| Summary: | <p>Long-term erosion rates in Tasmania, at the southern end of Australia's Great Dividing Range, are poorly known; yet, this knowledge is critical for making informed land-use decisions and improving the ecological health of coastal ecosystems. Here, we present quantitative, geologically relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in situ-produced <span class="inline-formula"><sup>10</sup>Be</span> (<span class="inline-formula"><sup>10</sup>Be<sub>i</sub></span>) measured from stream sand at two trunk channel sites and seven tributaries (mean: <span class="inline-formula">24.1±1.4</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">Mg</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">km</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="e6bd9f1982fb337ba4d0bf6e2cf823c1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-153-2022-ie00001.svg" width="64pt" height="15pt" src="gchron-4-153-2022-ie00001.png"/></svg:svg></span></span>; 1<span class="inline-formula"><i>σ</i></span>). These new
<span class="inline-formula"><sup>10</sup>Be<sub>i</sub></span>-based erosion rates are strongly related to elevation, which appears to control mean annual precipitation and temperature,
suggesting that elevation-dependent surface processes influence rates of erosion in northeast Tasmania. Erosion rates are not correlated with slope
in contrast to erosion rates along the mainland portions of Australia's Great Dividing Range. We also extracted and measured meteoric <span class="inline-formula"><sup>10</sup>Be</span>
(<span class="inline-formula"><sup>10</sup>Be<sub>m</sub></span>) from grain coatings of sand-sized stream sediment at each site, which we normalize to measured concentrations of reactive <span class="inline-formula"><sup>9</sup>Be</span>
and use to estimate <span class="inline-formula"><sup>10</sup>Be<sub>m</sub></span>-based denudation rates for the George River. <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msup><mi/><mn mathvariant="normal">10</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">m</mi></msub></mrow><mo>/</mo><mrow class="chem"><msup><mi/><mn mathvariant="normal">9</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">reac</mi></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="387ba0141a914539abecece6249ac28e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-153-2022-ie00002.svg" width="72pt" height="16pt" src="gchron-4-153-2022-ie00002.png"/></svg:svg></span></span> denudation rates
replicate <span class="inline-formula"><sup>10</sup>Be<sub>i</sub></span> erosion rates within a factor of 3 but are highly sensitive to the value of <span class="inline-formula"><sup>9</sup>Be</span> that is found in bedrock
(<span class="inline-formula"><sup>9</sup>Be<sub>parent</sub></span>), which was unmeasured in this study. <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msup><mi/><mn mathvariant="normal">10</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">m</mi></msub></mrow><mo>/</mo><mrow class="chem"><msup><mi/><mn mathvariant="normal">9</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">reac</mi></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="d5b04f3154bc4bfebedc21679e942ad7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-153-2022-ie00003.svg" width="72pt" height="16pt" src="gchron-4-153-2022-ie00003.png"/></svg:svg></span></span> denudation rates seem sensitive to recent
mining, forestry, and agricultural land use, all of which resulted in widespread topsoil disturbance. Our findings suggest that
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msup><mi/><mn mathvariant="normal">10</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">m</mi></msub></mrow><mo>/</mo><mrow class="chem"><msup><mi/><mn mathvariant="normal">9</mn></msup><msub><mi mathvariant="normal">Be</mi><mi mathvariant="normal">reac</mi></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="36f88919efe6ce2fa1edb5949cc0d3c5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gchron-4-153-2022-ie00004.svg" width="72pt" height="16pt" src="gchron-4-153-2022-ie00004.png"/></svg:svg></span></span> denudation metrics will be most useful in drainage basins that are geologically homogeneous, where recent
disturbances to topsoil profiles are minimal, and where <span class="inline-formula"><sup>9</sup>Be<sub>parent</sub></span> is well constrained.</p>
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