Novel plastic-derived materials such as plastiglomerates, pyroplastics, and plastitar have emerged as persistent pollutants in coastal environments, yet their chemical compositions remain inadequately characterized. This study presents a comparative chemical analysis of plastitar and pyroplastic collected from Panjang Island (Java Sea, Indonesia) and Palm Beach (Florida, USA), regions influenced by nearby and/or downstream oil production, refining, natural seeps, and maritime activity. Polymers were identified by infrared spectroscopy as polyethylene, polystyrene, or polyurethane derived from thermally affected plastic debris or embedded in tar matrices. Gas chromatography with flame ionization detection (GC-FID) analysis of Panjang Island samples, supplemented by comprehensive two-dimensional GC × GC-FID for selected specimens, revealed that the oil residue in the plastitar samples is dominated by n-alkanes (n-C16 to n-C37) and contains isoprenoids (pristane and phytane). Meanwhile, the plastic part of the pyroplastic and plasticrust samples without oil residues exhibited irregular, unresolved chromatographic patterns. The plastitar and pyroplastic samples from Panjang Island exhibited exceptionally high concentrations of total PAHs (2399 ± 190 ng g-1 to 247,951 ± 17,176 ng g-1) and total phthalates (1257 ± 24 ng g-1 to 3169 ± 527 ng g-1), with one sample yielding the highest concentration of ΣPAHs ever reported in marine plastic debris. The dominance of high-molecular-weight PAHs and phthalates highlights the dual role of plastitar and pyroplastic as both physical carriers and sources of chemical pollutants. This study contributes to the growing recognition of plastitar and novel thermally altered plastic debris as distinct and hazardous form of marine plastic pollution.

During the Miocene, sea surface temperature (SSTs) and CO 2 exceeded modern levels. Given the current decline of coral reefs due to rising summer temperatures, it is unclear how extensive reef systems developed and thrived in a warm Miocene world. This problem is exacerbated by a lack of SST reconstructions. Here, we use TEX 86 H to reconstruct summer SSTs between 5.0-17.4 Ma from a sediment core (IODP Site U1464) within the Miocene NW Australian shelf Barrier Reef system. During the Miocene Climate Optimum, summer SSTs reached up to 34 ºC. However, stable arid conditions and low subsidence rates allowed the reef to expand. Around 6 Ma, SSTs were ideal for coral reef growth, but increased terrestrial input and subsidence caused the relatively rapid collapse of almost all reefs. Multiple environmental stressors culminated in reef drowning. Therefore, a barrier reef system formed at > 30 °C SSTs, but this was only possible under otherwise ideal conditions.

We analyzed the hydrogen and oxygen isotope compositions of interstitial water collected from Miocene–Quaternary carbonate platforms beneath the continental shelf margin off northwestern Australia during the International Ocean Discovery Program Expedition 356. By integrating isotope data with onboard salinity and chemical concentration measurements, we investigated the behavior of interstitial water in this continental shelf system. The interstitial water was classified into three groups based on salinity. Group 1 (salinity = 34−40) consisted of upper low-salinity water infiltrating from the modern seafloor, transitioning downward into highly saline water. This high-salinity water likely formed in situ during glacial periods. Group 3, characterized by extremely high salinity (salinity = 101−153), likely originated from the Late Miocene seawater modified by evaporation in an arid coastal environment. Group 2 (salinity = 43−98) represented a mixture of Groups 1 and 3. This study offers valuable insights into the hydrology of modern and ancient carbonate platforms, with implications for similar systems worldwide.

The Mediterranean Sea is warming at a rate exceeding the global average. Long-term, high-resolution data are essential for contextualizing changes within broader temporal scales, and coral skeletons provide valuable environmental archives, especially in data-sparse regions or as supplements to existing records. While coral-based reconstructions are well established in tropical settings, they remain limited in temperate areas. As the only reef-building zooxanthellate coral in the Mediterranean, Cladocora caespitosa is particularly important for expanding coral-based environmental archives in these understudied regions. Here, we present records of delta 18O and delta 13C in the skeletons of C. caespitosa from a global change sentinel site in NW Mediterranean. This study provides the most accurate temperature-delta 18O calibration equations for C. caespitosa, including a traditional linear model and a novel exponential model that better accounts for the region's wide seasonal temperature range. Both calibrations rely on long-term in situ water temperature data and a multi-corallite composite approach to reduce non-climatic variability. Seasonal trends in delta 13C reveal, for the first time, variation in the coral's autotrophy-heterotrophy balance, while geochemical anomalies in the skeletons signal thermal stress effects on biomineralization. Our findings establish C. caespitosa skeletons as critical archives for reconstructing anthropogenic warming and its ecological effects in the Mediterranean.

