper Pliocene and Lower Middle Pleistocene (MN17-MN20). A Biharian mammal fauna (Lower Pleistocene) was collected at Algoz in similar deposits. In the present state of knowledge, Morgadinho and Algoz deposits may be correlative

Millennial-scale variability of deep-water temperature and δ18Odwindicating deep-water source variations in the Northeast Atlantic, 0-34 cal. ka BP

Paired measurements of Mg/Ca and δ18Occ (calcite δ18O) in benthic foraminifera from a deep-sea core recovered on the Iberian Margin (MD99-2334K; 37°48′N, 10°10′W; 3,146 m) have been performed in parallel with planktonic δ18Occ analyses and counts of ice-rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic δ18Occ allows the proxy records from MD99-2334K to be placed confidently on the GISP2 time-scale. This correlation is further corroborated by AMS 14C-dates. Benthic Mg/Ca measurements in MD99-2334K permit the reconstruction of past deep-water temperature (Tdw) changes since ∼34 cal. ka BP (calendar kiloyears before present). Using these Tdw estimates and parallel benthic δ18Occ measurements, a record of deep-water δ18O (δ18Odw) has been calculated. Results indicate greatly reduced Tdw in the deep Northeast Atlantic during the last glaciation until ∼15 cal. ka BP, when Tdw warmed abruptly to near-modern values in parallel with the onset of the Bølling-Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ∼13.4 and ∼11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice-rafting event. Similar millennial-scale Tdw changes also occurred during the last glaciation. Indeed, throughout the last ∼34 cal. ka, millennial δ18Odw and Tdw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower Tdw and δ18Odw conditions occurred. In general, millennial Tdw and δ18Odw variations recorded in MD99-2334K describe an alternation between colder, low-δ18Odw and warmer, high δ18Odw conditions, which suggests the changing local dominance of northern-sourced North Atlantic Deep Water (NADW) versus southern-sourced Antarctic Bottom Water (AABW). The observed similarity of the Tdw and GISP2 δ18Oice records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low-δ18Odw AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic δ18Occ signal since ∼34 cal. ka BP

Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series

Paired Mg/Ca and δ18O measurements on planktonic foraminiferal species (G. ruber white, G. ruber pink, G. sacculifer, G. conglobatus, G. aequilateralis, O. universa, N. dutertrei, P. obliquiloculata, G. inflata, G. truncatulinoides, G. hirsuta, and G. crassaformis) from a 6-year sediment trap time series in the Sargasso Sea were used to define the sensitivity of foraminiferal Mg/Ca to calcification temperature. Habitat depths and calcification temperatures were estimated from comparison of δ18O of foraminifera with equilibrium calcite, based on historical temperature and salinity data. When considered together, Mg/Ca (mmol/mol) of all species, except two, show a significant (r = 0.93) relationship with temperature (T °C) of the form Mg/Ca = 0.38 (±0.02) exp 0.090 (±0.003)T, equivalent to a 9.0 ± 0.3% change in Mg/Ca for a 1°C change in temperature. Small differences exist in calibrations between species and between different size fractions of the same species. O. universa and G. aequilateralis have higher Mg/Ca than other species, and in general, data can be best described with the same temperature sensitivity for all species and pre-exponential constants in the sequence O. universa > G. aequilateralis ≈ G. bulloides > G. ruber ≈ G. sacculifer ≈ other species. This approach gives an accuracy of ±1.2°C in the estimation of calcification temperature. The ∼9% sensitivity to temperature is similar to published studies from culture and core top calibrations, but differences exist from some literature values of pre-exponential constants. Different cleaning methodologies and artefacts of core top dissolution are probably implicated, and perhaps environmental factors yet understood. Planktonic foraminiferal Mg/Ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures (using G. ruber pink, G. ruber white, G. sacculifer, N. dutertrei, P. obliquiloculata, etc.). The existence of a single Mg thermometry equation is valuable for extinct species, although use of species-specific equations will, where statistically significant, provide more accurate evaluation of Mg/Ca paleotemperature

Calcite saturation, foraminiferal test mass, and Mg/Ca-based temperatures dissolution corrected using XDX—A 150 ka record from the western Indian Ocean

A record of deep-sea calcite saturation inline image, derived from X-ray computed tomography-based foraminifer dissolution index, XDX, was constructed for the past 150 ka for a core from the deep (4157 m) tropical western Indian Ocean. G. sacculifer and N. dutertrei recorded a similar dissolution history, consistent with the process of calcite compensation. Peaks in calcite saturation (∼15 µmol/kg higher than the present-day value) occurred during deglaciations and early in MIS 3. Dissolution maxima coincided with transitions to colder stages. The mass record of G. sacculifer better indicated preservation than did that of N. dutertrei or G. ruber. Dissolution-corrected Mg/Ca-derived SST records, like other SST records from marginal Indian Ocean sites, showed coolest temperatures of the last 150 ka in early MIS 3, when mixed layer temperatures were ∼4°C lower than present SST. Temperatures recorded by N. dutertrei showed the thermocline to be ∼4°C colder in MIS 3 compared to the Holocene (8 ka B.P.)

