Particulate pyrogenic carbon (PyC) transported by rivers and aerosols, and deposited in marine sediments, is an important part of the carbon cycle. The chemical composition of PyC is temperature dependent and levoglucosan is a source-specific burning marker used to trace low-temperature PyC. Levoglucosan associated to particulate material has been shown to be preserved during riverine transport and marine deposition in high- and mid-latitudes, but it is yet unknown if this is also the case for (sub)tropical areas, where 90% of global PyC is produced. Here, we investigate transport and deposition of levoglucosan in suspended and riverbed sediments from the Amazon River system and adjacent marine deposition areas. We show that the Amazon River exports negligible amounts of levoglucosan and that concentrations in sediments from the main Amazon tributaries are not related to long-term mean catchment-wide fire activity. Levoglucosan concentrations in marine sediments offshore the Amazon Estuary are positively correlated to total organic content regardless of terrestrial or marine origin, supporting the notion that association of suspended or dissolved PyC to biogenic particles is critical in the preservation of PyC. We estimate that 0.5–10 × 10⁶ g yr⁻¹ of levoglucosan is exported by the Amazon River. This represents only 0.5–10 ppm of the total exported PyC and thereby an insignificant fraction, indicating that riverine derived levoglucosan and low-temperature PyC in the tropics are almost completely degraded before deposition. Hence, we suggest caution in using levoglucosan as tracer for past fire activity in tropical settings near rivers.

中文翻译：

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微量低温热解碳颗粒通过亚马逊河到达大西洋

通过河流和气溶胶运输并沉积在海洋沉积物中的颗粒热原碳（PyC）是碳循环的重要组成部分。PyC 的化学成分与温度有关，左旋葡聚糖是一种来源特定的燃烧标记物，用于追踪低温 PyC。与颗粒物质相关的左旋葡聚糖已被证明在高纬度和中纬度地区的河流运输和海洋沉积过程中得以保存，但尚不清楚（亚）热带地区是否也是这种情况，全球 90% 的 PyC 是产生。在这里，我们研究了来自亚马逊河系统和邻近海洋沉积区的悬浮和河床沉积物中左旋葡聚糖的运输和沉积。我们表明，亚马逊河出口的左旋葡聚糖量可忽略不计，亚马逊主要支流沉积物中的浓度与长期平均流域范围内的火灾活动无关。亚马逊河口近海海洋沉积物中的左旋葡聚糖浓度与总有机物含量呈正相关，无论陆地或海洋来源如何，这支持了这样一种观点，即悬浮或溶解的热解碳与生物颗粒的关联对于热解碳的保存至关重要。我们估计 0.5–10 × 10 支持这样的观点，即悬浮或溶解的热解碳与生物颗粒的结合对于热解碳的保存至关重要。我们估计 0.5–10 × 10 支持这样的观点，即悬浮或溶解的热解碳与生物颗粒的结合对于热解碳的保存至关重要。我们估计 0.5–10 × 10⁶  g yr ^-1的左旋葡聚糖通过亚马逊河出口。这仅占总出口热解碳的 0.5-10 ppm，因此是微不足道的一部分，表明热带地区河流衍生的左旋葡聚糖和低温热解碳在沉积前几乎完全降解。因此，我们建议谨慎使用左旋葡聚糖作为河流附近热带地区过去火灾活动的示踪剂。