Coral reefs are increasingly threatened by anthropogenic stressors, including plastic pollution. This study investigates the abundance and possible ecological impact of microplastics (MPs) and microrubber pollution in sediments from a Cladocora caespitosa coral bed in the north-western Mediterranean. Despite being located in a remote marine protected area with no local plastic pollution sources, our results indicate exceptionally high MP concentrations (mean: 1514 particles/kg dry weight), attributed to long-distance transport of plastics by the Northern Current. Laser Directs Infrared (LDIR) Chemical Imaging and ATR-FTIR spectroscopy were used to characterize the MPs in terms of size, shape and polymer types. Most MPs are fragments (96 %), while fibers contribute only 4 %. The most abundant polymers were polyethylene (PE, 28 %), polyethylene terephthalate (PET, 25 %), and polystyrene (PS, 19 %), with significant contributions from polyurethane (PU) and microrubber. Particle size analysis showed that 92 % of MPs were smaller than 250 μm, with a median particle size varying by polymer type. Notably, polymers with heteroatoms in their main chain, such as PET and polyurethane, exhibited significantly smaller median sizes compared to polyolefins, possibly suggesting different degradation pathways. The high MP concentrations measured in sediments within coral colonies suggests that MPs could have adverse effects on heterotrophic feeding in C. caespitosa, a critical energy source during stress events. This study underscores the urgent need for targeted research on MP effects on the resilience of C. caespitosa and for increased global and regional efforts to curb plastic pollution mitigation in order to conserve coral populations in the Mediterranean.

Sea surface temperature (SST) variability in the south-eastern tropical Indian Ocean is crucial for rainfall variability in Indian Ocean rim countries. A large body of literature has focused on zonal variability associated with the Indian Ocean Dipole (IOD) which peaks in austral spring. In today's climate, northward shifts of the Tropical Convergence Zone (TCZ) co-vary with the IOD, and it is unclear whether these shifts may also occur independently. We have developed a new monthly resolved Sr/Ca record from a sub-fossil coral cored at Enggano Island (Sumatra, Indonesia). Core sections containing diagenetic phases are omitted from the SST reconstruction. U/Th dating shows that the Sr/Ca-based SST record extends from 1869–1918 and from 1824–1862 with a relative age uncertainty of ±3 years (2σ). At Enggano Island, coastal upwelling and cooling in austral spring impact SST seasonality and are coupled to the latitudinal position of the TCZ. The sub-fossil coral indicates an increase in SST seasonality between 1856 and 1918 relative to the 1930–2008 period. We attribute this to enhanced cooling due to stronger south-easterly (SE) winds driven by a northward shift in the TCZ in austral spring. A nearby sediment core indicates colder SSTs and a shallower thermocline prior to ∼1930. These results are consistent with an increase in the north–south SST gradient in the eastern Indian Ocean, calculated from historical temperature data, that is not seen in the zonal SST gradient. We conclude that the relationship between meridional and zonal variability in the eastern Indian Ocean is non-stationary and modulated by the long-term evolution of temperature gradients.

