GEOS2115
Oceans, Coasts and Climate Change
Tectonics, oceans and climate change: Ocean gateways –
effects on climate and ocean circulation and connections
between past and future climates
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. You will have five 2-hour practical classes to work on this exercise (Weeks
2-5). You are expected to complete and submit an essay by the end of Week 5 (Sunday
24th March 23:59pm). Essay format is outlined on page 8.
A late submission of the essay will incur a 5% penalty for every 24 hours after the submission
deadline. Late penalties can be waived, or alternative arrangements made, in cases of Special
Consideration approved by the Faculty of Science. Please read ALL instructions and ask the
lecturer or tutor if you have questions. Essays must be submitted in pdf format to Canvas.
The assessment for this Practical is worth 25% of your final mark for this unit.
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,
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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. (see https://www.iodp.org/expeditions/expeditions-
schedule)
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 Eocene-
Oligocene 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.
The evidence for and the processes that govern plate tectonics will be covered in later classes.
However, to begin with we will examine the relative motion of the southern continents since
100 Ma (the abbreviation Ma for mega-annum describes the point in time that is so many
millions of years before the present) and how the changing geography of the continents has
affected the development of the Southern Ocean and the Antarctic Circumpolar Current.
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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 at https://climatearchive.org/past_analogues.html
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.
Essential Background Reading:
Use Google Scholar or the Library website to find relevant articles. You need to have read
and understood the following papers to completing this assignment. These papers should be
included in your reference list. Note that there are additional papers listed on the
assignment page which will also prove to be quite useful.
➢ Barker, P.F., and Thomas, E., 2004, Origin, signature and palaeoclimatic influence of
the Antarctic Circumpolar Current: Earth-Science Reviews, v. 66, no. 1, p. 143- 162.
➢ Bijl, P. K., Schouten, S., Sluijs, A., Reichart, G.-J., Zachos, J. C., and Brinkhuis, H.,
2009, Early Palaeogene temperature evolution of the southwest Pacific Ocean:
Nature, v. 461, no. 7265, p. 776-779.
➢ Exon, N., Kennett, J., Malone, M., Brinkhuis, H., Chaproniere, G., Ennyu, A.,
Fothergill, P., Fuller, M., Grauert, M., and Hill, P., 2002, Drilling reveals climatic
consequences of Tasmanian gateway opening: Eos, Transactions American
Geophysical Union, v. 83, no. 23, p. 253-259.
➢ Scher, H. D., Whittaker, J. M., Williams, S. E., Latimer, J. C., Kordesch, W. E., &
Delaney, M. L., 2015, Onset of Antarctic Circumpolar Current 30 million years ago
as Tasmanian Gateway aligned with westerlies. Nature, 523 (7562), 580.
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➢ Sijp, W.P., England, M.H. and Huber, M., 2011. Effect of the deepening of the
Tasman Gateway on the global ocean. Paleoceanography, 26(4)
Finding, viewing and downloading data via GeoMapApp
In this part of the exercise you will use GeoMapApp to access the Ocean Floor Drilling portal
to find evidence of the Eocene-Oligocene transition in the Southern Ocean. You will need to
make maps and graphs, as well as extract core logs and photographs, for use in your essay.
Note: GeoMapApp is freely available for download here: http://www.geomapapp.org/
1. Open GeoMapApp from the Start Menu (or download the application to your personal
computer, install the program, and open it).
➢ It will download the Java-based application (which can take a few minutes),
and will launch automatically. Select the default Mercator projection, and
click Agree at the prompt to open the program.
2. Zoom to the region that includes the ocean floor between mainland Australia and
Antarctica (Figure 2) and activate the Ocean Floor Drilling portal in GeoMapApp by
clicking on Portals > Ocean Floor Drilling in the top menu:
Figure 1
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Let it load and do not touch the app! (Patience) A number of grey points will appear
in the oceans. Each represents one or more drill cores collected by the Ocean Drilling
Program (ODP), Deep Sea Drilling Program (DSDP) or the Integrated Ocean Drilling
Program (IODP – now International Ocean Discovery Program).
