Antarctic Ice Growth Research Articles

Eocene‐Oligocene Intensification of the Deep Western Boundary Current in the North Atlantic Ocean

AbstractThe role played by ocean circulation in major transitions in Earth's climate is debated. Here, we investigate the physical evolution of the Deep Western Boundary Current (DWBC) in the western North Atlantic Ocean through the late Eocene‐to‐mid Oligocene (35−26 Ma) using terrigenous grain size and geochemistry records of marine sediment cores. Our records cover the most pivotal transition in Cenozoic climate history, the Eocene‐Oligocene Transition (EOT; ∼33.7 Ma), when Earth first became sufficiently cool to sustain large ice sheets on Antarctica. To assess changes in deep‐water circulation in the northwest Atlantic across the EOT, we assembled sortable silt (10–63 μm) grain‐size and Nd, Hf, and Pb radiogenic isotope records at two Integrated Ocean Drilling Program (IODP) drill sites on the Newfoundland ridges (Sites U1406 and U1411). These records reveal an overall gradual increase in sortable silt abundance (SS%) at both sites with no change in sediment provenance. We interpret a steady, long‐term invigoration of the DWBC, likely driven by deepening of the Greenland‐Scotland Ridge and resultant enhanced inflow of waters sourced from deep‐water production sites in the Nordic Seas to the North Atlantic Ocean. Our results do not support abrupt and widespread invigoration of bottom current activity in the North Atlantic synchronous with accelerated cooling and Antarctic ice growth at the EOT. Instead, our records suggest that the DWBC started to intensify before this pivotal event in Cenozoic climate history (at ∼35 Ma) and then further strengthened gradually across the EOT (∼34 Ma) and through the early‐to‐mid Oligocene (∼34‒26 Ma).

An Antarctic stratigraphic record of stepwise ice growth through the Eocene-Oligocene transition

Earth's current icehouse phase began ?34 m.y. ago with the onset of major Antarctic glaciation at the Eocene-Oligocene transition. Changes in ocean circulation and a decline in atmospheric greenhouse gas levels were associated with stepwise cooling and ice growth at southern high latitudes. The Antarctic cryosphere plays a critical role in the ocean-atmosphere system, but its early evolution is still poorly known. With a near-field record from Prydz Bay, Antarctica, we demonstrate that Antarctic ice growth was stepwise and had an earlier onset than previously suggested. Prydz Bay lies downstream of a major East Antarctic Ice Sheet drainage system, and its sedimentary records uniquely constrain the timing of ice-sheet advance onto the continental shelf. We investigated a detrital record extracted from three Ocean Drilling Program drill holes within a new depositional and chronological framework spanning the late Eocene to early Oligocene (ca. 36?33 Ma). The chemical index of alteration (CIA) and the S index, calculated from the major-element geochemistry of bulk samples, yielded estimates of chemical weathering intensities and mean annual temperature on the East Antarctic continent. We document evidence for late Eocene mountain glaciation along with transient warm events at 35.8?34.8 Ma. From 34.4 Ma, associated with the Eocene-Oligocene transition precursor ?18O excursion, glaciers advanced into Prydz Bay, coincident with a decline in chemical weathering and temperature. We conclude that Antarctic continental ice growth commenced with the Eocene-Oligocene transition “precursor” glaciation, during a time of Subantarctic surface ocean cooling and a decline in atmospheric pCO2. These results call for dynamic high-latitude feedbacks that are currently poorly represented in Earth system models and emphasize the need for additional near-field glacio-sedimentological, high-latitude sea-surface temperature and pCO2 records across the Eocene-Oligocene transition.

Antarctic ice growth before and after the Eocene‐Oligocene transition: New estimates from clumped isotope paleothermometry

AbstractAcross the Eocene‐Oligocene transition, the oxygen isotopic composition (δ18O) of benthic and planktonic foraminifera increased by over 1‰. This shift is thought to represent a combination of global cooling and the growth of a large ice sheet on the Antarctic continent. To determine the contribution of each of these factors to the total change in δ18O, we measured the clumped isotopic composition of planktonic foraminifera tests from Ocean Drilling Program Site 689 in the Southern Ocean. Near‐surface temperatures were ~12°C in the intervals 0–1.5 Myr before and 1–2 Myr after the major (Oi‐1) transition, in agreement with estimates made using other proxies at nearby sites. Temperatures cooled by 0.4 ± 1.1°C between these intervals, indicating that the long‐term change in δ18O seen in planktonic foraminifera at this site is predominantly due to changes in ice volume. A larger instantaneous cooling may have occurred during Oi‐1 but is not captured in this study due to sampling resolution. The corresponding change in the isotopic composition of seawater (δ18Osw) is 0.75 ± 0.23‰, which is within the range of previous estimates, and represents global ice growth equivalent to roughly ~110–120% of the volume of the modern Antarctic ice sheet or ~80–90 m of eustatic sea level change.

