Biogenic sedimentation in the equatorial Pacific: Carbon cycling and paleoproduction, 12–24 Ma

Abstract

The equatorial Pacific is an important part of the global carbon cycle and has been affected by climate change through the Cenozoic (65 Ma to present). We present a Miocene (12–24 Ma) biogenic sediment record from Deep Sea Drilling Project (DSDP) Site 574 and show that a CaCO3 minimum at 17 Ma was caused by elevated CaCO3 dissolution. When Pacific Plate motion carried Site 574 under the equator at about 16.2 Ma, there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone. The burial rates of the primary productivity proxies biogenic silica (bio‐SiO2) and biogenic barium (bio‐Ba) increase, but biogenic CaCO3 decreases. The carbonate minimum is at ∼17 Ma coincident with the beginning of the Miocene climate optimum; the transient lasts from 18 to 15 Ma. Bio‐SiO2 and bio‐Ba are positively correlated and increase as the equator was approached. Corg is poorly preserved, and is strongly affected by changing carbonate burial. Terrestrial 232Th deposition, a proxy for aeolian dust, increases only after the Site 574 equator crossing. Since surface production of bio‐SiO2, bio‐Ba, and CaCO3 correlate in the modern equatorial Pacific, the decreased CaCO3 burial rate during the Site 574 equator crossing is driven by elevated CaCO3 dissolution, representing elevated ocean carbon storage and elevated atmospheric CO2. The length of the 17 Ma CaCO3 dissolution transient requires interaction with a ‘slow’ part of the carbon cycle, perhaps elevated mantle degassing associated with the early stages of Columbia River Basalt emplacement.

The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean

“…Goldberg and Arrhenius () originally suggested that the accumulation rate of barium in deep‐sea sediments is a function of the rate of organic production in the euphotic zone and used BaO/TiO 2 to trace the zone of upwelling‐related enhanced productivity in the equatorial Pacific Ocean. Total Ba, as measured by the XRF core scanner, closely matches biogenic Ba in deep marine sedimentary environments, which do not contain Ba from terrigenous sources and where no significant barite remobilization occurs (Dymond et al, ; Hendy, ; Horner et al, ; Piela et al, ; Torres et al, ; Von Breymann et al, ). The dissolution resistance of biogenic barium and its strong correlation with the organic carbon (C org ) export flux additionally make Ba/Al a robust indicator of C org export flux in sediments with low clay content (Dymond et al, ; Eagle et al, ; Piela et al, ).…”

“…Total Ba, as measured by the XRF core scanner, closely matches biogenic Ba in deep marine sedimentary environments, which do not contain Ba from terrigenous sources and where no significant barite remobilization occurs (Dymond et al, ; Hendy, ; Horner et al, ; Piela et al, ; Torres et al, ; Von Breymann et al, ). The dissolution resistance of biogenic barium and its strong correlation with the organic carbon (C org ) export flux additionally make Ba/Al a robust indicator of C org export flux in sediments with low clay content (Dymond et al, ; Eagle et al, ; Piela et al, ). We normalized XRF scanner Ba counts against Ti and Al, considered representative of the relatively constant clay flux over the 13.5 to 9 Ma interval (McNeill et al, ).…”

Particle sorting during sediment redistribution processes and the effect on 230Th‐normalized mass accumulation rates

“… Opal was measured by the base digestion technique described in Lyle and Lyle [] but using 1 M KOH rather than 2 M KOH following the modification by Piela et al . []. CaCO 3 % was measured by CO 2 evolved by acidification with 10% phosphoric acid on an Automate acidification module and then measured by a UIC 5012 coulometer.…”

A dated molecular phylogeny of manta and devil rays (Mobulidae) based on mitogenome and nuclear sequences

“…Upwelling has not been a stable phenomenon, but has waxed and waned following changes in the world's climate throughout the ages. Periods of global cooling with associated high upwelling intensities were alternated by extended periods of global warming (Zachos et al, 2001) during which upwelling areas (Schmittner, 2005;Fedorov et al, 2013;Ravelo et al, 2004) and related productivity (Diester-Haass et al, 2002;Marlow et al, 2000;Piela et al, 2012;Suto et al, 2012) were reduced. Hence, hypothetically, global warming may have resulted in fragmentation of the habitat of filter feeders, leading to different subpopulations eventually residing in smaller isolated regions, which may have facilitated speciation as suggested for the common minke whale (Balaenoptera acutorostrata) and Antarctic minke whale (B. bonaerensis) (Pastene et al, 2007).…”