3. Access drill core data for a particular site by clicking on that point, starting
with Leg 189 Site 1172 (shown in red below). This is one of the key sites described
by Exon et al. (2002). Activate the DSDP – ODP – IODP DRILL HOLES window
(under the Window menu) and click on the “View down-core measurements for
selected cores” button (red zig-zag line icon). The graphical display can show
various measurements as a function of depth in the sediments.
Figure 2
4. Explore the different measurements that are recorded for site 1172-A,
which is described by Exon et al. (2002). Check out the carbonate content in particular
and any other measurements that show strong variation near the Eocene-Oligocene
boundary. Such measurements are important in developing an interpretation of how
climate or oceanic circulation has changed through time.
➢ For each hole, the graphs will display the depth (meters below sea floor, mbsf),
the core number and the geological age. The Eocene (56-34 Ma) and the
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Oligocene (34-23 Ma) are two of the major divisions of the geological time-scale
in the present Cainozoic Era. These ages are defined in terms of micro-fossil
assemblages and calibrated using geochronological techniques.
5. Access the core photographs for site 1172-A. The small black squares in the
column next to the age scale are supposed to link to photographs of the cores, but since
this does not work in some cases, the photos can also be accessed directly from the
Core Photo web interface at:
http://iodp.tamu.edu/janusweb/imaging/photo.shtml.
Enter the leg (189), Site (1172) and Hole (A), and click Submit Request. You will see a
list of photos. Use your GeoMapApp graph and the depths to find
photographs of the cores near/at the Eocene-Oligocene boundary. The next column
of small black squares on the GeoMapApp graph links to core logs, which may be
useful in interpreting what you see in the photos.
6. Explore the data held for other drill sites mentioned by Exon et al. (2002). At
least look at sites 1168, 1170, 1171 and any others that might be interesting. Can you
find any evidence of whether the changes seen at the Eocene-Oligocene transition at
site 1172 are local to the East Tasman Plateau, or of greater regional extent? You will
find that many cores do not go deep enough to sample the Eocene-Oligocene transition
(at around 34 Ma), while other cores may have missing sections due to poor
recovery from the drill hole, and older sites generally have fewer measurement types
available.
Part 2. Climatearchive model analysis
The climate archive site at https://climatearchive.org/past_analogues.html 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.
The time slice plot shows annual temperature variations at a given time, while the time-
series plot shows the evolution of either surface temperature or precipitation at the selected
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location over the last 100 million years, compared to different future warming scenarios.
SSP scenarios and numerical climate models
SSP1: The sustainable and “green” pathway describes an increasingly sustainable world.
Global commons are being preserved, the limits of nature are being respected. The focus is
more on human well-being than on economic growth. Income inequalities between states and
within states are being reduced. Consumption is oriented towards minimizing material
resource and energy usage.
SSP2: The “Middle of the road” or medium pathway extrapolates the past and current global
development into the future. Income trends in different countries are diverging significantly.
There is a certain cooperation between states, but it is barely expanded. Global population
growth is moderate, leveling off in the second half of the century. Environmental systems are
facing a certain degradation.
SSP3: Regional rivalry. A revival of nationalism and regional conflicts pushes global issues
into the background. Policies increasingly focus on questions of national and regional
security. Investments in education and technological development are decreasing. Inequality
is rising. Some regions suffer drastic environmental damage.
SSP4: Inequality. The chasm between globally cooperating developed societies and those
stalling at a lower developmental stage with low income and a low level of education is
widening. Environmental policies are successful in tackling local problems in some regions,
but not in others.
SSP5: Fossil-fueled Development. Global markets are increasingly integrated, leading to
innovations and technological progress. The social and economic development, however, is
based on an intensified exploitation of fossil fuel resources with a high percentage of coal and
an energy-intensive lifestyle worldwide. The world economy is growing and local
environmental problems such as air pollution are being tackled successfully.
In order to structure the variety of possible scenarios, three substantial factors were
considered: the degree of climate change or rather the intensity of the additional radiative
forcing (due to the man-made greenhouse gas effect), the different socioeconomic pathways
(SSP1-SSP5) and, co-called "Shared Climate Policy Assumptions” (SPAs). The SPAs describe
different degrees of political efforts to curb and to adapt to climate change. The classes of
climate effects (radiative forcings) employed in this classification roughly correspond to RCP
scenarios RCP2.6, RCP4.5, RCP6.0 and RCP8.5.
