| 1. |
- Gallego-Sala, Angela V., et al.
(author)
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Latitudinal limits to the predicted increase of the peatland carbon sink with warming
- 2018
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
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Journal article (peer-reviewed)abstract
- The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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| 2. |
- Loisel, Julie, et al.
(author)
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A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation
- 2014
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 24:9, s. 1028-1042
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Journal article (peer-reviewed)abstract
- Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45 degrees N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 +/- 3% (standard deviation) for Sphagnum peat, 51 +/- 2% for non-Sphagnum peat, and at 49 +/- 2% overall. Dry bulk density averaged 0.12 +/- 0.07 g/cm(3), organic matter bulk density averaged 0.11 +/- 0.05 g/cm(3), and total carbon content in peat averaged 47 +/- 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 +/- 2 (standard error of mean) g C/m(2)/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25-28 g C/m(2)/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.
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| 3. |
- Auer, Gerald, et al.
(author)
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Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts
- 2019
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In: Paleoceanography and Paleoclimatology. - : AMER GEOPHYSICAL UNION. - 2572-4517 .- 2572-4525. ; 34:4, s. 635-657
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Journal article (peer-reviewed)abstract
- The Pliocene was characterized by a gradual shift of global climate toward cooler and drier conditions. This shift fundamentally reorganized Earth's climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high-resolution sediment geochemistry, calcareous nannofossil, and X-ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue-based interpretations of nannofossil assemblages indicate that ITF configuration culminated similar to 3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (similar to 3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul-Indian Ocean Bjerknes mechanism and increased the response to glacio-eustatic variability.
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| 4. |
- Christensen, Beth A., et al.
(author)
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Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene
- 2017
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:13, s. 6914-6925
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Journal article (peer-reviewed)abstract
- Late Miocene to mid-Pleistocene sedimentary proxy records reveal that northwest Australia underwent an abrupt transition from dry to humid climate conditions at 5.5 million years (Ma), likely receiving year-round rainfall, but after similar to 3.3 Ma, climate shifted toward an increasingly seasonal precipitation regime. The progressive constriction of the Indonesian Throughflow likely decreased continental humidity and transferred control of northwest Australian climate from the Pacific to the Indian Ocean, leading to drier conditions punctuated by monsoonal precipitation. The northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by similar to 2.4 Ma, well after the intensification of Northern Hemisphere glaciation. The transition from humid to arid conditions was driven by changes in Pacific and Indian Ocean circulation and regional atmospheric moisture transport, influenced by the emerging Maritime Continent. We conclude that the Maritime Continent is the switchboard modulating teleconnections between tropical and high-latitude climate systems. Plain Language Summary Australia is themost arid habitable continent on earth, however its climate is capable of dramatic changewith seasonalmonsoon rains in the otherwise arid northwest. We analyzed natural gamma radiation in a recently drilled borehole (IODP Expedition 356 Site U1463) off NW Australia to examine long-term climate changes over the last 6 million years. Based on variations in potassium, thorium and uranium, as well as common clay minerals, we show that the NW continent was more humid during the Pliocene period, between similar to 5.5 and 3.3 million years ago (Humid Interval), and became arid by the early Pleistocene, similar to 2.4 million years ago (Arid Interval). We attribute the Humid Interval to an expansion of warm surface waters in the western Pacific, supplying warm and moist air to the continent. As Australia moved north, the Maritime Continent (islands to the north) emerged, restricting the flow of warm surface currents from the Pacific (Indonesian Throughflow), resulting in drier conditions on land. The Arid Interval ushered in amodern-like Australian climate, with seasonal rainfall and dust storms, and a more modern Indian Ocean circulation. Our results show that the Maritime Continent is an important control on both Australian climate and Indian Ocean circulation.
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| 5. |
- Christensen, Beth A., et al.
(author)
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Late Miocene Onset of Tasman Leakage and Southern Hemisphere Supergyre Ushers in Near-Modern Circulation
- 2021
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:18
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Journal article (peer-reviewed)abstract
- This study provides a Miocene-to-recent history of Tasman Leakage (TL), driving surface-to-intermediate waters from the Pacific into the Indian Ocean. TL, in addition to Indonesian ThroughFlow (ITF), constitutes an important part of the Southern Hemisphere Supergyre. Here, we employ deep-sea benthic delta C-13 timeseries from the southwestern Pacific and eastern Indian Oceans to identify the history of Tasman Leakage. The delta C-13 results combined with sedimentary evidence show that an inter-ocean connection south of Australia existed from 7 Ma onward. A southward shift in Westerlies combined with a northward movement of Australia created the oceanic corridor necessary for Tasman Leakage (between Australia and the sub-Antarctic Front) at this time. Furthermore, changes in the northern limb of the Supergyre (ITF) are evident in the sedimentary record on Broken Ridge from similar to 3 to 2 Ma when Banda Sea intermediate waters started originating from the North Pacific.
