Natural Radionuclides as Tracers of the Cycling and Fate of Particulate Organic Carbon on the Mackenzie Shelf: Participation in the Canadian Arctic Shelf Exchange Study(CASES)

在世界上所有的海洋中，北极是独一无二的，因为它有持久的海冰覆盖，广阔的大陆架是碳循环的场所，光强的年变化很大。此外，北极可能是最容易受到全球变暖早期影响的海洋。虽然诸如冰盖变薄之类的变化可能有自然原因，例如与北极大气压力梯度的变化有关，但它们也可能与人类活动带来的气候变化有关。气候变暖可能通过冰盖的永久减少和河流排放量的增加来改变北极大陆架上的碳循环。反过来，这些变化可能导致碳向斜坡和深北极盆地的输出增加。北极最显著的特征之一是其广阔的大陆架面积，约占盆地面积的30%，接收约10%的世界河流流量。北极地区的河流流量主要是西伯利亚大河——叶尼塞河、勒拿河和鄂毕河。麦肯齐河的重要性仅次于这些河流，但在年沉积物流量方面排名第一。此外，它是北美唯一与西伯利亚大河类似的河流，而且在实际应用中是最容易研究的。河流主导的大陆架对北极生物地球化学循环的潜在重要性已经导致了一项国际努力——加拿大北极大陆架交换研究（CASES）——由加拿大组织，以了解海冰变化对麦肯齐大陆架的影响。基于先前在加拿大组织的东北和北水冰礁的北极项目的参与，PI被邀请参加案例项目。这里提出的对麦肯齐大陆架的研究将建立在PI先前在北极和其他地方的努力的基础上，即使用天然放射性核素作为颗粒有机碳和颗粒通量的示踪剂。case包括三个月的过程巡航（2002年8月、2003年8月和2004年8月），以及2003年8月到2004年之间为期一年的巡航，在此期间，研究破冰船将越冬。这项研究的结构将利用在麦肯齐大陆架上对生产力的整个年度周期进行采样的可能性。重点将放在系统中形成的三个不同的区域（一个被称为“麦肯齐湖”的淡水湖，由一座冰坝与缺铅多冰区和北极浮冰区隔开），并使用天然放射性核素作为示踪剂，用于区域内和区域之间的颗粒和颗粒有机碳运输。我们假设在春季到夏季，随着麦肯齐河的淡水开始，冰向近海退去，生产力增加，区域之间的重大交换将发生。我们将通过使用天然放射性核素来检验这一假设，以确定是否存在新鲜输入的河流沉积物到内部大陆架，从发光区输出POC的速率，并通过质量平衡来作为颗粒物质通过区域运输的指标。我们将使用的放射性核素包括宇宙射线与大气气体相互作用在大气中产生的宇宙源放射性核素（Be-7和C-14），以及自然发生的U-238衰变系列的放射性核素（Th-234, Pb-210）。

0136459CochranOf all the world oceans, the Arctic is unique in its persistent cover of sea ice, broad continental shelves that are loci for carbon cycling and strong annual variations in light intensity. Moreover the Arctic is perhaps the ocean most susceptible to showing the early effects of global warming. Although changes such as thinning ice cover may have natural causes, for example related to variations in the gradient of atmospheric pressure in the Arctic, they may also be related to changes in climate brought about by human activities. Climate warming may alter the cycling of carbon on arctic shelves through permanent reductions in ice cover and increases in riverine discharge. In turn these changes may lead to enhanced export of carbon to the slope and deep arctic basins.One of the most distinguishing features of the Arctic is its extensive shelf area, comprising about 30% of the basin area and receiving about 10% of the world river discharge. River discharge in the Arctic is dominated by the great Siberian rivers - the Yenisei, Lena and Ob. The Mackenzie River is fourth in importance after these, but is first in rank in terms of annual discharge of sediment. Moreover, it is the only North American analog of the large Siberian rivers, and in practical terms is the most readily studied.The potential importance of the river-dominated shelves to biogeochemical cycling in the Arctic has lead to an international effort --the Canadian Arctic Shelf Exchange Study (CASES)--organized by Canada to understand the consequences of sea- ice variability on the Mackenzie shelf. Based on prior involvement in Canadian-organized arctic programs in the Northeast and North Water Polynyas, the PI has been invited to participate in the CASES program. The research proposed here for the Mackenzie Shelf will build on the PI's prior efforts in the Arctic and elsewhere to use natural radionuclides as tracers for fluxes of particulate organic carbon and particles.CASES includes three month-long process cruises (in August 2002, 2003 and 2004) on the Mackenzie Shelf and a year-long period between the August 2003 and 2004 cruises during which the research icebreaker will over-winter. This research will be structured to take advantage of the possibility to sample the full annual cycle of productivity on the Mackenzie Shelf. Focus will be on the three distinct zones (an early season inner shelf pool of freshwater dubbed 'Lake Mackenzie' separated by an ice dam from a flaw-lead polynya and the arctic pack ice) that develop in the system, and employ natural radionuclides as tracers for the transport of particles and particulate organic carbon within and between the zones. We hypothesize that significant exchanges between the zones will occur in the spring through summer as the Mackenzie River freshet begins, the ice retreats offshore and productivity increases. We will test this hypothesis through the use of natural radionuclides to determine the presence of freshly input riverine sediments to the inner shelf, the rate of export of POC from the euphotic zone, and through mass balances, as indicators of the transport of particulate material through the zones. The radionuclides we will use include cosmogenic radionuclides (Be-7 and C-14) produced in the atmosphere from the interactions of cosmic rays with atmospheric gases, and radionuclides of the naturally occurring U-238 decay series (Th-234, Pb-210).