The tropical North West Shelf of Australia hosts a diverse range of modern reefs. Six shelf edge isolated atolls are present north of 18 degrees S including: Ashmore Reef, Scott Reef and Seringapatam Reef, and three Rowley Shoals. The Ningaloo Reef is a fringing reef around the North West Cape at 22 degrees S. All of these reefs are the remnants of a vast 2000 km long barrier reef that drowned during the Late Miocene (similar to 10 Ma). Despite extensive hydrocarbon exploration in the region, the history of these isolated reefs is not well known. Seismic analyses combined with stratigraphic analyses of International Ocean Discovery Site U1464 near the Rowley Shoals has revealed that these modern isolated atolls have a complex evolution related to climate and tectonism as they managed to survive on their Miocene barrier reef foundation. The first Miocene reefs (similar to 17 Ma) near the Rowley Shoals were isolated small, mound-shaped features. These evolved into a barrier reef by the Middle Miocene (similar to 16 Ma). However, by the Late Miocene (similar to 10 Ma) this barrier reef backstepped landward, evolved into isolated mounds/atolls and drowned prior to the Miocene-Pliocene boundary (similar to 6 Ma) largely due regional tectonic subsidence. Early Pliocene reef expansion (similar to 4.6 Ma) led to the growth of four isolated atolls (the Rowley Shoals) related to local faulting and Early Pliocene warmth. Subsequently a second Pliocene reef growth phase occurred from similar to 3.5 to 3 Ma when eastern Indian Ocean sea surface temperatures cooled by similar to 4 degrees C due to Indonesian Gateway constriction and a reduced Leeuwin Current. By the Pleistocene (similar to 2.4 Ma) one the four Rowley Shoals had drowned. Strong sea level variability, together with Indonesian Throughflow constriction and reduction in intensity of the Leeuwin Current after 2.4 Ma may have led to enhanced cooling and regional upwelling. These factors may have been sufficient to cause local drowning of the southerly fourth Rowley Shoal while the more northerly three Shoals survived until present.

The Late Miocene Cooling (LMC) has been recognized as a global event in the climate record and posited as the start of modern ecosystems. Whereas climate shifts in modern tropical terrestrial ecosystems around 7.0–5.4 Ma are known, little is known about the impact of the LMC on coral reefs, where few good proxy records exist. During the Pliocene, a stratigraphic interval is present in the Central Indo-Pacific, where reefs that were present at the start of the Messinian disappeared by the Early Pliocene. This “Pliocene Reef Gap” has often been ascribed to non-climatic factors. However, a lack of proxy data prevents an understanding of climatic changes during this time. Here, we present a TEX86H-based sea surface temperature (SST) record for the Coral Sea, suggesting that the LMC is present across the Central Indo-Pacific. During the LMC, SST at ODP Site 811 declined by about 2 °C, while cooling lasted from 7.0 to 5.4 Ma. This cooling has also been seen in other parts of the Central Indo-Pacific. The LMC caused many changes in the Central Indo-Pacific, including a southwest shift in the monsoon belt, changes in terrestrial inputs, and changes in the strength of ocean currents. All of these factors can be stressors affecting coral reef growth. This suggests the overall impact of the LMC was to increase the stress on reef systems, which could have provided a driver for the collapse of individual reefs and therefore a potential cause for the Pliocene Reef Gap. The change in SST and other stressors associated with the cooling caused coral reef systems to collapse across the Central Indo-Pacific.

The Great Barrier Reef is the largest reef system in the modern ocean. To date, the influence of temperature on the origin and long-term evolution of the Great Barrier Reef remains enigmatic. Here, we present a 900-thousand year TEX86H-derived temperature proxy record from Ocean Drilling Program Site 820 in the Coral Sea. It demonstrates that the onset of reef growth on the outer shelf was preceded by a rise in summer temperature from similar to 26 degrees to similar to 28 degrees C at around 700 thousand years ago (marine isotope stage 17). This approximately 2 degrees C rise in summer sea surface temperatures (SSTs) likely resulted in higher carbonate production rates, which were crucial for the formation of the Great Barrier Reef. Subsequently, reconstructed SSTs remained sufficiently warm for the Great Barrier Reef to thrive and evolve continuously. The evolution of the Great Barrier Reef, therefore, appears to be closely linked to SSTs.

Biofilms are mucilaginous-organic layers produced by microbial activity including viruses. Growing biofilms form microbial mats which enhance sediment stability by binding particles with extracellular polymeric substances and promoting growth through nutrient cycling and organic matter accumulation. They preferentially develop at the sediment-water interface of both marine and non-marine environments, and upon the growing surfaces of modern tufa and travertine. In this context, however, little is known about the factors, environmental or anthropogenic, which affect viral communities in freshwater spring settings. To explore this issue, geochemical and metagenomic data were subjected to multidimensional analyses (Principal Component Analysis, Classical Multidimensional Scaling, Partial Least Squares analysis and cluster analysis based on beta-diversity), and these show that viral composition is specific and dependent on environment. Indeed, waters precipitating tufa and travertine do vary in their geochemistry with their viruses showing distinct variability between sites. These differences between virus groups allow the formulation of a viral proxy, based on the Caudoviricetes/Megaviricetes ratio established on the most abundant groups of viruses. This ratio may be potentially used in analysing ancient DNA preserved in carbonate formations as an additional source of information on the microbiological community during sedimentation.

