Assignment Task
This component of the course aims to introduce the links between tectonics, ocean circulation and climate change, as well as a comparative analysis of past versus future climate change.
Background Information
Climate change has (and will continue to have) a profound impact on our lives in a multitude of ways. The scientific community is quite confident that present-day global climate change is instigated by anthropogenic greenhouse gas emissions into the atmosphere (IPCC, 2013). Nevertheless, global climate has never been stagnant; it has undergone considerable fluctuation since Earth’s inception ~4.6 billion years ago, alternating between “icehouse” periods (where global temperatures favour the formation of continental ice sheets) and “hothouse” periods (where global temperatures are so high that no glaciers form on Earth whatsoever). In order to contextualise the rapid rate of change we are witnessing today, we need to understand how, why, and to what degree earth’s climate has changed in the deep geologic past. To approach this problem, geologists and geophysicists examine the geologic record (i.e. the “rock record”) and run and analyse climate-ocean models.
The world’s ocean sediments provide an excellent catalogue of Earth’s major environmental changes. Sediments contain a wealth of information if you know how to read them; apart from recording Earth’s temperature through time (Riebeek 2005), ocean sediments record the ecosystems that were living in the oceans at the time, they can tell you where ancient river systems spilled into the sea, and they reveal where vast continental glaciers locked up fresh water and subsequently melted away. The oceans, covering the lowest points on Earth’s surface, act as excellent traps for these sediments. As a consequence, Page 2 GEOS2115 however, these areas are often highly inaccessible. Over the past several decades, the scientific community has come to understand the importance of the ocean sediment record in piecing together Earth’s climatic history. In 1968, about a year before Neil Armstrong first stepped onto the moon, the Deep Sea Drilling Project (DSDP), later to be renamed the ODP and then IODP (International Ocean Drilling Project), was created, affording geologists from all over the world the ability to venture out on massive research vessels to collect and analyse deep sea sediments.
Because of these drilling expeditions, we have learned that the arrangement of continents and ocean basins can play a dominant role in determining long-term oceanic circulation, sea level and climate. The surface of the planet has been shaped and re-shaped by plate tectonics, where continents break apart to form new ocean basins at the expense of older ocean basins that are destroyed at subduction zones. The process of ocean basin formation is part of the Wilson Cycle, named after the Canadian geologist J. Tuzo Wilson. Subsequent lectures will cover Plate Tectonics in more detail. For this exercise, the important thing to keep in mind is that continents move around, and consequently that oceanic gateways open and close through time, affecting the large-scale oceanic circulation that governs global climate.
The establishment of a continuous circum-Antarctic oceanic current during the EoceneOligocene transition (~34 Ma) is thought to have been one of the most profound shifts of oceanic circulation that was principally governed by plate tectonics (Fig. 1). At around the same time, vast inland ice sheets formed on the Antarctic continent, which caused global sea level to fall. Though the establishment of a deep-water oceanic gateway between Tasmania and Antarctica by ~34 Ma is consistent with the timing of Antarctica glaciation, it can be argued that the Drake Passage (between South American and Antarctica) only opened at 22 2 Ma (Barker and Thomas, 2004), suggesting that the development of the Antarctic Circumpolar Current (ACC) may be more complex than previously thought – however the opening time of the Drake Passage is still being debated. Paleoceanographers also continue to debate the regional climatic consequences of the ACC’s formation; initially, some argued that the gradual establishment of the ACC led to the thermal isolation of Antarctica, instigating glaciation on the continent. Others argue that the emergence of this ocean gateway played a lesser or minimal role in the onset of Antarctic glaciation.
Work Plan
You are provided with a reconstruction (and animation) of the South Polar continents made by the Earthbyte research group here at Sydney University (see paper by Wright et al., 2020). In this paper we have used combined geological and geophysical data to create maps of the age distribution of the ocean floor through time, which you can view interactively using a web browser on the GPlates Portal. The age of the ocean floor is of interest to us because it has a straightforward connection to water depth (the older the ocean crust, the deeper the ocean floor is, because of thermal cooling, contraction and subsidence of the plate)
You can view (and download) a reconstruction of the water depth, derived from the age of the crust, in the form of an animation in 1 million year intervals on Canvas, which renders the evolution of the Southern Ocean as a continuous process. The sequence highlights that Australia’s separation from Antarctica was the last stage in the extended breakup of Gondwanaland.
1. Review the plate tectonic evolution of the southern ocean using the resources we have pointed you to (use the hyperlinks above)
2. Use GeoMapApp to find and describe evidence in the sedimentary record for the onset of the Antarctic Circum-Polar Current
3. Use virtual interactive globes.
4. based on climate-ocean models to examine surface ocean circulation, temperature and precipitation through time
5. Summarise the key observational evidence for how the Southern Ocean Basins and gateways have developed during the Cainozoic, in the context of published papers on the topic. This will become the basis for your essay.
Climatearchive model analysis
The climate archive site at contains an interactive visualisation of climate model data across time and space. The site shows two globes side-by-side: One for past climates and one for future climates. The user can select different times in the past and the future using sliders below the globes, and one can also select different future warming scenarios based on s-called SSPs. The SSPs are “Shared Socio-economic Pathways” based on five narratives describing alternative socio-economic developments, including sustainable development, regional rivalry, inequality, fossil-fueled development, and middle-of-the-road development.
Each SSP drives a corresponding future projection of greenhouse gas emissions called “representative concentration pathways” (RCPs). RCP 2.6 is the lowest in terms of radiative forcing. RCP 4.5 is an intermediate scenario. In RCP 6, emissions peak around 2080, then decline. In RCP 8.5 emissions continue to rise throughout the 21st century. Individual locations on the continents can be selected on the globe on the right to make different types of plots, including a time-slice plot and a time-series plot.
