Carbon is a key control on the surface chemistry and climate of Earth. Significant volumes of carbon are input to the oceans and atmosphere from deep Earth in the form of degassed CO 2 and are returned to large carbon reservoirs in the mantle via subduction or burial. Different tectonic settings (e.g., volcanic arcs, mid-ocean ridges, and continental rifts) emit fluxes of CO 2 that are temporally and spatially variable, and together they represent a first-order control on carbon outgassing from the deep Earth. A change in the relative importance of different tectonic settings throughout Earth's history has therefore played a key role in balancing the deep carbon cycle on geological timescales. Over the past 10 years the Deep Carbon Observatory has made enormous progress in constraining estimates of carbon outgassing flux at different tectonic settings. Using plate boundary evolution modeling and our understanding of present-day carbon fluxes, we develop time series of carbon fluxes into and out of the Earth's interior through the past 200 million years. We highlight the increasing importance of carbonate-intersecting subduction zones over time to carbon outgassing, and the possible dominance of carbon outgassing at continental rift zones, which leads to maxima in outgassing at 130 and 15 Ma. To a first-order, carbon outgassing since 200 Ma may be net positive, averaging ∼50 Mt C yr −1 more than the ingassing flux at subduction zones. Our net outgassing curve is poorly correlated with atmospheric CO 2 , implying that surface carbon cycling processes play a significant role in modulating carbon concentrations and/or there is a long-term crustal or lithospheric storage of carbon which modulates the outgassing flux. Our results highlight the large uncertainties that exist in reconstructing the corresponding in-and outgassing fluxes of carbon. Our synthesis summarizes our current understanding of fluxes at tectonic settings and their influence on atmospheric CO 2 , and provides a framework for future research into Earth's deep carbon cycling, both today and in the past.

Sedimentation regimes on the Great Barrier Reef margin often do not conform to more conventional sequence stratigraphic models, presenting difficulties when attempting to identify key processes that control the margin's geomorphological evolution. By obstructing and modifying down-shelf and down-slope flows, carbonate platforms are thought to play a central role in altering the distribution and morphological presentation of common margin features. Using numerical simulations, we test the role of the carbonate platforms in reproducing several features (i.e., paleochannels, shelf-confined fluvial sediment mounds, shelf-edge deltas, canyons, and surface gravity flows) that have been described from observational data (seismic sections, multibeam bathymetry, sediment cores, and backscatter imagery). When carbonate platforms are present in model simulations, several notable geomorphological features appear, especially during lowstand. Upon exposure of the shelf, platforms reduce stream power, promoting mounding of fluvial sediments around platforms. On the outer shelf, rivers and streams are re-routed and coalesce between platforms, depositing shelf-edge deltas and incising paleochannels through knickpoint retreat. Additionally, steep platform topography triggers incision of slope canyons through turbidity currents, and platforms act as conduits for the localized delivery of land and shelf-derived sediments to the continental slope and basin. When platforms are absent from the topographic surface, the model is unable to reproduce many of these features. Instead, a more typical "reciprocal-type" sedimentation regime arises. Our results demonstrate the essential role of carbonate platform topography in modulating key bedload processes. Therefore, they exert direct control on the development of various geomorphological features within the shelf, slope, and basin environments.Plain Language Summary The modern Great Barrier Reef sits atop the skeletal remains of its ancestors. These remains form large (50-200 km 2 ) columns of chalk (or carbonate platforms) that rest on the northeast Australian continental shelf. By comparing observational data with computer simulations, we find that these platforms majorly disrupt and modify the flow of rivers and deep-sea density currents during periods of lower sea level. When platforms are exposed, they become hills, forming steep topographic high points that are large enough to re-route rivers and promote incision on the continental slope. On the modern seafloor, evidence of this activity is preserved in the form of ancient deltas, paleochannels, submarine canyons, and sediment flows that stretch across the abyssal plain. The morphology and distribution of these seafloor features are more robustly accounted for when carbonate platforms are present, and many of them do not appear in computer simulations where carbonate platforms are absent. Our work shows that carbonate platforms can alter seascapes in ways that are traditionally less understood.

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Subduction is a fundamental mechanism of material exchange between the planetary interior and the surface. Despite its significance, our current understanding of fluctuating subducting plate area and slab volume flux has been limited to a range of proxy estimates. Here we present a new detailed quantification of subduction zone parameters from the Late Triassic to present day (230 – 0 Ma). We use a community plate motion model with evolving plate topologies to extract trench-normal convergence rates through time to compute subducting plate areas, and we use seafloor paleo-age grids to estimate the thickness of subducting lithosphere to derive the slab flux through time. Our results imply that slab flux doubled to values greater than 500 km3/yr from 180 Ma in the Jurassic to 130 Ma in the mid-Cretaceous, subsequently halving again towards the Cretaceous-Paleogene boundary, largely driven by subduction zones rimming the Pacific ocean basin. The 130 Ma spike can be attributed to a two-fold increase in mid-ocean ridge lengths following the break-up of Pangea, and a coincident increase in convergence rates, with average speeds exceeding 10 cm/yr. With one third of the total 230 - 0 Ma subducted volume entering the mantle during this short ~ 50 Myr period, we suggest this slab superflux drove a surge in slab penetration into the lower mantle and an associated increase in the vigour of mantle return flow. This mid-Cretaceous event may have triggered, or at least contributed to, the formation of the Darwin Rise mantle superswell, dynamic elevation of the South African Plateau and the plume pulse that produced the Ontong-Java-Hikurangi-Manihiki and Kerguelen plateaus, among others. The models presented here contribute to an improved understanding of the time-evolving flux of material consumed by subduction, and suggest that slab superflux may be a general feature of continental dispersal following supercontinent breakup. These insights may be useful for better understanding how supercontinent cycles are related to transient episodes of large igneous province and superswell formation, and the associated deep cycling of minerals and volatiles, as well as leading to a better understanding of tectonic drivers of long-term climate and icehouse-to-greenhouse transitions.

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