AUS2K meeting 26-27th June 2014 – Melbourne

We are pleased to announce that the third workshop of the PAGES Australasia2k Working Group will be held in Melbourne on 26-27 June 2014. This will be a joint meeting with the Australian Climate Change Science Program (ACCSP) project “Variability of Australian climate over the last 1000 years in coupled model simulations and proxy data”.

The topic of the workshop will be the challenges and opportunities in the growing fields of (a) climate reconstructions from proxy evidence, and (b) comparison with the PMIP3/CMIP5 Last Millennium climate model simulations, for the Australasian and wider Southern Hemisphere regions. The focus will be on the interaction between climate modellers, meteorologists, scientists developing proxy records, and how to strengthen ties to better understand the past (and future) behaviour of the climate system.

Day 1 (Thursday) will feature presentations from (1) Aus2k Working Group participants, and (2) palaeoclimate work being conducted by the ACCSP and other related work.

Day 2 (Friday) will be focussed on planning for Phase Two of Aus2k.

Further details, including a call for presentations, will follow during the coming weeks. For now, save these dates to ensure that you are able to attend.

When organising travel, please note that this workshop immediately precedes the AQUA Biennial Conference, which will take place in Mildura from 29 June to 4 July 2014.

We look forward to seeing you all in Melbourne!

Joelle, Drew, Steven, Nerilie, Russell, Ben, Jonathan, Heidi, Pandora and Jo – On behalf of the Aus2k Steering Committee and the ACCSP Project “Variability of Australian climate over the last 1000 years in coupled model simulations and proxy data”

Southern Hemisphere Westerly Wind SHAPE workshop summary

A small workshop was held on the 28-29th January 2014 in Auckland to discuss the Southern Hemisphere Westerly Winds and how they might have changed over time.

See the SHAPE webpage and scroll down to find a link to the summary pdf. from this recent workshop. Please get in touch with anyone listed if you are interested in being involved in any of the new or ongoing projects.

Blog 7: Dust deposition in the Southern Ocean

By Ignacio A. Jara and Helen Bostock

Terrestrial dust is important to the climate system not only because it may alter the solar radiative balance of the earth, but also because it supplies the oceans with key iron (Fe), a limiting micronutrient for phytoplankton productivity in the Southern Ocean. The “Iron Hypothesis” was first proposed by Martin (1990) [1], who suggested that changes in Fe supplied impact on the biological productivity in the Southern Ocean which, in turn, could influence the glacial-interglacial changes in atmospheric CO2.  However over the last 20 years scientists have struggled to find evidence to support this theory.

In the present-day Atlantic Southern Ocean an increase in terrestrial dust influx or volcanic aerosols has been linked to vast biological blooms. An increase in biological activity is associated with a high consumption of nutrients and transfers carbon back to the deep ocean. In 2009 an article published in Nature [2] explored past dust-climate interactions in this part of the Southern Ocean (42°S) by presenting an offshore dust record extending back to 4 million years.

This study of a long Ocean Drilling Program (ODP) core from the South Atlantic provided -with unprecedented detail- evidence for a consistently enhanced terrestrial dust influx during ice ages. It also showed a tight coupling with dust deposition in Antarctic ice cores over the last 0.8 million years, indicating that large areas of the Southern Ocean and Antarctica were affected by the glacial dust plume. According to the authors, the glacial dust was the result of an increased aridity of the eastern Patagonian plains (just upwind from the coring site), which increased the dust availability; as well as stronger and northward shifted Southern Hemisphere Westerly Winds, which enhanced the offshore transport of the Patagonian dust.

Has something similar occurred in larger Pacific sector of the Southern Ocean?

The dust record from a new set of cores collected by the RV Sonne 2010 from the Pacific Southern Ocean has recently been published in Science [3], and shows a similar pattern of variability in dust fluxes for this region over the last 1 million years [3]. The increased glacial dust deposition in the Pacific Southern Ocean is probably the result of enhanced supply from the Australian continent (with potential contributions from New Zealand), as modelling suggests this landmass is the main present-day dust source in the southern Pacific. However, geochemical fingerprinting of the dust will be required to determine the exact source.