Coupling of marine and continental oxygen isotope records during the Eocene-Oligocene transition

While marine records of the Eocene-Oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on Antarctica, continental records indicate substantial spatial variability. Marine Eocene-Oligocene transition records are marked by an ∼+1.1‰ foraminiferal δ18O shift, but continental records rarely record the same geochemical signature, making both correlation and linking of causal mechanisms between marine and continental records challenging. Here, a new high-resolution continental δ18O record, derived from the freshwater gill-breathing gastropod Viviparus lentus , is presented from the Hampshire Basin, UK. The Solent Group records marine incursions and has an established magnetostratigraphy, making it possible to correlate the succession directly with marine records. The V. lentus δ18O record indicates a penecontemporaneous, higher-magnitude shift (>+1.4‰) than marine records, which reflects both cooling and a source moisture compositional shift consistent with the growth of Antarctic ice. When combined with “clumped” isotope measurements from the same succession, about half of the isotopic shift can be attributed to cooling and about half to source moisture change, proportions similar to marine foraminiferal records. Thus, the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the Eocene-Oligocene transition not observed in continental interior records.

Antarctic ice growth and retreat

Antarctic Ice Sheet change during the last glacial cycle is unclear. The timing of moraine development in the Ross basin suggests that the ice sheet reached maximum thickness under the warming temperatures of the last termination.

Clay mineral changes across the Eocene–Oligocene transition in the sedimentary sequence at Xining occurred prior to global cooling

During the Cenozoic, high-quality long-term sedimentary sequences formed in Xining basin at the northeastern margin of the Tibetan Plateau, which are characterized by alternating gypsiferous layers and reddish mudstone beds. The Tashan section was previously dated in detail by magnetostratigraphy, which yielded an age span of 16 to 35.7Ma. In this study, bulk and clay mineral assemblages and magnetic parameters of the 33.1–35.7Ma portion were analyzed using X-ray diffraction and magnetic methods to determine the behavior of the Eocene–Oligocene climate transition. Quartz, calcite, feldspar and clay fractions in sediments that are mainly derived from the surrounding catchments, gypsum and dolomite are authigenic minerals. Illite, chlorite, irregular mixed-layer illite-smectite and smectite are the four main clay-sized fractions (<2μm) in the gypsum/gypsiferous layers and the reddish mudstone beds, which suggest that no significant tectonic activity occurred in the catchment area of the Xining basin during the period of 35.7–33.1Ma. Dominant hematite, illite and gypsum in the sediments indicate that the climate was dominantly hot and dry in the Xining basin. This was controlled by a “planetary” subtropical aridity zonal pattern; the variations in gypsum, dolomite and smectite content are mainly controlled by the climate changes. The characteristics of the clay mineral assemblages suggest that warm and humid fluctuations with hot and dry conditions prevailed during ~35.7–34.1Ma in inner Asia. This changed to cold and dry conditions at ~34.1Ma and remained so from ~34.1 to 33.1Ma. Comparisons with open ocean marine records and Northern Hemisphere continental records indicate that the climate cooling in continental records occurred prior to the main drop of δ18O in foraminifera preserved in marine sediments at Oi-1 (33.545Ma). This demonstrates that the magnitude of Antarctic ice growth during the EOT was not the major contributor to inner Asian aridification, possibly due to the northward moving of subtropical highs that existed in northwest China and was induced by temperate zones moving during the late Eocene to early Oligocene.

