Tree pollen reveals 150,000 years of monsoon history in Northern Australia – News
Droughts in Southeast Asia and increasingly devastating floods in Northern Australia are not random anomalies—they are predictable consequences of climate change, as revealed by a 150,000-year record of monsoon patterns preserved in tree pollen from sediment in Girraween Lagoon near Darwin. This record, meticulously analysed and correlated with evidence of past climate change and ocean currents, offers a stark warning about what lies ahead.
Not only does this research thoroughly dismantle the juvenile creationist fantasy that Earth is a mere 6,000 to 10,000 years old, it also flatly contradicts the myth of a global flood just a few thousand years ago—such a cataclysm would have obliterated the very sediment that preserved this climate history. Moreover, it challenges the simplistic notion that Earth was "finely tuned" for life, since the data show a planet subject to instability and extreme hardship, at times rendering regions locally uninhabitable due to global climatic shifts.
The study, conducted by researchers at James Cook University and Flinders University, demonstrates that shifts in Northern Australia's monsoon patterns coincide with Heinrich events—sudden surges of cold meltwater into the North Atlantic that weaken the Gulf Stream. As the Gulf Stream drives much of Western Europe’s climate by transporting warm water across the Atlantic, its disruption would have profound consequences for Europe as well.
Can you tell me more about these Heinrich events, please.
Heinrich events are dramatic climatic episodes that occurred during the last glacial period, named after marine geologist Hartmut Heinrich who first identified them in the 1980s. These events represent sudden and massive discharges of icebergs into the North Atlantic Ocean, originating primarily from the Laurentide Ice Sheet in North America.
Key Features of Heinrich Events:
- Ice-Rafted Debris (IRD):
Heinrich events are identified by layers of sediment in North Atlantic marine cores that contain ice-rafted debris—fragments of rock and other materials carried by icebergs and dropped onto the seafloor as the ice melted.
- Abrupt Cooling:
The influx of cold, fresh meltwater into the North Atlantic during a Heinrich event disrupted thermohaline circulation (the so-called Atlantic Meridional Overturning Circulation, or AMOC), particularly the Gulf Stream. This led to abrupt regional cooling, especially in Europe and North America.
- Duration and Frequency:
These events occurred roughly every 7,000–10,000 years during the last glacial cycle (~70,000 to 10,000 years ago), though the exact timing and spacing varied. Each event may have lasted for several hundred to a few thousand years.
- Global Impact:
Although triggered by North Atlantic dynamics, Heinrich events had global repercussions. Evidence shows climate responses as far afield as the Indian monsoon, tropical Africa, and South America, where rainfall patterns shifted dramatically. The study you linked to adds Northern Australia to that list, showing that these events influenced monsoons far from their origin.
- Mechanism:
The most widely accepted model suggests that internal ice-sheet instability or subglacial processes triggered massive iceberg calving events. These icebergs melted in the North Atlantic, introducing vast amounts of fresh water and lowering ocean salinity. This in turn weakened or shut down deep-water formation, a key component of the global climate system.
Summary:
Heinrich events are natural examples of abrupt climate change—rapid and severe disruptions to the climate system caused by shifts in ocean circulation. They provide a powerful lesson for today: large-scale climatic systems can change quickly and globally in response to disturbances, especially involving the ocean’s role in heat and moisture distribution.
The team's findings are now
published in Quaternary Science Reviews, and are also explained in lay terms in a
Flinders University blog post.
Tree pollen reveals 150,000 years of monsoon history in Northern Australia
Northern Australia’s annual monsoon season brings relief to drought-stricken lands and revitalises crops and livestock for farmers. But a study of 150,000 years of climate records shows that the monsoon is likely to intensify, triggering a higher risk of flooding while worsening the impact of droughts in East Asia.
Led by Professor Michael Bird, researchers at James Cook University and Flinders University have assessed sediments at Girraween Lagoon near Darwin, revealing a continuous record of monsoon rainfall patterns dating back beyond the last interglacial period.
This research published in the scientific journal Quaternary Science Reviews offers insight into how climate change could alter monsoon patterns across East Asia and Australia.
This is the longest terrestrial record ever produced at the southern end of the Indo-Australian monsoon system, which delivers vital rainfall to millions across the Southern Hemisphere. The record also has implications for the Northern Hemisphere where tens of millions in Asia rely on monsoons for food and their livelihoods.