Abstract. Sea surface temperature (SST) variability in the south-eastern tropical Indian Ocean is crucial for rainfall variability in Indian Ocean rim countries. A large body of literature has focused on zonal variability associated with the Indian Ocean Dipole (IOD), but it is unclear whether meridional shifts in the position of the Intertropical Convergence Zone (ITCZ), which at present co-vary with the IOD, may also occur independently. We have developed a new, monthly resolved Sr/Ca record from a sub-fossil coral cored at Enggano Island (Indonesia, 5° S, 102° E). Core sections containing diagenetic phases are omitted from the SST reconstruction. U/Th dating shows that the Sr/Ca-based SST record extends from 1917–1868 and from 1861–1823 with a relative age uncertainty of ±2.4 years (2σ). At Enggano Island, coastal upwelling and cooling in austral spring is coupled to the position of the ITCZ, and impacts SST seasonality. The sub-fossil coral indicates an increase in SST seasonality due to enhanced austral spring cooling between 1917 and 1855, which we attribute to stronger SE winds and a northward shift in the position of the ITCZ in austral spring. A nearby sediment core indicates SST cooling and a shallowing of the thermocline prior to ~1930. These results are consistent with an increase in the North-South SST gradient in the eastern Indian Ocean calculated from historical temperature data, that is not seen in the zonal SST gradient. We conclude that the relationship between meridional and zonal variability in the eastern Indian Ocean is non-stationary and influenced by long-term temperature trends.

Evaporites are important sedimentary records of seawater history, and their Mg and K isotopic signatures could be used to constrain the evolution of surficial cycles of Mg and K on Earth. However, the lack of detailed understanding of the Mg and K isotopic behaviors during the precipitation of key evaporite minerals has impeded the applications of Mg and K isotopes in evaporites. In this study, we systematically investigated Mg and K isotope fractionation factors between carnallite (KCl & sdot; MgCl 2 & sdot; 6H 2 O) and saturated brine through mineral synthesis experiments, laboratory simulation of brine evaporation, and analysis of field samples. Carnallite synthesis experiments were performed at three different temperatures, and the results show that carnallite preferentially incorporates heavy Mg isotopes and light K isotopes over brines. Specifically, the Mg isotope fractionation factors ( Delta 26 Mg car-sol ) at 5, 25, and 50 degrees C are 0.83 +/- 0.09 %o, 0.84 +/- 0.09 %o, and 0.57 +/- 0.08 %o, respectively, whereas the measured K isotope fractionation factors ( Delta 41 K car-sol ) at 5, 25, and 50 degrees C are -0.49 +/- 0.08 %o, -0.43 +/- 0.11 %o, and -0.41 +/- 0.08 %o, respectively. The Mg and K isotope fractionation factors calibrated by the synthesis experiment were verified by brine evaporation experiments and field samples. Based on a set of laboratory brine evaporation experiment, the instantaneous isotope fractionation factors for carnallite are 0.82 %o - 0.83 %o ( Delta 26 Mg car-sol ) and -0.38 %o - -0.43 %o ( Delta 41 K car-sol ) after correction based on Li contents and a Rayleigh fractionation model. Additionally, based on analyses of brine and carnallite samples from the salt pan in the Qarhan Salt Lake region, Delta 26 Mg car-sol and Delta 41 K car-sol are determined to be 0.85 +/- 0.05 %o and -0.45 +/- 0.09 %o, respectively. Using the obtained Mg and K fractionation factors for evaporite minerals and thermodynamic calculations, we predicted how the Mg and K isotopes of brine would change in response to the evaporation of seawater with varying chemistries. The modeling results show that different initial seawater/brine chemistry (e.g., Ca-rich, sulfate-rich, and " Ca-SO 4 crossover " ) would result in different evolutionary trends of delta 41 K and delta 26 Mg in the brines during evaporation, primarily driven by carnallite precipitation. Therefore, Mg and K isotope signatures in evaporites or brines can provide key constraints for brine evolution in enclosed basins and ancient seawater chemistry.

