Forty million years of Antarctic glacial history yielded by Leg 119 of the Ocean Drilling Program

Polar Record ◽  
1989 ◽  
Vol 25 (153) ◽  
pp. 99-106 ◽  
Author(s):  
Michael J. Hambrey ◽  
Birger Larsen ◽  
Werner U. Ehrmann
Keyword(s):  
Large Scale ◽  
Middle Eocene ◽  
Prydz Bay ◽  
Glacial History ◽  
Ice Shelf ◽  
Ocean Drilling Program ◽  
Ocean Drilling ◽  
Early Oligocene ◽  
Amery Ice Shelf ◽  
Antarctic Continental Shelf

AbstractDuring Leg 119 of the Ocean Drilling Program, between December 1987 and February 1988, six holes were drilled in the Kerguelen Plateau, southern Indian Ocean, and five in Prydz Bay at the mouth of the Amery Ice Shelf, on the East Antarctic continental shelf. The Prydz Bay holes, reported here, form a transect from the inner shelf to the continental slope, recording a prograding sequence of possible Late Paleozoic to Eocene continental sediments of fluvial aspect, followed by several hundred metres of Early Oligocene (possibly Middle Eocene) to Quaternary glaciallydominated sediments. This extends the known onset of large-scale glaciation of Antarctica back to about 36–40 million years ago, the sedimentary record suggesting that a fully developed East Antarctic Ice Sheet reached the coast at Prydz Bay at this time, and was more extensive than the present sheet. Subsequent glacial history is complex, with the bulk of sedimentation in the outer shelf taking place close to the grounding line of an extended Amery Ice S helf. However, breaks in the record and intervals of no recovery may hide evidence of periods of glacial retreat.

scholarly journals Late oligocene–early miocene shortening in the Thrace Basin, northern Aegean

2021 ◽  
Author(s):  
Ümitcan Erbil ◽  
Aral I. Okay ◽  
Aynur Hakyemez
Keyword(s):  
Large Scale ◽  
Middle Eocene ◽  
Early Miocene ◽  
Fold Axis ◽  
Late Oligocene ◽  
The Balkans ◽  
Sedimentary Sequences ◽  
The North ◽  
Early Oligocene ◽  
Thrace Basin

AbstractLate Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.

Modelling the ocean circulation and the basal melting in the Prydz Bay-Amery Ice Shelf system

2021 ◽  
Author(s):  
Jing Jin ◽  
Antony J. Payne ◽  
William Seviour ◽  
Christopher Bull
Keyword(s):  
Heat Transport ◽  
Ocean Circulation ◽  
Water Masses ◽  
Prydz Bay ◽  
Effect Of Temperature ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Thermodynamic Structure ◽  
Amery Ice Shelf ◽  
Basal Melting

<p>The basal melting of the Amery Ice Shelf (AIS) in East Antarctica and its connections with the oceanic circulation are investigated by a regional ocean model. The simulated estimations of net melt rate over AIS from 1976 to 2005 vary from 1 to 2 m/yr depending primarily due to inflow of modified Circumpolar Deep Water (mCDW). Prydz Bay Eastern Costal Current (PBECC) and the eastern branch of Prydz Bay Gyre (PBG) are identified as two main mCDW intrusion pathways. The oceanic heat transport from both PBECC and PBG has significant seasonal variability, which is associated with the Antarctic Slope Current. The onshore heat transport has a long-lasting effect on basal melting. The basal melting is primarily driven by the inflowing water masses though a positive feedback mechanism. The intruding warm water masses destabilize the thermodynamic structure in the sub-ice shelf cavity therefore enhancing the overturning circulations, leading to further melting due to increasing heat transport. However, the inflowing saltier water masses due to sea-ice formation could offset the effect of temperature through stratifying the thermodynamic structure, then suppressing the overturning circulation and reducing the basal melting.</p>

scholarly journals IODP Expedition 318: From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin

2011 ◽  
Vol 12 ◽  
pp. 15-23 ◽  
Author(s):  
C. Escutia ◽  
H. Brinkhuis ◽  
A. Klaus ◽  
Keyword(s):  
Middle Eocene ◽  
Second Phase ◽  
Last Deglaciation ◽  
Ocean Drilling Program ◽  
Ocean Drilling ◽  
Integrated Ocean Drilling Program ◽  
Tectonic History ◽  
Wilkes Land ◽  
History Of

Integrated Ocean Drilling Program (IODP) Expedition 318, Wilkes Land Glacial History, drilled a transect of sites across the Wilkes Land margin of Antarctica to provide a long-term record of the sedimentary archives of Cenozoic Antarctic glaciation and its intimate relationships with global climatic and oceanographic change. The Wilkes Land drilling program was undertaken to constrain the age, nature, and paleoenvironment of the previously only seismically inferred glacial sequences. The expedition (January–March 2010) recovered ~2000 meters of high-quality middle Eocene–Holocene sediments from water depths between 400 m and 4000 m at four sites on the Wilkes Land rise (U1355, U1356, U1359, and U1361) and three sites on the Wilkes Land shelf (U1357, U1358, and U1360). <br><br> These records span ~53 million years of Antarctic history, and the various seismic units (WL-S4–WL-S9) have been successfully dated. The cores reveal the history of the Wilkes Land Antarctic margin from an ice-free “greenhouse” Antarctica, to the first cooling, to the onset and erosional consequences of the first glaciation and the subsequent dynamics of the waxing and waning ice sheets, all the way to thick, unprecedented "tree ring style" records with seasonal resolution of the last deglaciation that began ~10,000 y ago. The cores also reveal details of the tectonic history of the Australo-Antarctic Gulf from 53 Ma, portraying the onset of the second phase of rifting between Australia and Antarctica, to ever-subsiding margins and deepening, to the present continental and ever-widening ocean/continent configuration. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.12.02.2011" target="_blank">10.2204/iodp.sd.12.02.2011</a>

scholarly journals Maastrichtian–Rupelian paleoclimates in the southwest Pacific – a critical re-evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

2021 ◽  
Vol 17 (6) ◽  
pp. 2393-2425
Author(s):  
Peter K. Bijl ◽  
Joost Frieling ◽  
Margot J. Cramwinckel ◽  
Christine Boschman ◽  
Appy Sluijs ◽  
...  
Keyword(s):  
Marine Sediments ◽  
State Of The Art ◽  
Middle Eocene ◽  
Potential Temperature ◽  
Critical Evaluation ◽  
Marine Biodiversity ◽  
Early Eocene ◽  
Ocean Drilling Program ◽  
Ocean Drilling ◽  
Sw Pacific

Abstract. Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (SW) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects on the isoGDGT distribution in marine sediments. Here, we use the current proxy insights to (re-)assess the reliability of the isoGDGT-based SST signal in 69 newly analyzed and 242 reanalyzed sediments at Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We compare our results with paleoenvironmental and paleoclimatologic reconstructions based on dinoflagellate cysts. The resulting ∼ 130 kyr resolution Maastrichtian–Oligocene SST record based on the TetraEther indeX of tetraethers with 86 carbon atoms (TEX86) confirms previous conclusions of anomalous warmth in the early Eocene SW Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and assemblages show a strong response to the local SST evolution, supporting the robustness of the TEX86 record. Soil-derived branched GDGTs stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land using the Methylation index of Branched Tetraethers with 5-methyl bonds (MBT'5me) proxy. MAAT is consistently lower than SST during the early Eocene, independent of the calibration chosen. General trends in SST and MAAT are similar, except for (1) an enigmatic absence of MAAT rise during the Paleocene–Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and (2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocysts and GDGT signals suggest a mid-shelf depositional environment with strong river runoff during the Paleocene–early Eocene progressively becoming more marine thereafter. This trend reflects gradual subsidence and more pronounced wet/dry seasons in the northward-drifting Australian hinterland, which may also explain the subdued middle Eocene MAAT cooling relative to that of SST. The overall correlation between dinocyst assemblages, marine biodiversity and SST changes suggests that temperature exerted a strong influence on the surface-water ecosystem. Finally, we find support for a potential temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in marine sediments. It is encouraging that a critical evaluation of the GDGT signals confirms that most of the generated data are reliable. However, this also implies that the high TEX86-based SSTs for the Eocene SW Pacific and the systematic offset between absolute TEX86-based SST and MBT'5me-based MAAT estimates remain without definitive explanation.