Dust model

Figure: Modern terrestrial dust sources across the Southern Ocean based on modelling data (Lamy et al., 2014)

Interestingly, dust influxes during glaciations prior to 0.5 million years seem to have been significantly lower in the Pacific than in the Atlantic (Figure 2), something that may be explained by a less intense glacial desiccation of Australia due to its relatively northern position compared with Patagonia.

So has the increased dust/Fe translated into increased productivity?

There is evidence for some increase in productivity from opal flux, n-alkanes and barium concentrations in some of the cores north of the Polar Front. But there is a large reduction in productivity south of the Polar Front, resulting in an overall decrease in total biogenic opal production during the glacials in the South Pacific [4], and thus unlikely to draw-down the atmospheric CO2.

Dust and biology

Figure: Lithogenic and biogenic proxies from the subantarctic waters of the South Pacific (Lamy et al., 2014)

Modern iron fertilization experiments have also had mixed results; early experiments such as Ironex and SOIREE produced large blooms visible from space [5], while several subsequent experiments have not witnessed any major changes in phytoplankton concentrations. There is also the question of whether the blooms actually result in organic carbon being transferred to the deep ocean.

It is clear that more work is required to understand the link between dust, biological productivity and CO2 ventilation in the Southern Ocean .

References:

  • Martin, J.H., 1990. Glacial-interglacial CO2 change: The Iron Hypothesis. Paleoceanography, 5, 1-13.
  • Martinez-Garcia, A., et al., 2011. Southern Ocean dust-climate coupling over the past four million years. Nature 476, 312-315.
  • Lamy, F., et al., 2014. Increased dust deposition in the Pacific Southern Ocean during glacial periods. Science 343, 403-407.
  • Bradtmiller L., et al., 2009. Comparing glacial and Holocene opal fluxes in the Pacific sector of the Southern Ocean. Paleoceanography, 24, PA2214, doi:10.1029/2008PA001693
  • Boyd P.W. et al (2007) Iron enrichment experiments 1993-2005: synthesis and future directions. Science 315, 5812, 612-7.

Blog 6:Changes in radiocarbon surface reservoir ages in the SE Pacific

By Helen Bostock

Over the last decade the main theory to explain the changes in the atmospheric concentration of CO2 between glacials and interglacials, has primarily focussed on changes in the circulation of the Southern Ocean controlling the release of CO2 from the deep-ocean reservoir. However, there is still considerable debate about the path and timing of the CO2 release during the deglacial. A recent study on sediment cores from the SE Pacific has shed new light on this debate. Siani et al., (2013) found changes in the surface reservoir radiocarbon (14C) age, determined from the difference in the 14C age of planktic foraminifera compared to tephra ages in cores from the SE Pacific. The study found that periods of increased surface reservoir ages were coeval with the timing of upwelling events in the Southern Ocean and increases in atmospheric CO2 during the deglaciation. The increased upwelling of old, carbon-rich, deep-waters is supported by reductions in the difference between 14C benthic-planktic foram ages and the stable carbon isotopes (d13C), the latter of which are primarily controlled by biological production and respiration in the water column. They see three periods of upwelling initiating with a short pulse at the start of the deglaciation at 18.5 ka, then between 17.5 and 14.5 ka and finally between 12.5 to 11.5 ka.

The authors also recalculated the deep-water reservoir age for intermediate depths from the SE Pacific (De Pol Holz et al., 2010) and show that there is older Antarctic Intermediate Waters during the deglaciation. Thus providing a pathway for this old CO2 signal from the Southern Ocean.

This is also a critical study for showing that the surface 14C reservoir age can vary considerably overtime and if we do not adjust for these changing background reservoir age we cannot accurately compare paleoclimate records from the oceans with the ice and terrestrial records. Changes in the surface 14C reservoir age during the last deglacial have previously been suggested for the New Zealand region by comparing the 14C age of planktic foraminifera with local tephra (Sikes et al., 2000). But recent improved dating of some of the widely deposited tephra’s for example the original increased surface reservoir age around the time of the Waiohau Tephra no longer exists (Lowe et al., 2013). Perhaps it is time for a relook at the surface 14C reservoir ages around New Zealand before confidently comparing with other global records. This is however, trickier in regions where there is no widely deposited tephra layers that can act as chronostratigraphic timelines (e.g. Australia, South Africa).  One critical region where it will be very important is the Southern Ocean.

