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)

0136459科克伦在世界所有的海洋中，北极是独一无二的，它有着持久的海冰覆盖，广阔的大陆架是碳循环的场所，光照强度每年变化很大。此外，北极可能是最容易显示全球变暖早期影响的海洋。虽然冰盖变薄等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，但也可能与人类活动造成的气候变化有关。气候变暖可能会改变北极大陆架上的碳循环，因为冰盖会永久性减少，河流流量会增加。反过来，这些变化可能会导致增加的碳输出到斜坡和深北极盆地。北极最显着的特点之一是其广阔的大陆架面积，包括约30%的盆地面积和接收约10%的世界河流流量。北极地区的河流流量主要由西伯利亚大河--叶尼塞河、勒拿河和鄂毕河--控制。麦肯齐河的重要性仅次于这些河流，但在年沉积物排放量方面排名第一。此外，它是北美唯一类似于西伯利亚大河的河流，实际上也是最容易研究的河流，以河流为主的冰架对北极地球化学循环的潜在重要性导致了一项国际努力-加拿大北极冰架交换研究，由加拿大组织，以了解麦肯齐冰架海冰变化的后果。根据先前参与哥伦比亚在东北和北水Polynyas组织的北极方案，PI已被邀请参加CASES方案。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使用天然放射性核素作为颗粒有机碳和颗粒通量示踪剂的努力的基础上。（2002年、2003年和2004年8月）在麦肯齐大陆架上进行的考察，以及2003年8月至2004年8月之间为期一年的考察，在此期间，研究破冰船将越冬。这项研究的结构将利用对麦肯齐大陆架生产力的整个年度周期进行抽样的可能性。重点将放在该系统中发展的三个不同区域（被称为“麦肯齐湖”的早期内陆架淡水池，由冰坝与铅质冰间湖和北极浮冰隔开），并采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的运输。我们假设，从春季到夏季，随着麦肯齐河开始涨潮，冰向近海退去，生产力增加，这些区域之间将发生重大的交换。我们将测试这一假设，通过使用天然放射性核素，以确定存在的新鲜输入的河流沉积物的内架，出口的POC从透光带的速率，并通过质量平衡，作为指标的颗粒物质通过区域的运输。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成因放射性核素（Be-7和C-14），以及天然存在的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).