Persico, Davide

We investigated the calcareous nannofossil biostratigraphy and magnetostratigraphy of middle Eocene – lower Oligocene sediments from ODP Hole 709 C, equatorial Indian Ocean. The new bio-magnetostratigraphic analyses have resulted in an accurate biochronology of the interval span- ning Chrons C20r (middle Eocene) to C12r, in which 29 bioevents were investigated, in a 12 myr interval. The magnetostratigraphic signal is less clear across the Eocene-Oligocene transition (EOT) but becomes more reliable at the top of Chron C13n to Chron C12r (early Oligocene). Quantitative analyses of calcareous nannofossil as- semblages allowed recognition of the Middle Eocene Climatic Optimum (MECO) and the long cooling trend leading to the glacial state starting in the early Oligocene. We identify two hiatuses, in the lower middle Eocene and across the Eocene-Oligocene Transition (EOT). Across the latter unconformity, a major transition from oligotrophic to eutrophic favoring nannofossil taxa highlights the enhanced sea surface nutrient availability during the transition to the early Oligocene glacial system. Finally, a late Oligocene warming event is recorded at this site by the increase in calcareous nannofossil taxa that preferred warm water.

After the formalization of the base of the Miocene in the Lemme‐Carrosio section (Italy) at the base of Subchron C6Cn.2n, the calcareous plankton biostratigraphy was refined in several open ocean Deep Sea Drilling Project/Ocean Drilling Program sites. However, high‐resolution quantitative biostratigraphic studies, integrating planktonic foraminifera and calcareous nannofossils, are still lacking for the time interval spanning the Oligocene–Miocene transition. Here, we present a reinvestigation of Deep Sea Drilling Project Hole 516F (Rio Grande Rise) and 4 oil wells drilled by Petróbras Brasileiro SA in the Campos Basin (SW Atlantic Ocean). We identified 12 planktonic foraminiferal and 18 calcareous nannofossil bioevents that have been integrated with an updated magnetostratigraphy of Hole 516F allowing the correlation with the GPTS and the identification of the Oligocene/Miocene boundary (base of Subchron C6Cn.2n) between the Top of Sphenolithus delphix and the Base of common Paragloborotalia kugleri. Furthermore, our results give new insights on the reliability of major calcareous plankton events across the Oligocene–Miocene transition: (a) the Sphenolithus ciperoensis Top, the S. delphix Base and Top, and the Sphenolithus cometa Base are reliable events at a global scale; (b) the Bases of Globoquadrina dehiscens and Sphenolithus disbelemnos > 4 μm are correlatable events only within the study sector of the SW Atlantic Ocean; and (c) the Globoturborotalita ciperoensis Top, Globoturborotalita angulisuturalis Top, and Sphenolithus procerus Base are diachronous. Finally, previously unreported biostratigraphic data, such as the distribution range of S. disbelemnos < 4 μm and Sphenolithus cf. S. pseudoheteromorphus, the Tenuitellinata praestainforthi acme interval, and the Top of common Globigerinoides primordius were identified in the Campos Basin.

New magnetobiostratigraphic data for the late Oligocene through early Miocene at Deep Sea Drilling Project (DSDP) Hole 516F provide a significantly revised age model, which permits reevaluation of developments that led to the Mi-1 glacial event at the Oligocene-Miocene boundary. Our new high-resolution paleomagnetic study, which is supported by quantitative calcareous nannofossil and planktonic foraminiferal analyses, significantly refines previous age models for Oligocene-Miocene sediments from DSDP Hole 516F, with ages that are systematically younger than those previously determined. In some parts of the Oligocene, the discrepancy with previous studies exceeds 450 kyr. Based on this new age model, we infer a progressive increase in sedimentation rate and paleoproductivity between circa 23.9 Ma and circa 22.9 Ma, with the highest rate coinciding with the Mi-1 glacial event at the Oligocene-Miocene boundary. This productivity increase would have resulted in higher rates of carbon burial and in turn a drawdown of atmospheric CO2. Immediately afterward, an abrupt decrease in sedimentation rate and paleoproductivity suggests that the Mi-1 deglaciation was associated with decreased carbon input into the ocean. Elevated sedimentation rates are also documented at ~24.5 Ma, coincident with the Oi2D glacioeustatic event. The presence of volcanic material within the sediments during these glacial events is interpreted to have resulted from redeposition of sediment scoured from nearby sites on the Rio Grande Rise due to transient variations in bottom water flow patterns.