Our study shows how the two monsoon systems are interrelated over thousands of years and reveals what causes them to change. Our analyses shows that that rainfall in northern Australia is closely tied to sea level changes, which shift the location of the northern coastline by up to 320 km.
These shifts strongly alter local rainfall, with wetter periods occurring when the coastline is closer to the Australian landmass and the oppose effect is prolonged drought in East Asia.
Intriguingly, the research also uncovered what we consider bursts of intense monsoon activity — some lasting less than 10,000 years. These bursts align with Heinrich events — abrupt pulses of freshwater into the North Atlantic from rapidly melting ice linked to the weakening of the Gulf Stream in the Atlantic Ocean.
Professor Michael I. Bird, first author
College of Science and Engineering
James Cook University
Cairns, Queensland, Australia.
These findings carry a warning from scientists because the Gulf Stream is already weakening due to climate change, and the study suggests this could lead to increased rainfall in northern Australia while contributing to droughts in parts of East Asia.
This isn’t just ancient history. It is a window into the rainfall patterns that are emerging today. Our data suggest that the weather trends we’re witnessing like the drying in China and wetting in northern Australia could accelerate if the Gulf Stream continues to weaken, so we need to be ready for that scenario.
It’s not surprising. Decreasing rainfall in parts of the east Asian summer monsoon region has been identified in rainfall records since the 1960s, while increasing rainfall has been evident in north-western Australia since the last century, accelerating since the 1950s. Our new data suggest that further weakening of the Gulf Stream could reinforce these trends even more in the future, with consequences for both regions.
We need to put this impact into context because this region extends from China through Southeast Asia, the maritime continent, and western Indo-Pacific warm pool on the Equator, to Australia. The region is home to almost a billion people and five terrestrial Biodiversity Hotspots.
Professor Corey J. A. Bradshaw, co-author.
Global Ecology | Partuyarta Ngadluku Wardli Kuu
College of Science and Engineering
Flinders University,
Adelaide, South Australia, Australia.
Publication:
Bird, Michael I.; Brand, Michael; Comley, Rainy; Hadeen, Xennephone; Jacobs, Zenobia; Rowe, Cassandra; Saltré, Frédérik; Wurster, Christopher M.; Zwart, Costijn; Bradshaw, Corey J.A.
Quaternary Science Reviews (2025) 366 109504. DOI: 10.1016/j.quascirev.2025.109504
Highlights
- 150 kyr n-alkane δ2H and pollen record of monsoon strength from northern Australia.
- Coastline position strongly influenced local hydroclimate.
- Monsoon intensity broadly anti-phased with East Asian Summer Monsoon.
- Short (∼2–10 kyr) periods of dramatically increased monsoon intensity also occur.
- Short periods of increased monsoon intensity align with Heinrich events.
Abstract
Nearly two thirds of the world's population depend on monsoon rainfall, with monsoon failure and extreme precipitation affecting societies for millennia. Monsoon hydroclimate is predicted to change as the climate warms, albeit with uncertain regional trajectories. Multiple glacial-interglacial terrestrial records of east Asian monsoon variability exist, but there are no terrestrial records of equivalent length from the coupled Indo-Australian monsoon at its southern limit — Australia. We present a continuous 150,000-year lacustrine record of monsoon dynamics from the core monsoon region of northern Australia based on the proportion of dryland tree pollen in the total dryland pollen spectra and the hydrogen isotope composition of long chain n-alkanes. We show that rainfall at the site depends strongly on sea level, which changes proximity of the coast to the site by 320 km over the last glacial-interglacial cycle. Long-term trends in rainfall are broadly anti-phased with the east Asian monsoon modulated by coastal proximity. The record also contains multiple, short intervals (∼2 to < 10,000 years) of large changes in tree cover (from 5 to 95 % tree pollen over 3000 years in one instance). Changes in tree cover are frequently but not always, accompanied by synchronous large changes in the other hydroclimate proxies. While these wetter periods cannot be easily ascribed to orbitally induced changes in insolation or coastal proximity, they are correlated with most Heinrich events. This relationship implies that strong asymmetry in inter-hemispheric monsoon rainfall might be one outcome of the current weakening in the strength of the Atlantic meridional overturning circulation, through a reduction in oceanic heat transfer from the Southern to the Northern Hemisphere.
