Calcium Carbonate Sedimentation in the Global Ocean: Linkages Between the Neritic and Pelagic Environments

Other than fluvial sediment, calcium carbonate (CaCO3) is the greatest source of sediment in the present-day ocean. Interest in carbonate sedimentation extends beyond geologists because the carbonate system involves biologic and geochemicalprocesses. Carbonate production, for example, releases CO2 but its accumulation becomes a major sink for inorganic carbon. Unlike fluvial sediments, modern carbonates accumulate more or less equally in the neritic and pelagic environments. Neritic carbonates (benthic) are characterized by rapid production of (mostly) metastable aragonite and magnesian calcite:pelagic production of (primarily) calcite in the open ocean occurs at much slower rates but overmuch larger areas than does neritic production (Table 1). A global understanding of the production, preservation, and accumulation of calcium carbonate thus necessitates understanding both theneritic and pelagic systems, even though communication between researchers in the two subdisciplines often has been minimal

Benthic Foraminiferal response to sea level change in the mixed siliciclastic-carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic-carbonate depositional system where significant masses of both river-borne silicates and bank-derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3-m-long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off-shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf)

Calcium Carbonate Sedimentation in the Global Ocean: Linkages Between the Neritic and Pelagic Environments

Other than fluvial sediment, calcium carbonate (CaCO3) is the greatest source of sediment in the present-day ocean. Interest in carbonate sedimentation extends beyond geologists because the carbonate system involves biologic and geochemicalprocesses. Carbonate production, for example, releases CO2 but its accumulation becomes a major sink for inorganic carbon. Unlike fluvial sediments, modern carbonates accumulate more or less equally in the neritic and pelagic environments. Neritic carbonates (benthic) are characterized by rapid production of (mostly) metastable aragonite and magnesian calcite:pelagic production of (primarily) calcite in the open ocean occurs at much slower rates but overmuch larger areas than does neritic production (Table 1). A global understanding of the production, preservation, and accumulation of calcium carbonate thus necessitates understanding both theneritic and pelagic systems, even though communication between researchers in the two subdisciplines often has been minimal

Sea level influence on the nature and timing of a minibasin sedimentary fill (northwestern slope of the Gulf of Mexico)

International audienc

Excess 210Pb inventories and fluxes along the continental slope and basins of the Gulf of Papua

Sediment samples were collected from continental slopes and marginal basins in the Gulf of Papua and analyzed for excess 210Pb to elucidate transport processes of fine-grained particles to this region. Estimated excess 210Pb fluxes of 1.0-12.8 dpm cm-2 a-1 were derived from measured seabed inventories. Highest sediment accumulation rates (0.28-0.35 cm a-) were measured along the northeastern shelf edge, and they decrease in seaward directions and along isobaths to the southwest. The excess 210Pb flux could result from either focused deposition of high-210Pb activity sediments from the continental shelf and upper slope or scavenging of 210Pb brought landward from deep-sea waters. This sediment flux is concentrated in the northeastern Gulf of Papua, where the shelf is narrow and calcium carbonate contents are lowest. Analysis of sedimentary fabric and 210Pb distributions in cores suggests sediment delivery to the slope occurs on a 100-year timescale as both diffuse hemipelagic deposition as well as turbidity flows. The flux of sediment in turbidity flows is not well constrained but may be producing additional deep-sea accumulation in the Moresby Trough, as well as export from the study area

Assessing palaeobathymetry and sedimentation rates using palynomaceral analysis: A study of modern sediments from the Gulf of Papua, offshore Papua New Guinea

© 2015 © 2015 AASP - The Palynological Society. Palynologists interested in better understanding the sedimentation and energy of depositional environments have often included studies of palynomaceral fragments, particularly when performing palynofacies analyses. Due to the difficult nature of classifying these fragments, researchers have developed numerous, often overlapping, classification schemes. These different schemes make it difficult to compare and contrast between research projects. Determining the appropriate scheme to apply when counting these fragments can be confusing, and application of these schemes can yield inconclusive results, especially when sedimentation and energy are in constant flux. A scheme of five categories, including brown wood (palynomaceral 1-2), leaf cuticle (palynomaceral 3), black debris (palynomaceral 4), structureless organic matter (SOM) and resin, is utilised here. It is applied to the analysis of 64 modern samples from the top 0-4 cm of sediment collected throughout the Gulf of Papua, Papua New Guinea. These samples span a suite of common marine depositional environments: river mouths and deltas, the proximal portion of the continental shelf dominated by a large clinoform, and turbidite and hemipelagic/pelagic deposits on the slope and in the deep ocean basin. Principal component analysis (PCA) confirms this simplified classification scheme provides an indirect means of assessing distance from shore and shelf-slope break, overall water depth and sediment accumulation rate, but other factors, such as processing technique, marine productivity, sediment source, time in transport and residence and bioturbation, are taken into account to fully explain distribution

Late Pleistocene and Holocene sedimentation, rganic-carbon delivery, and paleoclimatic inferences on the continental slope of the northern Pandora Trough, Gulf of Papua

We investigated sediment and organic-carbon accumulation rates in two jumbo piston cores (MV-54, MV-51) retrieved from the midslope of the northeastern Pandora Trough in the Gulf of Papua, Papua New Guinea. Our data provide a first assessment of mass fluxes over the past ∼33,000 14C years B.P. and variations in organic-carbon sources. Core sediments were analyzed using a suite of physical properties, organic geochemistry, and micropaleontological measurements. MV-54 and MV-51 show two periods of rapid sediment accumulation. The first interval is from ∼15,000 to 20,400 Cal. years B.P. (MV-51: ∼1.09 in ka-1 and ∼81.2 g cm-2 ka-1) and the second occurs at >32,000 14C years B.P. (∼2.70 in ka-1 and ∼244 g cm-2 ka-1). Extremely high accumulation rates (∼3.96 in ka-1; ∼428 g cm-2 ka-1) characterize 15,800-17,700 Cal. years B.P. in MV-54 and likely correspond to early transgression when rivers delivered sediments much closer to the shelf edge. A benthic foraminiferal assemblage in NW-51 from ∼18,400 to 20,400 Cal. years B.P. indicates a seasonally variable flux of organic carbon, possibly resulting from enhanced contrast between monsoon seasons. The oldest sediments, >32,000 14C years B.P., contain TOC fluxes >200 g cm2 ka-1, with >50% of it derived from C3 vascular plant matter. Magnetic susceptibility values are 2 to 3 times higher and benthic foraminiferal accumulation rates are 6 times higher during this interval than at any younger time, indicating a greater influence of detrital minerals and labile organic carbon. The MS data suggest more direct dispersal pathways from central and eastern PNG Rivers to the core site

Bundled turbidite deposition in the central Pandora Trough (Gulf of Papua) since Last Glacial Maximum: Linking sediment nature and accumulation to sea level fluctuations at millennial timescale

Since Last Glacial Maximum (23-19 ka), Earth climate warming and deglaciation occurred in two major steps (Bølling-Allerød and Preboreal), interrupted by a short cooling interval referred to as the Younger Dryas (12.5-11.5 ka B.P.). In this study, thre