Geochemical and Sr–Nd isotopic variations in a deep-sea sediment core from Eastern Indian Ocean: Constraints on dust provenances, paleoclimate and volcanic eruption history in the last 300,000years (original) (raw)
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A geochemical approach to reconstruct modern dust fluxes and sources to the South Pacific
Geochimica et Cosmochimica Acta, 2019
We present the first comprehensive dust provenance and lithogenic flux data set extracted from surface sediments distributed across the polar and subpolar South Pacific. The dataset comprises 230 Th-normalized lithogenic fluxes combined with rare earth elements, strontium, neodymium and lead isotope data to determine lithogenic fluxes, spatial distribution and sources of dust (<10 mm) during the Holocene. We observe the highest lithogenic fluxes in surface sediments near New Zealand which most likely indicate a combination of Australian dust and riverine input from New Zealand. Similarly, high fluxes off West Antarctica are ascribed to sediment input from the nearby continental shelf and margin. In contrast, the lithogenic fluxes in the remote open ocean are derived from dust input. Isotopic and REE data suggest that the Lake Eyre Basin in central Australia is the most prominent potential source area for dust distributed over the South Pacific during the Holocene, with additional input from the Darling Basin in southeast Australia.
Adopting sequential extraction procedures, Ba, Cu, Mn, Ni, V and Zn concentrations were determined in the moderately reducible, organically bound, carbonateassociated and adsorbable fractions within a sediment core collected from the Indian sector of the Southern Ocean. The elemental abundances were studied with reference to the Last Glacial Maximum (LGM), deglaciation and Holocene periods. The study showed, with the exception of Ba, elemental abundances in the following order: moderately reducible > organically bound > carbonate-associated > adsorbable fractions. Ba showed high affinity to organically bound and carbonate-associated fractions. Ba concentration revealed large variability (200-1400 ppm) within the carbonateassociated fraction and is related to the reduced carbonate productivity during LGM and increased carbonate productivity during deglaciation as well as Holocene intervals. The relative increase in the concentration of V, Mn and Ni in the reducible fraction suggests enhanced suboxic conditions during LGM. The decreased concentrations of V, Mn and Ni during the deglaciation and late Holocene indicate oxygenated conditions. The suboxic conditions during LGM could be attributed to reduced ventilation resulting from reduced strength of the global thermohaline circulation at this time interval.
Correlation of the oldest Toba Tuff to sediments in the central Indian Ocean Basin
Journal of Earth System Science, 2010
We have identified an ash layer in association with Australasian microtektites of ∼ 0.77 Ma old in two sediment cores which are ∼ 450 km apart in the central Indian Ocean Basin (CIOB). Morphology and chemical composition of glass shards and associated microtektites have been used to trace their provenance. In ODP site 758 from Ninetyeast Ridge, ash layer-D (13 cm thick, 0.73-0.75 Ma) and layer-E (5 cm thick, 0.77-0.78 Ma) were previously correlated to the oldest Toba Tuff (OTT) eruptions of the Toba caldera, Sumatra. In this investigation, we found tephra ∼ 3100 km to the southwest of Toba caldera that is chemically identical to layer D of ODP site 758 and ash in the South China Sea correlated to the OTT. Layer E is not present in the CIOB or other ocean basins. The occurrence of tephra correlating to layer D suggests a widespread distribution of OTT tephra (∼ 3.6 × 10 7 km 2), an ash volume of at least ∼ 1800 km 3 , a total OTT volume of 2300 km 3 , and classification of the OTT eruption as a super-eruption.
