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 ~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 ~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.

Sediments from Western Australia show how westerly winds made the southwest wetter during the Miocene (18 to 6 million years ago).

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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 ~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 (~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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14We investigate the impact of superstorm Sandy on the lower shoreface and inner shelf 15 offshore the barrier island system of Fire Island, NY using before-and-after surveys involving 16 swath bathymetry, backscatter and CHIRP acoustic reflection data. As sea level rises over the 17 long term, the shoreface and inner shelf are eroded as barrier islands migrate landward; large 18 storms like Sandy are thought to be a primary driver of this largely evolutionary process. The 19 "before" data were collected in 2011 by the U.S. Geological Survey as part of a long-term 20 investigation of the Fire Island barrier system. The "after" data were collected in January, 2013, 21 ~two months after the storm. Surprisingly, no widespread erosional event was observed. Rather, 22 the primary impact of Sandy on the shoreface and inner shelf was to force migration of major 23 bedforms (sand ridges and sorted bedforms) 10's of meters WSW alongshore, decreasing in 24 migration distance with increasing water depth. Although greater in rate, this migratory behavior 25 is no different than observations made over the 15-year span prior to the 2011 survey. 26Stratigraphic observations of buried, offshore-thinning fluvial channels indicate that long-term 27 erosion of older sediments is focused in water depths ranging from the base of the shoreface 28 (~13-16 m) to ~21 m on the inner shelf, which is coincident with the range of depth over which 29 sand ridges and sorted bedforms migrated in response to Sandy. We hypothesize that bedform 30 migration regulates erosion over these water depths and controls the formation of a widely 31 observed transgressive ravinement; focusing erosion of older material occurs at the base of the 32 stoss (upcurrent) flank of the bedforms. Secondary storm impacts include the formation of 33 ephemeral hummocky bedforms and the deposition of a mud event layer. the New York City metropolitan area was heavily damaged, and the Long Island barrier island 46 system was both breached in places and seriously eroded . 47The impacts of this storm on the shoreface and inner shelf, which are permanently 48 submerged and therefore primarily accessible only through acoustic mapping, are harder to 49 observe. However, although the shoreface and inner shelf are neither populated nor veneered 50 with human infrastructure, they are nevertheless critical to both people and their structures, 51 because they are the first line of defense of barrier island systems against a naturally retreating, 52or "transgressing," coastline. Under rising sea level conditions, the natural condition today along 53 most of the U.S. east coast, barrier islands will back-step (retreat landward) by erosion on the 54 seaward side and deposition on the landward side (Bruun, 1962;Swift and Thorne, 1991; Thorne 55 and Swift, 1991). Large storms, with consequent high waves, strong currents and above-normal 56 tidal ranges/surges, are thought to be primary drivers of such shoreface erosion (Swift, 1968; 57 Swift and Thorne, 1991). Such storms...

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 TEX 86 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 TEX 86 cooling of~5°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 TEX 86 and long-chain diol index records is a strong cooling from~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. Plain Language Summary The Indonesian Throughflow (ITF) represents warm water masses flowing from the western Pacific into the Indian Ocean. The ITF flows through the narrow marine passages of the Indonesian Archipelago. This Indonesian Gateway in turn limits the amount of water moving from the Pacific into the Indian Ocean. The depth and width of the Indonesian Gateway has decreased gradually over the past 5 million years due to tectonic movement, which has caused Indonesian islands such as New Guinea and Halmahera to grow and block water entering the Indonesian Archipelago from the warm South Pacific. As a result, most ITF water now derives from the cooler North Pacific, which impacts Indian Ocean temperatures and broader global ocean circulation and heat distribution. The timing of this shallowing of the Indonesian Gateway and transition from warmer South Pacific to cooler North Pacific ITF source waters is not yet fully understood. Here, we present a new sea surface temperature record from near the ITF outlet that shows intense cooling just after 1.7 million years ago. We suggest that this cooling occurred in response to a significant step in the ongoing tectonic constriction and shallowing of the Indonesian Gateway.