Two-stepping into the icehouse: East Antarctic weathering during progressive ice-sheet expansion at the Eocene–Oligocene transition

Research Article| April 01, 2011 Two-stepping into the icehouse: East Antarctic weathering during progressive ice-sheet expansion at the Eocene–Oligocene transition Howie D. Scher; Howie D. Scher * 1Ocean Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA *Current address: Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, USA; E-mail: hscher@geol.sc.edu. Search for other works by this author on: GSW Google Scholar Steven M. Bohaty; Steven M. Bohaty † 2Earth and Planetary Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA †Current address: School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK. Search for other works by this author on: GSW Google Scholar James C. Zachos; James C. Zachos 2Earth and Planetary Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA Search for other works by this author on: GSW Google Scholar Margaret L. Delaney Margaret L. Delaney 1Ocean Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Howie D. Scher * 1Ocean Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA Steven M. Bohaty † 2Earth and Planetary Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA James C. Zachos 2Earth and Planetary Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA Margaret L. Delaney 1Ocean Sciences Department, and Institute of Marine Sciences, University of California−Santa Cruz, Santa Cruz, California 95064, USA *Current address: Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, USA; E-mail: hscher@geol.sc.edu. †Current address: School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK. Publisher: Geological Society of America Received: 07 Sep 2010 Revision Received: 18 Nov 2010 Accepted: 22 Nov 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (4): 383–386. https://doi.org/10.1130/G31726.1 Article history Received: 07 Sep 2010 Revision Received: 18 Nov 2010 Accepted: 22 Nov 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Howie D. Scher, Steven M. Bohaty, James C. Zachos, Margaret L. Delaney; Two-stepping into the icehouse: East Antarctic weathering during progressive ice-sheet expansion at the Eocene–Oligocene transition. Geology 2011;; 39 (4): 383–386. doi: https://doi.org/10.1130/G31726.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In conjunction with increasing benthic foraminiferal δ18O values at the Eocene–Oligocene transition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 μm) appears abruptly alongside fossil fish teeth with continentally derived neodymium (Nd) isotope ratios (εNd) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering flux, as inferred from two steps to less radiogenic εNd values, coincides with two steps in benthic foraminiferal δ18O values. These results indicate that two distinct surges of weathering were generated by East Antarctic ice growth during the EOT. Weathering by ice sheets during a precursor glaciation at 33.9 Ma did not produce significant IRD accumulation during the first εNd shift. Glacial weathering was sustained during a terrace interval between the two steps, probably by small high-elevation ice sheets. A large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca. 33.7 Ma. Rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions. Parallel changes in Antarctic weathering flux and deep-sea carbonate accumulation suggest that ice-sheet expansion during the EOT had a direct impact on the global carbon cycle; possible mechanisms include associated changes in silicate weathering on the East Antarctic craton and enhanced fertilization of Southern Ocean waters, both of which warrant further investigation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Does Antarctic glaciation force migration of the tropical rain belt?

High-resolution (similar to 3-6 k.y.) upper ocean temperature and salinity estimates derived from planktic foraminiferal delta(18)O and Mg/Ca in Ocean Drilling Program (ODP) Site 1146 reveal stepwise changes in the precipitation-evaporation balance of the subtropical northwestern Pacific during the Middle Miocene (15.7 to 12.7 Ma). We attribute the punctuated pattern of surface warming and freshening following Antarctic ice growth episodes at 14.6, 14.2, 13.9, and 13.1 Ma to successive northward movements of the Intertropical Convergence Zone, implying high sensitivity of tropical rain belts to the interhemispheric temperature gradient driven by high-latitude climate. This dynamic interaction has implications for future warmer climate regimes with differential warming of the Northern Hemisphere, as it may lead to changes in the latitudinal penetration of tropical Pacific moisture over Southeast Asia.

Acquiring High to Ultra-High Resolution Geological Records of Past Climate Change by Scientific Drilling

<strong class="journal-contentHeaderColor">Abstract.</strong> No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.8.08.2009" target="_blank">10.2204/iodp.sd.8.08.2009</a>

West Antarctic paleotopography estimated at the Eocene‐Oligocene climate transition

One generally recognized limitation of models for rapid growth of Antarctic ice near the Eocene‐Oligocene transition is that they are based on present topography, corrected only for removal of modern ice. For West Antarctica, this results in large areas below sea level that would not readily host ice. In the recently active West Antarctic rift system, other factors may have contributed to significant vertical motions since the Eocene: Additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 Ma restore most of West Antarctica to above sea level, increasing total Antarctic land area by 10–20%. Because ice sheets have convex slopes, the potential increase in ice volume is larger than the increase in land area. Accounting for large changes in West Antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early, large West Antarctic Ice Sheet.