Abstract The Great Barrier Reef (GBR) is by far the largest reef system in the modern ocean. Recently, it has been severely affected by coral bleaching due to human-induced warming. To date, however, the influence of temperature on the origin and long-term evolution of the GBR remains enigmatic. The only available sea surface temperature (SST) proxy data set extending beyond the origin of the GBR shows little variability. It has therefore been argued that other environmental factors must have been responsible for the development of the GBR. Here, we present a TEX86H-derived temperature proxy record from ODP Site 820. It demonstrates for the first time that the onset of reef growth on the outer shelf was preceded by a sharp rise in temperature from ~ 26°C before Marine Isotope Stage (MIS) 17 to ~ 28°C starting at MIS 17. After that, reconstructed temperatures remained relatively high (26 to 29°C). This period culminated in the development of a barrier reef system at MIS 13, suggesting that relatively stable SSTs were critical to its evolution. The glacial MIS 12 showed a renewed cooling to temperatures of ~ 25°C. From MIS 11 to the present, the glacial to interglacial temperature fluctuations approximate 3 to 4°C, with MIS 11 and 5 as particularly warm interglacials. The relatively warm temperatures after MIS 18 likely promoted extensive reef growth even during the glacials. These glacial reefs likely contributed to the persistence of the GBR over several glacial-interglacial cycles since the Middle Pleistocene. The evolution of the GBR, therefore, appears to be closely linked to seawater temperature. Our data suggest that sustained periods of optimal temperatures are a prerequisite for the development and maintenance of the GBR.

Proxy reconstructions suggest that mid-Holocene East African temperatures were warmer than today between 8 and 5 ka BP, but climate models cannot replicate this warming. Precessional forcing caused a shift of maximum insolation from boreal spring to fall in the mid-Holocene, which may have favored intense warming at the start of the warm season. Here, we use three Porites corals from Kenya that represent time windows from 6.55 to 5.87 ka BP to reconstruct past sea surface temperature (SST) seasonality from coral Sr/Ca ratios in the western Indian Ocean during the mid-Holocene. Although the Indian monsoon was reportedly stronger in the mid-Holocene, which should have amplified the seasonal cycle of SST in the western Indian Ocean, the corals suggest reduced seasonality (mean 3.2 °C) compared to the modern record (mean 4.3 °C). Warming in austral spring is followed by a prolonged period of warm SSTs, suggesting that an upper limit of tropical SSTs under mid-Holocene conditions was reached at the start of the warm season, and SSTs then remained stable. Similar changes are seen at the Seychelles. Bootstrap estimates suggest a reduction in SST seasonality of 1.3 ± 0.22 °C at Kenya and 1.7 ± 0.32 °C at the Seychelles. SST seasonality at Kenya corresponds to present-day SST seasonality at 55° E–60° E, while SST seasonality at the Seychelles corresponds to present day SST seasonality at ~ 65° E. This implies a significant westward expansion of the Indian Ocean warm pool. Furthermore, the coral data suggests that SST seasonality deviates from seasonal changes in orbital insolation due to ocean–atmosphere interactions.

This study reports on plastiglomerate and other new forms of plastic pollution in the tropical marine continent of Indonesia. Twenty-five samples were collected from an island beach in the Java Sea where plastiglomerate, plasticrusts, and pyroplastic were formed by the uncontrolled burning of plastic waste. The most common plastic types were polyethylene and polypropylene (PE/PP), as shown by ATR-FTIR spectroscopy. However, acrylates/polyurethane/varnish (PU) and a copolymer of styrene and acrylonitrile were found as well. This suggests that plastiglomerates can form from a wider variety of plastic polymers than previously reported. FTIR analysis also indicates thermo-oxidative weathering, making the charred plastic more brittle and susceptible to microplastic formation. A subset of the samples was analyzed for associated chemical contaminants. One plastiglomerate with a PU matrix showed high concentrations of phthalates. All samples had high concentrations of polycyclic aromatic hydrocarbons (PAHs), likely due to the burning of the plastic in open fires. The burning leads to a change in the physical and chemical properties of the plastics contained in the plastiglomerates. Plastiglomerate and plastic waste of similar origin are therefore often more weathered and contaminated with organic pollutants than their parent polymers. The highest PAH concentration was found in a plastitar sample. Plastitar is defined as an agglomerate of tar and plastics that adheres to coastal rocks. In contrast, our study documents a more mobile, clastic plastitar type. This clastic plastitar could pose an additional ecological risk because of its mobility. These new types of plastic pollution could be an important vector for chemical contamination of nearby coastal habitats such as coral reefs, seagrass meadows, and mangroves.