Shared economic pathways (SSP) scenario predictions for atmospheric CO2 are used as input
for climate models as part of the Climate Model Intercomparison Project (CMIP). The time-
slice plot compares four CMIP6 (6th generation of CMIP models) model outputs to a pre-
industrial reference and to the geological time (between 0 and 100 Ma) chosen by the user on
the left-hand globe. If the user chooses 0 Ma, this corresponds to a Holocene model, and say if
the user chooses 100 Ma, this corresponds to a Late Cretaceous model. The CMIP scenarios
compared here correspond to different levels of global warming of relative to pre-industrial
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conditions.
Figure 3. CO2 emissions based on SSP scenarios used for driving CMIP
climate models
Figure 4. Global atmospheric CO2 concentration evolution from CMIP
climate models
• SSP585: With an additional radiative forcing of 8.5 W/m² by the year 2100, this scenario
represents the upper boundary of the range of scenarios described in the literature.
• SSP370: With 7 W/m² by the year 2100, this scenario is in the upper-middle part of the full
range of scenarios.
• SSP245: This is an update to scenario RCP4.5 with an additional radiative forcing of 4.5
W/m² by the year 2100, representing the medium pathway of future greenhouse gas
emissions. This scenario assumes that climate protection measures are being taken.
• SSP126: This scenario with 2.6 W/m² by the year 2100 is a remake of the optimistic
scenario RCP2.6 and was designed with the aim of simulating a development that is
compatible with the 2°C target. This scenario, too, assumes climate protection measures
being taken.
Figure 3 shows the emission trajectories corresponding to the four different trajectories of
global CO2 concentrations. For the past, the historic emission trajectory is depicted.
According to this figure it would be necessary to start reducing emissions immediately, and to
even reach negative emissions on a global average by 2075 in order to ensure a radiative
forcing compatible with the 2°C target by the year 2100 (SSP126, green curve). Figure 4 shows
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the evolution of global atmospheric CO2 concentration resulting from the CMIP climate
models.
Figure 5. Screenshot of the climatearchive globes
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Figure 6. Time series plot for a location close to Sydney from 100 Ma to the
present, compared with four future warming scenarios
Figure 7. Time slice plot for a location close to Sydney at 66 Ma, the present
and future
Note that both temperature and precipitation along coastal regions is important for eroding
terrestrial sediments and transporting them into the ocean. In the absence of much
biological productivity in the surface ocean around Tasmania (i.e before the opening of the
Tasman gateway) these sediments were dominant. Think about the factors that led to the
relative fluctuation in deep-sea sediments around Tasmania. The strength and direction of
surface ocean currents plays an important role in driving surface ocean biological
productivity. This is because of upwelling, which in the right conditions bring nutrients from
deeper waters to the surface, driving plankton blooms. Study the surface currents in the
paleo-globes, comparing the 66 Ma globe as a pre-gateway opening scenario to the 30-0 Ma
globes. How do surface currents change in the eastern Great Australian Bight, around
Tasmania and along eastern Australia?
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Part 3. Essay writing
Based on your study of the essential reference papers, and your own investigation of the
IODP data using GeoMapApp and of climate-ocean model output you need to summarise
observational evidence for how and when the Southern Ocean developed around
Antarctica, and the global and regional changes that are associated with this process.
Note that a flaw in the climate-ocean models on the climatearchive site is that the paleo-
elevations models that the climate models are based on have the gateway between
Tasmania and Australia open too early. In order to get an idea what the region around
Tasmania might have looked like in terms of ocean currents and temperature, use the time
at 66 Ma as a proxy for the pre-gateway opening situation and use 30 Ma as a post-opening
time slice.
This report must be in your own words (and, after submitting it in week 5, together with the
rest of this assessment, the TurnItIn system will check that you are not using someone
else’s text).
Please address the following points:
1. Give a brief (and illustrative) synopsis of the tectonic events that led to the
establishment of the modern Antarctic Circumpolar Current (ACC). Can you
distinguish between the 3 scenarios proposed for pre-Tasman gateway opening
currents east of Australia by Exxon et al. (2002), Bijl et al. (2009) and Sijp et al.
