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)

天然放射性核素作为麦肯齐陆架颗粒有机碳循环和归宿的示踪剂：参与加拿大北极陆架交换研究（CASES）

• 批准号: 0136459
• 负责人: J Kirk Cochran
• 金额: $ 33.81万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0136459&HistoricalAwards=false
• 关键词: Natural; Radionuclides; Tracers; Cycling; Fate

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).

在世界上所有的海洋中，北冰洋的独特之处在于其持续的海冰覆盖，广阔的大陆架是碳循环的场所，以及强烈的光强年度变化。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带来的气候变化有关。气候变暖可能会通过冰盖的永久性减少和河流排放量的增加来改变北极大陆架上碳的循环。反过来，这些变化可能导致碳向北极斜坡和深层盆地的出口增加。北极最显著的特征之一是其广阔的陆架区域，约占盆地面积的30%，接收约占世界河流流量的10%。北极的河流流量主要由西伯利亚的大河-叶尼塞河、利纳河和鄂布河主导。麦肯齐河的重要性仅次于这些河流，但在年泥沙排放量方面却位居第一。此外，它是北美唯一与西伯利亚大河类似的河流，实际上也是最容易被研究的。以河流为主的大陆架对北极生物地球化学循环的潜在重要性导致了一项由加拿大组织的国际努力--加拿大北冰洋大陆架交换研究(CASES)--以了解海冰变化对麦肯齐大陆架的影响。基于之前参与了加拿大在东北和北水多尼亚地区组织的北极计划，国际和平协会已被邀请参加CASE计划。这里提出的麦肯齐大陆架研究将建立在PI之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的示踪剂的基础上。CASES包括在麦肯齐大陆架上进行三次为期一个月的过程巡航(2002年8月、2003年和2004年)，以及2003年8月和2004年巡航之间长达一年的巡航，在此期间研究破冰船将越冬。这项研究的结构将利用对麦肯齐大陆架上整个年度生产力周期进行采样的可能性。重点将放在该系统中形成的三个不同的区域(一个被冰坝与有缺陷的铅波尼亚和北极浮冰隔开的早期内陆架淡水池--麦肯齐湖)，并使用天然放射性核素作为示踪剂，在这些区域内和区域之间传输颗粒和颗粒有机碳。我们假设，随着麦肯齐河淡水的开始、近海冰层的消退和生产力的提高，这两个区域之间的重大交换将在春季到夏季发生。我们将通过使用天然放射性核素来测试这一假设，以确定内陆架新输入的河流沉积物的存在，从真光区输出POC的速率，并通过质量平衡，作为颗粒物通过这些区的运输的指标。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)，以及自然产生的U-238衰变系列的放射性核素(Th-234，Pb-210)。