Evidence shows that in the modern ocean, coral reefs are disappearing, and these losses are tied to climate change. However, research also shows that coral reefs can adapt rapidly to changing conditions leading some researchers to suggest that some reef systems will survive future climate change through adaptation. It is known that there were changes in the area covered by coral reefs in the past. Therefore, it is important to investigate the long-term response of coral reefs to environmental changes and high sea-surface temperatures (SSTs). However, because of diagenetic issues with SST proxies in neritic, metastable carbonate-rich environments, there is an incomplete and sometimes even incorrect understanding of how changes in SSTs affect carbonate reef systems. A good example is the Queensland Plateau offshore northeast Australia next to the threatened Great Barrier Reef. In the Late Miocene, between 11 and 7 Ma, a partial drowning caused the reef area on the Queensland Plateau to decline by ~ 50% leading to a Late Miocene change in platform geometry from a reef rimmed platform to a carbonate ramp. This reef decline was interpreted to be the result of SSTs at the lower limit of the modern reef growth window (20–18 °C). This article presents a new Late Miocene—ased SST record from the Coral Sea based on the TEX 86 H molecular paleothermometer, challenging this long held view. Our new record indicates warm tropical SSTs (27–32 °C) at the upper end of the modern reef growth window. We suggest that the observed temperatures potentially exceeded the optimal calcification temperatures of corals. In combination with a low aragonite supersaturation in the ocean, this could have reduced coral growth rates and ultimately lowered the aggradation potential of the reef system. These sub-optimal growth rates could have made the coral reefs more susceptible to other stressors, such as relative sea-level rise and/or changes in currents leading to reef drowning. Given that these changes affected coral reefs that were likely adapted to high temperature/low aragonite saturation conditions suggests that reefs that have adapted to non-ideal conditions may still be susceptible to future climate changes due to the interaction of multiple stressors associated with climate change.

The Great Barrier Reef is a unique environmental resource threatened by future climate change. However, it has always been unclear how this ecosystem developed in the Mid to Late Pleistocene. Work has shown that the reef developed between ~ 600-500 ka during MIS 15-13, although some records suggest a start at MIS 11 at 400 ka. There is a lack of Sea Surface Temperature (SST) records for this time for the area around the Great Barrier Reef. Furthermore, the few existing SST records do not show temperature changes during these key periods, leading researchers to suggest that factors other than temperature, such as sea-level change or sediment transport, explain the start of the reef. We used the TEX86 proxy to produce a new SST record starting at 900 ka from ODP Site 820. This core is located next to the northern Great Barrier Reef. In this new record, there are SST changes that seem to match both dates for the start of the Great Barrier Reef. First, there is a period of stable SST between 700-500 ka, with no glacial cooling during this time. This could promote the development of a reef system during this time, allowing the reef more time to evolve from isolated smaller reefs to a continuous barrier reef. However, there is some suggestion based on facies analyses that even though the barrier system developed around MIS 15, the modern coral reef system was not yet fully established. Our records show that glacial temperatures during MIS 14 still are similar to SSTs from records further south. However, this trend shifts around MIS 11 when glacials became warmer. In fact, while before MIS 11, SST at ODP 820 was colder than records from the Western Pacific Warm Pool, afterwards SST was either the same or sometimes warmer than at these sites. Also, unlike other nearby records, the difference in SSTs between glacials and interglacials is reduced after MIS 11. This suggests that the northern Coral Sea might have been protected from the extremes of glacial temperature changes after the MPT. This process might have allowed the development of a continuous coral reef system by encouraging the growth of reefs even during glacials. Therefore, our research suggests that major steps in the development of the Great Barrier Reef system are linked to changes in the SSTs. Our SST record suggests that SST changes are the primary driver of reef development and other non-SST factors are less important.