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| 6. |
- De Vleeschouwer, David, et al.
(author)
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The amplifying effect of Indonesian Throughflow heat transport on Late Pliocene Southern Hemisphere climate cooling
- 2018
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In: Earth and Planetary Science Letters. - : ELSEVIER SCIENCE BV. - 0012-821X .- 1385-013X. ; 500, s. 15-27
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Journal article (peer-reviewed)abstract
- An unusually short glaciation interrupted the warm Pliocene around 3.3 Ma (Marine Isotope Stage (MIS) M2). Different hypotheses exist to explain why this glaciation event was so pronounced, and why the global climate system returned to warm Pliocene conditions relatively quickly afterwards. One of these proposed mechanisms is a reduced equator-to-pole heat transfer, in response to a tectonically reduced Indonesian Throughflow (ITF). The ITF is a critical part of the global thermohaline ocean circulation, transporting heat from the Indo-Pacific Warm Pool to the Indian Ocean. When ITF connectivity is reduced, the water and heat supply for the Leeuwin Current, flowing poleward along Australia's west coast, is also diminished. To assess the possible relationship between mid-Pliocene glaciations and latitudinal heat transport through the Indonesian Throughflow, we constructed a multi-proxy orbital scale record for the 3.7-2.8 Ma interval from International Ocean Discovery Program (IODP) Site U1463, off northwest Australia. The comparison of the Site U1463 record with paleoclimate records from nearby Site 763 and West Pacific Warm Pool Site 806 allows for a detailed regional reconstruction of Pliocene paleoceanography and thus for testing the proposed hypothesis. An astronomically-paced decrease in potassium content characterizes the late Pliocene interval of U1463. This record documents the increasing aridity of northwest Australia, periodically alleviated by reinforced summer monsoon precipitation under summer insolation maxima. The 3180 record of the planktonic foraminifer Globigerinoides sacculifer correlates exceptionally well with the sea surface temperature (SST) record from Site 806 in the West Pacific Warm Pool, even during MIS M2. Hence, Site U1463 preserves an uninterrupted ITF signal even during Pliocene glaciations. However, the U1463 delta O-18(G.sacculifer) record exhibits a 0.5 parts per thousand offset with the nearby Site 763A record around MIS M2. This implies that Site 763A, about 500 km west of U1463, more closely tracks Indian Ocean SST records across MIS M2. The U1463 data reveal that heat-transport through the Indonesian Throughflow did not shut down completely during MIS M2, but rather its intensity decreased prior to and during MIS M2, causing Site 763A to temporarily reflect an Indian Ocean, rather than an ITF signal. We conclude that ITF variability significantly influenced latitudinal heat transport by means of the Leeuwin Current and hence contributed to the relative intensity of MIS M2. We propose the ITF valve between the Pacific and Indian Ocean as a positive feedback mechanism, in which an initial sea level lowering reduces ITF heat transport, in turn amplifying global cooling by advancing the thermal isolation of Antarctica.
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| 7. |
- Groeneveld, Jeroen, et al.
(author)
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Australian shelf sediments reveal shifts in Miocene Southern Hemisphere westerlies
- 2017
-
In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 3:5
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Journal article (peer-reviewed)abstract
- Global climate underwent a major reorganization when the Antarctic ice sheet expanded ~14 million years ago (Ma) (1). This event affected global atmospheric circulation, including the strength and position of the westerlies and the Intertropical Convergence Zone (ITCZ), and, therefore, precipitation patterns (2–5). We present new shallow-marine sediment records from the continental shelf of Australia (International Ocean Discovery Program Sites U1459 and U1464) providing the first empirical evidence linking high-latitude cooling around Antarctica to climate change in the (sub)tropics during the Miocene. We show that Western Australia was arid during most of the Middle Miocene. Southwest Australia became wetter during the Late Miocene, creating a climate gradient with the arid interior, whereas northwest Australia remained arid throughout. Precipitation and river runoff in southwest Australia gradually increased from 12 to 8 Ma, which we relate to a northward migration or intensification of the westerlies possibly due to increased sea ice in the Southern Ocean (5). Abrupt aridification indicates that the westerlies shifted back to a position south of Australia after 8 Ma. Our midlatitude Southern Hemisphere data are consistent with the inference that expansion of sea ice around Antarctica resulted in a northward movement of the westerlies. In turn, this may have pushed tropical atmospheric circulation and the ITCZ northward, shifting the main precipitation belt over large parts of Southeast Asia (4).