Cooling and ice growth across the Eocene-Oligocene transition

The Eocene-Oligocene (E-O) climate transition (ca. 34 Ma) marks a period of Antarctic ice growth and a major step from early Cenozoic greenhouse conditions toward today's glaciated climate state. The transition is represented by an increase in deep-sea benthic foraminiferal oxygen isotope (18O) values occurring in two main steps that reflect the temperature and 18O of seawater. Existing benthic Mg/Ca paleotemperature records do not display a cooling across the transition, possibly reflecting a saturation state effect on benthic foraminiferal Mg/Ca ratios at deep-water sites. Here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2.5 °C ocean cooling associated with the ice growth. This permits interpretation of E-O 18O records without invoking Northern Hemisphere continental-scale ice.

Cenozoic Antarctic cryosphere evolution: Tales from deep-sea sedimentary records

Antarctica and the Southern Ocean system evolved in the Cenozoic, but the details of this complex evolution are just beginning to emerge via high-resolution investigations of globally distributed marine sedimentary sequences. Here we review the recent progress in defining the orbital-scale evolution of the Antarctic/Southern Ocean system, with particular attention paid to new high-resolution multi-proxy records generated across intervals of abrupt Antarctic ice growth in the Paleogene and early Neogene. This more detailed perspective has allowed researchers to assess the processes and feedbacks involved in the Cenozoic evolution of the Antarctic cryosphere, absent potential complication of the paleoceanographic record by a substantial Northern Hemisphere ice volume signal. In this paper, we review the new tools being used to examine these high-resolution records, assess lead-lag relationships between ice volume, temperature, and carbon cycling during intervals of abrupt Antarctic ice growth, and consider the resulting implications for the global climate system. (C) 2007 Elsevier Ltd. All rights reserved.

Clay mineral assemblages, siliciclastic input and paleoproductivity at ODP Site 1085 off Southwest Africa: A late Miocene–early Pliocene history of Orange river discharges and Benguela current activity, and their relation to global sea level change

A late Miocene to early Pliocene sequence drilled on the continental slope of southwest Africa off the Orange river mouth (ODP Site 1085) has been investigated. Clay mineral assemblages, coarse siliciclastics and benthic foraminifer accumulation rates (BFAR) unravel a step by step evolution of marine and continental environments closely related to sea level variations, ocean circulation and global climate: (1) smectite is a typical tracer of the Orange river load, whereas illite is mostly transported by the Benguela current (like chlorite) and winds, and kaolinite is derived from low latitudes by the poleward undercurrent and the North Atlantic Deep Water (NADW); (2) increased erosion and influence of the Orange river after 9.6 Ma is linked to a sea level drop at a time of Antarctic ice-growth. This has been followed by an increased seasonality of precipitation and high productivity, but low oxygen content and associated dissolution of carbonates; (3) increased productivity and dissolution of carbonates, and coeval increase of continental aridity after 8.9 Ma express a further development of the Benguela current and upwelling; (4) better preservation of carbonates and increased contribution of terrigenous material from northern sources at 6.9 Ma are related to increased circulation of NADW after an early stage of northern hemisphere glaciation; (5) increased erosion and contribution from the Orange river and westward shift of the area of higher productivity from 5.9–5.8 Ma to 5.3–5.2 Ma are related to a significant fall of sea level, and encompass the time of the entire Mediterranean salinity crisis; (6) short-term variations of the smectite/illite ratio (S/I) and BFAR suggest a major control of productivity by wind and current activities (and related upwelling), but may express brief variations of sea level in specific intervals before 8.9 Ma and during the late Messinian especially.

