GEOS2115-2915

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 practical component introduces the links between tectonics, ocean

circulation and climate change. You will work through guided data analysis tasks

over five 2-hour practical classes (Weeks 5–9), which will directly support the

preparation of a final essay submitted at the end of Week 9.

Assessment details:

- Final submission: Essay (1500 words)

- Deadline: Friday Week 9, 23:59

- Submission format: PDF via Canvas

- Weighting: 25% of final mark

- Late penalty: 5% per 24 hours unless Special Consideration is approved

The practical work, GeoMapApp analysis, and literature review are all designed to build

the evidence base for your essay. You are therefore expected to integrate observations

from all components into a single, coherent scientific argument.

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,

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.

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. Summarise the key observational evidence for how the Southern Ocean Basins and

gateways have developed during the Cenozoic, 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.

➢ 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 use via web browser or 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

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

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.

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.

This report must be in your own words (and, after submitting it in week 9, 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)? Think about the presence or absence of coastal upwelling east of Tasmania in

the different scenarios, and the impact on sedimentation. 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. 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.

3. 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.

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).

4. 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?

 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.

 Make sure your figures have meaningful figure captions and are referred to in the text.

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 1500 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.

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