During the Eocene-Oligocene transition, Earth cooled significantly from a greenhouse to an icehouse climate. Nannofossil assemblages from Southern Ocean sites enable evaluation of paleoceanographic changes and, hence, of the oceanic response to Antarctic ice sheet evolution during the Eocene and Oligocene. A combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes. A cooling trend, started in the Middle Eocene, was interrupted by warming during the Middle Eocene Climatic optimum and by short cooling episodes. The cooling episode at 39.6Ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from ~39.1 to ~36.2Ma.We suggest that oligotrophic conditions were associated with increased water mass stratification, low nutrient contents, and high efficiency of the oceanic biological pump that, in turn, promoted sequestration of carbon from surface waters, which favored cooling. After 36.2Ma, we document a large synchronous surface water productivity turnoverwith a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance. This turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient Antarctic ice sheet and/or to iron delivery to the sea surface. Eutrophic conditions were maintained throughout the Oligocene, which was characterized by a nannofossil assemblage shift toward cool conditions at the Eocene-Oligocene transition. Finally, a warm nannofossil assemblage in the Late Oligocene indicates a warming phase.

The depositional history of the Storfjorden and Kveithola trough-mouth fans (TMFs) in the northwestern Barents Sea has been investigated within two coordinated Spanish and Italian projects in the framework of the International Polar Year (IPY) Activity 367, NICE STREAMS. The investigation has been conducted using a multidisciplinary approach to the study of sediment cores positioned on high-resolution multibeam bathymetry and TOPAS/CHIRP sub-bottom profiles. Core correlation and the age model were based on 27 AMS 14C samples, rock magnetic parameters, lithofacies sequences, and the presence of marker beds including two oxidized layers marking the post Last Glacial Maximum (LGM) inception of deglaciation (OX-2) and the Younger Dryas cold climatic event (OX-1). Sediment facies analysis allowed the distinction of a number of depositional processes whose onset appears closely related to ice stream dynamics and oceanographic patterns in response to climate change. The glacigenic diamicton with low water content, high density, and high shear strength, deposited during glacial maxima, indicates ice streams grounded at the shelf edge. Massive release of IRD occurred at the inception of deglaciation in response to increased calving rates with possible outer ice streams lift off and collapse. The presence of a several-meter-thick sequence of interlaminated sediments deposited by subglacial outbursts of turbid meltwater (plumites) indicates rapid ice streams' melting and retreat. Crudely-layered and heavily-bioturbated sediments were deposited by contour currents under climatic/environmental conditions favorable to bioproductivity. The extreme sedimentation rate of 3.4 cm a− 1 calculated for the plumites from the upper-slope area indicates a massive, nearly instantaneous (less than 150 years), terrigenous input corresponding to an outstanding meltwater event. We propose these interlaminated sediments to represent the high-latitude marine record of MeltWater Pulse 1a (MWP-1a). Different bathymetric and oceanographic conditions controlled locally the mode of glacial retreat, resulting in different thickness of plumites on the upper continental slope of the Storfjorden and Kveithola TMFs. It is possible that the southern part of Storfjorden TMF received additional sediments from the deglaciation of the neighboring Kveithola ice stream.

Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600 m and 40Ar/39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with well‐dated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of pre‐existing strata. The combined age model implies relatively rapid (1 m/2–5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basin‐wide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies: 1. The base of the cored succession (1275–1220 mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5 Ma by several reworked volcanic clasts; 2. A late-Miocene sub-polar orbitally controlled glacial–interglacial succession (1220–760 mbsf) bounded by two unconformities correlated with basin‐wide reflectors associated with early development of the terror rift; 3. A late Miocene volcanigenic succession (760–596 mbsf) terminating with a ~1 my hiatus at 596.35 mbsf which spans the Miocene–Pliocene boundary and is not recognised in regional seismic data; 4. An early Pliocene obliquity-controlled alternating diamictite and diatomite glacial–interglacial succession(590–440 mbsf), separated from; 5. A late Pliocene obliquity-controlled alternating diamictite and diatomite glacial–interglacial succession (440–150 mbsf) by a 750 ky unconformity interpreted to represent a major sequence boundary at other locations; 6. An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150–80 mbsf), and; 7. A late Pleistocene glacigene succession (80–0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment.

Thirty years after oxygen isotope records frommicrofossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth’s orbital geometry control the ice ages1, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles2. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the ‘warmer-than- present’ early-Pliocene epoch (̃5–3Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming3. Here we present a marine glacial record from the upper 600 m of theAND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ̃40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ̃3 C warmer than today4 and atmospheric CO2 concentration was as high as ̃400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model7 that simulates fluctuations in Antarctic ice volume of up to + 7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the EastAntarctic ice sheet, in response to ocean-induced melting paced by obliquity.During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt8 under conditions of elevated CO2.