Middle to late Miocene stepwise climate cooling: Evidence from a high-resolution deep water isotope curve spanning 8 million years

Abstract

We present high‐resolution (2–3 kyr) benthic foraminiferal stable isotopes in a continuous, well‐preserved sedimentary archive from the West Pacific Ocean (Ocean Drilling Program Site 1146), which track climate evolution in unprecedented resolution over the period 12.9 to 8.4 Ma. We developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long‐term climate and ocean circulation development between 16.4 and 8.4 Ma. This extended perspective reveals that the long eccentricity (400 kyr) cycle is prominently encoded in the δ13C signal over most of the record, reflecting long‐term fluctuations in the carbon cycle. The δ18O signal closely follows variations in short eccentricity (100 kyr) and obliquity (41 kyr). In particular, the obliquity cycle is prominent from ~14.6 to 14.1 Ma and from ~9.8 to 9.2 Ma, when high‐amplitude variability in obliquity is congruent with low‐amplitude variability in short eccentricity. The δ18O curve is additionally characterized by a series of incremental steps at ~14.6, 13.9, 13.1, 10.6, 9.9, and 9.0 Ma, which we attribute to progressive deep water cooling and/or glaciation episodes following the end of the Miocene climatic optimum. On the basis of δ18O amplitudes, we find that climate variability decreased substantially after ~13 Ma, except for a remarkable warming episode at ~10.8–10.7 Ma at peak insolation during eccentricity maxima (100 and 400 kyr). This transient warming, associated with a massive negative carbon isotope shift, is reminiscent of intense global warming events at eccentricity maxima during the Miocene climatic optimum.

Newfoundland Neogene sediment drifts: transition from the Paleogene greenhouse to the modern icehouse

“…This gap persists despite the importance of this area and time interval for understanding the evolution of the cryosphere, Northern Hemisphere ecosystem structure, and the history of ocean productivity and chemical balances. Recent drilling in this time interval has focused on the Pacific where new, very highly resolved records with good chronology have been produced (e.g., Holbourn et al, 2013;Tian et al, 2013). A key task is therefore to produce comparable records from the sites of deep ocean overturning in the Atlantic for understanding the relative contributions of regional and global signals preserved in the Pacific records.…”

Miocene sepiids (Cephalopoda, Coleoidea) from Australia

“…Foraminifera were picked and identified for the biostratigraphical analyses using a binocular stereoscopic microscope, a biological polarising microscope and a scanning electron microscope (SEM). Determination of foraminifers followed Loeblich and Tappan (1992), Holbourn et al (2013) and Turco et al (2011). Palaeoecological parameters of the obtained foraminiferal assemblage were evaluated based on the presence and dominance of taxa exhibiting special environmental significance Boltovskoy and Wright, 1976;Murray, 2006).…”

Untitled

“…• Understand the timing and conditions under which monsoonal circulation initiated and reconstruct the variability of the Indian monsoon at orbital timescales; • Understand the relationship between Indian monsoon variability and major past global climatic events such as the Oligocene/Miocene cooling (Zachos et al, 1997), the onset of the mid-Miocene climatic optimum (Holbourn et al, 2007(Holbourn et al, , 2014Zachos et al, 2001), mid-Miocene cooling and Antarctic cryosphere expansion (Holbourn et al, 2013), and the PliocenePleistocene enhancement of Northern Hemisphere glaciation Raymo, 2005, 2007); • Establish a complete Oligocene-present astronomically tuned timescale based on high-resolution benthic and planktonic isotope reference curves for the Indian Ocean; and • Integrate high-resolution distribution studies of well-preserved Oligocene-recent calcareous and siliceous microfossils from the Indian Ocean into global compilation studies of paleoclimatic and biotic evolution.…”