Minor Element and Stable Isotopic Composition of the Carbonate Fine Fraction: Site 709, Indian Ocean
Proceedings of the Ocean Drilling Program, 115 Scientific Results, 1990
Stable isotopic and minor element compositions were measured on the fine fraction of pelagic carbonate sediments from Ocean Drilling Program Site 709 in the central Indian Ocean. This section ranges in age from 47 Ma to the present. The observed compositional variations are the result of either paleoceanographic changes (past oceanic chemical or temperature variations) or diagenetic changes. The CaCO 3 record is little affected by diagenesis. From previous work, carbonate content is known to be determined by the interplay of biological productivity, water column dissolution, and dilution. The carbon isotopic record is generally similar to previously published curves. A good correlation was observed between sea-level high stands and high 13 C/ 12 C ratios. This supports Shackleton's hypothesis that as the proportion of organic carbon buried in marine sediments becomes larger, oceanic-dissolved inorganic carbon becomes isotopically heavier. This proportion appears to be higher when sea level is higher and organic carbon is buried in more extensive shallow-shelf sediments. The strontium content and oxygen isotopic composition of carbonate sediments are much more affected by burial diagenesis. Low strontium concentrations are invariably associated with high values of S 18 O, probably indicating zones of greater carbonate recrystallization. Nevertheless, there is an inverse correlation between strontium concentration and sea level that is thought to be a result of high-strontium aragonitic sedimentation on shallow banks and shelves during high stands. Iron and manganese concentrations and, to a lesser extent, magnesium and strontium concentrations and carbon isotopic ratios are affected by early diagenetic reactions. These reactions are best observed in a slumped interval of sediments that occurs between 13.0 and 17.5 Ma. As a result of microbial reduction of manganese and iron oxides and dissolved sulfate, it is hypothesized that small amounts of mixed-metal carbonate cements are precipitated. These have low carbon isotopic ratios and high concentrations of metals.
Proceedings of the Ocean Drilling Program, 1992
Epiclastic volcanogenic rocks recovered from the Kerguelen Plateau during Ocean Drilling Program Legs 119 and 120 comprise (pre-)Cenomanian(?) claystones (52 m thick, Site 750); a Turonian(?) basaltic pebble conglomerate (1.2 m thick, Site 748; Danian mass flows (45 m thick, Site 747); and volcanogenic debris flows of Quaternary age at Site 736 (clastic apron of Kerguelen Island). Pyroclastic rocks comprise numerous Oligocene to Quaternary marine ash layers. The epiclastic sediments with transitional mid-ocean-ridge basalt (T-MORB) origin indicate weathering (Site 750) and erosion (Site 747) of Early Cretaceous T-MORB from a then-emergent Kerguelen Plateau, connected to Late Cretaceous tectonic events. The basal pebble conglomerate of Site 748 has an oceanic-island basalt (OIB) composition and denotes erosion and reworking of seamount to oceanic-island-type volcanic sources. The vitric-to crystal-rich marine ash layers are a few centimeters thick, have rather uniform grain sizes around 60 ± 40 µm, and are a result of Plinian eruptions. Crystal-poor silicic vitric ashes may also represent co-ignimbrite ashes. The ash layers have bimodal, basaltic, and silicic compositions with a few intermediate shards. The basaltic ashes are evolved high-titanium T-MORB; a few grains in a silicic pumice lapilli layer have a low-titanium basaltic composition. The silicic ashes comprise trachytic and rhyolitic glass shards belonging to a high-K series, except for a few low-K glasses admixed to a basaltic ash layer. Feldspar and clinopyroxene compositions fit the glass chemistry: high-Ti tholeiite-basaltic glasses have Plagioclase of An 40 _ 80 and pigeonite to augite clinopyroxene compositions. Silicic ashes have K-rich anorthoclase and minor Plagioclase around An^ and ferriaugitic to hedenbergitic clinopyroxene compositions. The line of magmatic evolution for the glass shards is not compatible with simple two-end member (high-Ti T-MORB and high-K rhyolite) mixing, but favors successive Ca-Mg-Fe pyroxene, Ti magnetite, and apatite fractionation, and K-rich alkali feldspar fractionation in trachytic magmas to yield rhyolitic compositions. Plagioclase fractionation occurs throughout. This qualitative model is in basic accordance with the observed mineral assemblage. However, as the time span for explosive volcanism spans >30 m.y., this basic model cannot comply with fractional crystallization in a single magma reservoir. The ash layers resulted from highly explosive eruptions on Kerguelen and, with less probability, Heard islands since the Oligocene. The explosive history starts with widespread Oligocene basaltic ash layers that indicate sea-level or subaerial volcanism on the Northern Kerguelen Plateau. After a hiatus of 24 m.y.(?), explosive magmatic activity was vigorously renewed in the late Miocene with more silicic eruptions. A peak in explosive activity is inferred for the Pliocene-Pleistocene. The composition and evolution of Kerguelen Plateau ash layers resemble those from other hotspot-induced, oceanic-island realms such as Iceland and Jan Mayen in the North Atlantic, and the Canary Islands archipelago in the Central Atlantic.
