Modelled ocean changes at the Plio-Pleistocene transition driven by Antarctic ice advance

The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition. However, recent data show that the ocean also underwent a significant change, with the convergence of deep water mass properties in the North Pacific and North Atlantic Ocean. Here we show that the lack of coastal ice in the Pacific sector of Antarctica leads to major reductions in Pacific Ocean overturning and the loss of the modern North Pacific Deep Water (NPDW) mass in climate models of the warmest periods of the Pliocene. These results potentially explain the convergence of global deep water mass properties at the Plio-Pleistocene transition, as Circumpolar Deep Water (CDW) became the common source

Ocean Planet: An ANZIC workshop report focused on future research challenges and opportunities for collaborative international scientific ocean drilling.

Executive summary: The ANZIC Ocean Planet Workshop (14-16 April 2019) and focused Working Group sessions represent a multidisciplinary community effort that defines scientific themes and challenges for the next phase of marine research using the capabilities of current and anticipated platforms of the International Ocean Discovery Program (IODP). Attended by 75 mostly early- and mid-career participants from Australia, New Zealand, Japan, and the United States, the workshop featured nine keynote presentations. Working groups identified important themes and challenges that are fundamental to understanding the Earth system. This research relies upon ocean-going research platforms to recover geological, geobiological, and microbiological information preserved in sediment and rock beneath the seafloor and to monitor subseafloor environments through the global ocean. The workshop program was built around five scientific themes: Biosphere Frontiers, Earth Dynamics, Core to Crust, Global Climate, Natural Hazards, and Ocean Health through Time. Workshop sessions focused on these themes and developed 19 associated scientific challenges. Underpinning these are legacy samples and data, technology, engineering, education, public outreach, big data, and societal impact. Although all challenges are important, the asterisks that follow denote those of particular relevance and interest to ANZIC. Ocean Health through Time comprises the ocean’s response to natural perturbations in biogeochemical cycles*; the lateral and vertical influence of human disturbance on the ocean floor; and the drivers and proxies of evolution, extinction, and recovery of life*. Global Climate entails coupling between the climate system and the carbon cycle; the drivers, rates, and magnitudes of sea level change in a dynamic world*; the extremes, variations, drivers, and impacts of Earth’s hydrologic cycle*; and cryosphere dynamics*. Biosphere Frontiers addresses the habitable limits for life*; the composition, complexity, diversity, and mobility of subseafloor communities*; the sensitivity of ecosystems to environmental changes; and how the signatures of life are preserved through time and space*. Earth Dynamics: Core to Crust encompasses the controls on the lifecycle of ocean basins and continents*; how the core and mantle interact with Earth’s surface*; the rates, magnitudes, and pathways of physico-chemical transfer among the geosphere, hydrosphere, and biosphere*; and the composition, structure, and dynamics of Earth’s upper mantle. Natural Hazards involves the mechanisms and periodicities of destructive earthquakes*; the impacts of submarine and coastal volcanism; the consequences of submarine slope failures on coastal communities and critical infrastructure*; and the magnitudes, frequencies, and impacts of natural disasters*. The ANZIC Ocean Planet Workshop will contribute to formulating the next science framework for scientific ocean drilling which in turn will guide the focused planning of specific drilling, logging, and monitoring projects.(1) Funded through ANZIC and the Australian Research Council Linkage Infrastructure, Equipment and Facilities (LIEF)scheme (LE160100067). The grant title is “Australian Membership of the International Ocean Discovery Program.” and the PI’s are: R. Arculus, D. Cohen, S. Gallagher, P. Vasconcelos, C. Elders, J. Foden, M. Coffin, O. Nebel, H. McGregor, C. Sloss, J. Webster, A. Kemp, S. George, M. Clennell, and A. Heap. (2) ANZIC is a consortium of 16 Australian and New Zealand universities and four national research institutions (CSIRO, Geoscience Australia, GNS Science and NIWA)

Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene

© 2014 Macmillan Publishers Limited. All rights reserved. The Pliocene and Early Pleistocene, between 5.3 and 0.8 million years ago, span a transition from a global climate state that was 2-3 °C warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles. Growth and decay of these ice sheets was paced by variations in the Earth's orbit around the Sun. However, the nature of the influence of orbital forcing on the ice sheets is unclear, particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level. Here we present a record of the rate of accumulation of iceberg-rafted debris oshore from the East Antarctic ice sheet, adjacent to the Wilkes Subglacial Basin, between 4.3 and 2.2 million years ago. We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat. In the warmer part of the record, between 4.3 and 3.5 million years ago, spectral analyses show a dominant periodicity of about 40,000 years. Subsequently, the powers of the 100,000-year and 20,000-year signals strengthen. We suggest that, as the Southern Ocean cooled between 3.5 and 2.5 million years ago, the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet. After this threshold was crossed, substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima, as controlled by the precession cycle

Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO 2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene. © 2013 Macmillan Publishers Limited. All rights reserved

Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO 2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene. © 2013 Macmillan Publishers Limited. All rights reserved

Early and middle miocene antarctic glacial history from the sedimentary facies distribution in the AND-2A drill hole, Ross sea, Antarctica

In 2007, the Antarctic Geological Drilling Program (ANDRILL) drilled 1138.54 m of strata ̃10 km off the East Antarctic coast, includ ing an expanded early to middle Miocene succession not previously recovered from the Antarctic continental shelf. Here, we pre sent a facies model, distribution, and paleoclimatic interpretation for the AND-2A drill hole, which enable us, for the first time, to reconstruct periods of early and middle Miocene glacial advance and retreat and paleo environmental changes at an ice-proximal site. Three types of facies associations can be recognized that imply significantly different paleoclimatic interpretations. (1) A diamictite-dominated facies association represents glacially dominated depositional environments, including subglacial environments, with only brief intervals where ice-free coasts existed, and periods when the ice sheet was periodically larger than the modern ice sheet. (2) A stratified diamictite and mudstone facies association includes facies characteristic of open-marine to iceberg-influenced depositional environments and is more consistent with a very dynamic ice sheet, with a grounding line south of the modern position. (3) A mudstone-dominated facies association generally lacks diamictites and was produced in a glacially influenced hemipelagic depositional environment. Based on the distribution of these facies associations, we can conclude that the Antarctic ice sheets were dynamic, with grounding lines south of the modern location at ca. 20.1-19.6 Ma and ca. 19.3-18.7 Ma and during the Miocene climatic optimum, ca. 17.6-15.4 Ma, with ice-sheet and sea-ice minima at ca. 16.5-16.3 Ma and ca. 15.7-15.6 Ma. While glacial minima at ca. 20.1-19.6 Ma and ca. 19.3-18.7 Ma were characterized by temperate margins, an increased abundance of gravelly facies and diatomaceous siltstone and a lack of meltwater plume deposits suggest a cooler and drier climate with polythermal conditions for the Miocene climatic optimum (ca. 17.6-15.4 Ma). Several periods of major ice growth with a grounding line traversing the drill site are recognized between ca. 20.2 and 17.6 Ma, and after ca. 15.4 Ma, with evidence of cold polar glaciers with ice shelves. The AND-2A core provides proximal evidence that during the middle Miocene climate transition, an ice sheet larger than the modern ice sheet was already present by ca. 14.7 Ma, ̃1 m.y. earlier than generally inferred from deep-sea oxygen isotope records. These findings highlight the importance of high-latitude ice-proximal records for the interpretation of far-field proxies across major climate transitions. © 2011 Geological Society of America