This work suggests we need to be careful comparing marine records dated using 14C and an assumed constant reservoir age with other paleoclimate records…..one of the main objectives of the INTIMATE and SHAPE projects.

References

De Pol Holz et al., 2010. No signature of abyssal carbon in intermediate waters off Chile during the deglaciation. Nature Geoscience,  3 , 192-195.

Lowe et a., 2013 Ages of 24 widespread tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of the timing and palaeoclimatic implications of the Lateglacial cool episode recorded at Kaipo bog. Quaternary Science Reviews,74, 170-194.

Siani et al., 2013 Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation. Nature Communications, doi:10.1038/ncomms3758.

Sikes et al., 2000. Old radiocarbon ages in the southwest Pacific Ocean during the last glacial period and deglaciation. Nature, 405, 555-559.

Membership

Memberships are well and truly due and you can pay these easily online.

It is easy, so please get yourself signed up and encourage your colleagues, students and friends. This is a great time to sign new people up, as anyone that joins AQUA now will automatically have their membership extended right through to 28 February 2015. Members also have reduced registration fees at the upcoming AQUA Mildura 2014 – “Back to the Core” conference.

If, in the rare case you do have an issue with the online system, please contact our treasurer, Steven Phipps (treasurer@aqua.org.au).

Blog 5: Precipitation and human occupation changes in arid environments

Written by Ignacio Jara, Victoria University Wellington.

While the abrupt climate transitions of the glacial termination and the establishment of the present-day modes of climate variation during the Holocene seems to be well characterized in proxy records around the Southern Hemisphere, there is still sparse evidence about the impact of those changes on the migration, settlement and cultural development of ancient human populations.

A recent approach to this subject includes to compile the radiocarbon dates from archaeological sites as a proxy for human density. The underlying assumption is that period of increasing human presence should be reflected as a higher number of sites with dates falling within such the time interval. Whereas biases and limitations may be reduced by using larger radiocarbon data set, the main advantage of this method is that it provides a chronology of human population that can be directly compared with climate proxies. Two newly-published articles use this technique to uncover human responses to late Quaternary climate events.

The first of them combines a data set of more than 5,000 radiocarbon dates from all around the Australian continent with geospatial modelling (1). The main goal is to investigate the association between contractions and expansions of aboriginal population and climate instability during the terminal Pleistocene.

In Australia, cold intervals such as the Last Glacial Maximum (LGM; 23,000-18,000 years ago) have been associated with increased aridity and the expansion of grassland and non-vegetated landscapes (see blog number 3). What it is new from this study is that human population seems to have experienced a significant reduction during the LGM, as indicated by a decrease in the total number of radiocarbon dates of that age. Moreover, archaeological sites show what appears to be an interruption of elaborated cultural behaviour common prior to the LGM such as rock art, ritual burials and coloured ornamentation. These types of cultural expressions are only resumed in the early part of the Holocene Period.

The hyper arid Atacama Desert in northern Chile is also an interesting region to investigate relationship between precipitation and population changes since it is a natural passageway to southern South America, an area where the oldest evidence of human settlement in the continent.

The most intense pulses of occupation in Atacama seem to be coeval  with late Quaternary rainfall events in the Central Andes. For instance, a well preserved archaeological site published this year shows continuous human occupation in the rainless part of the dessert during one of the last of these rainfall pulses between 12,700-9700 year ago (2). Under increasing moisture, the previously plantless landscape would have been scattered by small wetlands and woodlands, becoming oases for migrating populations and a bio-geographic corridor connecting the dessert with the more humid biomes of the south.

But perhaps more tantalizing is the cultural developments associated with increasing precipitation between 7,000-4,000 years ago in Atacama. Using a data set of more than 400 radiocarbon dates, a noteworthy scientific contribution published last year correlates increased rainfall with a notable increment in human density (3). The authors point out that more water availability and larger groups of people led to a period of rapid technological and cultural innovation which resulted in the emergence of the oldest examples of artificial mummification in the world (as early as 7,000 year ago).

Atacama mummy
Increasing water availability could have been one of
the environmental drivers behind the oldest known examples of artificial mummification in the Atacama Desert between 8,000 and 7,000 years ago. Photograph from Marquett et al. 2013.

