Global chemical weathering dominated by continental arcs since the mid-Paleozoic

since the mid-Paleozoic Thomas M. Gernona,∗, Thea K. Hincksa, Andrew S. Merdithb, Eelco J. Rohlingc, Martin R. Palmera, Gavin L. Fostera, Clément P. Batailled, R. Dietmar Müllere aSchool of Ocean & Earth Science, University of Southampton, Southampton SO14 3ZH, UK bLaboratoire de Géologie, Université of Lyon 1, France cResearch School of Earth Sciences, The Australian National University, Canberra, Australia dEarth and Environmental Sciences, University of Ottawa, Ottawa, ON K1N, Canada eEarthByte Group, School of Geosciences, The University of Sydney, Australia

with continental landmasses shown in pink, present-day coastlines in black, and the tropics (±20 • of the equator) in beige; b, atmospheric CO 2 concentration (multi-proxy, black line) 12 , and phytane-based estimates in red 13 ; continental ice latitude 5 is shown as the blue line (blue shaded regions denote glaciations); c, continental arc length 14 ; d, seafloor production rates (Methods); e, suture zone lengths 5 ; f, fragmentation index (i.e., continental perimeter/area, as black line), and total area of continents in the tropics (red line); g, ( 87 Sr/ 86 Sr) sw from marine carbonates 15 , calculated as a ±0.25 Myr window in red; h, normalised ( 87 Sr/ 86 Sr) sw curve removing the signal caused by radioactive 87 Rb decay in the crust 16 . search the set of predictor variables to find maximum values of proach is based on the method for partial autocorrelation, and 99 efficiently accounts for multiple joint dependencies and lags 100 (Methods). Whilst our focus below is on C Cond , for context 101 we also provide C Emp and C BN (Fig. 3). Note that the smallest value that occurs in the data set is ranked 1. b, Probability density for continental arc length 14 , identifying short (<16,100 km), intermediate (16,,300 km), and extensive (≥29,300 km) arcs (note: these divisions denote approximately equal quantiles); the distributions show that extensive continental arc systems favour low ( 87 Sr/ 86 Sr) sw , and vice versa.
Identification of chemical weathering drivers 103 We find that the spatial extent of continental volcanic 104 arcs 14 (Fig. 1c) <0.5 Myr (Fig. 3a). Before exploring the importance of these observations, we need to quantitatively evaluate how other processes combine to drive ( 87 Sr/ 86 Sr) sw .
However, it is also feasible that ophiolites acquire radiogenic 137 signatures during regional metamorphism 24 . Irrespective of the 138 mechanism, our analysis confirms a key role for arc-continent 139 collisions in driving increased weathering fluxes 5 .

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Chemical weathering is also sensitive to continental frag-

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It is well established that seafloor basalt alteration 31  seafloor production rate (Fig. 1d), which we calculate as the 181 product of ridge length and spreading rate (Extended Data Fig.   182 7), adapting an existing plate model 26 . We find that seafloor 183 productivity is negatively correlated with ( 87 Sr/ 86 Sr) sw at short 184 lags (Fig. 3d), reflecting the effects of early high temperature

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Investigating the effect of continental ice coverage, we find a

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Any methods, additional references, Nature Research reporting summaries, source data, extended data, supplementary information, acknowledgements, peer review information; details of author contributions and competing interests; and statements of data and code availability are available at https://doi.org/10.1038/s12345-111-2222-3.   It is important to note that we also repeated the BN data min-    Data File S1). In contrast to ref. 26     percentile ranges (Fig. 1b). We note that recent phytane-520 based measurements 13 are in reasonable agreement with 521 this long-term pCO 2 record (Fig. 1b). The time-series 522 from Foster et al. 12