Environmental Science and Geography Program, University of Alaska Southeast, Juneau, Alaska 99801, USA.
Nature. 2009 Dec 24;462(7276):1044-7. doi: 10.1038/nature08580.
Riverine organic matter supports of the order of one-fifth of estuarine metabolism. Coastal ecosystems are therefore sensitive to alteration of both the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to vary with age, with younger, relatively unaltered organic matter being more easily metabolized by aquatic heterotrophs than older, heavily modified material. This view is developed exclusively from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM. Here we characterize streamwater DOM from 11 coastal watersheds on the Gulf of Alaska that vary widely in glacier coverage (0-64 per cent). In contrast to non-glacial rivers, we find that the bioavailability of DOM to marine microorganisms is significantly correlated with increasing (14)C age. Moreover, the most heavily glaciated watersheds are the source of the oldest ( approximately 4 kyr (14)C age) and most labile (66 per cent bioavailable) DOM. These glacial watersheds have extreme runoff rates, in part because they are subject to some of the highest rates of glacier volume loss on Earth. We estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13 +/- 0.01 Tg yr(-1) (1 Tg = 10(12) g), of which approximately 0.10 Tg is highly labile. This indicates that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems. Moreover, because glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system, our findings indicate that climatically driven changes in glacier volume could alter the age, quantity and reactivity of DOM entering coastal oceans.
河流有机物质支撑了河口代谢的约五分之一。因此，沿海生态系统对河流输送的陆源溶解有机物质（DOM）的数量和可变性都很敏感。DOM 的可变性被认为随年龄而变化，较年轻、相对未经改变的有机物质比年老、高度改性的物质更容易被水生异养生物代谢。这种观点仅从以陆地植物和土壤为主要水源的流域中得到发展。在这里，我们描述了阿拉斯加湾 11 个沿海流域的地表水 DOM，这些流域的冰川覆盖率（0-64%）差异很大。与非冰川河流不同，我们发现 DOM 对海洋微生物的生物利用度与（14）C 年龄的增加呈显著相关。此外，冰川最严重的流域是最古老（约 4 千年前（14）C 年龄）和最易生物降解（66%生物可利用）DOM 的来源。这些冰川流域具有极高的径流量，部分原因是它们受到地球上最高的冰川体积损失率的影响。我们估计，从为阿拉斯加湾提供径流的冰川中溶解有机碳的累积通量为 0.13 +/- 0.01 Tg yr(-1)（1 Tg = 10(12) g），其中约 0.10 Tg 是高度易生物降解的。这表明，冰川径流是海洋生态系统中可生物降解的还原碳的重要定量来源。此外，由于冰川和冰盖是全球水文系统中第二大储水库，我们的研究结果表明，气候驱动的冰川体积变化可能会改变进入沿海海洋的 DOM 的年龄、数量和反应性。