scholarly journals Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

2015 ◽  
Vol 11 (4) ◽  
pp. 2977-3018 ◽  
Author(s):  
K. M. Pascher ◽  
C. J. Hollis ◽  
S. M. Bohaty ◽  
G. Cortese ◽  
R. M. McKay
Keyword(s):  
Oxygen Isotope ◽  
High Latitude ◽  
Large Scale ◽  
Middle Eocene ◽  
Late Eocene ◽  
Climate History ◽  
Southwest Pacific ◽  
Early Oligocene ◽  
Radiolarian Assemblages

Abstract. The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene–Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40–33 Ma) to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM) event – a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma) there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are absent. These data indicate that, once the Tasman Gateway was fully open in the early Oligocene, a frontal system similar to the present day was established, with nutrient-depleted subantarctic waters bathing the area around DSDP Site 277, resulting in a more oligotrophic siliceous plankton assemblage.

High resolution CO2 record of the great Plio-Pleistocene glaciations using boron isotopes

2020 ◽  
Author(s):  
Rachel Brown ◽  
Thomas Chalk ◽  
Paul Wilson ◽  
Eelco Rohling ◽  
Gavin Foster
Keyword(s):  
High Resolution ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Boron Isotope ◽  
Ocean Drilling Program ◽  
Proxy Record ◽  
Ocean Drilling ◽  
Integrated Ocean Drilling Program ◽  
Great Transition ◽  
Adequate Test

&lt;p&gt;The intensification of Northern Hemisphere glaciation (iNHG) at 3.4-2.5 million years ago (Ma) represents the last great transition in Cenozoic climate state with the development of large scale ice sheets in the Northern Hemisphere that waxed and waned with changes in insolation. Declining atmospheric CO&lt;sub&gt;2&lt;/sub&gt; levels are widely suggested to have been the main cause of iNHG but the CO&lt;sub&gt;2&lt;/sub&gt; proxy record is too poorly resolved to provide an adequate test of this hypothesis. The boron isotope-pH proxy, in particular, has shown promise when it comes to accurately estimating past CO&lt;sub&gt;2&lt;/sub&gt; concentrations and is very good at reconstructing relative changes in CO&lt;sub&gt;2&lt;/sub&gt; on orbital timescales. Here we present a new orbitally resolved record of atmospheric CO&lt;sub&gt;2 &lt;/sub&gt;(1 sample per 3 kyr) change from Integrated Ocean Drilling Program Site 999 (12.74&amp;#730;N, -78.74 &amp;#730;E) spanning ~2.6&amp;#8211;2.4&amp;#160;Ma based on the boron isotope (&amp;#948;&lt;sup&gt;11&lt;/sup&gt;B) composition of planktic foraminiferal calcite, &lt;em&gt;Globingerinoides ruber&lt;/em&gt; (senso stricto, white). &amp;#160;We find that &amp;#948;&lt;sup&gt;11&lt;/sup&gt;B values of &lt;em&gt;G. ruber&lt;/em&gt; show clear glacial-interglacial cycles with a magnitude that is similar to those of the Mid-Pleistocene at the same site and elsewhere.&amp;#160; This new high-resolution view of CO&lt;sub&gt;2&lt;/sub&gt; during the first large glacial events of the Pleistocene confirms the importance of CO&lt;sub&gt;2&lt;/sub&gt; in amplifying orbital forcing of climate and offers new insights into the mechanistic drivers of natural CO&lt;sub&gt;2&lt;/sub&gt; change.&amp;#160;&lt;/p&gt;

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