Radiolarian assemblages of the late Neogene North Pacific

Radiolarian census and abundance data were collected from three deep-sea cores drilled by the Ocean Drilling Program Sites 884, 887 and 1151 to investigate patterns of ecologic changes in space and time during the last 16 million years for the mid-latitude to subarctic North Pacific. High concentrations of radiolarians occurred between 9.0 and 2.7 Ma. Radiolarian species richness was highest in the early middle Miocene at each site and gradually decreased up to about 7 Ma, coinciding with a well-established global cooling trend. A degree of overlap index calculated for radiolarian assemblages revealed 11 faunal change events, of which 8 corresponded to global cooling events and expansions of polar ice sheets. Three of the faunal change events were observed within the peak of radiolarian accumulation rate and were ascribed to changes in primary productivity in the North Pacific rather than global climatic changes. Our assemblage analyses revealed that north-south differentiation in radiolarian assemblages in the northwestern Pacific has existed since 16 Ma and became more distinct via major steps at 6.8 Ma and 2.7 Ma, coinciding with major glaciation events, and that east-west faunal contrasts in the subarctic region became obvious beginning at 11.7 Ma and changed to a different mode around 6.8 Ma. The observed east-west faunal differences possibly reflect east to west climate differences that were characterized by cooler temperatures in the east than the west during the late Miocene (11.7-6.8 Ma) and then by the opposite temperature trend (6.8 Ma-Recent). A severe glaciation at 2.7 Ma played a large role, particularly in temporal changes in radiolarian accumulation rate and assemblage composition.

Pacific Neogene carbonate accumulation rates

I have compiled CaCO3 mass accumulation rates (MARs) for the period 0-25 Ma for 144 Deep Sea Drilling Project and Ocean Drilling Program drill sites in the Pacific in order to investigate the history of CaCO3 burial in the world's largest ocean basin. This is the first synthesis of data since the beginning of the Ocean Drilling Program. Sedimentation rates, CaCO3 contents, and bulk density were estimated for 0.5 Myr time intervals from 0 to 14 Ma and for 1 Myr time intervals from 14 to 25 Ma using mostly data from Initial Reports volumes. There is surprisingly little coherence between CaCO3 MAR time series from different Pacific regions, although regional patterns exist. A transition from high to low CaCO3 MAR from 23-20 Ma is the only event common to the entire Pacific Ocean. This event is found worldwide. The most likely cause of lowered pelagic carbonate burial is a rising sea-level trend in the early Miocene. The central and eastern equatorial Pacific is the only region with adequate drill site coverage to study carbonate compensation depth (CCD) changes in detail for the entire Neogene. The latitude-dependent decrease in CaCO3 production away from the equator is an important defining factor of the regional CCD, which shallows away from the equatorial region. Examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production ('productivity') from changes in bottom water chemistry ('dissolution') upon carbonate burial.

Sapientia, 1982, Vol. XXXVII, nº 145 (número completo)

Contenido: La participación del ser III : la participación del acto de ser o existencia / Octavio N. Derisi – La metafísica cristiana en el desarrollo del pensamiento occidental / Alberto Caturelli – El “principium essendi” del hombre y su conocimiento / Julio R. Méndez – El intelecto en el De Anima de Aristóteles : comentario a los capítulos cuarto y quinto del libro III / Ciro Schmidt Andrade – La formación metafísica cristiana en la universidad / Octavio N. Derisi – Rasgos actuales del pensamiento político de Aristóteles / Alberto Buela – Notas y comentarios -- Bibliografía