1. Introduction
The dominant feature of climate across most of the tropics and subtropics is a seasonal reversal of the prevailing winds across the Equator, resulting in a wetter summer season and a drier winter in each hemisphere. At an annual scale, the ‘global monsoon’, approximated hydrologically by the zone of maximum rainfall associated with the intertropical convergence zone, oscillates between the Northern and Southern Hemispheres (An et al., 2015; Wang et al., 2017). This oscillation is driven by the annual cycle of maximum insolation between each hemisphere (Deininger et al., 2020), leading to anti-phased summer rainy seasons in each (Eroglu et al., 2016; Deininger et al., 2020). Agriculture and ecosystems across the tropics and subtropics depend on monsoon rainfall (An et al., 2015), and so growing populations and climate change increase vulnerability to any change in monsoon dynamics (Zhang et al., 2018; Martinez-Villalobos and Neelin, 2023). Indeed, drought associated with monsoon failure, as well as monsoon-related flooding, have driven major demographic changes in prehistory (e.g., Cook et al., 2010) and the recent past (Li et al., 2011; Qian et al., 2012; Wang et al., 2015.1).
The monsoon system that affects the largest land area and human population is the east Asian summer monsoon north of the Equator, coupled by cross-equatorial airflow to the Indo-Australian summer monsoon south of the Equator (Li and Li, 2014) (Fig. 1). This region extends from China through Southeast Asia, the maritime continent and western Indo-Pacific warm pool on the Equator, to Australia. The region is home to almost a billion people and five terrestrial biodiversity hotspots (Myers et al., 2000).
Fig. 1. Location of Girraween Lagoon in monsoonal north Australia. Also shown are the Sunda and Sahul continental shelves, with areas landward exposed at times of lower sea level, and the major pathways for water and heat transport between the Pacific and Indian Oceans via the Indonesian throughflow. Approximate boundaries of the true and ‘pseudo’ monsoon domains and directions of wet season airflow are in yellow (Suppiah,
1992). Insert shows the approximate dominant flows of the east Asian summer monsoon (EASM) and the Indo-Australian summer monsoon (IASM). Additional locations mentioned in the text are: 1 and 2: speleothem stable isotope records from KNI-51 and Ballgown Cave, respectively (Denniston et al.,
2017.1); 3: marine core geochemical record of runoff and dust flux (Zhang et al.,
2020.1; Pei et al.,
2021; Sarim et al.,
2023.1); 4: speleothem isotope record from Flores (Scroxton et al.,
2022); 5 and 6: Woods and Gregory ‘megalakes’, respectively (Bowler et al.,
1998,
2001; Fitzsimmons et al.,
2012.1). Base image data: Google © 2023 Maxar Technologies. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
The Indo-Australian summer monsoon represents the dominant source of rainfall in northern Australia, although atmospheric teleconnections to other sources of global interannual climate variability, particularly El Niño-Southern Oscillation, contribute to rainfall variability (Sharmila and Hendon, 2020.2; Heidemann et al., 2023.2; Gallagher et al., 2024). The Indo-Australian summer monsoon in northern Australia also exhibits its own internal dynamics, due in approximately equal measure to local oceanic (sea surface temperature, evaporation, and wind) and terrestrial (land cover, soil moisture, evaporation, and wind) influences on rainfall (Yu and Notaro, 2020.3; Sekizawa et al., 2021.1; Heidemann et al., 2023.2; Sekizawa et al., 2023.3). While the east Asian summer monsoon is dominant due to the large, high-altitude Asian landmass, the internal dynamics of the Indo-Australian summer monsoon can also drive variability in east Asian winter monsoon rainfall in southern China, suggesting close linkages (Yu and Notaro, 2020.3; Sekizawa et al., 2021.1; Heidemann et al., 2023.2; Sekizawa et al., 2023.3).
Terrestrial speleothem oxygen isotope and pollen records (e.g., Ma et al., 2023.4; Chen et al., 2023.5) spanning one or more glacial-interglacial cycles have demonstrated periods of enhanced/(reduced) east Asian summer monsoon rainfall at times of higher/(lower) Northern Hemisphere insolation and distinct, weak monsoon intervals, some of which are coincident with Heinrich events (Cheng et al., 2009, 2016.1). However, equivalent long terrestrial records from the southern end of the Indo-Australian summer monsoon in northern Australia are conspicuously absent.