There is growing interest in the use of pteropods as potential archives of past changes in ocean chemistry. However, pteropods have rarely been used in studies of millennial-scale sedimentary records, especially in shallow-marine environments. This study obtained core data for the last 16 kyr from the Northwest Shelf of Australia (NWS). Changes in the carbonate saturation state were assessed based on the carbon isotope ratios (δ 13 C) of shells and the Limacina dissolution index (LDX) measured on the planktonic pteropod species Heliconoides inflatus . In addition, the calcification depth of the pteropods was estimated based on oxygen isotope values (δ 18 O) of pteropod shells and seawater. Our findings indicate that H. inflatus calcifies at a depth of 95–140 m. This confirms that H. inflatus records a shallow-marine signal on the NWS. The δ 13 C values of the pteropods record a notable decrease in carbonate ion concentrations after 8.5 ka. This decrease is associated with the post-glacial onset of humid conditions on the NWS. The studied pteropod shells are pristine throughout the 16 kyr section and have low LDX values. Therefore, the LDX proxy appears to lack the sensitivity to be applicable in this highly supersaturated, shallow-marine environment. Until this study, proxies derived from H. inflatus have been exclusively utilized in open-marine settings. Our results indicate that the δ 13 C values of H. inflatus also represent a useful proxy for carbonate ion concentrations in shallow-marine environments.

The Queensland Plateau in the Coral Sea has one of the best constrained geologic histories of coral reef expansion and demise since the early Miocene. The development coral reefs in the past is not well understood with a number of theories proposed for their loss and expansion. Coral reefs were first established in the Early Miocene in the Coral Sea. In the Late Miocene, between 11 and 7 Ma, the reef area on the Queensland Plateau declined by ~50% leading to a partial drowning and a change in platform geometry from a reef rimmed platform to a carbonate ramp. The modern atoll reefs were reestablished around 3.6 Ma although the Great Barrier Reef only developed around 0.7-0.6 Ma. The loss of the reefs has often been tied to the expansion cool nutrient rich waters in the Coral Sea during the Late Miocene. This model has been used to explain the loss and expansion of corals in other parts of the globe. However, there have been questions about the planktonic δ18O based Sea Surface Temperature (SST) records on which they are based and how accurately they reflect SSTs. Here we show new TEX86 SST data from the Queensland Plateau from ODP site 811 showing temperature changes from the Late Miocene to 1 Ma. Our data shows instead of cooler SSTs during the Late Miocene in fact SSTs were warmer than the modern Coral Sea and at the upper end of the modern coral window. Therefore, it is unlikely that cooler SSTs during the Late Miocene caused the loss of corals on the Queensland Plateau. Instead, the loss seems to have been driven by the restricted growth combined with high SST driven lower growth rate and increases in subsidence at the same time among other drivers. We also will discuss changes in the latitudinal extent of the warm pool during the late Pliocene and what caused the re-expansion of corals during this period of time. Given the modern debate about the future of coral reefs under current climate predictive scenarios it is worth pointing out that a similar series of changes is occurring in the modern ocean.

The loss of coral reefs in the past is not well understood with a number of theories proposed for their loss and expansion. The Queensland Plateau has one of the best-established coral histories. It is known that coral reefs were first established in the Early Miocene. These reefs then disappeared between 11-6 Ma during the Late Miocene but reestablished around 3.6 Ma. The loss of the reefs has often been tied to cool nutrient rich water during the Late Miocene where as the reestablishment of the reefs have been tied to increases in warmer nutrient poor waters. This model has been used to explain the loss of corals in other parts of the globe. However, there have been questions about the d18O records this has been based on and how accurately they reflect SSTs. In this presentation, we show new TEX86 SST data from the Queensland Plateau. Our data shows, instead of cooler SSTs during the Late Miocene, warmer SSTs than the modern Coral Sea and similar temperatures than the West Pacific Warm Pool. In fact, our temperatures fall comfortably in the modern coral growth window. Furthermore, we found little evidence of increases in local nutrients during this time. All this makes it unlikely that cooler SSTs during the Late Miocene caused the loss of corals on the Queensland Plateau. Instead, the changes seem to be linked to more Pacific wide changes during this period of time. Given the modern debate about the future of coral reefs in a warmer world it is critical to understand what changes drive the loss of coral reefs in the past. Our records show that new ideas about coral loss are needed and that better paleoclimate records are needed from these critical environments.