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| 8. |
- Karatsolis, Boris-Theofanis
(author)
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Late Miocene to Pliocene orbital and climatic forcing on marine productivity
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- The late Miocene to Pliocene was a geological time interval of global cooling, albeit in a warmer-than-present world, which is commonly used as a past analogue for future anthropogenic climate change. The investigation of marine sediments recovered by the International Ocean Discovery Program (IODP) sheds light on different paleoclimatic, paleoceanographic and paleobiological characteristics of this period. The NW Australian shelf represents an interesting area for such investigation, because it is strategically positioned near the only remaining equatorial warm-water valve on Earth. In Chapter I and Chapter II, focus is given on calcareous nannofossil time-series data and records of the element potassium (K), which is mainly delivered by rivers to the shelf, at IODP Sites U1463 and U1464. Results demonstrate that humid conditions were probably prevailing earlier than previously thought (at least since ~6 Ma), but that regional tectonics (basin subsidence) has complicated the identification of the exact onset. In addition, nannofossil assemblages data and paleotemperature gradients between the shelfal area and the eastern Indian Ocean reveal a shift in oceanographic and climatic regime that occurred between 5.4-5.2 Ma, as a likely result of an overall long-term increase in seasonality. Finally, an interval of decreasing nannofossil accumulation rates (fluxes) and a distinct change in the dominant nannoplankton species occurred between 4.6-4.4 Ma and is hypothesized to be part of broader changes in ocean nutrient availability. This hypothesis is further explored in Chapter III and Chapter IV through the investigation of a well-established period of globally elevated biogenic sedimentation (and related marine export productivity) known as the late Miocene to early Pliocene biogenic bloom. In Chapter III, age model accuracy and sample resolution of previously published biogenic sediment accumulation rate records are evaluated. The compilation of multiple records shows that an abrupt reduction in ocean paleoproductivity occurred between 4.6-4.4 Ma at (sub)tropical latitudes. This event coincided with a rather unique configuration of the Earth’s orbit, which could have led to a weakened Asian monsoon activity and therefore reduced river runoff and nutrient supply to the ocean. Chapter IV focuses on the comparison between the calcareous nannofossil assemblages at the NW Australian shelf sites and ODP Site 1264 in the South Atlantic Ocean, across the termination of the biogenic bloom. Although the overall decrease in paleoproductivity occurred around the same time, the shift in species dominance across the end of the biogenic bloom, as shown in the tropical Indian Ocean, is not observed at ODP Site 1264.
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| 9. |
- Karatsolis, Boris-Theofanis, 1992-, et al.
(author)
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Ocean productivity response to orbital forcing during the early Pliocene
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Other publication (other academic/artistic)abstract
- The early Pliocene was a warm period with increased ocean primary productivity, as part of a global paleoceanographic event called the late Miocene-early Pliocene biogenic bloom (~9-3.5 Ma). Many tectonic and paleoclimatic mechanisms, mainly linked to an increase and redistribution of nutrient supply in the ocean, have been proposed as driving forces for this event. However, the main phase of increased productivity and the termination of this event appear to be diachronous in different ocean basins. Here, we compiled proxy data for early Pliocene paleoproductivity from all major ocean basins, including both calcareous and siliceous plankton groups. After re-evaluating the age model resolution of the available paleo-records, we demonstrate that a main stage of decrease in primary productivity occurred during ~4.6-4.4 Ma. We then show that this productivity collapse coincided with an orbital configuration of long-term reduction in eccentricity amplitude and low amplitude obliquity. This combination of orbital parameters could have significantly affected seasonality and nutrient availability in the global ocean and suggests a previously undescribed paleoclimatic forcing that may have been a crucial step in contributing to the end of the biogenic bloom.
