NSFGEO-NERC: WOOD-BASED CARBON DISCHARGE TO THE ARCTIC OCEAN

摘要：侵蚀将土壤和陆地植被中的有机碳迁移和输送到土壤中。由此产生的有机碳向海洋的河流排放在全球范围内具有重大意义。然而，目前对这一流量的估计没有考虑到大于约0.5毫米的材料，因此也没有考虑到大木片。由于很少有研究调查木材输送、腐烂和运输的流域尺度模式，我们对大木材如何影响有机碳排放到海洋的了解有限。这一知识差距导致了我们的主要研究目标，即(I)量化从加拿大麦肯齐河流域到北冰洋的每年以大木材形式排放的粗颗粒有机碳与其他来源的溶解有机碳和颗粒有机碳的排放量，以及(Ii)估计大木材在流域中的储存量、停留时间和腐烂率。我们在麦肯齐河流域进行这项工作，因为它是一个相对原始的大型河流流域，以向海洋出口木材的高比率而闻名。我们的主要研究目标是量化大型木材(LW)的排放量，评估其对麦肯齐河和北冰洋有机碳(OC)预算的贡献，同时确定LW运输的动态及其在河网中的停留时间。我们有两个具体目标：(1)利用地面延时摄影和高分辨率卫星图像，通过LW量化年度生物圈颗粒有机碳通量。(2)利用地面测量的LW累积和卫星图像，确定LW的传输动力学和LW的停留时间。我们将使用基于14C的LW年表来表征停留时间和衰减率。研究计划将在两年内包括五个主要组成部分：在麦肯齐河流域的关键位置，我们将(1)测量LW通量，(2)估计LW的吸收和储存，(3)测量LW体积和年龄分布，(4)对细悬浮沉积物进行采样，以改进颗粒有机碳通量估计，以及(5)收集可用于限制LW年龄、来源以及运输过程中LW的物理和化学降解的树芯。拟议研究的变革性方面是：(1)量化作为木材出口的有机碳与来自大河流的较细材料的比例，深入了解不同来源的有机碳在当代条件下的相对重要性，以及(2)首次评估大河流携带的从500微米到大木材的各种颗粒尺寸的材料的相对年龄，为预测气候变暖下粗颗粒有机碳命运的变化可能如何影响碳循环提供更明确的基础。该项目还将极大地促进对气候变暖下大流域木材动态的了解，气候变暖将改变木材的招募、运输和沉积过程，改变向麦肯齐三角洲和北极出口木材的时间、数量和位置。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Abstract: Erosion mobilizes and delivers organic carbon from soils and terrestrial vegetation to soils. The resultant river discharge of organic carbon to oceans is globally significant. Current estimates of this discharge, however, do not account for material larger than about 0.5 millimeters and thus do not account for pieces of large wood. Because few studies have investigated the drainage-basin-scale patterns of wood delivery, decay, and transport, we have limited knowledge of how large wood influences organic carbon discharge to the ocean. This knowledge gap leads to our primary research goals, which are to (i) quantify annual coarse particulate organic carbon discharge in the form of large wood versus other sources of dissolved and particulate organic carbon from the Mackenzie River drainage of Canada to the Arctic Ocean and (ii) estimate the storage volume, residence time, and decay rates of large wood in the drainage basin. We are conducting this work in the Mackenzie River drainage because it is a relatively pristine large river drainage basin that is known for high rates of wood export to the ocean.Our primary research aim is to quantify the discharge of large wood (LW) and assess its contribution to the organic carbon (OC) budget of the Mackenzie and the Arctic Ocean, while determining the dynamics of LW transport and its residence time in the river network. We have two specific objectives: (1) Quantify annual biospheric particulate organic carbon flux by LW using ground-based time-lapse photography and high-resolution satellite imagery. (2) Determine LW transport dynamics and the residence time, of LW using ground-based measurements of LW accumulations and satellite imagery. We will characterize residence time and decay rates with a 14C-based chronology of LW. The research plan includes five primary components over two years: At key locations within the Mackenzie River drainage, we will (1) measure LW fluxes, (2) estimate LW recruitment and storage, (3) measure LW volume and age distribution, (4) sample fine suspended sediment to improve particulate OC flux estimates, and (5) collect tree cores that can be used to constrain LW age, provenance, and physical and chemical degradation of LW during transport. The transformative aspects of the proposed research are: (1) quantification of proportions of OC exported as wood versus finer material from a large river, providing insight into the relative importance of different sources of OC under contemporary conditions, and (2) the first assessment of the relative ages of material across the full range of particulate sizes carried by a large river from 500 microns to large wood, providing a clearer basis for predicting how changes in the fate of coarse POC may impact the carbon cycle under a warming climate. This project will also substantially advance understanding of wood dynamics in large river basins under a warming climate that will alter wood recruitment, transport, and deposition processes, altering timing, volume, and placement of wood exports to the Mackenzie Delta and the Arctic.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.