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).

0136459Cochran 在世界所有海洋中，北极的独特之处在于其持续的海冰覆盖、广阔的大陆架（碳循环的场所）以及每年强烈的光照强度变化。此外，北极也许是最容易受到全球变暖早期影响的海洋。尽管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引起的气候变化有关。气候变暖可能会通过永久减少冰盖和增加河流排放来改变北极大陆架上的碳循环。反过来，这些变化可能会导致向北极斜坡和深部盆地的碳输出增加。北极最显着的特征之一是其广阔的陆架面积，约占盆地面积的 30%，容纳了世界约 10% 的碳。河流排放。北极河流的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，但就年沉积物排放量而言排名第一。此外，它是北美唯一一条与西伯利亚大河类似的河流，实际上也是最容易研究的。河流主导的陆架对北极生物地球化学循环的潜在重要性引起了国际社会的努力——加拿大北极陆架交换研究（CASES）——由加拿大组织，旨在了解海冰变化对麦肯齐陆架的影响。基于之前参与加拿大在东北和北水间湖组织的北极项目的经验，PI 已受邀参加 CASES 项目。这里提出的麦肯齐大陆架研究将建立在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。案例包括为期三个月的过程巡航（2002年8月、2003年8月和2003年8月）。 2004年）在麦肯齐大陆架上以及2003年8月至2004年航行期间长达一年的时间里，研究破冰船将过冬。这项研究的结构将利用对麦肯齐大陆架的完整年度生产力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区域（被称为“麦肯齐湖”的早季内陆架淡水池，由冰坝与缺陷铅冰间湖和北极浮冰隔开），并采用天然放射性核素作为用于区域内和区域之间颗粒和颗粒有机碳传输的示踪剂。我们假设，随着麦肯齐河淡水开始、冰退到近海和生产力增加，这些区域之间将在春季到夏季发生显着的交换。我们将通过使用天然放射性核素来测试这一假设，以确定新输入的河流沉积物是否存在内陆架、POC从富光带的输出率，并通过质量平衡作为颗粒物质通过内陆架运输的指标。区域。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），以及自然发生的 U-238 衰变系列的放射性核素（Th-234、Pb-210） ）。