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| 10. |
- Karatsolis, Boris-Theofanis, et al.
(author)
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The late Miocene to early Pliocene “Humid Interval” on the NW Australian shelf : disentangling climate forcing from regional basin evolution
- 2020
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In: Paleoceanography and Paleoclimatology. - : American Geophysical Union. - 2572-4517 .- 2572-4525. ; 35:9
-
Journal article (peer-reviewed)abstract
- Pre-Quaternary paleoclimate studies in Australia mainly focus on terrestrial records from the southeastern part of the continent. IODP Expedition 356 drilled on the northwestern Australian shelf, yielding Miocene-Pleistocene paleoclimate records in an area where climate archives are scarce. Postexpedition research revealed a dry-to-humid transition across the latest Miocene and early Pliocene (start of the "Humid Interval"). However, the complex tectonic history of the area makes these interpretations challenging. In this study, we investigate late Miocene to early Pliocene sediment cores from two sites that are only 100 km apart but situated in two adjacent basins (Northern Carnarvon and Roebuck Basins). Combining lithofacies study, time series analysis of potassium content (K wt%), and calcareous nannofossil abundance counts (N/g), this work disentangles the complex interplay between basin evolution and climate change between 6.1 and 4 Ma. Overall, the investigated proxies show high correlation between both sites, except during 6.1-5.7 Ma. During this interval, Site U1463 records a gradual increase in K wt%, correlated with basin deepening, whereas Site U1464 records an abrupt rise in K wt% at similar to 6 Ma. We explain this diachronicity by differential basin subsidence. The tectonic interplay with our paleorecords makes it difficult to pinpoint the exact onset of the "Humid Interval," but we conclude that K wt% and coccolith abundances at Site U1464 indicate that a fluvial deposition system was already established since at least 6 Ma. This age is consistent with data supporting a southward movement of the Intertropical Convergence Zone rain belt at similar to 7 Ma.
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| 11. |
- Narkiewicz, Marek, et al.
(author)
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Palaeoenvironments of the Eifelian dolomites with earliest tetrapod trackways (Holy Cross Mountains, Poland)
- 2015
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In: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 420, s. 173-192
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Journal article (peer-reviewed)abstract
- The Eifelian dolomites in the Zachelmie Quarry (Holy Cross Mountains, Poland) contain tracicways and tracks of tetrapods 390-391 Ma old, and thus the oldest known so far. The environments of the trackway-bearing beds have been investigated using sedimentological, palaeontological, geochemical and palaeomagnetic methods. The reconstructed tetrapod habitats comprised shallow-water lagoons separated from an open marine basin by sparsely vegetated islands and spits. The lagoonal waters were well-aerated and a few metres deep at most, undergoing periodic desiccation. The dolomitic sediments, primarily of microbial origin, formed in tropical waters of slightly modified marine composition. Oxygen isotope data obtained from the dolomicrites suggest water temperatures around 30 degrees C. The seasonal semi-arid to sub-humid climate, deduced from paleosol characteristics, was probably of a tropical monsoonal type. The degree of restriction of the lagoonal system evolved from relatively open, evaporation-dominated towards increasingly closed, freshwater influenced. The detailed observations of the footprint-bearing beds, as well as the characteristics of the tracks, indicate that they were formed mostly under subaqueous conditions, by wading, walking on the bottom or swimming animals. Lack of tidal indicators in the restricted Zachelmie lagoons argues against previous concept that tidal flats served as a food source for the early tetrapods. Nor is a hypothesis of flooded woodlands confirmed as a habitat promoting the "fish-to-tetrapod" transition. We propose that functional limbs emerged among aqueous animals that acquired their locomotional capabilities in a shallow lagoonal water before attempting longer excursions on land.
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| 12. |
- Smith, Rebecca A., et al.
(author)
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Plio-Pleistocene Indonesian Throughflow Variability Drove Eastern Indian Ocean Sea Surface Temperatures
- 2020
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In: PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY. - : American Geophysical Union (AGU). - 2572-4517 .- 2572-4525. ; 35:10
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Journal article (peer-reviewed)abstract
- Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio-Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX86 and the long-chain diol index, provide insight into past ITF variability (3.5-1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of similar to 5 degrees C occurs within the mid-Pliocene Warm Period (3.3-3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and long-chain diol index records is a strong cooling from similar to 1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.
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