Coupled productivity and carbon isotope records in the southwest Pacific Ocean during the late Miocene–early Pliocene biogenic bloom

Abstract

Biogenic components of sediment accumulated at high rates beneath frontal zones of the Indian and Pacific oceans during the late Miocene and early Pliocene. The N 13 C of bulk and foraminiferal carbonate also decreased during this time interval. Although the two observations may be causally linked, and signify a major perturbation in global biogeochemical cycling, no site beneath a frontal zone has independent records of export production and N 13 C on multiple carbonate phases across the critical interval of interest. Deep Sea Drilling Project (DSDP) site 590 lies beneath the Tasman Front (TF), an eddy-generating jetstream in the southwest Pacific Ocean. To complement previous N 13 C records of planktic and benthic foraminifera at this location, late Neogene records of CaCO 3 mass accumulation rate (MAR), Ca/Ti, Ba/Ti, Al/Ti, and of bulk carbonate and foraminiferal N 13 C were constructed at site 590. The N 13 C records include bulk sediment, bulk sediment fractions ( 6 63 Wm and 5^25 Wm), and the planktic foraminifera Globigerina bulloides, Globigerinoides sacculifer (with and without sac), and Orbulina universa. Using current time scales, CaCO 3 MARs, Ca/Ti, Al/Ti and Ba/Ti ratios are two to three times higher in upper Miocene and lower Pliocene sediment relative to overlying and underlying units. A significant decrease also occurs in all N 13 C records. All evidence indicates that enhanced export production^the 'biogenic bloom'^extended to the southwest Pacific Ocean between ca. 9 and 3.8 Ma, and this phenomenon is coupled with changes in N 13 C^the 'Chron C3AR carbon shift'. However, CaCO 3 MARs peak ca. 5 Ma whereas elemental ratios are highest ca. 6.5 Ma; foraminiferal N 13 C starts to decrease ca. 8 Ma whereas bulk carbonate N 13 C begins to drop ca. 5.6 Ma. Temporal discrepancies between the records can be explained by changes in the upwelling regime at the TF, perhaps signifying a link between changes in ocean^atmosphere circulation change and widespread primary productivity. ß

Sedimentary changes on the Southeastern Brazilian upper slope during the last 35,000 years

“…In this sense, the only age-depth models which could be assumed to be reliable were the cubic spline and linear interpolation between radiocarbon values. As stated by Grant and Dickens (2002), the linear interpolation leads to artifi cial sedimentation rate values and, consequently, the cubic spline approach was adopted as the age-depth model and used for the calculation of sedimentation rates and accumulation values.…”

“…Mass accumulation rates of calcium carbonate (CaCO 3 MAR) and organic carbon ( org C MAR), in g.cm −2 .kyr −1 , were calculated in accordance with the formula described in Grant and Dickens (2002):…”

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“…Between about 9 and 4 Ma, the accumulation of biogenic components (e.g., carbonate, biosilica, and barite) increases significantly at many sites beneath regions of modern surface water divergence (e.g., along the Equator of the eastern Pacific [van Andel et al, 1975;Farrell et al, 1995], the far North Pacific [Rea et al, 1995], and the Oman margin [Brummer and Van Eijden, 1992]). At DSDP Site 590, which lies beneath the Tasman Front (southern boundary of the easterly flowing EAC), carbonate accumulation rates doubled between the late Miocene and early Pliocene, consistent with the bio-genic bloom phenomenon (Grant and Dickens, 2002). The coincidence of elevated export production at numerous locations suggests far-field oceanographic teleconnections during the Neogene, such as via an acceleration of Indo-Pacific upwelling and nutrient delivery to the photic zone.…”

“…However, the significance of unconformities in the Tasman Sea has not, so far, included consideration of regional vertical tectonics or local faulting (Sutherland et al, 2010(Sutherland et al, , 2017. Records from the Tasman Sea may also offer insights into understanding Neogene paleoceanography across the Pacific and phenomena such as the late Miocene-early Pliocene biogenic bloom (Farrell et al, 1995;Grant and Dickens, 2002).…”

Influência da quantidade e qualidade da matéria orgânica sedimentar na estrutura e distribuição vertical e horizontal das comunidades bentônicas na plataforma de São Sebastião, São Paulo, Brasil

“…A determinação das características granulométricas dos sedimentos foi realizada pelo método tradicional de peneiramento e pipetagem descrito em Suguio (1973) Clifton et al (1995), estimar a densidade seca do sedimento (Grant & Dickens, 2002) e calcular a razão de espaços vazios (e = Vpw/Vs), a qual é definida como a razão entre o volume de água intersticial (Vpw) e o volume das partículas sólidas (Vs) (Blum, 1997). A taxa de acumulação dos sólidos totais (mtv) foi calculada através da seguinte fórmula proposta por Fukue et al (1996):…”