Late Miocene carbon isotope records and marine biological productivity: Was there a (dusty) link?

Abstract

We examine whether or not a relationship exists between the late Miocene carbon isotope shift (∼7.6–6.6 Ma) and marine productivity at four sites from the Indian and Pacific Oceans (Ocean Drilling Program Sites 721, 1146, 1172, and 846). We use a multiproxy approach based on benthic foraminiferal accumulation rates, elemental ratios, and dissolution indices, and we compare these data to benthic foraminiferal δ13C values measured on the same samples. Although some of these sites have been targeted previously in studies of either the late Miocene/early Pliocene “biogenic bloom” (Sites 721 and 846) or the late Miocene carbon isotope shift (Site 1172), our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link. Our results indicate that at all sites, productivity increased sometime during the δ13C shift; at three sites (721, 1146, and 846), productivity increased at the beginning of the shift. The correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal δ13C values are relatively high during the time interval containing the late Miocene δ13C shift (and statistically significant at three of the sites). Carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity. We note that long‐term trend in the Site 846 paleoproductivity record can be correlated to the long‐term trend in the Site 848 eolian flux reconstructions of Hovan (1995) hinting at a link between strengthened wind regime and productivity during the late Miocene.

Quaternary primary productivity in Porcupine Seabight, NE North Atlantic

“…A similar relationship between MAR and δ 13 C values of foraminiferal tests has been reported in the Miocene [51].…”

“…The only clue is the so-called Eltanin impact event [47] in the Southern Ocean. It is estimated that the asteroid is over 1 km in diameter, and the records of impact were found in 3000 m below sea level and were distributed on submarine in 500 km [51]. This impact event may have caused quick global paleoenvironmental and paleoclimatic impacts, and even transmitted in a substantial distance to North Atlantic.…”

Deciphering the State of the Late Miocene to Early Pliocene Equatorial Pacific

“…Prior to and during most of the LMCIS (~8.0–7.1 Ma), the Site U1338 δ 13 C gradients remain comparatively constant: the planktic‐benthic δ 13 C gradient is ~2.1‰, the fine‐benthic δ 13 C gradient is ~0.8‰, and the planktic‐fine δ 13 C gradients is ~1.25‰ (dashed lines, Figure c). The late Miocene Biogenic Bloom (LMBB), also observed in all oceanic basins, is partially coeval with the LMCIS, suggesting that increased global productivity may have driven the LMCIS (Diester‐Haass et al, , ; Expedition 320/321 Scientists, ; Grant & Dickens, ; Lyle et al, ; Lyle & Baldauf, ; Pälike et al, ). At Site U1338, sedimentation rates are generally higher between ~8.0–4.6 Ma (Figure f), supporting the proposed 8.0 to 4.5 Ma timing of the LMBB at Site U1338 (Lyle & Baldauf, ; Reghellin et al, ).…”

“…However, these observations contradict evidence for either oscillating dominant El Niño‐/La Niña‐like conditions during the late Miocene (Nathan & Leckie, ) or stable E‐W equatorial SST gradients for the last 12 Myr (Zhang et al, ). Further complicating understanding of the equatorial Pacific Ocean, is the globally recognized, but not globally synchronous Late Miocene Biogenic Bloom (LMBB), which occurred in both upwelling zones and oligotrophic regions between ~8.0 and 4.5 Ma, and may reflect increased surface ocean nutrient delivery via either increased upwelling of cool nutrient‐rich waters or increased continental runoff (Diester‐Haass et al, , , ; Grant & Dickens, ; Hermoyian & Owen, ; Liao & Lyle, ; Lyle & Baldauf, ; Herbert et al, ). However, a forcing mechanism of increased upwelling (Grant & Dickens, ) is difficult to reconcile with observations of eastern equatorial Pacific surface warmth and a deep E‐W thermocline across the equatorial Pacific Ocean (LaRiviere et al, ).…”

Monsoon-induced partial carbonate platform drowning (Maldives, Indian Ocean)

“…Such a close proximity of thriving and drowned reefs also occurs in the Caribbean, where it is controlled by the occurrence of local nutrient plumes triggered by turbulent mixing of uppermost nutricline waters into surface waters (Hallock, 2001). Surface-water nutrient injection may even have been intensifi ed during the late Miocene, a time when the Indian Ocean was reported to be characterized by a on August 3, 2015 geology.gsapubs.org Downloaded from higher productivity (Diester-Haass et al, 2006) and a substantially expanded oxygen minimum zone (Dickens and Owen, 1999).…”