Although arid environments can restrict human settlement and migration, they also provide extraordinary conditions for the conservation of archaeological sites which might be a great advantage for future studies that address climate-human relationship during the past. What makes the results meaningful is the possibility that natural conditions for human preservation became a distinctive and influential cultural trait upon early human groups. The preservation of the soul with the body after death is a common belief among traditional societies. So the lack of decomposition is not just a relevant issue for Quaternarists.

References

  1. A. N. Williams, S. Ulm, A. R. Cook, M. C. Langley, M. Collard, Journal of Archaeological Science 40, 4612 (2013).
  2. C. Latorre et al., Quaternary Science Reviews 77, 19 (2013).
  3. P. A. Marquet et al., Proceedings of the National Academy of Sciences 109, 14754 (September 11, 2012, 2012).

Blog 4: Long-term orbital changes and glaciations in the Southern South America

Written by Ignacio Jara, Victoria University Wellington

Although the long-term changes in solar insolation between Northern Hemisphere (NH) and the Southern Hemisphere (SH) are in anti-phase, marine and ice core records from both hemispheres show highly synchronous glacial/interglacial cycles over the last 800 kyr. This disparity between the insolation and the paleo-records is probably the most important caveat concerning Milankovitch’s theory of orbital parameters controlling Earth’s climate. Particularly puzzling for the SH is that glacial/interglacial transitions follow the NH summer insolation, and therefore deglaciations in southern latitudes occur under decreasing local summer insolation1. In order to resolve this apparent conflict it is necessary to develop new detailed glacial chronologies which are able to be compared with other glacial and climate reconstructions from both hemispheres.

Southern South America has the most extensive ice sheets of the Southern Hemisphere outside of Antarctica, and thus it is not surprising this area boasts outstanding geomorphologic evidence of late Quaternary glacial fluctuations. Yet, the timing of these fluctuations has remained more or less equivocal until recently. Two newly-published glacial reconstructions from this part of the world provide new interesting insights into this topic.

Firstly, a detailed geomorphological map of the Torres del Paine area (51°S) has been produced. This is a region with extensive glaciers and massive moraine belts extending up to 35 km from present-day ice margins2. The boulder exposure 10Be dates indicate a major glacial advance culminating at 14,200 cal yr BP, while basal 14C dates from peat sections embedded in the moraine complexes indicate that ice sheet remained extended until 12,500 cal yr BP.

This chronology is supported by a more recent publication of surface exposure and radiocarbon ages from moraine complexes in Tierra de Fuego (54°S), the southern-most tip of South America and a region whose geomorphology was previously poorly mapped and dated3. The authors attribute the lack of early-Holocene moraines as evidence for dry and warm conditions during this period and suggest that the glaciers may have reached near present-day positions as early as 11,200 cal yr BP.

Overall, these two reconstructions show clear evidence for a net glacial retreat between 16,000-11,000 cal yr BP, a period of decreasing SH summer insolation. Likewise, the Tierra del Fuego reconstruction shows the absence of sustained glacial retreat during the Holocene, a period of increasing summer SH insolation. Hence, these studies are consistent with the orbital/climate paradox, suggesting that the SH summer insolation does not control (at least not directly) the ice fluctuations on the Southern American continent.

So what caused this change?

Apart from the NH summer insolation, it has been argued that other orbital parameters such as the SH summer duration and SH spring insolation could be important drivers1. The remarkable detail in the glacial reconstructions presented in these two publications may provide other clues. The ice advances during the Antarctic Cold Reversal (ACR; 14,500-12,900 cal yr BP) are observed at both the Torres del Paine and Tierra del Fuego regions, suggesting a strong Antarctic influence. Moreover, ACR glacial advances have also been recorded in the Southern Alps of New Zealand4, suggesting a zonally synchronous response across the SH, which may point to the Southern Westerly Winds and/or the Southern Ocean as important players.

Taken together, these recent publications are important contributions to better constrain the timing and forces affecting the SH glacial history over the last 16,000 years. They also highlight the potential of Southern South America for glacial reconstructions, and show the importance of glacial geomorphology studies for late Quaternary global climate reconstructions.