Proxy records of terrestrial runoff have been derived from marine records off north-western Australia and are correlated with east Asian summer monsoon records (Pei et al., 2021; Zhang et al., 2020.1; Sarim et al., 2023.1) (Fig. 1). However, those records are potentially confounded by the adjacent wide continental shelf that introduces an effect of sea-level change at orbital timescales on the delivery of runoff-derived sediment to the core locations. The locations are also likely affected by the large changes in land-sea distribution in the maritime continent that modify heat and mass transfer through the Indonesian throughflow upstream of the core sites (Lee et al., 2019). On land, a discontinuous speleothem time series of oxygen isotope has been generated covering the last 40 kyr (1 kyr = 1000 years) from northern Western Australia (Denniston et al., 2017.1), a location that is under the influence of the ‘pseudo’ monsoon (Suppiah, 1992; Gallagher et al., 2024) where airflow originates in the eastern Indian Ocean, rather than from equatorial regions to the north (Fig. 1).
In the arid interior of Australia, sediments from the former Woods and Gregory ‘megalakes’ (now small, ephemeral bodies of water) show that large perennial water bodies existed, dominantly during periods in Marine Isotope Stage (MIS) 3 around ∼ 50 ka ago, MIS 5 around 100 ka ago, as well as earlier (Bowler et al., 1998, 2001; Veth et al., 2009.1; Fitzsimmons et al., 2012.1). These megalakes were fed by monsoon rain falling into south-draining catchments, with drainage divides at least 300 km south of the modern north Australian coast (Fig. 1). Kati Thandi-Lake Eyre in central Southern Australia receives water from the core monsoon area (and other regions), but it also contains a record of megalake periods through MIS 5 to ∼ 116 ka ago and from 65 to 45 ka ago (Cohen et al., 2022.1).
The existence of interior megalakes, orders of magnitude larger than today's, implies past periods of higher monsoon rainfall penetrating these arid interior catchments (Wyrwoll and Valdes, 2003). Debate on the drivers of megalake-filling events has centred on the relative importance of sea level, sea surface temperatures, and Northern Hemisphere ‘push’ versus Southern Hemisphere ‘pull’ of monsoonal rain into the continental interior, as well as the role of vegetation feedbacks in augmenting moisture transfer inland (Wyrwoll and Valdes, 2003; Liu et al., 2004; Miller et al., 2005; Pitman and Hesse, 2007; Marshall and Lynch, 2008; Wyrwoll et al., 2007.1, 2012.2).
Here we present multiple, absolute-dated proxy records of sedimentological, hydroclimatic, and vegetation change over the last 150 kyr from a sediment core obtained from the core monsoon region of northern Australia, the Girraween Lagoon (Fig. 1). This record enables an assessment of the timing of variation in monsoon strength in the Indo-Australian summer monsoon domain that can be compared with records of east Asian summer monsoon strength and tropical hydroclimate. Together, this enables an assessment of the drivers of variability in the Indo-Australian summer monsoon.
The detailed sedimentary record from the Girraween Lagoon in Northern Australia, which includes evidence of Heinrich events spanning the last 150,000 years, presents a serious challenge to young Earth creationist claims. These events, triggered by massive iceberg discharges into the North Atlantic and linked to widespread climatic shifts—including monsoon disruptions in Australia—can be correlated across multiple geological archives worldwide. This implies a stable, continuous, and datable sequence of climatic change that extends far beyond the 6,000 to 10,000 years typically allowed by biblical literalists.
Creationist claims of a recent, global, catastrophic flood—often tied to the story of Noah—are also incompatible with this evidence. A flood of such scale would have scoured landscapes, disrupted or homogenised sedimentary layers, and left a very different geological signal. Instead, the sediments in Girraween Lagoon preserve a finely layered and uninterrupted record of environmental conditions, including pollen and isotopic data, spanning well over 100,000 years. Such a record simply could not survive the violent upheaval proposed by a recent global deluge.
Furthermore, the evidence of repeated, severe climatic disruptions also undermines the notion that Earth was perfectly created and "finely tuned" for life. The Heinrich events were episodes of extreme instability, during which entire regions became uninhabitable or suffered ecological collapse. This shows Earth’s climate system as dynamic and often harsh—not the static, life-friendly world one might expect from an intelligent designer. In short, the geological and climatological evidence paints a picture of an ancient, evolving Earth shaped by natural processes—one that flatly contradicts creationist dogma.