Cenozoic stratigraphic succession in southeastern Australia

Strata of Cenozoic age occur around the southern margin of Australia as thin and discontinuous outcrops, interpolated and fleshed out by economic exploration onshore and offshore. The neritic strata fall into four sequences or allostratigraphic packages of (I) Paleocene — Early Eocene, (II) Middle Eocene — Early Oligocene, (III) Late Oligocene — Middle Miocene, and (IV) Late Miocene — Holocene age: a four‐part pattern that can be seen also in the flanking pelagic and terrestrial realms including regolith deep weathering. Problems of correlation and age determination (predominantly biostratigraphic) have included biogeographical constraints (endemism in neritic molluscs and terrestrial palynomorphs, mid‐latitude assemblages in calcareous plankton), and slow progress in magnetostratigraphy and chemostratigraphy. Sequence I largely repeats the Cretaceous siliciclastic‐coal, marginal‐marine facies (carbonate‐poor, with marine and non‐marine palynomorphs and agglutinated foraminifers) punctuated by marine ingressions with microfaunas and sparse macrofaunas. Sequence II contains the first carbonates in the region since the Palaeozoic and the most extensive coals of the Cenozoic anywhere. Sequence III contains the most extensive neritic carbonates and the last major coals. Sequence IV is more strongly siliciclastic than the two preceding. Each of these four second‐order entities (107 years duration) comprises third‐order packages each with an unconformity and marine transgression. These packages hold true right along the southern Australian margin in the sense that the hiatuses and transgression do not display significant diachroneity at the relevant time‐scales (105–106 years). Recognised, delimited and correlated independently of the putatively global Exxon sequences, they are remarkably consistent with the latter, thereby providing a significant regional test. There are two widespread emphases on southern Australian geohistory and biohistory: (i) to regard the regional story as part of the global story of accreting continents, an expiring Tethys, and an episodically cooling planet; and (ii) a somewhat contrary emphasis, with the region being a special case of rapid longitudinal motion towards the equator. Both emphases are plausible with the former being the more heuristic. The stratigraphic record is strongly punctuated, the four sequences being separated by both tectonic and climatic events. Thus: the sequence I/II gap involved extensive plate‐tectonic reorganisation and a new spreading regime from ca 43 Ma, coevally with early growth of Antarctic ice; in the II/III gap, deformation in marginal basins is coeval with a global low in cooling, large ice sheet and falling sea‐level to ca 30 Ma; and the III/IV gap is marked by widespread cessation or contraction of stratal accumulation and withdrawal of thermophilic taxa coevally with the major expansion at ca 14 Ma of the Antarctic ice sheet, onset of intense canyon cutting, and plate‐wide basin inversion.

Middle Miocene ocean‐climate transition: High‐resolution oxygen and carbon isotopic records from Deep Sea Drilling Project Site 588A, southwest Pacific

High‐resolution stable isotopic records are presented for the epi‐benthic foraminifer Cibicidoides, the inferred shallow‐dwelling planktonic Globigerinoides quadrilobatus, and the inferred deep‐dwelling planktonic Globoquadrina dehiscens from the middle Miocene (∼16–12 Ma) of Deep Sea Drilling Project site 588A, Lord Howe Rise, southwest Pacific. High‐resolution, multiple species oxygen and carbon isotopic data define the timing and character of the well‐known middle Miocene climatic‐oceanographic transition with a resolution comparable to Quaternary records. The benthic foraminiferal δ18O record is marked by several large fluctuations from ∼16 to 14.8 Ma, followed by a series of rapid (&lt;50 kyr) δ18O increases that suggest a new state of the ocean‐climate system after 14.8 Ma. The total middle Miocene benthic oxygen isotopic increase of 1.2‰ is largely incorporated in two steps, an increase of 0.8‰ from 14.5 to 14.0 Ma and a second increase of 0.7‰ from 13.45 to 12.45 Ma. Each step is comprised of a series of marked δ18O increases, indicative of rapid East Antarctic ice sheet growth and contemporaneous deepwater cooling. A strong covariance of 0.7‰ between the benthic and deep‐dwelling planktonic species from 14.5 to 14.0 Ma (including a rapid increase from 14.1 to 14.05 Ma) suggests a 0.7‰ increase in the δ18O composition of seawater (δ18Osw) because of East Antarctic ice sheet growth. Comparison of the δ18O record of Gs. quadrilobatus suggests that surface waters warmed at this site by ∼3°C from 14.1 to 13.6 Ma. Carbon isotopic time series for each species generally covary throughout the early to middle Miocene interval (∼16–12 Ma), confirming that δ13C variations in this interval largely represent reservoir changes. High‐resolution δ13C data allow improved resolution of the latter five of six δ13C maxima within the well‐known early to middle Miocene carbon isotopic excursion (the Monterey Carbon Isotopic Excursion from 17.0 to 13.5 Ma). This is useful for global correlation. The last of these maxima ends with a 1‰ decrease centered from 13.9 to 13.7 Ma, ∼300 kyr after the δ18O increase considered to reflect East Antarctic ice growth. Covariance between benthic δ18O and δ13C from ∼16 to 13.8 Ma suggests a sensitive relation between global carbon cycling and the ocean‐climate system prior to 13.8 Ma. Episodic increases in organic carbon burial may have contributed to deep‐sea benthic δ13C maxima and synchronous global cooling. The positive relationship ended at ∼13.8 Ma, indicative of changing relations between global carbon cycling and the ocean‐climate system brought on by the increased stability of the East Antarctic ice sheet after a major growth phase from 14.5 to 14.0 Ma.