S Am glaciers

Glacial retreat between 16,000-11,000 cal yr BP in Tierra del Fuego occurs under decreasing Southern Hemisphere summer insolation. ACR, YD and LIA denote Antarctic Cold Reversal, Younger Dryas and the Little Ice Age respectively. Pink circles and green squares indicate 10Be dates, while red triangles indicate radiocarbon dates from the different sites from Menounos et al. (2013).

References   

1.            Huybers, P. & Denton, G. Antarctic temperature at orbital timescales controlled by local summer duration. Nature Geosci 1, 787-792 (2008).

2.            García, J.L., et al. Glacier expansion in southern Patagonia throughout the Antarctic cold reversal. Geology 40, 859-862 (2012).

3.            Menounos, B., et al. Latest Pleistocene and Holocene glacier fluctuations in southernmost Tierra del Fuego, Argentina. Quaternary Science Reviews 77, 70-79 (2013).

4.            Putnam, A.E., et al. Glacier advance in southern middle-latitudes during the Antarctic Cold Reversal. Nature Geosci 3, 700-704 (2010).

Inaugural SHAPE workshop Sept 2013

The first SHAPE workshop was held at GNS Science on the 16-17th September 2013. A summary of the talks and discussion at the workshop can be found on the SHAPE project page.

Lots of ideas were discussed and it was clear that there is still momentum continuing on from the Aus-INTIMATE project. There is a long list of possible topics towards the end of the summary with names of the lead on each (mostly people at the meeting). If you think you have something to contribute to any of these projects and would like to get involved then get in touch with the lead. With such a short time frame between now and the next INQUA in Japan in 2015, this long list of topics is clearly ambitious – so please help us out by getting involved.

 

Blog 3: Environmental transformation of Australia linked to the Late Quaternary demise of the megafauna

Australia provides an outstanding case study to resolve the relationship between Late Quaternary environmental drivers such as climate variability, vegetation changes, wildfires, faunal extinctions and human activities. The interval between 50,000-40,000 years BP is critical for understanding the interplay of some of these factors and how they transformed the Australian landscape. During this period, humans arrived and spread throughout most the continent. At the same time, a diverse range of large browsing mammals, reptiles and birds became extinct; and there is evidence for a marked vegetation change, including more intense and frequent wildfires. Despite this paleo-environmental information, the lack of well dated environmental records has prevented scientists from resolving the relationships between these events.

Tim Flannery was probably the first to propose a causal relationship between the disappearance of great browsing mammals and the increase in fires (1). He suggested the disappearance of the big herbivores was caused by over-hunting, which triggered a massive change in the distribution and structure of plant communities that favoured wildfires, and the extinction of several other smaller animal species. Two recent high-resolution vegetation reconstructions have addressed this hypothesis, providing more detail and support for this theory.

Published last year, a radiocarbon-dated pollen and charcoal profile from northern Australia used changes of the abundance of the fungus spore Sporormiella – a genus of fungi that grows in herbivores dung - as a proxy for large browsing animal activity (2). Between 43,000-38,000 yr BP a succession of environmental changes started with a rapid decline of Sporormiella, followed by an increase in charcoal accumulation and subsequently followed by a decline of rainforest pollen taxa at the expense of grasses and Sclerophyll shrub species. Critically, fire and vegetation changes lagged behind the decline of browsing activity, suggesting that neither of these factors was directly responsible for the faunal extinction. Based on these results, the authors further suggest that the decline in herbivory led to a build up of burnable light fuels and resulted in the increase in wildfires.

A more recent environmental reconstruction from a marine sediment core offshore of southern Australia uses novel proxies for regional vegetation and wildfires over the last 130,000 years (3). Based on biochemical changes in lipids derived from leaf waxes, the regional abundance of C3 and C4 plants is inferred. These two groups of plants have different metabolisms reflecting their preferential distribution over the southern (cold climate with winter precipitation) and northern (warm climate with summer precipitation) parts of the continent respectively. Additionally, paleo-fire activity is inferred from the changes in the accumulation of a biomarker formed during burning and transported offshore by dust and smoke. The record shows how warming periods such as the onset of the present and last interglacial periods are associated with increases in C4 plants, while cooling events such as Last Glacial Maximum are associated with increased C3 plants. However, the most prominent drop in C4 plants between 44,000-42,000 yr BP does not match any climate event. This drastic vegetation transformation is accompanied by high fire activity and occurs right after the interval of disappearance of mega fauna. Similarly, the authors argue for a large-scale ecological transformation caused by the disappearance of large browsers.