Paleoceanography, 2002
1] The large-diameter piston core LL44-GPC3 from the central North Pacific Ocean records continuous sedimentation of eolian dust since the Late Cretaceous. Two intervals resolved by Nd and Pb isotopic data relate to dust coming from America (prior to 40Ma)anddustcomingfromAsia(since40 Ma) and dust coming from Asia (since 40Ma)anddustcomingfromAsia(since40 Ma). The Intertropical Convergence Zone (ITCZ) separates these depositional regimes today and may have been at a paleolatitude of 23°Npriorto40Ma.SuchanortherlylocationoftheITCZisconsistentwithsluggishatmosphericcirculationandwarmclimatefortheNorthernHemisphereoftheearlytomiddleEocene.Since23°N prior to 40 Ma. Such a northerly location of the ITCZ is consistent with sluggish atmospheric circulation and warm climate for the Northern Hemisphere of the early to middle Eocene. Since 23°Npriorto40Ma.SuchanortherlylocationoftheITCZisconsistentwithsluggishatmosphericcirculationandwarmclimatefortheNorthernHemisphereoftheearlytomiddleEocene.Since40 Ma, correlations between Nd (À7.55 > e Nd(t) > À10.81) and Pb (18.625 < 206/4 Pb < 18.879; 15.624 < 207/4 Pb < 15.666; 38.611 < 208/4 Pb < 38.960; 0.8294 < 207/6 Pb < 0.8389; 2.0539 < 208/6 Pb < 2.0743) isotopes reflect the progressive drying of central Asia triggered by the westward retreat of the paleo-Tethys. Comparisons between the changes with time in the isotopically well-defined dust flux and Nd and Pb isotopic compositions of Pacific deep water allow one to draw two major conclusions: (1) dust-bound Nd became a resolvable contribution to Pacific seawater only after the one order of magnitude increase in dust flux starting at $3.5 Ma. Therefore eolian Nd was unimportant for Pacific seawater Nd prior to 3.5 Ma.
Geochemistry, Geophysics, Geosystems, 2011
Analyses of radiogenic neodymium (Nd), strontium (Sr), and lead (Pb) isotope compositions of claysized detrital sediments allow detailed tracing of source areas of sediment supply and present and past transport of particles by water masses in the eastern Indian Ocean. Isotope signatures in surface sediments range from −21.5 ("Nd), 0.8299 (87 Sr/ 86 Sr), and 19.89 (206 Pb/ 204 Pb) off northwest Australia to +0.7 ("Nd), 0.7069 (87 Sr/ 86 Sr), and 17.44 (206 Pb/ 204 Pb) southwest of Java. The radiogenic isotope signatures primarily reflect petrographic characteristics of the surrounding continental bedrocks but are also influenced by weathering-induced grain size effects of Pb and Sr isotope systems with superimposed features that are caused by current transport of clay-sized particles, as evidenced off Australia where a peculiar isotopic signature characterizes sediments underlying the southward flowing Leeuwin Current and the northward flowing West Australian Current (WAC). Gravity core FR10/95-GC17 off west Australia recorded a major isotopic change from Last Glacial Maximum values of −10 ("Nd), 0.745 (87 Sr/ 86 Sr), and 18.8 (206 Pb/ 204 Pb) to Holocene values of −22 ("Nd), 0.8 (87 Sr/ 86 Sr), and 19.3 (206 Pb/ 204 Pb), which documents major climatically driven changes of the WAC and in local riverine particle supply from Australia during the past 20 kyr. In contrast, gravity core FR10/95-GC5 located below the present-day pathway of the Indonesian throughflow (ITF) shows a much smaller isotopic variability, indicating a relatively stable ITF hydrography over most of the past 92 kyr. Only the surface sediments differ significantly in their isotopic composition, indicating substantial changes in erosional sources attributed to a change of the current regime during the past 5 kyr.