Evidence for elevated alkalinity in the glacial Southern Ocean

An increase in whole ocean alkalinity during glacial periods could account, in part, for the drawdown of atmospheric CO2 into the ocean. Such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity. We present evidence, based on downcore measurements of benthic foraminiferal B/Ca and Mg/Ca from a core in the Weddell Sea, that the deep ocean carbonate ion concentration, [CO32-], was elevated by similar to 25 mu mol/kg during each glacial period of the last 800 kyr. The heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the Atlantic and Pacific by the changing ventilation and chemistry of Weddell Sea waters. These waters are more corrosive than interglacial northern sourced waters but not as undersaturated as interglacial southern sourced waters. Our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification. The Weddell records display low [CO32-] during deglaciations and peak interglacial warmth, coincident with maxima in percent CaCO3 in the Atlantic and Pacific oceans. Should the burial rate of alkalinity in the more alkaline glacial deep waters outstrip the rate of alkalinity supply, then pelagic carbonate production by the coccolithophores at the end of the glacial maximum could drive a decrease in ocean [CO32-] and act to trigger the deglacial rise in pCO(2)

Partially and Fully Frustrated Coupled Oscillators With Random Pinning Fields

We have studied two specific models of frustrated and disordered coupled Kuramoto oscillators, all driven with the same natural frequency, in the presence of random external pinning fields. Our models are structurally similar, but differ in their degree of bond frustration and in their finite size ground state properties (one has random ferro- and anti-ferromagnetic interactions; the other has random chiral interactions). We have calculated the equilibrium properties of both models in the thermodynamic limit using the replica method, with emphasis on the role played by symmetries of the pinning field distribution, leading to explicit predictions for observables, transitions, and phase diagrams. For absent pinning fields our two models are found to behave identically, but pinning fields (provided with appropriate statistical properties) break this symmetry. Simulation data lend satisfactory support to our theoretical predictions.Comment: 37 pages, 7 postscript figure

Temporal changes in North Atlantic circulation constrained by planktonic foraminiferal shell weights

Records of planktonic foraminiferal shell weights for Globigerina bulloides, covering Termination I from four proximal sites at waters depths from 1150 to 4045 m in the northeast Atlantic, demonstrate the influence of dissolution superimposed upon initial shell weight variability. Records of shell weight, unaffected by dissolution, may be used as a reference for interpreting deeper records in terms of preservation history. Combining records of planktonic shell weight (and benthic δ13C) from shallow and deep sites suggests that maximum oceanic stratification and incursion of southern sourced deep waters in the North Atlantic occurred at about 18–20 ka, defining the glacial mode of Atlantic circulation. Reduced stratification and enhanced preservation in deeper waters reflect conditions during Heinrich event 1. A state similar to the modern mode of Atlantic circulation was attained by about 10 ka

Freshwater input and abrupt deglacial climate change in the North Atlantic

Greenland ice core records indicate that the last deglaciation (∼7–21 ka) was punctuated by numerous abrupt climate reversals involving temperature changes of up to 5°C–10°C within decades. However, the cause behind many of these events is uncertain. A likely candidate may have been the input of deglacial meltwater, from the Laurentide ice sheet (LIS), to the high-latitude North Atlantic, which disrupted ocean circulation and triggered cooling. Yet the direct evidence of meltwater input for many of these events has so far remained undetected. In this study, we use the geochemistry (paired Mg/Ca-δ18O) of planktonic foraminifera from a sediment core south of Iceland to reconstruct the input of freshwater to the northern North Atlantic during abrupt deglacial climate change. Our record can be placed on the same timescale as ice cores and therefore provides a direct comparison between the timing of freshwater input and climate variability. Meltwater events coincide with the onset of numerous cold intervals, including the Older Dryas (14.0 ka), two events during the Allerød (at ∼13.1 and 13.6 ka), the Younger Dryas (12.9 ka), and the 8.2 ka event, supporting a causal link between these abrupt climate changes and meltwater input. During the Bølling-Allerød warm interval, we find that periods of warming are associated with an increased meltwater flux to the northern North Atlantic, which in turn induces abrupt cooling, a cessation in meltwater input, and eventual climate recovery. This implies that feedback between climate and meltwater input produced a highly variable climate. A comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the LIS causing rerouting of LIS meltwater between southern and eastern drainage outlets, as proposed by Clark et al. (2001)