These two recent articles provide evidence to support a notable ecosystem rearrangement occurring only after faunal extinction, and not the opposite way around. The implication of this is that hunting was probably the main, if not the only, driver responsible for this extinction process. The disappearance of large herbivores may have promoted the accumulation of fire-prone vegetation, permitting the occurrence and spread of human-lit fires. Further support for a leading role of hunting in the Australian late Quaternary mega fauna extinction come from the fact that other processes of faunal disappearance in the Americas (between 15,000-10,000 yr BP) and New Zealand (750 yr BP) occur coincidently with human colonization of these regions.

1.            T. F. Flannery, Archaeology in Oceania 25, 45 (1990).
2.            S. Rule et al., Science 335, 1483 (March 23, 2012, 2012).
3.            R. A. Lopes dos Santos et al., Nature Geosci 6, 627 (2013).

Australian vegetation

Relative abundance of C4 plant and seasonal precipitation regimes in the Australian Continent. A prominent decreased in C4 plant between 44,000-42,000 yr BP is preceded by the Late Quaternary mega fauna extinction period (49,000-44,000 yr BP). Figure taken from reference Lopes dos Santos et al. (2013).
Diprotodon

Some Australian mega fauna browsers such as the Diprotodon (in the picture) may have weighed up to several tonnes.  Image courtesy of the South Australian Museum

UPDATE: INQUA ECR

AQUA travel awards for the INQUA ECR now due on the 1st October – see previous blog for forms

UPDATE: INQUA 2013 Early Career Researcher Inter-congress meeting:  2nd- 6th December, 2013, Wollongong, New South Wales, Australia. Details attached INQUA 2013 Early Career Researcher Inter-congress meeting:  2nd- 6th December, 2013 for MSc, PhD Candidates and Early Career Researchers

The International Union for Quaternary Research (INQUA) is committed to developing the next generation of Quaternary Scientists. The INQUA Executive Committee has approved the inaugural INQUA Early Career Researcher inter-congress meeting to provide an avenue for MSc/PhD candidates, Post-Doctoral Researchers and research-active academics in the early stage of their careers (within 5 years of obtaining their PhD) to attend valuable workshops designed to assist ECRs with career development, to present their science and gain invaluable mentoring from more senior scientists.

– INQUA Travel Award Applications Due September 1

– Abstracts and Registration Due 1st October

If you intend presenting/poster at the meeting (or applying for the travel prize) or submitting to the Quaternary International Special Issue please use the abstract template you can find this on the FB page https://www.facebook.com/groups/620885067945716/

Please register via the following link: http://www.inqua.org/meetings.html

Quaternary International Special Issue

QI has kindly agreed to run a special issue for ECRs. The aim is for ECRs (MSc/PhD candidates, Post-Doctoral Researchers and research-active academics within 5 years of obtaining their PhD) to either be the primary or single author with manuscripts that are at an advanced stage and ready for submission to the QI editorial process (see attached document for details on how to submit to the Special Issue).

Indication of Submitting for the Quaternary International ECR Special Issue Due Sept 15 and submission via the QI submission process before the meeting (preferably sooner rather than latter so you can get the most out of the review process and writing workshop).

Submissions associated with the commission themes and associated INQUA projects are welcome (http://www.inqua.org/commissions.html).

– Coastal and marine processes [CMP]
– Palaeoclimate [PALCOMM]
– Humans and Biosphere [HaBCom]
– Stratigraphy and Chronology [SACCOM]
– Terrestrial Processes, Deposits and History [TERPRO]

Submissions need to be at the required standard for publication in QI and will undergo the normal QI editorial process. The aim is to have manuscripts submitted before the meeting in December and followed up with writing workshops at the ECR meeting to assist in addressing reviewer’s comments and further developing the manuscripts.

If you have any questions or would like to discuss a submission please contact the Guest Editors of this special Issue Dr. Craig R. Sloss (c.sloss@qut.edu.au<mailto:c.sloss@qut.edu.au>) or Dr. Lynda Petherick (lynda.petherick@qut.edu.au<mailto:lynda.petherick@qut.edu.au>)

Please note: You do not have be attending the meeting to submit to the special issue.