Mid‐Miocene paleoproductivity in the Atlantic Ocean and implications for the global carbon cycle

Abstract

[1] A prominent, middle Miocene (17.5-13.5 Ma) carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13 C depleted organic carbon in marine sediments or enhanced carbon burial in peat/lignite deposits on land. Here we test the hypothesis that the marine d 13 C record reflects a change in productivity with proxy records from three Atlantic Ocean sites (Deep Sea Drilling Program Site 608 and Ocean Drilling Program Sites 925 and 1265). Our multiproxy approach is based on benthic foraminiferal accumulation rates, elemental ratios (Ba/Al and P/Al), the d 13 C of bulk sedimentary organic matter, and dissolution indices. We compare these proxies to benthic foraminiferal d13 C values measured on the same samples. Our results indicate that marine paleoproductivity in the Atlantic Ocean is not related to the benthic foraminiferal d 13 C excursion. A numerical box model confirms that marine productivity cannot account for the d 13C maximum. The model shows that sequestration of 1.5 Â 10 18 mol C in the terrestrial realm over a period of 3 Ma leads to a 0.9% d 13C increase in the deep ocean, which is near the observed records. Therefore, an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean's carbon pool with 13 C, which is consistent with coeval lignite deposits worldwide. The

Effects of CO<sup>2</sup>, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study

“…Correcting for inherent biases could thus help to reconcile model results to proxy-based reconstructions. However, as emphasised by Diester-Haass et al (2009), a high CO 2 level at the Middle Miocene would be difficult to reconcile with the high δ 13 C values of benthic foraminifera, which suggest large deposition rates of organic carbon tending to reduce atmospheric CO 2 levels. Therefore model results should be interpreted with care.…”

Paleoproductivity during the middle Miocene carbon isotope events: A data‐model approach

“…These results agree with the observations of Diester‐Haass et al . [] who found no evidence for long‐term changes in productivity to parallel Atlantic Ocean benthic foraminiferal δ 13 C records during this interval of time.…”

“…To assess potential relationships between the benthic foraminiferal‐derived productivity and the CM events, we use an updated version of the box model used by Diester‐Haass et al . [] and further developed by Lefebvre [] and Lefebvre et al . [].…”

“…Two sites are located in the southern Pacific Ocean (Deep Sea Drilling Project (DSDP) Hole 588A, and Ocean Drilling Program (ODP) Site 1171), and one lies in the Indian Ocean sector of the Southern Ocean (ODP Site 747); they represent a meridional transect of hydrographic regimes ranging from the subtropical gyre to the south of the modern ocean Polar Frontal Zone (Figure ). Together with published data from the Atlantic Ocean (ODP Sites 925 and 1265 and DSDP Site 608, see Figure for location) [ Diester‐Haass et al ., ], the data set allows us to investigate the extent to which individual Miocene CM events are indeed related to global ocean processes.…”

Reconstructing Cenozoic vegetation from proxy data and models – A NECLIME synthesis (Editorial)

“…At the end of the Oligocene, global climate warmed again (De Man and Van Simaeys, 2004;Villa and Persico, 2006) and this warming culminated in the Miocene near 15 Ma, with another climate optimum, the so-called mid-Miocene climatic optimum (Zachos et al, 2001). This warm phase is characterized by a heavy carbon isotopic composition of deep sea carbonate sediments, suggesting high deposition fluxes of organic matter, either from the marine realm (Vincent and Berger, 1985) or from the land (Diester-Haass et al, 2009, 2013. This phase ended with the middle Miocene climate transition, between 14.2 and 13.8 Ma, when the Antarctic ice sheet started to grow again (Shevenell et al, 2004).…”