(2011)? How does the timing compare to the opening of the Drake Passage? Do you
think it is more likely that the Drake Passage opened before 33 Ma or long after 33
Ma (like 16 Ma, as proposed by some)
2. According to the scientific literature, how does the presence of the ACC affect the pole-
to-equator thermal gradient? Use a comparison between the 66 Ma and 30 Ma
climate models, as explained above, and choose two key locations at high and low
latitudes at these times to approximate the latitudinal temperature gradients at these
times. Compare the seasonal temperature variations at 66 and 30 Ma at an
equatorial and a polar location.
3. What evidence for the establishment of the Tasman Gateway, a necessary precursor
for the modern ACC, can you see from the ocean drilling results available via
GeoMapApp?
 You must include material from Site 1172 on the East Tasman Plateau.
 You must include your own figures and maps made using GeoMapApp.
 If you choose to include the core photographs, make sure you annotate them
appropriately, and provide a meaningful figure caption.
4. Comparing Cenozoic with projected future climate change, which past times are
comparable to different future scenarios? Discuss temperature and precipitation
trajectories for two selected coastal locations on the east coast of Australia and
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around Tasmania. Also discuss differences in annual temperature cycles, comparing
relevant times in the past and future scenarios. Consider different future warming
scenarios, and changing surface current conditions.
5. Figures. Figures should be embedded in the report and cited within the text by Figure
number. Each figure should have a meaningful, self-explanatory and succinct caption.
You are limited to 8 display items (figures/tables) total for this part of the
assignment. At least 6 items should be your own original figures produced with
GeoMapApp or with climatearchive globes. You can generate multi-panel figures. Published
display items provided to help support your answers should be properly cited after the
caption (e.g., from Smith et al., 2017).
6. References: Any references you use must be properly cited throughout your answers, and you
must use the Harvard citation style. We expect to see at least a couple of additional relevant
references based on your independent search. We encourage you to use EndNote or a similar
bibliography manager to help manage your citations
Some Writing Tips:
 The primary rule in scientific writing is that it should be concise and accurate, and
contain enough information to be understood by the audience. If a sentence includes
words that don’t add any useful meaning, delete them. If the meaning is unclear, what
additional context is needed?
 The second rule is: proofread before submission – check what you have written; does
the text really say what you mean it to say? And will it be understood?
 Avoid passive voice (e.g., “the following measurements were made”). Better to say who
made the measurements.
 Keep the grammar simple, i.e., follow the basic pattern of: subject – verb – object, with
qualifying clauses as appropriate.
 Be quantitative rather than qualitative where possible. Physical quantities have units,
make sure they get attached to the numbers (preferably use a non-breaking space).
 Read published journal articles to get a better idea of the language style that is
expected. It will help you write better figure captions as well.
 Follow a single referencing style in your document – start using EndNote (it is
available free from the Library website).
 Use the Library search engine to find relevant papers. Also, Google Scholar is your
friend – it even has a link to directly import citations into EndNote.
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 Make sure your figures have meaningful figure captions and are referred to in the text.
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Essay format
Your essay must be typed, 1.5 line spacing, on A4 paper with 2.5 cm margins all around. Font
type must be 12 pt Times New Roman and essay text must be no more than 2500 words
(excluding references, figures and tables with captions). Pages must be numbered and those
over the limit will not be read/marked. Remember, an important aim of this exercise is for
you to learn how to write concisely and effectively. Any figures or tables that you choose to
include must be embedded in the report and must have succinct and meaningful captions.
You are limited to 8 display items (figures/tables) for this essay so make them count!
Figures and tables should be referred to in the text in the appropriate manner (i.e “see Figure
1” or “In Figure 2….”). All material that is not your own must be appropriately cited (see
examples in this document). This essay is worth 25% of your final mark.
Figure examples below:
Figure 1. The pole-to-equator Sea Surface Temperature gradients since the Eocene from Bijl
et al. (2009).
Figure 2. Long-term eustatic (global) sea level curve from Haq et al. (1987) with respect to
present day.